memcg: zap mem_cgroup_lookup()

mem_cgroup_lookup() is a wrapper around mem_cgroup_from_id(), which checks
that id != 0 before issuing the function call.  Today, there is no point
in this additional check apart from optimization, because there is no css
with id <= 0, so that css_from_id, called by mem_cgroup_from_id, will
return NULL for any id <= 0.

Since mem_cgroup_from_id is only called from mem_cgroup_lookup, let us zap
mem_cgroup_lookup, substituting calls to it with mem_cgroup_from_id and
moving the check if id > 0 to css_from_id.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 29a7b2cc593e3f50a425f1dbbf187d5d1fb4542f..747e953ffee9b850aa908f3c9fa70fda9cddd668 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5451,7 +5451,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
 {
        WARN_ON_ONCE(!rcu_read_lock_held());
-       return idr_find(&ss->css_idr, id);
+       return id > 0 ? idr_find(&ss->css_idr, id) : NULL;
 }
 
 #ifdef CONFIG_CGROUP_DEBUG

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c3f09b2dda5f9cf00e4250e7b68745575bd806d1..0a06628470cc0e02d81382f49a94d88ea1c81f1e 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -460,6 +460,12 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
        return memcg->css.id;
 }
 
+/*
+ * A helper function to get mem_cgroup from ID. must be called under
+ * rcu_read_lock().  The caller is responsible for calling
+ * css_tryget_online() if the mem_cgroup is used for charging. (dropping
+ * refcnt from swap can be called against removed memcg.)
+ */
 static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 {
        struct cgroup_subsys_state *css;
@@ -2348,20 +2354,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
        css_put_many(&memcg->css, nr_pages);
 }
 
-/*
- * A helper function to get mem_cgroup from ID. must be called under
- * rcu_read_lock().  The caller is responsible for calling
- * css_tryget_online() if the mem_cgroup is used for charging. (dropping
- * refcnt from swap can be called against removed memcg.)
- */
-static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
-{
-       /* ID 0 is unused ID */
-       if (!id)
-               return NULL;
-       return mem_cgroup_from_id(id);
-}
-
 /*
  * try_get_mem_cgroup_from_page - look up page's memcg association
  * @page: the page
@@ -2388,7 +2380,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
                ent.val = page_private(page);
                id = lookup_swap_cgroup_id(ent);
                rcu_read_lock();
-               memcg = mem_cgroup_lookup(id);
+               memcg = mem_cgroup_from_id(id);
                if (memcg && !css_tryget_online(&memcg->css))
                        memcg = NULL;
                rcu_read_unlock();
@@ -5869,7 +5861,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry)
 
        id = swap_cgroup_record(entry, 0);
        rcu_read_lock();
-       memcg = mem_cgroup_lookup(id);
+       memcg = mem_cgroup_from_id(id);
        if (memcg) {
                if (!mem_cgroup_is_root(memcg))
                        page_counter_uncharge(&memcg->memsw, 1);