memcg: fix LRU accounting with THP

[mv-sheeva.git] / mm / memcontrol.c

/* memcontrol.c - Memory Controller
 *
 * Copyright IBM Corporation, 2007
 * Author Balbir Singh <balbir@linux.vnet.ibm.com>
 *
 * Copyright 2007 OpenVZ SWsoft Inc
 * Author: Pavel Emelianov <xemul@openvz.org>
 *
 * Memory thresholds
 * Copyright (C) 2009 Nokia Corporation
 * Author: Kirill A. Shutemov
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/res_counter.h>
#include <linux/memcontrol.h>
#include <linux/cgroup.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/smp.h>
#include <linux/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/limits.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/spinlock.h>
#include <linux/eventfd.h>
#include <linux/sort.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/mm_inline.h>
#include <linux/page_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include "internal.h"

#include <asm/uaccess.h>

#include <trace/events/vmscan.h>

struct cgroup_subsys mem_cgroup_subsys __read_mostly;
#define MEM_CGROUP_RECLAIM_RETRIES      5
struct mem_cgroup *root_mem_cgroup __read_mostly;

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
int do_swap_account __read_mostly;

/* for remember boot option*/
#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED
static int really_do_swap_account __initdata = 1;
#else
static int really_do_swap_account __initdata = 0;
#endif

#else
#define do_swap_account         (0)
#endif

/*
 * Per memcg event counter is incremented at every pagein/pageout. This counter
 * is used for trigger some periodic events. This is straightforward and better
 * than using jiffies etc. to handle periodic memcg event.
 *
 * These values will be used as !((event) & ((1 <<(thresh)) - 1))
 */
#define THRESHOLDS_EVENTS_THRESH (7) /* once in 128 */
#define SOFTLIMIT_EVENTS_THRESH (10) /* once in 1024 */

/*
 * Statistics for memory cgroup.
 */
enum mem_cgroup_stat_index {
        /*
         * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
         */
        MEM_CGROUP_STAT_CACHE,     /* # of pages charged as cache */
        MEM_CGROUP_STAT_RSS,       /* # of pages charged as anon rss */
        MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
        MEM_CGROUP_STAT_PGPGIN_COUNT,   /* # of pages paged in */
        MEM_CGROUP_STAT_PGPGOUT_COUNT,  /* # of pages paged out */
        MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
        MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
        /* incremented at every  pagein/pageout */
        MEM_CGROUP_EVENTS = MEM_CGROUP_STAT_DATA,
        MEM_CGROUP_ON_MOVE,     /* someone is moving account between groups */

        MEM_CGROUP_STAT_NSTATS,
};

struct mem_cgroup_stat_cpu {
        s64 count[MEM_CGROUP_STAT_NSTATS];
};

/*
 * per-zone information in memory controller.
 */
struct mem_cgroup_per_zone {
        /*
         * spin_lock to protect the per cgroup LRU
         */
        struct list_head        lists[NR_LRU_LISTS];
        unsigned long           count[NR_LRU_LISTS];

        struct zone_reclaim_stat reclaim_stat;
        struct rb_node          tree_node;      /* RB tree node */
        unsigned long long      usage_in_excess;/* Set to the value by which */
                                                /* the soft limit is exceeded*/
        bool                    on_tree;
        struct mem_cgroup       *mem;           /* Back pointer, we cannot */
                                                /* use container_of        */
};
/* Macro for accessing counter */
#define MEM_CGROUP_ZSTAT(mz, idx)       ((mz)->count[(idx)])

struct mem_cgroup_per_node {
        struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};

struct mem_cgroup_lru_info {
        struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
};

/*
 * Cgroups above their limits are maintained in a RB-Tree, independent of
 * their hierarchy representation
 */

struct mem_cgroup_tree_per_zone {
        struct rb_root rb_root;
        spinlock_t lock;
};

struct mem_cgroup_tree_per_node {
        struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
};

struct mem_cgroup_tree {
        struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
};

static struct mem_cgroup_tree soft_limit_tree __read_mostly;

struct mem_cgroup_threshold {
        struct eventfd_ctx *eventfd;
        u64 threshold;
};

/* For threshold */
struct mem_cgroup_threshold_ary {
        /* An array index points to threshold just below usage. */
        int current_threshold;
        /* Size of entries[] */
        unsigned int size;
        /* Array of thresholds */
        struct mem_cgroup_threshold entries[0];
};

struct mem_cgroup_thresholds {
        /* Primary thresholds array */
        struct mem_cgroup_threshold_ary *primary;
        /*
         * Spare threshold array.
         * This is needed to make mem_cgroup_unregister_event() "never fail".
         * It must be able to store at least primary->size - 1 entries.
         */
        struct mem_cgroup_threshold_ary *spare;
};

/* for OOM */
struct mem_cgroup_eventfd_list {
        struct list_head list;
        struct eventfd_ctx *eventfd;
};

static void mem_cgroup_threshold(struct mem_cgroup *mem);
static void mem_cgroup_oom_notify(struct mem_cgroup *mem);

/*
 * The memory controller data structure. The memory controller controls both
 * page cache and RSS per cgroup. We would eventually like to provide
 * statistics based on the statistics developed by Rik Van Riel for clock-pro,
 * to help the administrator determine what knobs to tune.
 *
 * TODO: Add a water mark for the memory controller. Reclaim will begin when
 * we hit the water mark. May be even add a low water mark, such that
 * no reclaim occurs from a cgroup at it's low water mark, this is
 * a feature that will be implemented much later in the future.
 */
struct mem_cgroup {
        struct cgroup_subsys_state css;
        /*
         * the counter to account for memory usage
         */
        struct res_counter res;
        /*
         * the counter to account for mem+swap usage.
         */
        struct res_counter memsw;
        /*
         * Per cgroup active and inactive list, similar to the
         * per zone LRU lists.
         */
        struct mem_cgroup_lru_info info;

        /*
          protect against reclaim related member.
        */
        spinlock_t reclaim_param_lock;

        /*
         * While reclaiming in a hierarchy, we cache the last child we
         * reclaimed from.
         */
        int last_scanned_child;
        /*
         * Should the accounting and control be hierarchical, per subtree?
         */
        bool use_hierarchy;
        atomic_t        oom_lock;
        atomic_t        refcnt;

        unsigned int    swappiness;
        /* OOM-Killer disable */
        int             oom_kill_disable;

        /* set when res.limit == memsw.limit */
        bool            memsw_is_minimum;

        /* protect arrays of thresholds */
        struct mutex thresholds_lock;

        /* thresholds for memory usage. RCU-protected */
        struct mem_cgroup_thresholds thresholds;

        /* thresholds for mem+swap usage. RCU-protected */
        struct mem_cgroup_thresholds memsw_thresholds;

        /* For oom notifier event fd */
        struct list_head oom_notify;

        /*
         * Should we move charges of a task when a task is moved into this
         * mem_cgroup ? And what type of charges should we move ?
         */
        unsigned long   move_charge_at_immigrate;
        /*
         * percpu counter.
         */
        struct mem_cgroup_stat_cpu *stat;
        /*
         * used when a cpu is offlined or other synchronizations
         * See mem_cgroup_read_stat().
         */
        struct mem_cgroup_stat_cpu nocpu_base;
        spinlock_t pcp_counter_lock;
};

/* Stuffs for move charges at task migration. */
/*
 * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
 * left-shifted bitmap of these types.
 */
enum move_type {
        MOVE_CHARGE_TYPE_ANON,  /* private anonymous page and swap of it */
        MOVE_CHARGE_TYPE_FILE,  /* file page(including tmpfs) and swap of it */
        NR_MOVE_TYPE,
};

/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
        spinlock_t        lock; /* for from, to */
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        unsigned long precharge;
        unsigned long moved_charge;
        unsigned long moved_swap;
        struct task_struct *moving_task;        /* a task moving charges */
        wait_queue_head_t waitq;                /* a waitq for other context */
} mc = {
        .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
        .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};

static bool move_anon(void)
{
        return test_bit(MOVE_CHARGE_TYPE_ANON,
                                        &mc.to->move_charge_at_immigrate);
}

static bool move_file(void)
{
        return test_bit(MOVE_CHARGE_TYPE_FILE,
                                        &mc.to->move_charge_at_immigrate);
}

/*
 * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
 * limit reclaim to prevent infinite loops, if they ever occur.
 */
#define MEM_CGROUP_MAX_RECLAIM_LOOPS            (100)
#define MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS (2)

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_MAPPED,
        MEM_CGROUP_CHARGE_TYPE_SHMEM,   /* used by page migration of shmem */
        MEM_CGROUP_CHARGE_TYPE_FORCE,   /* used by force_empty */
        MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
        MEM_CGROUP_CHARGE_TYPE_DROP,    /* a page was unused swap cache */
        NR_CHARGE_TYPE,
};

/* only for here (for easy reading.) */
#define PCGF_CACHE      (1UL << PCG_CACHE)
#define PCGF_USED       (1UL << PCG_USED)
#define PCGF_LOCK       (1UL << PCG_LOCK)
/* Not used, but added here for completeness */
#define PCGF_ACCT       (1UL << PCG_ACCT)

/* for encoding cft->private value on file */
#define _MEM                    (0)
#define _MEMSWAP                (1)
#define _OOM_TYPE               (2)
#define MEMFILE_PRIVATE(x, val) (((x) << 16) | (val))
#define MEMFILE_TYPE(val)       (((val) >> 16) & 0xffff)
#define MEMFILE_ATTR(val)       ((val) & 0xffff)
/* Used for OOM nofiier */
#define OOM_CONTROL             (0)

/*
 * Reclaim flags for mem_cgroup_hierarchical_reclaim
 */
#define MEM_CGROUP_RECLAIM_NOSWAP_BIT   0x0
#define MEM_CGROUP_RECLAIM_NOSWAP       (1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
#define MEM_CGROUP_RECLAIM_SHRINK_BIT   0x1
#define MEM_CGROUP_RECLAIM_SHRINK       (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
#define MEM_CGROUP_RECLAIM_SOFT_BIT     0x2
#define MEM_CGROUP_RECLAIM_SOFT         (1 << MEM_CGROUP_RECLAIM_SOFT_BIT)

static void mem_cgroup_get(struct mem_cgroup *mem);
static void mem_cgroup_put(struct mem_cgroup *mem);
static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
static void drain_all_stock_async(void);

static struct mem_cgroup_per_zone *
mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
{
        return &mem->info.nodeinfo[nid]->zoneinfo[zid];
}

struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem)
{
        return &mem->css;
}

static struct mem_cgroup_per_zone *
page_cgroup_zoneinfo(struct page_cgroup *pc)
{
        struct mem_cgroup *mem = pc->mem_cgroup;
        int nid = page_cgroup_nid(pc);
        int zid = page_cgroup_zid(pc);

        if (!mem)
                return NULL;

        return mem_cgroup_zoneinfo(mem, nid, zid);
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_node_zone(int nid, int zid)
{
        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_from_page(struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static void
__mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz,
                                unsigned long long new_usage_in_excess)
{
        struct rb_node **p = &mctz->rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct mem_cgroup_per_zone *mz_node;

        if (mz->on_tree)
                return;

        mz->usage_in_excess = new_usage_in_excess;
        if (!mz->usage_in_excess)
                return;
        while (*p) {
                parent = *p;
                mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
                                        tree_node);
                if (mz->usage_in_excess < mz_node->usage_in_excess)
                        p = &(*p)->rb_left;
                /*
                 * We can't avoid mem cgroups that are over their soft
                 * limit by the same amount
                 */
                else if (mz->usage_in_excess >= mz_node->usage_in_excess)
                        p = &(*p)->rb_right;
        }
        rb_link_node(&mz->tree_node, parent, p);
        rb_insert_color(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = true;
}

static void
__mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz)
{
        if (!mz->on_tree)
                return;
        rb_erase(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = false;
}

static void
mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
                                struct mem_cgroup_per_zone *mz,
                                struct mem_cgroup_tree_per_zone *mctz)
{
        spin_lock(&mctz->lock);
        __mem_cgroup_remove_exceeded(mem, mz, mctz);
        spin_unlock(&mctz->lock);
}


static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
{
        unsigned long long excess;
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup_tree_per_zone *mctz;
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);
        mctz = soft_limit_tree_from_page(page);

        /*
         * Necessary to update all ancestors when hierarchy is used.
         * because their event counter is not touched.
         */
        for (; mem; mem = parent_mem_cgroup(mem)) {
                mz = mem_cgroup_zoneinfo(mem, nid, zid);
                excess = res_counter_soft_limit_excess(&mem->res);
                /*
                 * We have to update the tree if mz is on RB-tree or
                 * mem is over its softlimit.
                 */
                if (excess || mz->on_tree) {
                        spin_lock(&mctz->lock);
                        /* if on-tree, remove it */
                        if (mz->on_tree)
                                __mem_cgroup_remove_exceeded(mem, mz, mctz);
                        /*
                         * Insert again. mz->usage_in_excess will be updated.
                         * If excess is 0, no tree ops.
                         */
                        __mem_cgroup_insert_exceeded(mem, mz, mctz, excess);
                        spin_unlock(&mctz->lock);
                }
        }
}

static void mem_cgroup_remove_from_trees(struct mem_cgroup *mem)
{
        int node, zone;
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup_tree_per_zone *mctz;

        for_each_node_state(node, N_POSSIBLE) {
                for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                        mz = mem_cgroup_zoneinfo(mem, node, zone);
                        mctz = soft_limit_tree_node_zone(node, zone);
                        mem_cgroup_remove_exceeded(mem, mz, mctz);
                }
        }
}

static inline unsigned long mem_cgroup_get_excess(struct mem_cgroup *mem)
{
        return res_counter_soft_limit_excess(&mem->res) >> PAGE_SHIFT;
}

static struct mem_cgroup_per_zone *
__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct rb_node *rightmost = NULL;
        struct mem_cgroup_per_zone *mz;

retry:
        mz = NULL;
        rightmost = rb_last(&mctz->rb_root);
        if (!rightmost)
                goto done;              /* Nothing to reclaim from */

        mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
        /*
         * Remove the node now but someone else can add it back,
         * we will to add it back at the end of reclaim to its correct
         * position in the tree.
         */
        __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
        if (!res_counter_soft_limit_excess(&mz->mem->res) ||
                !css_tryget(&mz->mem->css))
                goto retry;
done:
        return mz;
}

static struct mem_cgroup_per_zone *
mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct mem_cgroup_per_zone *mz;

        spin_lock(&mctz->lock);
        mz = __mem_cgroup_largest_soft_limit_node(mctz);
        spin_unlock(&mctz->lock);
        return mz;
}

/*
 * Implementation Note: reading percpu statistics for memcg.
 *
 * Both of vmstat[] and percpu_counter has threshold and do periodic
 * synchronization to implement "quick" read. There are trade-off between
 * reading cost and precision of value. Then, we may have a chance to implement
 * a periodic synchronizion of counter in memcg's counter.
 *
 * But this _read() function is used for user interface now. The user accounts
 * memory usage by memory cgroup and he _always_ requires exact value because
 * he accounts memory. Even if we provide quick-and-fuzzy read, we always
 * have to visit all online cpus and make sum. So, for now, unnecessary
 * synchronization is not implemented. (just implemented for cpu hotplug)
 *
 * If there are kernel internal actions which can make use of some not-exact
 * value, and reading all cpu value can be performance bottleneck in some
 * common workload, threashold and synchonization as vmstat[] should be
 * implemented.
 */
static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
                enum mem_cgroup_stat_index idx)
{
        int cpu;
        s64 val = 0;

        get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(mem->stat->count[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&mem->pcp_counter_lock);
        val += mem->nocpu_base.count[idx];
        spin_unlock(&mem->pcp_counter_lock);
#endif
        put_online_cpus();
        return val;
}

static s64 mem_cgroup_local_usage(struct mem_cgroup *mem)
{
        s64 ret;

        ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
        ret += mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
        return ret;
}

static void mem_cgroup_swap_statistics(struct mem_cgroup *mem,
                                         bool charge)
{
        int val = (charge) ? 1 : -1;
        this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_SWAPOUT], val);
}

static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
                                         bool file, int nr_pages)
{
        preempt_disable();

        if (file)
                __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_CACHE], nr_pages);
        else
                __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_RSS], nr_pages);

        /* pagein of a big page is an event. So, ignore page size */
        if (nr_pages > 0)
                __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGIN_COUNT]);
        else
                __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGOUT_COUNT]);

        __this_cpu_add(mem->stat->count[MEM_CGROUP_EVENTS], nr_pages);

        preempt_enable();
}

static unsigned long mem_cgroup_get_local_zonestat(struct mem_cgroup *mem,
                                        enum lru_list idx)
{
        int nid, zid;
        struct mem_cgroup_per_zone *mz;
        u64 total = 0;

        for_each_online_node(nid)
                for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                        mz = mem_cgroup_zoneinfo(mem, nid, zid);
                        total += MEM_CGROUP_ZSTAT(mz, idx);
                }
        return total;
}

static bool __memcg_event_check(struct mem_cgroup *mem, int event_mask_shift)
{
        s64 val;

        val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);

        return !(val & ((1 << event_mask_shift) - 1));
}

/*
 * Check events in order.
 *
 */
static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
{
        /* threshold event is triggered in finer grain than soft limit */
        if (unlikely(__memcg_event_check(mem, THRESHOLDS_EVENTS_THRESH))) {
                mem_cgroup_threshold(mem);
                if (unlikely(__memcg_event_check(mem, SOFTLIMIT_EVENTS_THRESH)))
                        mem_cgroup_update_tree(mem, page);
        }
}

static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
{
        return container_of(cgroup_subsys_state(cont,
                                mem_cgroup_subsys_id), struct mem_cgroup,
                                css);
}

struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
        /*
         * mm_update_next_owner() may clear mm->owner to NULL
         * if it races with swapoff, page migration, etc.
         * So this can be called with p == NULL.
         */
        if (unlikely(!p))
                return NULL;

        return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
                                struct mem_cgroup, css);
}

static struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
{
        struct mem_cgroup *mem = NULL;

        if (!mm)
                return NULL;
        /*
         * Because we have no locks, mm->owner's may be being moved to other
         * cgroup. We use css_tryget() here even if this looks
         * pessimistic (rather than adding locks here).
         */
        rcu_read_lock();
        do {
                mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
                if (unlikely(!mem))
                        break;
        } while (!css_tryget(&mem->css));
        rcu_read_unlock();
        return mem;
}

/* The caller has to guarantee "mem" exists before calling this */
static struct mem_cgroup *mem_cgroup_start_loop(struct mem_cgroup *mem)
{
        struct cgroup_subsys_state *css;
        int found;

        if (!mem) /* ROOT cgroup has the smallest ID */
                return root_mem_cgroup; /*css_put/get against root is ignored*/
        if (!mem->use_hierarchy) {
                if (css_tryget(&mem->css))
                        return mem;
                return NULL;
        }
        rcu_read_lock();
        /*
         * searching a memory cgroup which has the smallest ID under given
         * ROOT cgroup. (ID >= 1)
         */
        css = css_get_next(&mem_cgroup_subsys, 1, &mem->css, &found);
        if (css && css_tryget(css))
                mem = container_of(css, struct mem_cgroup, css);
        else
                mem = NULL;
        rcu_read_unlock();
        return mem;
}

static struct mem_cgroup *mem_cgroup_get_next(struct mem_cgroup *iter,
                                        struct mem_cgroup *root,
                                        bool cond)
{
        int nextid = css_id(&iter->css) + 1;
        int found;
        int hierarchy_used;
        struct cgroup_subsys_state *css;

        hierarchy_used = iter->use_hierarchy;

        css_put(&iter->css);
        /* If no ROOT, walk all, ignore hierarchy */
        if (!cond || (root && !hierarchy_used))
                return NULL;

        if (!root)
                root = root_mem_cgroup;

        do {
                iter = NULL;
                rcu_read_lock();

                css = css_get_next(&mem_cgroup_subsys, nextid,
                                &root->css, &found);
                if (css && css_tryget(css))
                        iter = container_of(css, struct mem_cgroup, css);
                rcu_read_unlock();
                /* If css is NULL, no more cgroups will be found */
                nextid = found + 1;
        } while (css && !iter);

        return iter;
}
/*
 * for_eacn_mem_cgroup_tree() for visiting all cgroup under tree. Please
 * be careful that "break" loop is not allowed. We have reference count.
 * Instead of that modify "cond" to be false and "continue" to exit the loop.
 */
#define for_each_mem_cgroup_tree_cond(iter, root, cond) \
        for (iter = mem_cgroup_start_loop(root);\
             iter != NULL;\
             iter = mem_cgroup_get_next(iter, root, cond))

#define for_each_mem_cgroup_tree(iter, root) \
        for_each_mem_cgroup_tree_cond(iter, root, true)

#define for_each_mem_cgroup_all(iter) \
        for_each_mem_cgroup_tree_cond(iter, NULL, true)


static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
{
        return (mem == root_mem_cgroup);
}

/*
 * Following LRU functions are allowed to be used without PCG_LOCK.
 * Operations are called by routine of global LRU independently from memcg.
 * What we have to take care of here is validness of pc->mem_cgroup.
 *
 * Changes to pc->mem_cgroup happens when
 * 1. charge
 * 2. moving account
 * In typical case, "charge" is done before add-to-lru. Exception is SwapCache.
 * It is added to LRU before charge.
 * If PCG_USED bit is not set, page_cgroup is not added to this private LRU.
 * When moving account, the page is not on LRU. It's isolated.
 */

void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;

        if (mem_cgroup_disabled())
                return;
        pc = lookup_page_cgroup(page);
        /* can happen while we handle swapcache. */
        if (!TestClearPageCgroupAcctLRU(pc))
                return;
        VM_BUG_ON(!pc->mem_cgroup);
        /*
         * We don't check PCG_USED bit. It's cleared when the "page" is finally
         * removed from global LRU.
         */
        mz = page_cgroup_zoneinfo(pc);
        /* huge page split is done under lru_lock. so, we have no races. */
        MEM_CGROUP_ZSTAT(mz, lru) -= 1 << compound_order(page);
        if (mem_cgroup_is_root(pc->mem_cgroup))
                return;
        VM_BUG_ON(list_empty(&pc->lru));
        list_del_init(&pc->lru);
}

void mem_cgroup_del_lru(struct page *page)
{
        mem_cgroup_del_lru_list(page, page_lru(page));
}

void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
{
        struct mem_cgroup_per_zone *mz;
        struct page_cgroup *pc;

        if (mem_cgroup_disabled())
                return;

        pc = lookup_page_cgroup(page);
        /*
         * Used bit is set without atomic ops but after smp_wmb().
         * For making pc->mem_cgroup visible, insert smp_rmb() here.
         */
        smp_rmb();
        /* unused or root page is not rotated. */
        if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
                return;
        mz = page_cgroup_zoneinfo(pc);
        list_move(&pc->lru, &mz->lists[lru]);
}

void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;

        if (mem_cgroup_disabled())
                return;
        pc = lookup_page_cgroup(page);
        VM_BUG_ON(PageCgroupAcctLRU(pc));
        /*
         * Used bit is set without atomic ops but after smp_wmb().
         * For making pc->mem_cgroup visible, insert smp_rmb() here.
         */
        smp_rmb();
        if (!PageCgroupUsed(pc))
                return;

        mz = page_cgroup_zoneinfo(pc);
        /* huge page split is done under lru_lock. so, we have no races. */
        MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
        SetPageCgroupAcctLRU(pc);
        if (mem_cgroup_is_root(pc->mem_cgroup))
                return;
        list_add(&pc->lru, &mz->lists[lru]);
}

/*
 * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
 * lru because the page may.be reused after it's fully uncharged (because of
 * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
 * it again. This function is only used to charge SwapCache. It's done under
 * lock_page and expected that zone->lru_lock is never held.
 */
static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)
{
        unsigned long flags;
        struct zone *zone = page_zone(page);
        struct page_cgroup *pc = lookup_page_cgroup(page);

        spin_lock_irqsave(&zone->lru_lock, flags);
        /*
         * Forget old LRU when this page_cgroup is *not* used. This Used bit
         * is guarded by lock_page() because the page is SwapCache.
         */
        if (!PageCgroupUsed(pc))
                mem_cgroup_del_lru_list(page, page_lru(page));
        spin_unlock_irqrestore(&zone->lru_lock, flags);
}

static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
{
        unsigned long flags;
        struct zone *zone = page_zone(page);
        struct page_cgroup *pc = lookup_page_cgroup(page);

        spin_lock_irqsave(&zone->lru_lock, flags);
        /* link when the page is linked to LRU but page_cgroup isn't */
        if (PageLRU(page) && !PageCgroupAcctLRU(pc))
                mem_cgroup_add_lru_list(page, page_lru(page));
        spin_unlock_irqrestore(&zone->lru_lock, flags);
}


void mem_cgroup_move_lists(struct page *page,
                           enum lru_list from, enum lru_list to)
{
        if (mem_cgroup_disabled())
                return;
        mem_cgroup_del_lru_list(page, from);
        mem_cgroup_add_lru_list(page, to);
}

int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
{
        int ret;
        struct mem_cgroup *curr = NULL;
        struct task_struct *p;

        p = find_lock_task_mm(task);
        if (!p)
                return 0;
        curr = try_get_mem_cgroup_from_mm(p->mm);
        task_unlock(p);
        if (!curr)
                return 0;
        /*
         * We should check use_hierarchy of "mem" not "curr". Because checking
         * use_hierarchy of "curr" here make this function true if hierarchy is
         * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
         * hierarchy(even if use_hierarchy is disabled in "mem").
         */
        if (mem->use_hierarchy)
                ret = css_is_ancestor(&curr->css, &mem->css);
        else
                ret = (curr == mem);
        css_put(&curr->css);
        return ret;
}

static int calc_inactive_ratio(struct mem_cgroup *memcg, unsigned long *present_pages)
{
        unsigned long active;
        unsigned long inactive;
        unsigned long gb;
        unsigned long inactive_ratio;

        inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_ANON);
        active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_ANON);

        gb = (inactive + active) >> (30 - PAGE_SHIFT);
        if (gb)
                inactive_ratio = int_sqrt(10 * gb);
        else
                inactive_ratio = 1;

        if (present_pages) {
                present_pages[0] = inactive;
                present_pages[1] = active;
        }

        return inactive_ratio;
}

int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
{
        unsigned long active;
        unsigned long inactive;
        unsigned long present_pages[2];
        unsigned long inactive_ratio;

        inactive_ratio = calc_inactive_ratio(memcg, present_pages);

        inactive = present_pages[0];
        active = present_pages[1];

        if (inactive * inactive_ratio < active)
                return 1;

        return 0;
}

int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
{
        unsigned long active;
        unsigned long inactive;

        inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
        active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);

        return (active > inactive);
}

unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
                                       struct zone *zone,
                                       enum lru_list lru)
{
        int nid = zone_to_nid(zone);
        int zid = zone_idx(zone);
        struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);

        return MEM_CGROUP_ZSTAT(mz, lru);
}

struct zone_reclaim_stat *mem_cgroup_get_reclaim_stat(struct mem_cgroup *memcg,
                                                      struct zone *zone)
{
        int nid = zone_to_nid(zone);
        int zid = zone_idx(zone);
        struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);

        return &mz->reclaim_stat;
}

struct zone_reclaim_stat *
mem_cgroup_get_reclaim_stat_from_page(struct page *page)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;

        if (mem_cgroup_disabled())
                return NULL;

        pc = lookup_page_cgroup(page);
        /*
         * Used bit is set without atomic ops but after smp_wmb().
         * For making pc->mem_cgroup visible, insert smp_rmb() here.
         */
        smp_rmb();
        if (!PageCgroupUsed(pc))
                return NULL;

        mz = page_cgroup_zoneinfo(pc);
        if (!mz)
                return NULL;

        return &mz->reclaim_stat;
}

unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
                                        struct list_head *dst,
                                        unsigned long *scanned, int order,
                                        int mode, struct zone *z,
                                        struct mem_cgroup *mem_cont,
                                        int active, int file)
{
        unsigned long nr_taken = 0;
        struct page *page;
        unsigned long scan;
        LIST_HEAD(pc_list);
        struct list_head *src;
        struct page_cgroup *pc, *tmp;
        int nid = zone_to_nid(z);
        int zid = zone_idx(z);
        struct mem_cgroup_per_zone *mz;
        int lru = LRU_FILE * file + active;
        int ret;

        BUG_ON(!mem_cont);
        mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);
        src = &mz->lists[lru];

        scan = 0;
        list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
                if (scan >= nr_to_scan)
                        break;

                page = pc->page;
                if (unlikely(!PageCgroupUsed(pc)))
                        continue;
                if (unlikely(!PageLRU(page)))
                        continue;

                scan++;
                ret = __isolate_lru_page(page, mode, file);
                switch (ret) {
                case 0:
                        list_move(&page->lru, dst);
                        mem_cgroup_del_lru(page);
                        nr_taken += hpage_nr_pages(page);
                        break;
                case -EBUSY:
                        /* we don't affect global LRU but rotate in our LRU */
                        mem_cgroup_rotate_lru_list(page, page_lru(page));
                        break;
                default:
                        break;
                }
        }

        *scanned = scan;

        trace_mm_vmscan_memcg_isolate(0, nr_to_scan, scan, nr_taken,
                                      0, 0, 0, mode);

        return nr_taken;
}

#define mem_cgroup_from_res_counter(counter, member)    \
        container_of(counter, struct mem_cgroup, member)

static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
{
        if (do_swap_account) {
                if (res_counter_check_under_limit(&mem->res) &&
                        res_counter_check_under_limit(&mem->memsw))
                        return true;
        } else
                if (res_counter_check_under_limit(&mem->res))
                        return true;
        return false;
}

static unsigned int get_swappiness(struct mem_cgroup *memcg)
{
        struct cgroup *cgrp = memcg->css.cgroup;
        unsigned int swappiness;

        /* root ? */
        if (cgrp->parent == NULL)
                return vm_swappiness;

        spin_lock(&memcg->reclaim_param_lock);
        swappiness = memcg->swappiness;
        spin_unlock(&memcg->reclaim_param_lock);

        return swappiness;
}

static void mem_cgroup_start_move(struct mem_cgroup *mem)
{
        int cpu;

        get_online_cpus();
        spin_lock(&mem->pcp_counter_lock);
        for_each_online_cpu(cpu)
                per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1;
        mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] += 1;
        spin_unlock(&mem->pcp_counter_lock);
        put_online_cpus();

        synchronize_rcu();
}

static void mem_cgroup_end_move(struct mem_cgroup *mem)
{
        int cpu;

        if (!mem)
                return;
        get_online_cpus();
        spin_lock(&mem->pcp_counter_lock);
        for_each_online_cpu(cpu)
                per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1;
        mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] -= 1;
        spin_unlock(&mem->pcp_counter_lock);
        put_online_cpus();
}
/*
 * 2 routines for checking "mem" is under move_account() or not.
 *
 * mem_cgroup_stealed() - checking a cgroup is mc.from or not. This is used
 *                        for avoiding race in accounting. If true,
 *                        pc->mem_cgroup may be overwritten.
 *
 * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
 *                        under hierarchy of moving cgroups. This is for
 *                        waiting at hith-memory prressure caused by "move".
 */

static bool mem_cgroup_stealed(struct mem_cgroup *mem)
{
        VM_BUG_ON(!rcu_read_lock_held());
        return this_cpu_read(mem->stat->count[MEM_CGROUP_ON_MOVE]) > 0;
}

static bool mem_cgroup_under_move(struct mem_cgroup *mem)
{
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        bool ret = false;
        /*
         * Unlike task_move routines, we access mc.to, mc.from not under
         * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
         */
        spin_lock(&mc.lock);
        from = mc.from;
        to = mc.to;
        if (!from)
                goto unlock;
        if (from == mem || to == mem
            || (mem->use_hierarchy && css_is_ancestor(&from->css, &mem->css))
            || (mem->use_hierarchy && css_is_ancestor(&to->css, &mem->css)))
                ret = true;
unlock:
        spin_unlock(&mc.lock);
        return ret;
}

static bool mem_cgroup_wait_acct_move(struct mem_cgroup *mem)
{
        if (mc.moving_task && current != mc.moving_task) {
                if (mem_cgroup_under_move(mem)) {
                        DEFINE_WAIT(wait);
                        prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
                        /* moving charge context might have finished. */
                        if (mc.moving_task)
                                schedule();
                        finish_wait(&mc.waitq, &wait);
                        return true;
                }
        }
        return false;
}

/**
 * mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.
 * @memcg: The memory cgroup that went over limit
 * @p: Task that is going to be killed
 *
 * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
 * enabled
 */
void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
{
        struct cgroup *task_cgrp;
        struct cgroup *mem_cgrp;
        /*
         * Need a buffer in BSS, can't rely on allocations. The code relies
         * on the assumption that OOM is serialized for memory controller.
         * If this assumption is broken, revisit this code.
         */
        static char memcg_name[PATH_MAX];
        int ret;

        if (!memcg || !p)
                return;


        rcu_read_lock();

        mem_cgrp = memcg->css.cgroup;
        task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);

        ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                /*
                 * Unfortunately, we are unable to convert to a useful name
                 * But we'll still print out the usage information
                 */
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        printk(KERN_INFO "Task in %s killed", memcg_name);

        rcu_read_lock();
        ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
        if (ret < 0) {
                rcu_read_unlock();
                goto done;
        }
        rcu_read_unlock();

        /*
         * Continues from above, so we don't need an KERN_ level
         */
        printk(KERN_CONT " as a result of limit of %s\n", memcg_name);
done:

        printk(KERN_INFO "memory: usage %llukB, limit %llukB, failcnt %llu\n",
                res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->res, RES_FAILCNT));
        printk(KERN_INFO "memory+swap: usage %llukB, limit %llukB, "
                "failcnt %llu\n",
                res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
                res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
}

/*
 * This function returns the number of memcg under hierarchy tree. Returns
 * 1(self count) if no children.
 */
static int mem_cgroup_count_children(struct mem_cgroup *mem)
{
        int num = 0;
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, mem)
                num++;
        return num;
}

/*
 * Return the memory (and swap, if configured) limit for a memcg.
 */
u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
{
        u64 limit;
        u64 memsw;

        limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
        limit += total_swap_pages << PAGE_SHIFT;

        memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
        /*
         * If memsw is finite and limits the amount of swap space available
         * to this memcg, return that limit.
         */
        return min(limit, memsw);
}

/*
 * Visit the first child (need not be the first child as per the ordering
 * of the cgroup list, since we track last_scanned_child) of @mem and use
 * that to reclaim free pages from.
 */
static struct mem_cgroup *
mem_cgroup_select_victim(struct mem_cgroup *root_mem)
{
        struct mem_cgroup *ret = NULL;
        struct cgroup_subsys_state *css;
        int nextid, found;

        if (!root_mem->use_hierarchy) {
                css_get(&root_mem->css);
                ret = root_mem;
        }

        while (!ret) {
                rcu_read_lock();
                nextid = root_mem->last_scanned_child + 1;
                css = css_get_next(&mem_cgroup_subsys, nextid, &root_mem->css,
                                   &found);
                if (css && css_tryget(css))
                        ret = container_of(css, struct mem_cgroup, css);

                rcu_read_unlock();
                /* Updates scanning parameter */
                spin_lock(&root_mem->reclaim_param_lock);
                if (!css) {
                        /* this means start scan from ID:1 */
                        root_mem->last_scanned_child = 0;
                } else
                        root_mem->last_scanned_child = found;
                spin_unlock(&root_mem->reclaim_param_lock);
        }

        return ret;
}

/*
 * Scan the hierarchy if needed to reclaim memory. We remember the last child
 * we reclaimed from, so that we don't end up penalizing one child extensively
 * based on its position in the children list.
 *
 * root_mem is the original ancestor that we've been reclaim from.
 *
 * We give up and return to the caller when we visit root_mem twice.
 * (other groups can be removed while we're walking....)
 *
 * If shrink==true, for avoiding to free too much, this returns immedieately.
 */
static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
                                                struct zone *zone,
                                                gfp_t gfp_mask,
                                                unsigned long reclaim_options)
{
        struct mem_cgroup *victim;
        int ret, total = 0;
        int loop = 0;
        bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
        bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
        bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
        unsigned long excess = mem_cgroup_get_excess(root_mem);

        /* If memsw_is_minimum==1, swap-out is of-no-use. */
        if (root_mem->memsw_is_minimum)
                noswap = true;

        while (1) {
                victim = mem_cgroup_select_victim(root_mem);
                if (victim == root_mem) {
                        loop++;
                        if (loop >= 1)
                                drain_all_stock_async();
                        if (loop >= 2) {
                                /*
                                 * If we have not been able to reclaim
                                 * anything, it might because there are
                                 * no reclaimable pages under this hierarchy
                                 */
                                if (!check_soft || !total) {
                                        css_put(&victim->css);
                                        break;
                                }
                                /*
                                 * We want to do more targetted reclaim.
                                 * excess >> 2 is not to excessive so as to
                                 * reclaim too much, nor too less that we keep
                                 * coming back to reclaim from this cgroup
                                 */
                                if (total >= (excess >> 2) ||
                                        (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
                                        css_put(&victim->css);
                                        break;
                                }
                        }
                }
                if (!mem_cgroup_local_usage(victim)) {
                        /* this cgroup's local usage == 0 */
                        css_put(&victim->css);
                        continue;
                }
                /* we use swappiness of local cgroup */
                if (check_soft)
                        ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,
                                noswap, get_swappiness(victim), zone);
                else
                        ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
                                                noswap, get_swappiness(victim));
                css_put(&victim->css);
                /*
                 * At shrinking usage, we can't check we should stop here or
                 * reclaim more. It's depends on callers. last_scanned_child
                 * will work enough for keeping fairness under tree.
                 */
                if (shrink)
                        return ret;
                total += ret;
                if (check_soft) {
                        if (res_counter_check_under_soft_limit(&root_mem->res))
                                return total;
                } else if (mem_cgroup_check_under_limit(root_mem))
                        return 1 + total;
        }
        return total;
}

/*
 * Check OOM-Killer is already running under our hierarchy.
 * If someone is running, return false.
 */
static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
{
        int x, lock_count = 0;
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, mem) {
                x = atomic_inc_return(&iter->oom_lock);
                lock_count = max(x, lock_count);
        }

        if (lock_count == 1)
                return true;
        return false;
}

static int mem_cgroup_oom_unlock(struct mem_cgroup *mem)
{
        struct mem_cgroup *iter;

        /*
         * When a new child is created while the hierarchy is under oom,
         * mem_cgroup_oom_lock() may not be called. We have to use
         * atomic_add_unless() here.
         */
        for_each_mem_cgroup_tree(iter, mem)
                atomic_add_unless(&iter->oom_lock, -1, 0);
        return 0;
}


static DEFINE_MUTEX(memcg_oom_mutex);
static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

struct oom_wait_info {
        struct mem_cgroup *mem;
        wait_queue_t    wait;
};

static int memcg_oom_wake_function(wait_queue_t *wait,
        unsigned mode, int sync, void *arg)
{
        struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg;
        struct oom_wait_info *oom_wait_info;

        oom_wait_info = container_of(wait, struct oom_wait_info, wait);

        if (oom_wait_info->mem == wake_mem)
                goto wakeup;
        /* if no hierarchy, no match */
        if (!oom_wait_info->mem->use_hierarchy || !wake_mem->use_hierarchy)
                return 0;
        /*
         * Both of oom_wait_info->mem and wake_mem are stable under us.
         * Then we can use css_is_ancestor without taking care of RCU.
         */
        if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
            !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
                return 0;

wakeup:
        return autoremove_wake_function(wait, mode, sync, arg);
}

static void memcg_wakeup_oom(struct mem_cgroup *mem)
{
        /* for filtering, pass "mem" as argument. */
        __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, mem);
}

static void memcg_oom_recover(struct mem_cgroup *mem)
{
        if (mem && atomic_read(&mem->oom_lock))
                memcg_wakeup_oom(mem);
}

/*
 * try to call OOM killer. returns false if we should exit memory-reclaim loop.
 */
bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
{
        struct oom_wait_info owait;
        bool locked, need_to_kill;

        owait.mem = mem;
        owait.wait.flags = 0;
        owait.wait.func = memcg_oom_wake_function;
        owait.wait.private = current;
        INIT_LIST_HEAD(&owait.wait.task_list);
        need_to_kill = true;
        /* At first, try to OOM lock hierarchy under mem.*/
        mutex_lock(&memcg_oom_mutex);
        locked = mem_cgroup_oom_lock(mem);
        /*
         * Even if signal_pending(), we can't quit charge() loop without
         * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
         * under OOM is always welcomed, use TASK_KILLABLE here.
         */
        prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
        if (!locked || mem->oom_kill_disable)
                need_to_kill = false;
        if (locked)
                mem_cgroup_oom_notify(mem);
        mutex_unlock(&memcg_oom_mutex);

        if (need_to_kill) {
                finish_wait(&memcg_oom_waitq, &owait.wait);
                mem_cgroup_out_of_memory(mem, mask);
        } else {
                schedule();
                finish_wait(&memcg_oom_waitq, &owait.wait);
        }
        mutex_lock(&memcg_oom_mutex);
        mem_cgroup_oom_unlock(mem);
        memcg_wakeup_oom(mem);
        mutex_unlock(&memcg_oom_mutex);

        if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
                return false;
        /* Give chance to dying process */
        schedule_timeout(1);
        return true;
}

/*
 * Currently used to update mapped file statistics, but the routine can be
 * generalized to update other statistics as well.
 *
 * Notes: Race condition
 *
 * We usually use page_cgroup_lock() for accessing page_cgroup member but
 * it tends to be costly. But considering some conditions, we doesn't need
 * to do so _always_.
 *
 * Considering "charge", lock_page_cgroup() is not required because all
 * file-stat operations happen after a page is attached to radix-tree. There
 * are no race with "charge".
 *
 * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
 * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
 * if there are race with "uncharge". Statistics itself is properly handled
 * by flags.
 *
 * Considering "move", this is an only case we see a race. To make the race
 * small, we check MEM_CGROUP_ON_MOVE percpu value and detect there are
 * possibility of race condition. If there is, we take a lock.
 */

void mem_cgroup_update_page_stat(struct page *page,
                                 enum mem_cgroup_page_stat_item idx, int val)
{
        struct mem_cgroup *mem;
        struct page_cgroup *pc = lookup_page_cgroup(page);
        bool need_unlock = false;
        unsigned long uninitialized_var(flags);

        if (unlikely(!pc))
                return;

        rcu_read_lock();
        mem = pc->mem_cgroup;
        if (unlikely(!mem || !PageCgroupUsed(pc)))
                goto out;
        /* pc->mem_cgroup is unstable ? */
        if (unlikely(mem_cgroup_stealed(mem)) || PageTransHuge(page)) {
                /* take a lock against to access pc->mem_cgroup */
                move_lock_page_cgroup(pc, &flags);
                need_unlock = true;
                mem = pc->mem_cgroup;
                if (!mem || !PageCgroupUsed(pc))
                        goto out;
        }

        switch (idx) {
        case MEMCG_NR_FILE_MAPPED:
                if (val > 0)
                        SetPageCgroupFileMapped(pc);
                else if (!page_mapped(page))
                        ClearPageCgroupFileMapped(pc);
                idx = MEM_CGROUP_STAT_FILE_MAPPED;
                break;
        default:
                BUG();
        }

        this_cpu_add(mem->stat->count[idx], val);

out:
        if (unlikely(need_unlock))
                move_unlock_page_cgroup(pc, &flags);
        rcu_read_unlock();
        return;
}
EXPORT_SYMBOL(mem_cgroup_update_page_stat);

/*
 * size of first charge trial. "32" comes from vmscan.c's magic value.
 * TODO: maybe necessary to use big numbers in big irons.
 */
#define CHARGE_SIZE     (32 * PAGE_SIZE)
struct memcg_stock_pcp {
        struct mem_cgroup *cached; /* this never be root cgroup */
        int charge;
        struct work_struct work;
};
static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
static atomic_t memcg_drain_count;

/*
 * Try to consume stocked charge on this cpu. If success, PAGE_SIZE is consumed
 * from local stock and true is returned. If the stock is 0 or charges from a
 * cgroup which is not current target, returns false. This stock will be
 * refilled.
 */
static bool consume_stock(struct mem_cgroup *mem)
{
        struct memcg_stock_pcp *stock;
        bool ret = true;

        stock = &get_cpu_var(memcg_stock);
        if (mem == stock->cached && stock->charge)
                stock->charge -= PAGE_SIZE;
        else /* need to call res_counter_charge */
                ret = false;
        put_cpu_var(memcg_stock);
        return ret;
}

/*
 * Returns stocks cached in percpu to res_counter and reset cached information.
 */
static void drain_stock(struct memcg_stock_pcp *stock)
{
        struct mem_cgroup *old = stock->cached;

        if (stock->charge) {
                res_counter_uncharge(&old->res, stock->charge);
                if (do_swap_account)
                        res_counter_uncharge(&old->memsw, stock->charge);
        }
        stock->cached = NULL;
        stock->charge = 0;
}

/*
 * This must be called under preempt disabled or must be called by
 * a thread which is pinned to local cpu.
 */
static void drain_local_stock(struct work_struct *dummy)
{
        struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);
        drain_stock(stock);
}

/*
 * Cache charges(val) which is from res_counter, to local per_cpu area.
 * This will be consumed by consume_stock() function, later.
 */
static void refill_stock(struct mem_cgroup *mem, int val)
{
        struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);

        if (stock->cached != mem) { /* reset if necessary */
                drain_stock(stock);
                stock->cached = mem;
        }
        stock->charge += val;
        put_cpu_var(memcg_stock);
}

/*
 * Tries to drain stocked charges in other cpus. This function is asynchronous
 * and just put a work per cpu for draining localy on each cpu. Caller can
 * expects some charges will be back to res_counter later but cannot wait for
 * it.
 */
static void drain_all_stock_async(void)
{
        int cpu;
        /* This function is for scheduling "drain" in asynchronous way.
         * The result of "drain" is not directly handled by callers. Then,
         * if someone is calling drain, we don't have to call drain more.
         * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if
         * there is a race. We just do loose check here.
         */
        if (atomic_read(&memcg_drain_count))
                return;
        /* Notify other cpus that system-wide "drain" is running */
        atomic_inc(&memcg_drain_count);
        get_online_cpus();
        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                schedule_work_on(cpu, &stock->work);
        }
        put_online_cpus();
        atomic_dec(&memcg_drain_count);
        /* We don't wait for flush_work */
}

/* This is a synchronous drain interface. */
static void drain_all_stock_sync(void)
{
        /* called when force_empty is called */
        atomic_inc(&memcg_drain_count);
        schedule_on_each_cpu(drain_local_stock);
        atomic_dec(&memcg_drain_count);
}

/*
 * This function drains percpu counter value from DEAD cpu and
 * move it to local cpu. Note that this function can be preempted.
 */
static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *mem, int cpu)
{
        int i;

        spin_lock(&mem->pcp_counter_lock);
        for (i = 0; i < MEM_CGROUP_STAT_DATA; i++) {
                s64 x = per_cpu(mem->stat->count[i], cpu);

                per_cpu(mem->stat->count[i], cpu) = 0;
                mem->nocpu_base.count[i] += x;
        }
        /* need to clear ON_MOVE value, works as a kind of lock. */
        per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) = 0;
        spin_unlock(&mem->pcp_counter_lock);
}

static void synchronize_mem_cgroup_on_move(struct mem_cgroup *mem, int cpu)
{
        int idx = MEM_CGROUP_ON_MOVE;

        spin_lock(&mem->pcp_counter_lock);
        per_cpu(mem->stat->count[idx], cpu) = mem->nocpu_base.count[idx];
        spin_unlock(&mem->pcp_counter_lock);
}

static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,
                                        unsigned long action,
                                        void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        struct memcg_stock_pcp *stock;
        struct mem_cgroup *iter;

        if ((action == CPU_ONLINE)) {
                for_each_mem_cgroup_all(iter)
                        synchronize_mem_cgroup_on_move(iter, cpu);
                return NOTIFY_OK;
        }

        if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)
                return NOTIFY_OK;

        for_each_mem_cgroup_all(iter)
                mem_cgroup_drain_pcp_counter(iter, cpu);

        stock = &per_cpu(memcg_stock, cpu);
        drain_stock(stock);
        return NOTIFY_OK;
}


/* See __mem_cgroup_try_charge() for details */
enum {
        CHARGE_OK,              /* success */
        CHARGE_RETRY,           /* need to retry but retry is not bad */
        CHARGE_NOMEM,           /* we can't do more. return -ENOMEM */
        CHARGE_WOULDBLOCK,      /* GFP_WAIT wasn't set and no enough res. */
        CHARGE_OOM_DIE,         /* the current is killed because of OOM */
};

static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
                                int csize, bool oom_check)
{
        struct mem_cgroup *mem_over_limit;
        struct res_counter *fail_res;
        unsigned long flags = 0;
        int ret;

        ret = res_counter_charge(&mem->res, csize, &fail_res);

        if (likely(!ret)) {
                if (!do_swap_account)
                        return CHARGE_OK;
                ret = res_counter_charge(&mem->memsw, csize, &fail_res);
                if (likely(!ret))
                        return CHARGE_OK;

                mem_over_limit = mem_cgroup_from_res_counter(fail_res, memsw);
                flags |= MEM_CGROUP_RECLAIM_NOSWAP;
        } else
                mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);

        if (csize > PAGE_SIZE) /* change csize and retry */
                return CHARGE_RETRY;

        if (!(gfp_mask & __GFP_WAIT))
                return CHARGE_WOULDBLOCK;

        ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
                                        gfp_mask, flags);
        /*
         * try_to_free_mem_cgroup_pages() might not give us a full
         * picture of reclaim. Some pages are reclaimed and might be
         * moved to swap cache or just unmapped from the cgroup.
         * Check the limit again to see if the reclaim reduced the
         * current usage of the cgroup before giving up
         */
        if (ret || mem_cgroup_check_under_limit(mem_over_limit))
                return CHARGE_RETRY;

        /*
         * At task move, charge accounts can be doubly counted. So, it's
         * better to wait until the end of task_move if something is going on.
         */
        if (mem_cgroup_wait_acct_move(mem_over_limit))
                return CHARGE_RETRY;

        /* If we don't need to call oom-killer at el, return immediately */
        if (!oom_check)
                return CHARGE_NOMEM;
        /* check OOM */
        if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask))
                return CHARGE_OOM_DIE;

        return CHARGE_RETRY;
}

/*
 * Unlike exported interface, "oom" parameter is added. if oom==true,
 * oom-killer can be invoked.
 */
static int __mem_cgroup_try_charge(struct mm_struct *mm,
                                   gfp_t gfp_mask,
                                   struct mem_cgroup **memcg, bool oom,
                                   int page_size)
{
        int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct mem_cgroup *mem = NULL;
        int ret;
        int csize = max(CHARGE_SIZE, (unsigned long) page_size);

        /*
         * Unlike gloval-vm's OOM-kill, we're not in memory shortage
         * in system level. So, allow to go ahead dying process in addition to
         * MEMDIE process.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE)
                     || fatal_signal_pending(current)))
                goto bypass;

        /*
         * We always charge the cgroup the mm_struct belongs to.
         * The mm_struct's mem_cgroup changes on task migration if the
         * thread group leader migrates. It's possible that mm is not
         * set, if so charge the init_mm (happens for pagecache usage).
         */
        if (!*memcg && !mm)
                goto bypass;
again:
        if (*memcg) { /* css should be a valid one */
                mem = *memcg;
                VM_BUG_ON(css_is_removed(&mem->css));
                if (mem_cgroup_is_root(mem))
                        goto done;
                if (page_size == PAGE_SIZE && consume_stock(mem))
                        goto done;
                css_get(&mem->css);
        } else {
                struct task_struct *p;

                rcu_read_lock();
                p = rcu_dereference(mm->owner);
                /*
                 * Because we don't have task_lock(), "p" can exit.
                 * In that case, "mem" can point to root or p can be NULL with
                 * race with swapoff. Then, we have small risk of mis-accouning.
                 * But such kind of mis-account by race always happens because
                 * we don't have cgroup_mutex(). It's overkill and we allo that
                 * small race, here.
                 * (*) swapoff at el will charge against mm-struct not against
                 * task-struct. So, mm->owner can be NULL.
                 */
                mem = mem_cgroup_from_task(p);
                if (!mem || mem_cgroup_is_root(mem)) {
                        rcu_read_unlock();
                        goto done;
                }
                if (page_size == PAGE_SIZE && consume_stock(mem)) {
                        /*
                         * It seems dagerous to access memcg without css_get().
                         * But considering how consume_stok works, it's not
                         * necessary. If consume_stock success, some charges
                         * from this memcg are cached on this cpu. So, we
                         * don't need to call css_get()/css_tryget() before
                         * calling consume_stock().
                         */
                        rcu_read_unlock();
                        goto done;
                }
                /* after here, we may be blocked. we need to get refcnt */
                if (!css_tryget(&mem->css)) {
                        rcu_read_unlock();
                        goto again;
                }
                rcu_read_unlock();
        }

        do {
                bool oom_check;

                /* If killed, bypass charge */
                if (fatal_signal_pending(current)) {
                        css_put(&mem->css);
                        goto bypass;
                }

                oom_check = false;
                if (oom && !nr_oom_retries) {
                        oom_check = true;
                        nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
                }

                ret = __mem_cgroup_do_charge(mem, gfp_mask, csize, oom_check);

                switch (ret) {
                case CHARGE_OK:
                        break;
                case CHARGE_RETRY: /* not in OOM situation but retry */
                        csize = page_size;
                        css_put(&mem->css);
                        mem = NULL;
                        goto again;
                case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
                        css_put(&mem->css);
                        goto nomem;
                case CHARGE_NOMEM: /* OOM routine works */
                        if (!oom) {
                                css_put(&mem->css);
                                goto nomem;
                        }
                        /* If oom, we never return -ENOMEM */
                        nr_oom_retries--;
                        break;
                case CHARGE_OOM_DIE: /* Killed by OOM Killer */
                        css_put(&mem->css);
                        goto bypass;
                }
        } while (ret != CHARGE_OK);

        if (csize > page_size)
                refill_stock(mem, csize - page_size);
        css_put(&mem->css);
done:
        *memcg = mem;
        return 0;
nomem:
        *memcg = NULL;
        return -ENOMEM;
bypass:
        *memcg = NULL;
        return 0;
}

/*
 * Somemtimes we have to undo a charge we got by try_charge().
 * This function is for that and do uncharge, put css's refcnt.
 * gotten by try_charge().
 */
static void __mem_cgroup_cancel_charge(struct mem_cgroup *mem,
                                                        unsigned long count)
{
        if (!mem_cgroup_is_root(mem)) {
                res_counter_uncharge(&mem->res, PAGE_SIZE * count);
                if (do_swap_account)
                        res_counter_uncharge(&mem->memsw, PAGE_SIZE * count);
        }
}

static void mem_cgroup_cancel_charge(struct mem_cgroup *mem,
                                     int page_size)
{
        __mem_cgroup_cancel_charge(mem, page_size >> PAGE_SHIFT);
}

/*
 * A helper function to get mem_cgroup from ID. must be called under
 * rcu_read_lock(). The caller must check css_is_removed() or some if
 * it's concern. (dropping refcnt from swap can be called against removed
 * memcg.)
 */
static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
{
        struct cgroup_subsys_state *css;

        /* ID 0 is unused ID */
        if (!id)
                return NULL;
        css = css_lookup(&mem_cgroup_subsys, id);
        if (!css)
                return NULL;
        return container_of(css, struct mem_cgroup, css);
}

struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
        struct mem_cgroup *mem = NULL;
        struct page_cgroup *pc;
        unsigned short id;
        swp_entry_t ent;

        VM_BUG_ON(!PageLocked(page));

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                mem = pc->mem_cgroup;
                if (mem && !css_tryget(&mem->css))
                        mem = NULL;
        } else if (PageSwapCache(page)) {
                ent.val = page_private(page);
                id = lookup_swap_cgroup(ent);
                rcu_read_lock();
                mem = mem_cgroup_lookup(id);
                if (mem && !css_tryget(&mem->css))
                        mem = NULL;
                rcu_read_unlock();
        }
        unlock_page_cgroup(pc);
        return mem;
}

static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
                                       struct page_cgroup *pc,
                                       enum charge_type ctype,
                                       int page_size)
{
        int nr_pages = page_size >> PAGE_SHIFT;

        /* try_charge() can return NULL to *memcg, taking care of it. */
        if (!mem)
                return;

        lock_page_cgroup(pc);
        if (unlikely(PageCgroupUsed(pc))) {
                unlock_page_cgroup(pc);
                mem_cgroup_cancel_charge(mem, page_size);
                return;
        }
        /*
         * we don't need page_cgroup_lock about tail pages, becase they are not
         * accessed by any other context at this point.
         */
        pc->mem_cgroup = mem;
        /*
         * We access a page_cgroup asynchronously without lock_page_cgroup().
         * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
         * is accessed after testing USED bit. To make pc->mem_cgroup visible
         * before USED bit, we need memory barrier here.
         * See mem_cgroup_add_lru_list(), etc.
         */
        smp_wmb();
        switch (ctype) {
        case MEM_CGROUP_CHARGE_TYPE_CACHE:
        case MEM_CGROUP_CHARGE_TYPE_SHMEM:
                SetPageCgroupCache(pc);
                SetPageCgroupUsed(pc);
                break;
        case MEM_CGROUP_CHARGE_TYPE_MAPPED:
                ClearPageCgroupCache(pc);
                SetPageCgroupUsed(pc);
                break;
        default:
                break;
        }

        mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), nr_pages);
        unlock_page_cgroup(pc);
        /*
         * "charge_statistics" updated event counter. Then, check it.
         * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
         * if they exceeds softlimit.
         */
        memcg_check_events(mem, pc->page);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (1 << PCG_MOVE_LOCK) |\
                        (1 << PCG_ACCT_LRU) | (1 << PCG_MIGRATION))
/*
 * Because tail pages are not marked as "used", set it. We're under
 * zone->lru_lock, 'splitting on pmd' and compund_lock.
 */
void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)
{
        struct page_cgroup *head_pc = lookup_page_cgroup(head);
        struct page_cgroup *tail_pc = lookup_page_cgroup(tail);
        unsigned long flags;

        /*
         * We have no races with charge/uncharge but will have races with
         * page state accounting.
         */
        move_lock_page_cgroup(head_pc, &flags);

        tail_pc->mem_cgroup = head_pc->mem_cgroup;
        smp_wmb(); /* see __commit_charge() */
        if (PageCgroupAcctLRU(head_pc)) {
                enum lru_list lru;
                struct mem_cgroup_per_zone *mz;

                /*
                 * LRU flags cannot be copied because we need to add tail
                 *.page to LRU by generic call and our hook will be called.
                 * We hold lru_lock, then, reduce counter directly.
                 */
                lru = page_lru(head);
                mz = page_cgroup_zoneinfo(head_pc);
                MEM_CGROUP_ZSTAT(mz, lru) -= 1;
        }
        tail_pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
        move_unlock_page_cgroup(head_pc, &flags);
}
#endif

/**
 * __mem_cgroup_move_account - move account of the page
 * @pc: page_cgroup of the page.
 * @from: mem_cgroup which the page is moved from.
 * @to: mem_cgroup which the page is moved to. @from != @to.
 * @uncharge: whether we should call uncharge and css_put against @from.
 *
 * The caller must confirm following.
 * - page is not on LRU (isolate_page() is useful.)
 * - the pc is locked, used, and ->mem_cgroup points to @from.
 *
 * This function doesn't do "charge" nor css_get to new cgroup. It should be
 * done by a caller(__mem_cgroup_try_charge would be usefull). If @uncharge is
 * true, this function does "uncharge" from old cgroup, but it doesn't if
 * @uncharge is false, so a caller should do "uncharge".
 */

static void __mem_cgroup_move_account(struct page_cgroup *pc,
        struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
{
        VM_BUG_ON(from == to);
        VM_BUG_ON(PageLRU(pc->page));
        VM_BUG_ON(!page_is_cgroup_locked(pc));
        VM_BUG_ON(!PageCgroupUsed(pc));
        VM_BUG_ON(pc->mem_cgroup != from);

        if (PageCgroupFileMapped(pc)) {
                /* Update mapped_file data for mem_cgroup */
                preempt_disable();
                __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
                preempt_enable();
        }
        mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -1);
        if (uncharge)
                /* This is not "cancel", but cancel_charge does all we need. */
                mem_cgroup_cancel_charge(from, PAGE_SIZE);

        /* caller should have done css_get */
        pc->mem_cgroup = to;
        mem_cgroup_charge_statistics(to, PageCgroupCache(pc), 1);
        /*
         * We charges against "to" which may not have any tasks. Then, "to"
         * can be under rmdir(). But in current implementation, caller of
         * this function is just force_empty() and move charge, so it's
         * garanteed that "to" is never removed. So, we don't check rmdir
         * status here.
         */
}

/*
 * check whether the @pc is valid for moving account and call
 * __mem_cgroup_move_account()
 */
static int mem_cgroup_move_account(struct page_cgroup *pc,
                struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
{
        int ret = -EINVAL;
        unsigned long flags;

        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
                move_lock_page_cgroup(pc, &flags);
                __mem_cgroup_move_account(pc, from, to, uncharge);
                move_unlock_page_cgroup(pc, &flags);
                ret = 0;
        }
        unlock_page_cgroup(pc);
        /*
         * check events
         */
        memcg_check_events(to, pc->page);
        memcg_check_events(from, pc->page);
        return ret;
}

/*
 * move charges to its parent.
 */

static int mem_cgroup_move_parent(struct page_cgroup *pc,
                                  struct mem_cgroup *child,
                                  gfp_t gfp_mask)
{
        struct page *page = pc->page;
        struct cgroup *cg = child->css.cgroup;
        struct cgroup *pcg = cg->parent;
        struct mem_cgroup *parent;
        int ret;

        /* Is ROOT ? */
        if (!pcg)
                return -EINVAL;

        ret = -EBUSY;
        if (!get_page_unless_zero(page))
                goto out;
        if (isolate_lru_page(page))
                goto put;

        parent = mem_cgroup_from_cont(pcg);
        ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false,
                                      PAGE_SIZE);
        if (ret || !parent)
                goto put_back;

        ret = mem_cgroup_move_account(pc, child, parent, true);
        if (ret)
                mem_cgroup_cancel_charge(parent, PAGE_SIZE);
put_back:
        putback_lru_page(page);
put:
        put_page(page);
out:
        return ret;
}

/*
 * Charge the memory controller for page usage.
 * Return
 * 0 if the charge was successful
 * < 0 if the cgroup is over its limit
 */
static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask, enum charge_type ctype)
{
        struct mem_cgroup *mem = NULL;
        struct page_cgroup *pc;
        int ret;
        int page_size = PAGE_SIZE;

        if (PageTransHuge(page)) {
                page_size <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
        }

        pc = lookup_page_cgroup(page);
        /* can happen at boot */
        if (unlikely(!pc))
                return 0;
        prefetchw(pc);

        ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, true, page_size);
        if (ret || !mem)
                return ret;

        __mem_cgroup_commit_charge(mem, pc, ctype, page_size);
        return 0;
}

int mem_cgroup_newpage_charge(struct page *page,
                              struct mm_struct *mm, gfp_t gfp_mask)
{
        if (mem_cgroup_disabled())
                return 0;
        /*
         * If already mapped, we don't have to account.
         * If page cache, page->mapping has address_space.
         * But page->mapping may have out-of-use anon_vma pointer,
         * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
         * is NULL.
         */
        if (page_mapped(page) || (page->mapping && !PageAnon(page)))
                return 0;
        if (unlikely(!mm))
                mm = &init_mm;
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
                                        enum charge_type ctype);

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        int ret;

        if (mem_cgroup_disabled())
                return 0;
        if (PageCompound(page))
                return 0;
        /*
         * Corner case handling. This is called from add_to_page_cache()
         * in usual. But some FS (shmem) precharges this page before calling it
         * and call add_to_page_cache() with GFP_NOWAIT.
         *
         * For GFP_NOWAIT case, the page may be pre-charged before calling
         * add_to_page_cache(). (See shmem.c) check it here and avoid to call
         * charge twice. (It works but has to pay a bit larger cost.)
         * And when the page is SwapCache, it should take swap information
         * into account. This is under lock_page() now.
         */
        if (!(gfp_mask & __GFP_WAIT)) {
                struct page_cgroup *pc;

                pc = lookup_page_cgroup(page);
                if (!pc)
                        return 0;
                lock_page_cgroup(pc);
                if (PageCgroupUsed(pc)) {
                        unlock_page_cgroup(pc);
                        return 0;
                }
                unlock_page_cgroup(pc);
        }

        if (unlikely(!mm))
                mm = &init_mm;

        if (page_is_file_cache(page))
                return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_CACHE);

        /* shmem */
        if (PageSwapCache(page)) {
                struct mem_cgroup *mem = NULL;

                ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
                if (!ret)
                        __mem_cgroup_commit_charge_swapin(page, mem,
                                        MEM_CGROUP_CHARGE_TYPE_SHMEM);
        } else
                ret = mem_cgroup_charge_common(page, mm, gfp_mask,
                                        MEM_CGROUP_CHARGE_TYPE_SHMEM);

        return ret;
}

/*
 * While swap-in, try_charge -> commit or cancel, the page is locked.
 * And when try_charge() successfully returns, one refcnt to memcg without
 * struct page_cgroup is acquired. This refcnt will be consumed by
 * "commit()" or removed by "cancel()"
 */
int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
                                 struct page *page,
                                 gfp_t mask, struct mem_cgroup **ptr)
{
        struct mem_cgroup *mem;
        int ret;

        if (mem_cgroup_disabled())
                return 0;

        if (!do_swap_account)
                goto charge_cur_mm;
        /*
         * A racing thread's fault, or swapoff, may have already updated
         * the pte, and even removed page from swap cache: in those cases
         * do_swap_page()'s pte_same() test will fail; but there's also a
         * KSM case which does need to charge the page.
         */
        if (!PageSwapCache(page))
                goto charge_cur_mm;
        mem = try_get_mem_cgroup_from_page(page);
        if (!mem)
                goto charge_cur_mm;
        *ptr = mem;
        ret = __mem_cgroup_try_charge(NULL, mask, ptr, true, PAGE_SIZE);
        css_put(&mem->css);
        return ret;
charge_cur_mm:
        if (unlikely(!mm))
                mm = &init_mm;
        return __mem_cgroup_try_charge(mm, mask, ptr, true, PAGE_SIZE);
}

static void
__mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
                                        enum charge_type ctype)
{
        struct page_cgroup *pc;

        if (mem_cgroup_disabled())
                return;
        if (!ptr)
                return;
        cgroup_exclude_rmdir(&ptr->css);
        pc = lookup_page_cgroup(page);
        mem_cgroup_lru_del_before_commit_swapcache(page);
        __mem_cgroup_commit_charge(ptr, pc, ctype, PAGE_SIZE);
        mem_cgroup_lru_add_after_commit_swapcache(page);
        /*
         * Now swap is on-memory. This means this page may be
         * counted both as mem and swap....double count.
         * Fix it by uncharging from memsw. Basically, this SwapCache is stable
         * under lock_page(). But in do_swap_page()::memory.c, reuse_swap_page()
         * may call delete_from_swap_cache() before reach here.
         */
        if (do_swap_account && PageSwapCache(page)) {
                swp_entry_t ent = {.val = page_private(page)};
                unsigned short id;
                struct mem_cgroup *memcg;

                id = swap_cgroup_record(ent, 0);
                rcu_read_lock();
                memcg = mem_cgroup_lookup(id);
                if (memcg) {
                        /*
                         * This recorded memcg can be obsolete one. So, avoid
                         * calling css_tryget
                         */
                        if (!mem_cgroup_is_root(memcg))
                                res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
                        mem_cgroup_swap_statistics(memcg, false);
                        mem_cgroup_put(memcg);
                }
                rcu_read_unlock();
        }
        /*
         * At swapin, we may charge account against cgroup which has no tasks.
         * So, rmdir()->pre_destroy() can be called while we do this charge.
         * In that case, we need to call pre_destroy() again. check it here.
         */
        cgroup_release_and_wakeup_rmdir(&ptr->css);
}

void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
{
        __mem_cgroup_commit_charge_swapin(page, ptr,
                                        MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
{
        if (mem_cgroup_disabled())
                return;
        if (!mem)
                return;
        mem_cgroup_cancel_charge(mem, PAGE_SIZE);
}

static void
__do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
              int page_size)
{
        struct memcg_batch_info *batch = NULL;
        bool uncharge_memsw = true;
        /* If swapout, usage of swap doesn't decrease */
        if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
                uncharge_memsw = false;

        batch = &current->memcg_batch;
        /*
         * In usual, we do css_get() when we remember memcg pointer.
         * But in this case, we keep res->usage until end of a series of
         * uncharges. Then, it's ok to ignore memcg's refcnt.
         */
        if (!batch->memcg)
                batch->memcg = mem;
        /*
         * do_batch > 0 when unmapping pages or inode invalidate/truncate.
         * In those cases, all pages freed continously can be expected to be in
         * the same cgroup and we have chance to coalesce uncharges.
         * But we do uncharge one by one if this is killed by OOM(TIF_MEMDIE)
         * because we want to do uncharge as soon as possible.
         */

        if (!batch->do_batch || test_thread_flag(TIF_MEMDIE))
                goto direct_uncharge;

        if (page_size != PAGE_SIZE)
                goto direct_uncharge;

        /*
         * In typical case, batch->memcg == mem. This means we can
         * merge a series of uncharges to an uncharge of res_counter.
         * If not, we uncharge res_counter ony by one.
         */
        if (batch->memcg != mem)
                goto direct_uncharge;
        /* remember freed charge and uncharge it later */
        batch->bytes += PAGE_SIZE;
        if (uncharge_memsw)
                batch->memsw_bytes += PAGE_SIZE;
        return;
direct_uncharge:
        res_counter_uncharge(&mem->res, page_size);
        if (uncharge_memsw)
                res_counter_uncharge(&mem->memsw, page_size);
        if (unlikely(batch->memcg != mem))
                memcg_oom_recover(mem);
        return;
}

/*
 * uncharge if !page_mapped(page)
 */
static struct mem_cgroup *
__mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
{
        int count;
        struct page_cgroup *pc;
        struct mem_cgroup *mem = NULL;
        int page_size = PAGE_SIZE;

        if (mem_cgroup_disabled())
                return NULL;

        if (PageSwapCache(page))
                return NULL;

        if (PageTransHuge(page)) {
                page_size <<= compound_order(page);
                VM_BUG_ON(!PageTransHuge(page));
        }

        count = page_size >> PAGE_SHIFT;
        /*
         * Check if our page_cgroup is valid
         */
        pc = lookup_page_cgroup(page);
        if (unlikely(!pc || !PageCgroupUsed(pc)))
                return NULL;

        lock_page_cgroup(pc);

        mem = pc->mem_cgroup;

        if (!PageCgroupUsed(pc))
                goto unlock_out;

        switch (ctype) {
        case MEM_CGROUP_CHARGE_TYPE_MAPPED:
        case MEM_CGROUP_CHARGE_TYPE_DROP:
                /* See mem_cgroup_prepare_migration() */
                if (page_mapped(page) || PageCgroupMigration(pc))
                        goto unlock_out;
                break;
        case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
                if (!PageAnon(page)) {  /* Shared memory */
                        if (page->mapping && !page_is_file_cache(page))
                                goto unlock_out;
                } else if (page_mapped(page)) /* Anon */
                                goto unlock_out;
                break;
        default:
                break;
        }

        mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), -count);

        ClearPageCgroupUsed(pc);
        /*
         * pc->mem_cgroup is not cleared here. It will be accessed when it's
         * freed from LRU. This is safe because uncharged page is expected not
         * to be reused (freed soon). Exception is SwapCache, it's handled by
         * special functions.
         */

        unlock_page_cgroup(pc);
        /*
         * even after unlock, we have mem->res.usage here and this memcg
         * will never be freed.
         */
        memcg_check_events(mem, page);
        if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
                mem_cgroup_swap_statistics(mem, true);
                mem_cgroup_get(mem);
        }
        if (!mem_cgroup_is_root(mem))
                __do_uncharge(mem, ctype, page_size);

        return mem;

unlock_out:
        unlock_page_cgroup(pc);
        return NULL;
}

void mem_cgroup_uncharge_page(struct page *page)
{
        /* early check. */
        if (page_mapped(page))
                return;
        if (page->mapping && !PageAnon(page))
                return;
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_uncharge_cache_page(struct page *page)
{
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping);
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
}

/*
 * Batch_start/batch_end is called in unmap_page_range/invlidate/trucate.
 * In that cases, pages are freed continuously and we can expect pages
 * are in the same memcg. All these calls itself limits the number of
 * pages freed at once, then uncharge_start/end() is called properly.
 * This may be called prural(2) times in a context,
 */

void mem_cgroup_uncharge_start(void)
{
        current->memcg_batch.do_batch++;
        /* We can do nest. */
        if (current->memcg_batch.do_batch == 1) {
                current->memcg_batch.memcg = NULL;
                current->memcg_batch.bytes = 0;
                current->memcg_batch.memsw_bytes = 0;
        }
}

void mem_cgroup_uncharge_end(void)
{
        struct memcg_batch_info *batch = &current->memcg_batch;

        if (!batch->do_batch)
                return;

        batch->do_batch--;
        if (batch->do_batch) /* If stacked, do nothing. */
                return;

        if (!batch->memcg)
                return;
        /*
         * This "batch->memcg" is valid without any css_get/put etc...
         * bacause we hide charges behind us.
         */
        if (batch->bytes)
                res_counter_uncharge(&batch->memcg->res, batch->bytes);
        if (batch->memsw_bytes)
                res_counter_uncharge(&batch->memcg->memsw, batch->memsw_bytes);
        memcg_oom_recover(batch->memcg);
        /* forget this pointer (for sanity check) */
        batch->memcg = NULL;
}

#ifdef CONFIG_SWAP
/*
 * called after __delete_from_swap_cache() and drop "page" account.
 * memcg information is recorded to swap_cgroup of "ent"
 */
void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
{
        struct mem_cgroup *memcg;
        int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;

        if (!swapout) /* this was a swap cache but the swap is unused ! */
                ctype = MEM_CGROUP_CHARGE_TYPE_DROP;

        memcg = __mem_cgroup_uncharge_common(page, ctype);

        /*
         * record memcg information,  if swapout && memcg != NULL,
         * mem_cgroup_get() was called in uncharge().
         */
        if (do_swap_account && swapout && memcg)
                swap_cgroup_record(ent, css_id(&memcg->css));
}
#endif

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
/*
 * called from swap_entry_free(). remove record in swap_cgroup and
 * uncharge "memsw" account.
 */
void mem_cgroup_uncharge_swap(swp_entry_t ent)
{
        struct mem_cgroup *memcg;
        unsigned short id;

        if (!do_swap_account)
                return;

        id = swap_cgroup_record(ent, 0);
        rcu_read_lock();
        memcg = mem_cgroup_lookup(id);
        if (memcg) {
                /*
                 * We uncharge this because swap is freed.
                 * This memcg can be obsolete one. We avoid calling css_tryget
                 */
                if (!mem_cgroup_is_root(memcg))
                        res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
                mem_cgroup_swap_statistics(memcg, false);
                mem_cgroup_put(memcg);
        }
        rcu_read_unlock();
}

/**
 * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
 * @entry: swap entry to be moved
 * @from:  mem_cgroup which the entry is moved from
 * @to:  mem_cgroup which the entry is moved to
 * @need_fixup: whether we should fixup res_counters and refcounts.
 *
 * It succeeds only when the swap_cgroup's record for this entry is the same
 * as the mem_cgroup's id of @from.
 *
 * Returns 0 on success, -EINVAL on failure.
 *
 * The caller must have charged to @to, IOW, called res_counter_charge() about
 * both res and memsw, and called css_get().
 */
static int mem_cgroup_move_swap_account(swp_entry_t entry,
                struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
        unsigned short old_id, new_id;

        old_id = css_id(&from->css);
        new_id = css_id(&to->css);

        if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
                mem_cgroup_swap_statistics(from, false);
                mem_cgroup_swap_statistics(to, true);
                /*
                 * This function is only called from task migration context now.
                 * It postpones res_counter and refcount handling till the end
                 * of task migration(mem_cgroup_clear_mc()) for performance
                 * improvement. But we cannot postpone mem_cgroup_get(to)
                 * because if the process that has been moved to @to does
                 * swap-in, the refcount of @to might be decreased to 0.
                 */
                mem_cgroup_get(to);
                if (need_fixup) {
                        if (!mem_cgroup_is_root(from))
                                res_counter_uncharge(&from->memsw, PAGE_SIZE);
                        mem_cgroup_put(from);
                        /*
                         * we charged both to->res and to->memsw, so we should
                         * uncharge to->res.
                         */
                        if (!mem_cgroup_is_root(to))
                                res_counter_uncharge(&to->res, PAGE_SIZE);
                }
                return 0;
        }
        return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
                struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
        return -EINVAL;
}
#endif

/*
 * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
 * page belongs to.
 */
int mem_cgroup_prepare_migration(struct page *page,
        struct page *newpage, struct mem_cgroup **ptr)
{
        struct page_cgroup *pc;
        struct mem_cgroup *mem = NULL;
        enum charge_type ctype;
        int ret = 0;

        VM_BUG_ON(PageTransHuge(page));
        if (mem_cgroup_disabled())
                return 0;

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                mem = pc->mem_cgroup;
                css_get(&mem->css);
                /*
                 * At migrating an anonymous page, its mapcount goes down
                 * to 0 and uncharge() will be called. But, even if it's fully
                 * unmapped, migration may fail and this page has to be
                 * charged again. We set MIGRATION flag here and delay uncharge
                 * until end_migration() is called
                 *
                 * Corner Case Thinking
                 * A)
                 * When the old page was mapped as Anon and it's unmap-and-freed
                 * while migration was ongoing.
                 * If unmap finds the old page, uncharge() of it will be delayed
                 * until end_migration(). If unmap finds a new page, it's
                 * uncharged when it make mapcount to be 1->0. If unmap code
                 * finds swap_migration_entry, the new page will not be mapped
                 * and end_migration() will find it(mapcount==0).
                 *
                 * B)
                 * When the old page was mapped but migraion fails, the kernel
                 * remaps it. A charge for it is kept by MIGRATION flag even
                 * if mapcount goes down to 0. We can do remap successfully
                 * without charging it again.
                 *
                 * C)
                 * The "old" page is under lock_page() until the end of
                 * migration, so, the old page itself will not be swapped-out.
                 * If the new page is swapped out before end_migraton, our
                 * hook to usual swap-out path will catch the event.
                 */
                if (PageAnon(page))
                        SetPageCgroupMigration(pc);
        }
        unlock_page_cgroup(pc);
        /*
         * If the page is not charged at this point,
         * we return here.
         */
        if (!mem)
                return 0;

        *ptr = mem;
        ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false, PAGE_SIZE);
        css_put(&mem->css);/* drop extra refcnt */
        if (ret || *ptr == NULL) {
                if (PageAnon(page)) {
                        lock_page_cgroup(pc);
                        ClearPageCgroupMigration(pc);
                        unlock_page_cgroup(pc);
                        /*
                         * The old page may be fully unmapped while we kept it.
                         */
                        mem_cgroup_uncharge_page(page);
                }
                return -ENOMEM;
        }
        /*
         * We charge new page before it's used/mapped. So, even if unlock_page()
         * is called before end_migration, we can catch all events on this new
         * page. In the case new page is migrated but not remapped, new page's
         * mapcount will be finally 0 and we call uncharge in end_migration().
         */
        pc = lookup_page_cgroup(newpage);
        if (PageAnon(page))
                ctype = MEM_CGROUP_CHARGE_TYPE_MAPPED;
        else if (page_is_file_cache(page))
                ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
        else
                ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
        __mem_cgroup_commit_charge(mem, pc, ctype, PAGE_SIZE);
        return ret;
}

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *mem,
        struct page *oldpage, struct page *newpage, bool migration_ok)
{
        struct page *used, *unused;
        struct page_cgroup *pc;

        if (!mem)
                return;
        /* blocks rmdir() */
        cgroup_exclude_rmdir(&mem->css);
        if (!migration_ok) {
                used = oldpage;
                unused = newpage;
        } else {
                used = newpage;
                unused = oldpage;
        }
        /*
         * We disallowed uncharge of pages under migration because mapcount
         * of the page goes down to zero, temporarly.
         * Clear the flag and check the page should be charged.
         */
        pc = lookup_page_cgroup(oldpage);
        lock_page_cgroup(pc);
        ClearPageCgroupMigration(pc);
        unlock_page_cgroup(pc);

        __mem_cgroup_uncharge_common(unused, MEM_CGROUP_CHARGE_TYPE_FORCE);

        /*
         * If a page is a file cache, radix-tree replacement is very atomic
         * and we can skip this check. When it was an Anon page, its mapcount
         * goes down to 0. But because we added MIGRATION flage, it's not
         * uncharged yet. There are several case but page->mapcount check
         * and USED bit check in mem_cgroup_uncharge_page() will do enough
         * check. (see prepare_charge() also)
         */
        if (PageAnon(used))
                mem_cgroup_uncharge_page(used);
        /*
         * At migration, we may charge account against cgroup which has no
         * tasks.
         * So, rmdir()->pre_destroy() can be called while we do this charge.
         * In that case, we need to call pre_destroy() again. check it here.
         */
        cgroup_release_and_wakeup_rmdir(&mem->css);
}

/*
 * A call to try to shrink memory usage on charge failure at shmem's swapin.
 * Calling hierarchical_reclaim is not enough because we should update
 * last_oom_jiffies to prevent pagefault_out_of_memory from invoking global OOM.
 * Moreover considering hierarchy, we should reclaim from the mem_over_limit,
 * not from the memcg which this page would be charged to.
 * try_charge_swapin does all of these works properly.
 */
int mem_cgroup_shmem_charge_fallback(struct page *page,
                            struct mm_struct *mm,
                            gfp_t gfp_mask)
{
        struct mem_cgroup *mem = NULL;
        int ret;

        if (mem_cgroup_disabled())
                return 0;

        ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
        if (!ret)
                mem_cgroup_cancel_charge_swapin(mem); /* it does !mem check */

        return ret;
}

static DEFINE_MUTEX(set_limit_mutex);

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                unsigned long long val)
{
        int retry_count;
        u64 memswlimit, memlimit;
        int ret = 0;
        int children = mem_cgroup_count_children(memcg);
        u64 curusage, oldusage;
        int enlarge;

        /*
         * For keeping hierarchical_reclaim simple, how long we should retry
         * is depends on callers. We set our retry-count to be function
         * of # of children which we should visit in this loop.
         */
        retry_count = MEM_CGROUP_RECLAIM_RETRIES * children;

        oldusage = res_counter_read_u64(&memcg->res, RES_USAGE);

        enlarge = 0;
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee mem->res.limit < mem->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }

                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit < val)
                        enlarge = 1;

                ret = res_counter_set_limit(&memcg->res, val);
                if (!ret) {
                        if (memswlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
                                                MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);

        return ret;
}

static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                                        unsigned long long val)
{
        int retry_count;
        u64 memlimit, memswlimit, oldusage, curusage;
        int children = mem_cgroup_count_children(memcg);
        int ret = -EBUSY;
        int enlarge = 0;

        /* see mem_cgroup_resize_res_limit */
        retry_count = children * MEM_CGROUP_RECLAIM_RETRIES;
        oldusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
        while (retry_count) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                /*
                 * Rather than hide all in some function, I do this in
                 * open coded manner. You see what this really does.
                 * We have to guarantee mem->res.limit < mem->memsw.limit.
                 */
                mutex_lock(&set_limit_mutex);
                memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
                if (memlimit > val) {
                        ret = -EINVAL;
                        mutex_unlock(&set_limit_mutex);
                        break;
                }
                memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                if (memswlimit < val)
                        enlarge = 1;
                ret = res_counter_set_limit(&memcg->memsw, val);
                if (!ret) {
                        if (memlimit == val)
                                memcg->memsw_is_minimum = true;
                        else
                                memcg->memsw_is_minimum = false;
                }
                mutex_unlock(&set_limit_mutex);

                if (!ret)
                        break;

                mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
                                                MEM_CGROUP_RECLAIM_NOSWAP |
                                                MEM_CGROUP_RECLAIM_SHRINK);
                curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        }
        if (!ret && enlarge)
                memcg_oom_recover(memcg);
        return ret;
}

unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                                            gfp_t gfp_mask)
{
        unsigned long nr_reclaimed = 0;
        struct mem_cgroup_per_zone *mz, *next_mz = NULL;
        unsigned long reclaimed;
        int loop = 0;
        struct mem_cgroup_tree_per_zone *mctz;
        unsigned long long excess;

        if (order > 0)
                return 0;

        mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
        /*
         * This loop can run a while, specially if mem_cgroup's continuously
         * keep exceeding their soft limit and putting the system under
         * pressure
         */
        do {
                if (next_mz)
                        mz = next_mz;
                else
                        mz = mem_cgroup_largest_soft_limit_node(mctz);
                if (!mz)
                        break;

                reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
                                                gfp_mask,
                                                MEM_CGROUP_RECLAIM_SOFT);
                nr_reclaimed += reclaimed;
                spin_lock(&mctz->lock);

                /*
                 * If we failed to reclaim anything from this memory cgroup
                 * it is time to move on to the next cgroup
                 */
                next_mz = NULL;
                if (!reclaimed) {
                        do {
                                /*
                                 * Loop until we find yet another one.
                                 *
                                 * By the time we get the soft_limit lock
                                 * again, someone might have aded the
                                 * group back on the RB tree. Iterate to
                                 * make sure we get a different mem.
                                 * mem_cgroup_largest_soft_limit_node returns
                                 * NULL if no other cgroup is present on
                                 * the tree
                                 */
                                next_mz =
                                __mem_cgroup_largest_soft_limit_node(mctz);
                                if (next_mz == mz) {
                                        css_put(&next_mz->mem->css);
                                        next_mz = NULL;
                                } else /* next_mz == NULL or other memcg */
                                        break;
                        } while (1);
                }
                __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
                excess = res_counter_soft_limit_excess(&mz->mem->res);
                /*
                 * One school of thought says that we should not add
                 * back the node to the tree if reclaim returns 0.
                 * But our reclaim could return 0, simply because due
                 * to priority we are exposing a smaller subset of
                 * memory to reclaim from. Consider this as a longer
                 * term TODO.
                 */
                /* If excess == 0, no tree ops */
                __mem_cgroup_insert_exceeded(mz->mem, mz, mctz, excess);
                spin_unlock(&mctz->lock);
                css_put(&mz->mem->css);
                loop++;
                /*
                 * Could not reclaim anything and there are no more
                 * mem cgroups to try or we seem to be looping without
                 * reclaiming anything.
                 */
                if (!nr_reclaimed &&
                        (next_mz == NULL ||
                        loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
                        break;
        } while (!nr_reclaimed);
        if (next_mz)
                css_put(&next_mz->mem->css);
        return nr_reclaimed;
}

/*
 * This routine traverse page_cgroup in given list and drop them all.
 * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
 */
static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
                                int node, int zid, enum lru_list lru)
{
        struct zone *zone;
        struct mem_cgroup_per_zone *mz;
        struct page_cgroup *pc, *busy;
        unsigned long flags, loop;
        struct list_head *list;
        int ret = 0;

        zone = &NODE_DATA(node)->node_zones[zid];
        mz = mem_cgroup_zoneinfo(mem, node, zid);
        list = &mz->lists[lru];

        loop = MEM_CGROUP_ZSTAT(mz, lru);
        /* give some margin against EBUSY etc...*/
        loop += 256;
        busy = NULL;
        while (loop--) {
                ret = 0;
                spin_lock_irqsave(&zone->lru_lock, flags);
                if (list_empty(list)) {
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        break;
                }
                pc = list_entry(list->prev, struct page_cgroup, lru);
                if (busy == pc) {
                        list_move(&pc->lru, list);
                        busy = NULL;
                        spin_unlock_irqrestore(&zone->lru_lock, flags);
                        continue;
                }
                spin_unlock_irqrestore(&zone->lru_lock, flags);

                ret = mem_cgroup_move_parent(pc, mem, GFP_KERNEL);
                if (ret == -ENOMEM)
                        break;

                if (ret == -EBUSY || ret == -EINVAL) {
                        /* found lock contention or "pc" is obsolete. */
                        busy = pc;
                        cond_resched();
                } else
                        busy = NULL;
        }

        if (!ret && !list_empty(list))
                return -EBUSY;
        return ret;
}

/*
 * make mem_cgroup's charge to be 0 if there is no task.
 * This enables deleting this mem_cgroup.
 */
static int mem_cgroup_force_empty(struct mem_cgroup *mem, bool free_all)
{
        int ret;
        int node, zid, shrink;
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct cgroup *cgrp = mem->css.cgroup;

        css_get(&mem->css);

        shrink = 0;
        /* should free all ? */
        if (free_all)
                goto try_to_free;
move_account:
        do {
                ret = -EBUSY;
                if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
                        goto out;
                ret = -EINTR;
                if (signal_pending(current))
                        goto out;
                /* This is for making all *used* pages to be on LRU. */
                lru_add_drain_all();
                drain_all_stock_sync();
                ret = 0;
                mem_cgroup_start_move(mem);
                for_each_node_state(node, N_HIGH_MEMORY) {
                        for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
                                enum lru_list l;
                                for_each_lru(l) {
                                        ret = mem_cgroup_force_empty_list(mem,
                                                        node, zid, l);
                                        if (ret)
                                                break;
                                }
                        }
                        if (ret)
                                break;
                }
                mem_cgroup_end_move(mem);
                memcg_oom_recover(mem);
                /* it seems parent cgroup doesn't have enough mem */
                if (ret == -ENOMEM)
                        goto try_to_free;
                cond_resched();
        /* "ret" should also be checked to ensure all lists are empty. */
        } while (mem->res.usage > 0 || ret);
out:
        css_put(&mem->css);
        return ret;

try_to_free:
        /* returns EBUSY if there is a task or if we come here twice. */
        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children) || shrink) {
                ret = -EBUSY;
                goto out;
        }
        /* we call try-to-free pages for make this cgroup empty */
        lru_add_drain_all();
        /* try to free all pages in this cgroup */
        shrink = 1;
        while (nr_retries && mem->res.usage > 0) {
                int progress;

                if (signal_pending(current)) {
                        ret = -EINTR;
                        goto out;
                }
                progress = try_to_free_mem_cgroup_pages(mem, GFP_KERNEL,
                                                false, get_swappiness(mem));
                if (!progress) {
                        nr_retries--;
                        /* maybe some writeback is necessary */
                        congestion_wait(BLK_RW_ASYNC, HZ/10);
                }

        }
        lru_add_drain();
        /* try move_account...there may be some *locked* pages. */
        goto move_account;
}

int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
{
        return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
}


static u64 mem_cgroup_hierarchy_read(struct cgroup *cont, struct cftype *cft)
{
        return mem_cgroup_from_cont(cont)->use_hierarchy;
}

static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
                                        u64 val)
{
        int retval = 0;
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
        struct cgroup *parent = cont->parent;
        struct mem_cgroup *parent_mem = NULL;

        if (parent)
                parent_mem = mem_cgroup_from_cont(parent);

        cgroup_lock();
        /*
         * If parent's use_hierarchy is set, we can't make any modifications
         * in the child subtrees. If it is unset, then the change can
         * occur, provided the current cgroup has no children.
         *
         * For the root cgroup, parent_mem is NULL, we allow value to be
         * set if there are no children.
         */
        if ((!parent_mem || !parent_mem->use_hierarchy) &&
                                (val == 1 || val == 0)) {
                if (list_empty(&cont->children))
                        mem->use_hierarchy = val;
                else
                        retval = -EBUSY;
        } else
                retval = -EINVAL;
        cgroup_unlock();

        return retval;
}


static u64 mem_cgroup_get_recursive_idx_stat(struct mem_cgroup *mem,
                                enum mem_cgroup_stat_index idx)
{
        struct mem_cgroup *iter;
        s64 val = 0;

        /* each per cpu's value can be minus.Then, use s64 */
        for_each_mem_cgroup_tree(iter, mem)
                val += mem_cgroup_read_stat(iter, idx);

        if (val < 0) /* race ? */
                val = 0;
        return val;
}

static inline u64 mem_cgroup_usage(struct mem_cgroup *mem, bool swap)
{
        u64 val;

        if (!mem_cgroup_is_root(mem)) {
                if (!swap)
                        return res_counter_read_u64(&mem->res, RES_USAGE);
                else
                        return res_counter_read_u64(&mem->memsw, RES_USAGE);
        }

        val = mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_CACHE);
        val += mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_RSS);

        if (swap)
                val += mem_cgroup_get_recursive_idx_stat(mem,
                                MEM_CGROUP_STAT_SWAPOUT);

        return val << PAGE_SHIFT;
}

static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
        u64 val;
        int type, name;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);
        switch (type) {
        case _MEM:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(mem, false);
                else
                        val = res_counter_read_u64(&mem->res, name);
                break;
        case _MEMSWAP:
                if (name == RES_USAGE)
                        val = mem_cgroup_usage(mem, true);
                else
                        val = res_counter_read_u64(&mem->memsw, name);
                break;
        default:
                BUG();
                break;
        }
        return val;
}
/*
 * The user of this function is...
 * RES_LIMIT.
 */
static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                            const char *buffer)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
        int type, name;
        unsigned long long val;
        int ret;

        type = MEMFILE_TYPE(cft->private);
        name = MEMFILE_ATTR(cft->private);
        switch (name) {
        case RES_LIMIT:
                if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
                        ret = -EINVAL;
                        break;
                }
                /* This function does all necessary parse...reuse it */
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (ret)
                        break;
                if (type == _MEM)
                        ret = mem_cgroup_resize_limit(memcg, val);
                else
                        ret = mem_cgroup_resize_memsw_limit(memcg, val);
                break;
        case RES_SOFT_LIMIT:
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (ret)
                        break;
                /*
                 * For memsw, soft limits are hard to implement in terms
                 * of semantics, for now, we support soft limits for
                 * control without swap
                 */
                if (type == _MEM)
                        ret = res_counter_set_soft_limit(&memcg->res, val);
                else
                        ret = -EINVAL;
                break;
        default:
                ret = -EINVAL; /* should be BUG() ? */
                break;
        }
        return ret;
}

static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
                unsigned long long *mem_limit, unsigned long long *memsw_limit)
{
        struct cgroup *cgroup;
        unsigned long long min_limit, min_memsw_limit, tmp;

        min_limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
        min_memsw_limit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
        cgroup = memcg->css.cgroup;
        if (!memcg->use_hierarchy)
                goto out;

        while (cgroup->parent) {
                cgroup = cgroup->parent;
                memcg = mem_cgroup_from_cont(cgroup);
                if (!memcg->use_hierarchy)
                        break;
                tmp = res_counter_read_u64(&memcg->res, RES_LIMIT);
                min_limit = min(min_limit, tmp);
                tmp = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
                min_memsw_limit = min(min_memsw_limit, tmp);
        }
out:
        *mem_limit = min_limit;
        *memsw_limit = min_memsw_limit;
        return;
}

static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
{
        struct mem_cgroup *mem;
        int type, name;

        mem = mem_cgroup_from_cont(cont);
        type = MEMFILE_TYPE(event);
        name = MEMFILE_ATTR(event);
        switch (name) {
        case RES_MAX_USAGE:
                if (type == _MEM)
                        res_counter_reset_max(&mem->res);
                else
                        res_counter_reset_max(&mem->memsw);
                break;
        case RES_FAILCNT:
                if (type == _MEM)
                        res_counter_reset_failcnt(&mem->res);
                else
                        res_counter_reset_failcnt(&mem->memsw);
                break;
        }

        return 0;
}

static u64 mem_cgroup_move_charge_read(struct cgroup *cgrp,
                                        struct cftype *cft)
{
        return mem_cgroup_from_cont(cgrp)->move_charge_at_immigrate;
}

#ifdef CONFIG_MMU
static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
                                        struct cftype *cft, u64 val)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);

        if (val >= (1 << NR_MOVE_TYPE))
                return -EINVAL;
        /*
         * We check this value several times in both in can_attach() and
         * attach(), so we need cgroup lock to prevent this value from being
         * inconsistent.
         */
        cgroup_lock();
        mem->move_charge_at_immigrate = val;
        cgroup_unlock();

        return 0;
}
#else
static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
                                        struct cftype *cft, u64 val)
{
        return -ENOSYS;
}
#endif


/* For read statistics */
enum {
        MCS_CACHE,
        MCS_RSS,
        MCS_FILE_MAPPED,
        MCS_PGPGIN,
        MCS_PGPGOUT,
        MCS_SWAP,
        MCS_INACTIVE_ANON,
        MCS_ACTIVE_ANON,
        MCS_INACTIVE_FILE,
        MCS_ACTIVE_FILE,
        MCS_UNEVICTABLE,
        NR_MCS_STAT,
};

struct mcs_total_stat {
        s64 stat[NR_MCS_STAT];
};

struct {
        char *local_name;
        char *total_name;
} memcg_stat_strings[NR_MCS_STAT] = {
        {"cache", "total_cache"},
        {"rss", "total_rss"},
        {"mapped_file", "total_mapped_file"},
        {"pgpgin", "total_pgpgin"},
        {"pgpgout", "total_pgpgout"},
        {"swap", "total_swap"},
        {"inactive_anon", "total_inactive_anon"},
        {"active_anon", "total_active_anon"},
        {"inactive_file", "total_inactive_file"},
        {"active_file", "total_active_file"},
        {"unevictable", "total_unevictable"}
};


static void
mem_cgroup_get_local_stat(struct mem_cgroup *mem, struct mcs_total_stat *s)
{
        s64 val;

        /* per cpu stat */
        val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
        s->stat[MCS_CACHE] += val * PAGE_SIZE;
        val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
        s->stat[MCS_RSS] += val * PAGE_SIZE;
        val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_FILE_MAPPED);
        s->stat[MCS_FILE_MAPPED] += val * PAGE_SIZE;
        val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_PGPGIN_COUNT);
        s->stat[MCS_PGPGIN] += val;
        val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_PGPGOUT_COUNT);
        s->stat[MCS_PGPGOUT] += val;
        if (do_swap_account) {
                val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_SWAPOUT);
                s->stat[MCS_SWAP] += val * PAGE_SIZE;
        }

        /* per zone stat */
        val = mem_cgroup_get_local_zonestat(mem, LRU_INACTIVE_ANON);
        s->stat[MCS_INACTIVE_ANON] += val * PAGE_SIZE;
        val = mem_cgroup_get_local_zonestat(mem, LRU_ACTIVE_ANON);
        s->stat[MCS_ACTIVE_ANON] += val * PAGE_SIZE;
        val = mem_cgroup_get_local_zonestat(mem, LRU_INACTIVE_FILE);
        s->stat[MCS_INACTIVE_FILE] += val * PAGE_SIZE;
        val = mem_cgroup_get_local_zonestat(mem, LRU_ACTIVE_FILE);
        s->stat[MCS_ACTIVE_FILE] += val * PAGE_SIZE;
        val = mem_cgroup_get_local_zonestat(mem, LRU_UNEVICTABLE);
        s->stat[MCS_UNEVICTABLE] += val * PAGE_SIZE;
}

static void
mem_cgroup_get_total_stat(struct mem_cgroup *mem, struct mcs_total_stat *s)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, mem)
                mem_cgroup_get_local_stat(iter, s);
}

static int mem_control_stat_show(struct cgroup *cont, struct cftype *cft,
                                 struct cgroup_map_cb *cb)
{
        struct mem_cgroup *mem_cont = mem_cgroup_from_cont(cont);
        struct mcs_total_stat mystat;
        int i;

        memset(&mystat, 0, sizeof(mystat));
        mem_cgroup_get_local_stat(mem_cont, &mystat);

        for (i = 0; i < NR_MCS_STAT; i++) {
                if (i == MCS_SWAP && !do_swap_account)
                        continue;
                cb->fill(cb, memcg_stat_strings[i].local_name, mystat.stat[i]);
        }

        /* Hierarchical information */
        {
                unsigned long long limit, memsw_limit;
                memcg_get_hierarchical_limit(mem_cont, &limit, &memsw_limit);
                cb->fill(cb, "hierarchical_memory_limit", limit);
                if (do_swap_account)
                        cb->fill(cb, "hierarchical_memsw_limit", memsw_limit);
        }

        memset(&mystat, 0, sizeof(mystat));
        mem_cgroup_get_total_stat(mem_cont, &mystat);
        for (i = 0; i < NR_MCS_STAT; i++) {
                if (i == MCS_SWAP && !do_swap_account)
                        continue;
                cb->fill(cb, memcg_stat_strings[i].total_name, mystat.stat[i]);
        }

#ifdef CONFIG_DEBUG_VM
        cb->fill(cb, "inactive_ratio", calc_inactive_ratio(mem_cont, NULL));

        {
                int nid, zid;
                struct mem_cgroup_per_zone *mz;
                unsigned long recent_rotated[2] = {0, 0};
                unsigned long recent_scanned[2] = {0, 0};

                for_each_online_node(nid)
                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);

                                recent_rotated[0] +=
                                        mz->reclaim_stat.recent_rotated[0];
                                recent_rotated[1] +=
                                        mz->reclaim_stat.recent_rotated[1];
                                recent_scanned[0] +=
                                        mz->reclaim_stat.recent_scanned[0];
                                recent_scanned[1] +=
                                        mz->reclaim_stat.recent_scanned[1];
                        }
                cb->fill(cb, "recent_rotated_anon", recent_rotated[0]);
                cb->fill(cb, "recent_rotated_file", recent_rotated[1]);
                cb->fill(cb, "recent_scanned_anon", recent_scanned[0]);
                cb->fill(cb, "recent_scanned_file", recent_scanned[1]);
        }
#endif

        return 0;
}

static u64 mem_cgroup_swappiness_read(struct cgroup *cgrp, struct cftype *cft)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);

        return get_swappiness(memcg);
}

static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
                                       u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup *parent;

        if (val > 100)
                return -EINVAL;

        if (cgrp->parent == NULL)
                return -EINVAL;

        parent = mem_cgroup_from_cont(cgrp->parent);

        cgroup_lock();

        /* If under hierarchy, only empty-root can set this value */
        if ((parent->use_hierarchy) ||
            (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
                cgroup_unlock();
                return -EINVAL;
        }

        spin_lock(&memcg->reclaim_param_lock);
        memcg->swappiness = val;
        spin_unlock(&memcg->reclaim_param_lock);

        cgroup_unlock();

        return 0;
}

static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
{
        struct mem_cgroup_threshold_ary *t;
        u64 usage;
        int i;

        rcu_read_lock();
        if (!swap)
                t = rcu_dereference(memcg->thresholds.primary);
        else
                t = rcu_dereference(memcg->memsw_thresholds.primary);

        if (!t)
                goto unlock;

        usage = mem_cgroup_usage(memcg, swap);

        /*
         * current_threshold points to threshold just below usage.
         * If it's not true, a threshold was crossed after last
         * call of __mem_cgroup_threshold().
         */
        i = t->current_threshold;

        /*
         * Iterate backward over array of thresholds starting from
         * current_threshold and check if a threshold is crossed.
         * If none of thresholds below usage is crossed, we read
         * only one element of the array here.
         */
        for (; i >= 0 && unlikely(t->entries[i].threshold > usage); i--)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* i = current_threshold + 1 */
        i++;

        /*
         * Iterate forward over array of thresholds starting from
         * current_threshold+1 and check if a threshold is crossed.
         * If none of thresholds above usage is crossed, we read
         * only one element of the array here.
         */
        for (; i < t->size && unlikely(t->entries[i].threshold <= usage); i++)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* Update current_threshold */
        t->current_threshold = i - 1;
unlock:
        rcu_read_unlock();
}

static void mem_cgroup_threshold(struct mem_cgroup *memcg)
{
        while (memcg) {
                __mem_cgroup_threshold(memcg, false);
                if (do_swap_account)
                        __mem_cgroup_threshold(memcg, true);

                memcg = parent_mem_cgroup(memcg);
        }
}

static int compare_thresholds(const void *a, const void *b)
{
        const struct mem_cgroup_threshold *_a = a;
        const struct mem_cgroup_threshold *_b = b;

        return _a->threshold - _b->threshold;
}

static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem)
{
        struct mem_cgroup_eventfd_list *ev;

        list_for_each_entry(ev, &mem->oom_notify, list)
                eventfd_signal(ev->eventfd, 1);
        return 0;
}

static void mem_cgroup_oom_notify(struct mem_cgroup *mem)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, mem)
                mem_cgroup_oom_notify_cb(iter);
}

static int mem_cgroup_usage_register_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        int type = MEMFILE_TYPE(cft->private);
        u64 threshold, usage;
        int i, size, ret;

        ret = res_counter_memparse_write_strategy(args, &threshold);
        if (ret)
                return ret;

        mutex_lock(&memcg->thresholds_lock);

        if (type == _MEM)
                thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
                thresholds = &memcg->memsw_thresholds;
        else
                BUG();

        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

        /* Check if a threshold crossed before adding a new one */
        if (thresholds->primary)
                __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        size = thresholds->primary ? thresholds->primary->size + 1 : 1;

        /* Allocate memory for new array of thresholds */
        new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
                        GFP_KERNEL);
        if (!new) {
                ret = -ENOMEM;
                goto unlock;
        }
        new->size = size;

        /* Copy thresholds (if any) to new array */
        if (thresholds->primary) {
                memcpy(new->entries, thresholds->primary->entries, (size - 1) *
                                sizeof(struct mem_cgroup_threshold));
        }

        /* Add new threshold */
        new->entries[size - 1].eventfd = eventfd;
        new->entries[size - 1].threshold = threshold;

        /* Sort thresholds. Registering of new threshold isn't time-critical */
        sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
                        compare_thresholds, NULL);

        /* Find current threshold */
        new->current_threshold = -1;
        for (i = 0; i < size; i++) {
                if (new->entries[i].threshold < usage) {
                        /*
                         * new->current_threshold will not be used until
                         * rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                }
        }

        /* Free old spare buffer and save old primary buffer as spare */
        kfree(thresholds->spare);
        thresholds->spare = thresholds->primary;

        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();

unlock:
        mutex_unlock(&memcg->thresholds_lock);

        return ret;
}

static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        int type = MEMFILE_TYPE(cft->private);
        u64 usage;
        int i, j, size;

        mutex_lock(&memcg->thresholds_lock);
        if (type == _MEM)
                thresholds = &memcg->thresholds;
        else if (type == _MEMSWAP)
                thresholds = &memcg->memsw_thresholds;
        else
                BUG();

        /*
         * Something went wrong if we trying to unregister a threshold
         * if we don't have thresholds
         */
        BUG_ON(!thresholds);

        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

        /* Check if a threshold crossed before removing */
        __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        /* Calculate new number of threshold */
        size = 0;
        for (i = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd != eventfd)
                        size++;
        }

        new = thresholds->spare;

        /* Set thresholds array to NULL if we don't have thresholds */
        if (!size) {
                kfree(new);
                new = NULL;
                goto swap_buffers;
        }

        new->size = size;

        /* Copy thresholds and find current threshold */
        new->current_threshold = -1;
        for (i = 0, j = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd == eventfd)
                        continue;

                new->entries[j] = thresholds->primary->entries[i];
                if (new->entries[j].threshold < usage) {
                        /*
                         * new->current_threshold will not be used
                         * until rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                }
                j++;
        }

swap_buffers:
        /* Swap primary and spare array */
        thresholds->spare = thresholds->primary;
        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();

        mutex_unlock(&memcg->thresholds_lock);
}

static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup_eventfd_list *event;
        int type = MEMFILE_TYPE(cft->private);

        BUG_ON(type != _OOM_TYPE);
        event = kmalloc(sizeof(*event), GFP_KERNEL);
        if (!event)
                return -ENOMEM;

        mutex_lock(&memcg_oom_mutex);

        event->eventfd = eventfd;
        list_add(&event->list, &memcg->oom_notify);

        /* already in OOM ? */
        if (atomic_read(&memcg->oom_lock))
                eventfd_signal(eventfd, 1);
        mutex_unlock(&memcg_oom_mutex);

        return 0;
}

static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
        struct cftype *cft, struct eventfd_ctx *eventfd)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup_eventfd_list *ev, *tmp;
        int type = MEMFILE_TYPE(cft->private);

        BUG_ON(type != _OOM_TYPE);

        mutex_lock(&memcg_oom_mutex);

        list_for_each_entry_safe(ev, tmp, &mem->oom_notify, list) {
                if (ev->eventfd == eventfd) {
                        list_del(&ev->list);
                        kfree(ev);
                }
        }

        mutex_unlock(&memcg_oom_mutex);
}

static int mem_cgroup_oom_control_read(struct cgroup *cgrp,
        struct cftype *cft,  struct cgroup_map_cb *cb)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);

        cb->fill(cb, "oom_kill_disable", mem->oom_kill_disable);

        if (atomic_read(&mem->oom_lock))
                cb->fill(cb, "under_oom", 1);
        else
                cb->fill(cb, "under_oom", 0);
        return 0;
}

static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
        struct cftype *cft, u64 val)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
        struct mem_cgroup *parent;

        /* cannot set to root cgroup and only 0 and 1 are allowed */
        if (!cgrp->parent || !((val == 0) || (val == 1)))
                return -EINVAL;

        parent = mem_cgroup_from_cont(cgrp->parent);

        cgroup_lock();
        /* oom-kill-disable is a flag for subhierarchy. */
        if ((parent->use_hierarchy) ||
            (mem->use_hierarchy && !list_empty(&cgrp->children))) {
                cgroup_unlock();
                return -EINVAL;
        }
        mem->oom_kill_disable = val;
        if (!val)
                memcg_oom_recover(mem);
        cgroup_unlock();
        return 0;
}

static struct cftype mem_cgroup_files[] = {
        {
                .name = "usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
                .read_u64 = mem_cgroup_read,
                .register_event = mem_cgroup_usage_register_event,
                .unregister_event = mem_cgroup_usage_unregister_event,
        },
        {
                .name = "max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_MAX_USAGE),
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
                .write_string = mem_cgroup_write,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "soft_limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
                .write_string = mem_cgroup_write,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "failcnt",
                .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "stat",
                .read_map = mem_control_stat_show,
        },
        {
                .name = "force_empty",
                .trigger = mem_cgroup_force_empty_write,
        },
        {
                .name = "use_hierarchy",
                .write_u64 = mem_cgroup_hierarchy_write,
                .read_u64 = mem_cgroup_hierarchy_read,
        },
        {
                .name = "swappiness",
                .read_u64 = mem_cgroup_swappiness_read,
                .write_u64 = mem_cgroup_swappiness_write,
        },
        {
                .name = "move_charge_at_immigrate",
                .read_u64 = mem_cgroup_move_charge_read,
                .write_u64 = mem_cgroup_move_charge_write,
        },
        {
                .name = "oom_control",
                .read_map = mem_cgroup_oom_control_read,
                .write_u64 = mem_cgroup_oom_control_write,
                .register_event = mem_cgroup_oom_register_event,
                .unregister_event = mem_cgroup_oom_unregister_event,
                .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
        },
};

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
static struct cftype memsw_cgroup_files[] = {
        {
                .name = "memsw.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
                .read_u64 = mem_cgroup_read,
                .register_event = mem_cgroup_usage_register_event,
                .unregister_event = mem_cgroup_usage_unregister_event,
        },
        {
                .name = "memsw.max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_MAX_USAGE),
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "memsw.limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
                .write_string = mem_cgroup_write,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "memsw.failcnt",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_FAILCNT),
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
};

static int register_memsw_files(struct cgroup *cont, struct cgroup_subsys *ss)
{
        if (!do_swap_account)
                return 0;
        return cgroup_add_files(cont, ss, memsw_cgroup_files,
                                ARRAY_SIZE(memsw_cgroup_files));
};
#else
static int register_memsw_files(struct cgroup *cont, struct cgroup_subsys *ss)
{
        return 0;
}
#endif

static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
{
        struct mem_cgroup_per_node *pn;
        struct mem_cgroup_per_zone *mz;
        enum lru_list l;
        int zone, tmp = node;
        /*
         * This routine is called against possible nodes.
         * But it's BUG to call kmalloc() against offline node.
         *
         * TODO: this routine can waste much memory for nodes which will
         *       never be onlined. It's better to use memory hotplug callback
         *       function.
         */
        if (!node_state(node, N_NORMAL_MEMORY))
                tmp = -1;
        pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, tmp);
        if (!pn)
                return 1;

        mem->info.nodeinfo[node] = pn;
        for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                mz = &pn->zoneinfo[zone];
                for_each_lru(l)
                        INIT_LIST_HEAD(&mz->lists[l]);
                mz->usage_in_excess = 0;
                mz->on_tree = false;
                mz->mem = mem;
        }
        return 0;
}

static void free_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
{
        kfree(mem->info.nodeinfo[node]);
}

static struct mem_cgroup *mem_cgroup_alloc(void)
{
        struct mem_cgroup *mem;
        int size = sizeof(struct mem_cgroup);

        /* Can be very big if MAX_NUMNODES is very big */
        if (size < PAGE_SIZE)
                mem = kzalloc(size, GFP_KERNEL);
        else
                mem = vzalloc(size);

        if (!mem)
                return NULL;

        mem->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
        if (!mem->stat)
                goto out_free;
        spin_lock_init(&mem->pcp_counter_lock);
        return mem;

out_free:
        if (size < PAGE_SIZE)
                kfree(mem);
        else
                vfree(mem);
        return NULL;
}

/*
 * At destroying mem_cgroup, references from swap_cgroup can remain.
 * (scanning all at force_empty is too costly...)
 *
 * Instead of clearing all references at force_empty, we remember
 * the number of reference from swap_cgroup and free mem_cgroup when
 * it goes down to 0.
 *
 * Removal of cgroup itself succeeds regardless of refs from swap.
 */

static void __mem_cgroup_free(struct mem_cgroup *mem)
{
        int node;

        mem_cgroup_remove_from_trees(mem);
        free_css_id(&mem_cgroup_subsys, &mem->css);

        for_each_node_state(node, N_POSSIBLE)
                free_mem_cgroup_per_zone_info(mem, node);

        free_percpu(mem->stat);
        if (sizeof(struct mem_cgroup) < PAGE_SIZE)
                kfree(mem);
        else
                vfree(mem);
}

static void mem_cgroup_get(struct mem_cgroup *mem)
{
        atomic_inc(&mem->refcnt);
}

static void __mem_cgroup_put(struct mem_cgroup *mem, int count)
{
        if (atomic_sub_and_test(count, &mem->refcnt)) {
                struct mem_cgroup *parent = parent_mem_cgroup(mem);
                __mem_cgroup_free(mem);
                if (parent)
                        mem_cgroup_put(parent);
        }
}

static void mem_cgroup_put(struct mem_cgroup *mem)
{
        __mem_cgroup_put(mem, 1);
}

/*
 * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
 */
static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem)
{
        if (!mem->res.parent)
                return NULL;
        return mem_cgroup_from_res_counter(mem->res.parent, res);
}

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
static void __init enable_swap_cgroup(void)
{
        if (!mem_cgroup_disabled() && really_do_swap_account)
                do_swap_account = 1;
}
#else
static void __init enable_swap_cgroup(void)
{
}
#endif

static int mem_cgroup_soft_limit_tree_init(void)
{
        struct mem_cgroup_tree_per_node *rtpn;
        struct mem_cgroup_tree_per_zone *rtpz;
        int tmp, node, zone;

        for_each_node_state(node, N_POSSIBLE) {
                tmp = node;
                if (!node_state(node, N_NORMAL_MEMORY))
                        tmp = -1;
                rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, tmp);
                if (!rtpn)
                        return 1;

                soft_limit_tree.rb_tree_per_node[node] = rtpn;

                for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                        rtpz = &rtpn->rb_tree_per_zone[zone];
                        rtpz->rb_root = RB_ROOT;
                        spin_lock_init(&rtpz->lock);
                }
        }
        return 0;
}

static struct cgroup_subsys_state * __ref
mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
{
        struct mem_cgroup *mem, *parent;
        long error = -ENOMEM;
        int node;

        mem = mem_cgroup_alloc();
        if (!mem)
                return ERR_PTR(error);

        for_each_node_state(node, N_POSSIBLE)
                if (alloc_mem_cgroup_per_zone_info(mem, node))
                        goto free_out;

        /* root ? */
        if (cont->parent == NULL) {
                int cpu;
                enable_swap_cgroup();
                parent = NULL;
                root_mem_cgroup = mem;
                if (mem_cgroup_soft_limit_tree_init())
                        goto free_out;
                for_each_possible_cpu(cpu) {
                        struct memcg_stock_pcp *stock =
                                                &per_cpu(memcg_stock, cpu);
                        INIT_WORK(&stock->work, drain_local_stock);
                }
                hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
        } else {
                parent = mem_cgroup_from_cont(cont->parent);
                mem->use_hierarchy = parent->use_hierarchy;
                mem->oom_kill_disable = parent->oom_kill_disable;
        }

        if (parent && parent->use_hierarchy) {
                res_counter_init(&mem->res, &parent->res);
                res_counter_init(&mem->memsw, &parent->memsw);
                /*
                 * We increment refcnt of the parent to ensure that we can
                 * safely access it on res_counter_charge/uncharge.
                 * This refcnt will be decremented when freeing this
                 * mem_cgroup(see mem_cgroup_put).
                 */
                mem_cgroup_get(parent);
        } else {
                res_counter_init(&mem->res, NULL);
                res_counter_init(&mem->memsw, NULL);
        }
        mem->last_scanned_child = 0;
        spin_lock_init(&mem->reclaim_param_lock);
        INIT_LIST_HEAD(&mem->oom_notify);

        if (parent)
                mem->swappiness = get_swappiness(parent);
        atomic_set(&mem->refcnt, 1);
        mem->move_charge_at_immigrate = 0;
        mutex_init(&mem->thresholds_lock);
        return &mem->css;
free_out:
        __mem_cgroup_free(mem);
        root_mem_cgroup = NULL;
        return ERR_PTR(error);
}

static int mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
                                        struct cgroup *cont)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);

        return mem_cgroup_force_empty(mem, false);
}

static void mem_cgroup_destroy(struct cgroup_subsys *ss,
                                struct cgroup *cont)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);

        mem_cgroup_put(mem);
}

static int mem_cgroup_populate(struct cgroup_subsys *ss,
                                struct cgroup *cont)
{
        int ret;

        ret = cgroup_add_files(cont, ss, mem_cgroup_files,
                                ARRAY_SIZE(mem_cgroup_files));

        if (!ret)
                ret = register_memsw_files(cont, ss);
        return ret;
}

#ifdef CONFIG_MMU
/* Handlers for move charge at task migration. */
#define PRECHARGE_COUNT_AT_ONCE 256
static int mem_cgroup_do_precharge(unsigned long count)
{
        int ret = 0;
        int batch_count = PRECHARGE_COUNT_AT_ONCE;
        struct mem_cgroup *mem = mc.to;

        if (mem_cgroup_is_root(mem)) {
                mc.precharge += count;
                /* we don't need css_get for root */
                return ret;
        }
        /* try to charge at once */
        if (count > 1) {
                struct res_counter *dummy;
                /*
                 * "mem" cannot be under rmdir() because we've already checked
                 * by cgroup_lock_live_cgroup() that it is not removed and we
                 * are still under the same cgroup_mutex. So we can postpone
                 * css_get().
                 */
                if (res_counter_charge(&mem->res, PAGE_SIZE * count, &dummy))
                        goto one_by_one;
                if (do_swap_account && res_counter_charge(&mem->memsw,
                                                PAGE_SIZE * count, &dummy)) {
                        res_counter_uncharge(&mem->res, PAGE_SIZE * count);
                        goto one_by_one;
                }
                mc.precharge += count;
                return ret;
        }
one_by_one:
        /* fall back to one by one charge */
        while (count--) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                if (!batch_count--) {
                        batch_count = PRECHARGE_COUNT_AT_ONCE;
                        cond_resched();
                }
                ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false,
                                              PAGE_SIZE);
                if (ret || !mem)
                        /* mem_cgroup_clear_mc() will do uncharge later */
                        return -ENOMEM;
                mc.precharge++;
        }
        return ret;
}

/**
 * is_target_pte_for_mc - check a pte whether it is valid for move charge
 * @vma: the vma the pte to be checked belongs
 * @addr: the address corresponding to the pte to be checked
 * @ptent: the pte to be checked
 * @target: the pointer the target page or swap ent will be stored(can be NULL)
 *
 * Returns
 *   0(MC_TARGET_NONE): if the pte is not a target for move charge.
 *   1(MC_TARGET_PAGE): if the page corresponding to this pte is a target for
 *     move charge. if @target is not NULL, the page is stored in target->page
 *     with extra refcnt got(Callers should handle it).
 *   2(MC_TARGET_SWAP): if the swap entry corresponding to this pte is a
 *     target for charge migration. if @target is not NULL, the entry is stored
 *     in target->ent.
 *
 * Called with pte lock held.
 */
union mc_target {
        struct page     *page;
        swp_entry_t     ent;
};

enum mc_target_type {
        MC_TARGET_NONE, /* not used */
        MC_TARGET_PAGE,
        MC_TARGET_SWAP,
};

static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
                                                unsigned long addr, pte_t ptent)
{
        struct page *page = vm_normal_page(vma, addr, ptent);

        if (!page || !page_mapped(page))
                return NULL;
        if (PageAnon(page)) {
                /* we don't move shared anon */
                if (!move_anon() || page_mapcount(page) > 2)
                        return NULL;
        } else if (!move_file())
                /* we ignore mapcount for file pages */
                return NULL;
        if (!get_page_unless_zero(page))
                return NULL;

        return page;
}

static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        int usage_count;
        struct page *page = NULL;
        swp_entry_t ent = pte_to_swp_entry(ptent);

        if (!move_anon() || non_swap_entry(ent))
                return NULL;
        usage_count = mem_cgroup_count_swap_user(ent, &page);
        if (usage_count > 1) { /* we don't move shared anon */
                if (page)
                        put_page(page);
                return NULL;
        }
        if (do_swap_account)
                entry->val = ent.val;

        return page;
}

static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        struct page *page = NULL;
        struct inode *inode;
        struct address_space *mapping;
        pgoff_t pgoff;

        if (!vma->vm_file) /* anonymous vma */
                return NULL;
        if (!move_file())
                return NULL;

        inode = vma->vm_file->f_path.dentry->d_inode;
        mapping = vma->vm_file->f_mapping;
        if (pte_none(ptent))
                pgoff = linear_page_index(vma, addr);
        else /* pte_file(ptent) is true */
                pgoff = pte_to_pgoff(ptent);

        /* page is moved even if it's not RSS of this task(page-faulted). */
        if (!mapping_cap_swap_backed(mapping)) { /* normal file */
                page = find_get_page(mapping, pgoff);
        } else { /* shmem/tmpfs file. we should take account of swap too. */
                swp_entry_t ent;
                mem_cgroup_get_shmem_target(inode, pgoff, &page, &ent);
                if (do_swap_account)
                        entry->val = ent.val;
        }

        return page;
}

static int is_target_pte_for_mc(struct vm_area_struct *vma,
                unsigned long addr, pte_t ptent, union mc_target *target)
{
        struct page *page = NULL;
        struct page_cgroup *pc;
        int ret = 0;
        swp_entry_t ent = { .val = 0 };

        if (pte_present(ptent))
                page = mc_handle_present_pte(vma, addr, ptent);
        else if (is_swap_pte(ptent))
                page = mc_handle_swap_pte(vma, addr, ptent, &ent);
        else if (pte_none(ptent) || pte_file(ptent))
                page = mc_handle_file_pte(vma, addr, ptent, &ent);

        if (!page && !ent.val)
                return 0;
        if (page) {
                pc = lookup_page_cgroup(page);
                /*
                 * Do only loose check w/o page_cgroup lock.
                 * mem_cgroup_move_account() checks the pc is valid or not under
                 * the lock.
                 */
                if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
                        ret = MC_TARGET_PAGE;
                        if (target)
                                target->page = page;
                }
                if (!ret || !target)
                        put_page(page);
        }
        /* There is a swap entry and a page doesn't exist or isn't charged */
        if (ent.val && !ret &&
                        css_id(&mc.from->css) == lookup_swap_cgroup(ent)) {
                ret = MC_TARGET_SWAP;
                if (target)
                        target->ent = ent;
        }
        return ret;
}

static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
                                        unsigned long addr, unsigned long end,
                                        struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;

        VM_BUG_ON(pmd_trans_huge(*pmd));
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; pte++, addr += PAGE_SIZE)
                if (is_target_pte_for_mc(vma, addr, *pte, NULL))
                        mc.precharge++; /* increment precharge temporarily */
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        return 0;
}

static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
{
        unsigned long precharge;
        struct vm_area_struct *vma;

        down_read(&mm->mmap_sem);
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                struct mm_walk mem_cgroup_count_precharge_walk = {
                        .pmd_entry = mem_cgroup_count_precharge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                walk_page_range(vma->vm_start, vma->vm_end,
                                        &mem_cgroup_count_precharge_walk);
        }
        up_read(&mm->mmap_sem);

        precharge = mc.precharge;
        mc.precharge = 0;

        return precharge;
}

static int mem_cgroup_precharge_mc(struct mm_struct *mm)
{
        unsigned long precharge = mem_cgroup_count_precharge(mm);

        VM_BUG_ON(mc.moving_task);
        mc.moving_task = current;
        return mem_cgroup_do_precharge(precharge);
}

/* cancels all extra charges on mc.from and mc.to, and wakes up all waiters. */
static void __mem_cgroup_clear_mc(void)
{
        struct mem_cgroup *from = mc.from;
        struct mem_cgroup *to = mc.to;

        /* we must uncharge all the leftover precharges from mc.to */
        if (mc.precharge) {
                __mem_cgroup_cancel_charge(mc.to, mc.precharge);
                mc.precharge = 0;
        }
        /*
         * we didn't uncharge from mc.from at mem_cgroup_move_account(), so
         * we must uncharge here.
         */
        if (mc.moved_charge) {
                __mem_cgroup_cancel_charge(mc.from, mc.moved_charge);
                mc.moved_charge = 0;
        }
        /* we must fixup refcnts and charges */
        if (mc.moved_swap) {
                /* uncharge swap account from the old cgroup */
                if (!mem_cgroup_is_root(mc.from))
                        res_counter_uncharge(&mc.from->memsw,
                                                PAGE_SIZE * mc.moved_swap);
                __mem_cgroup_put(mc.from, mc.moved_swap);

                if (!mem_cgroup_is_root(mc.to)) {
                        /*
                         * we charged both to->res and to->memsw, so we should
                         * uncharge to->res.
                         */
                        res_counter_uncharge(&mc.to->res,
                                                PAGE_SIZE * mc.moved_swap);
                }
                /* we've already done mem_cgroup_get(mc.to) */
                mc.moved_swap = 0;
        }
        memcg_oom_recover(from);
        memcg_oom_recover(to);
        wake_up_all(&mc.waitq);
}

static void mem_cgroup_clear_mc(void)
{
        struct mem_cgroup *from = mc.from;

        /*
         * we must clear moving_task before waking up waiters at the end of
         * task migration.
         */
        mc.moving_task = NULL;
        __mem_cgroup_clear_mc();
        spin_lock(&mc.lock);
        mc.from = NULL;
        mc.to = NULL;
        spin_unlock(&mc.lock);
        mem_cgroup_end_move(from);
}

static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
                                struct cgroup *cgroup,
                                struct task_struct *p,
                                bool threadgroup)
{
        int ret = 0;
        struct mem_cgroup *mem = mem_cgroup_from_cont(cgroup);

        if (mem->move_charge_at_immigrate) {
                struct mm_struct *mm;
                struct mem_cgroup *from = mem_cgroup_from_task(p);

                VM_BUG_ON(from == mem);

                mm = get_task_mm(p);
                if (!mm)
                        return 0;
                /* We move charges only when we move a owner of the mm */
                if (mm->owner == p) {
                        VM_BUG_ON(mc.from);
                        VM_BUG_ON(mc.to);
                        VM_BUG_ON(mc.precharge);
                        VM_BUG_ON(mc.moved_charge);
                        VM_BUG_ON(mc.moved_swap);
                        mem_cgroup_start_move(from);
                        spin_lock(&mc.lock);
                        mc.from = from;
                        mc.to = mem;
                        spin_unlock(&mc.lock);
                        /* We set mc.moving_task later */

                        ret = mem_cgroup_precharge_mc(mm);
                        if (ret)
                                mem_cgroup_clear_mc();
                }
                mmput(mm);
        }
        return ret;
}

static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
                                struct cgroup *cgroup,
                                struct task_struct *p,
                                bool threadgroup)
{
        mem_cgroup_clear_mc();
}

static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
                                unsigned long addr, unsigned long end,
                                struct mm_walk *walk)
{
        int ret = 0;
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;

retry:
        VM_BUG_ON(pmd_trans_huge(*pmd));
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; addr += PAGE_SIZE) {
                pte_t ptent = *(pte++);
                union mc_target target;
                int type;
                struct page *page;
                struct page_cgroup *pc;
                swp_entry_t ent;

                if (!mc.precharge)
                        break;

                type = is_target_pte_for_mc(vma, addr, ptent, &target);
                switch (type) {
                case MC_TARGET_PAGE:
                        page = target.page;
                        if (isolate_lru_page(page))
                                goto put;
                        pc = lookup_page_cgroup(page);
                        if (!mem_cgroup_move_account(pc,
                                                mc.from, mc.to, false)) {
                                mc.precharge--;
                                /* we uncharge from mc.from later. */
                                mc.moved_charge++;
                        }
                        putback_lru_page(page);
put:                    /* is_target_pte_for_mc() gets the page */
                        put_page(page);
                        break;
                case MC_TARGET_SWAP:
                        ent = target.ent;
                        if (!mem_cgroup_move_swap_account(ent,
                                                mc.from, mc.to, false)) {
                                mc.precharge--;
                                /* we fixup refcnts and charges later. */
                                mc.moved_swap++;
                        }
                        break;
                default:
                        break;
                }
        }
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        if (addr != end) {
                /*
                 * We have consumed all precharges we got in can_attach().
                 * We try charge one by one, but don't do any additional
                 * charges to mc.to if we have failed in charge once in attach()
                 * phase.
                 */
                ret = mem_cgroup_do_precharge(1);
                if (!ret)
                        goto retry;
        }

        return ret;
}

static void mem_cgroup_move_charge(struct mm_struct *mm)
{
        struct vm_area_struct *vma;

        lru_add_drain_all();
retry:
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                /*
                 * Someone who are holding the mmap_sem might be waiting in
                 * waitq. So we cancel all extra charges, wake up all waiters,
                 * and retry. Because we cancel precharges, we might not be able
                 * to move enough charges, but moving charge is a best-effort
                 * feature anyway, so it wouldn't be a big problem.
                 */
                __mem_cgroup_clear_mc();
                cond_resched();
                goto retry;
        }
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                int ret;
                struct mm_walk mem_cgroup_move_charge_walk = {
                        .pmd_entry = mem_cgroup_move_charge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                ret = walk_page_range(vma->vm_start, vma->vm_end,
                                                &mem_cgroup_move_charge_walk);
                if (ret)
                        /*
                         * means we have consumed all precharges and failed in
                         * doing additional charge. Just abandon here.
                         */
                        break;
        }
        up_read(&mm->mmap_sem);
}

static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                struct cgroup *cont,
                                struct cgroup *old_cont,
                                struct task_struct *p,
                                bool threadgroup)
{
        struct mm_struct *mm;

        if (!mc.to)
                /* no need to move charge */
                return;

        mm = get_task_mm(p);
        if (mm) {
                mem_cgroup_move_charge(mm);
                mmput(mm);
        }
        mem_cgroup_clear_mc();
}
#else   /* !CONFIG_MMU */
static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
                                struct cgroup *cgroup,
                                struct task_struct *p,
                                bool threadgroup)
{
        return 0;
}
static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
                                struct cgroup *cgroup,
                                struct task_struct *p,
                                bool threadgroup)
{
}
static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                struct cgroup *cont,
                                struct cgroup *old_cont,
                                struct task_struct *p,
                                bool threadgroup)
{
}
#endif

struct cgroup_subsys mem_cgroup_subsys = {
        .name = "memory",
        .subsys_id = mem_cgroup_subsys_id,
        .create = mem_cgroup_create,
        .pre_destroy = mem_cgroup_pre_destroy,
        .destroy = mem_cgroup_destroy,
        .populate = mem_cgroup_populate,
        .can_attach = mem_cgroup_can_attach,
        .cancel_attach = mem_cgroup_cancel_attach,
        .attach = mem_cgroup_move_task,
        .early_init = 0,
        .use_id = 1,
};

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
static int __init enable_swap_account(char *s)
{
        /* consider enabled if no parameter or 1 is given */
        if (!s || !strcmp(s, "1"))
                really_do_swap_account = 1;
        else if (!strcmp(s, "0"))
                really_do_swap_account = 0;
        return 1;
}
__setup("swapaccount", enable_swap_account);

static int __init disable_swap_account(char *s)
{
        enable_swap_account("0");
        return 1;
}
__setup("noswapaccount", disable_swap_account);
#endif