mm/ksm.c

   1 /*
   2  * Memory merging support.
   3  *
   4  * This code enables dynamic sharing of identical pages found in different
   5  * memory areas, even if they are not shared by fork()
   6  *
   7  * Copyright (C) 2008-2009 Red Hat, Inc.
   8  * Authors:
   9  *      Izik Eidus
  10  *      Andrea Arcangeli
  11  *      Chris Wright
  12  *      Hugh Dickins
  13  *
  14  * This work is licensed under the terms of the GNU GPL, version 2.
  15  */
  16
  17 #include <linux/errno.h>
  18 #include <linux/mm.h>
  19 #include <linux/fs.h>
  20 #include <linux/mman.h>
  21 #include <linux/sched.h>
  22 #include <linux/rwsem.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/rmap.h>
  25 #include <linux/spinlock.h>
  26 #include <linux/jhash.h>
  27 #include <linux/delay.h>
  28 #include <linux/kthread.h>
  29 #include <linux/wait.h>
  30 #include <linux/slab.h>
  31 #include <linux/rbtree.h>
  32 #include <linux/mmu_notifier.h>
  33 #include <linux/ksm.h>
  34
  35 #include <asm/tlbflush.h>
  36
  37 /*
  38  * A few notes about the KSM scanning process,
  39  * to make it easier to understand the data structures below:
  40  *
  41  * In order to reduce excessive scanning, KSM sorts the memory pages by their
  42  * contents into a data structure that holds pointers to the pages' locations.
  43  *
  44  * Since the contents of the pages may change at any moment, KSM cannot just
  45  * insert the pages into a normal sorted tree and expect it to find anything.
  46  * Therefore KSM uses two data structures - the stable and the unstable tree.
  47  *
  48  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  49  * by their contents.  Because each such page is write-protected, searching on
  50  * this tree is fully assured to be working (except when pages are unmapped),
  51  * and therefore this tree is called the stable tree.
  52  *
  53  * In addition to the stable tree, KSM uses a second data structure called the
  54  * unstable tree: this tree holds pointers to pages which have been found to
  55  * be "unchanged for a period of time".  The unstable tree sorts these pages
  56  * by their contents, but since they are not write-protected, KSM cannot rely
  57  * upon the unstable tree to work correctly - the unstable tree is liable to
  58  * be corrupted as its contents are modified, and so it is called unstable.
  59  *
  60  * KSM solves this problem by several techniques:
  61  *
  62  * 1) The unstable tree is flushed every time KSM completes scanning all
  63  *    memory areas, and then the tree is rebuilt again from the beginning.
  64  * 2) KSM will only insert into the unstable tree, pages whose hash value
  65  *    has not changed since the previous scan of all memory areas.
  66  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
  67  *    colors of the nodes and not on their contents, assuring that even when
  68  *    the tree gets "corrupted" it won't get out of balance, so scanning time
  69  *    remains the same (also, searching and inserting nodes in an rbtree uses
  70  *    the same algorithm, so we have no overhead when we flush and rebuild).
  71  * 4) KSM never flushes the stable tree, which means that even if it were to
  72  *    take 10 attempts to find a page in the unstable tree, once it is found,
  73  *    it is secured in the stable tree.  (When we scan a new page, we first
  74  *    compare it against the stable tree, and then against the unstable tree.)
  75  */
  76
  77 /**
  78  * struct mm_slot - ksm information per mm that is being scanned
  79  * @link: link to the mm_slots hash list
  80  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
  81  * @rmap_list: head for this mm_slot's list of rmap_items
  82  * @mm: the mm that this information is valid for
  83  */
  84 struct mm_slot {
  85         struct hlist_node link;
  86         struct list_head mm_list;
  87         struct list_head rmap_list;
  88         struct mm_struct *mm;
  89 };
  90
  91 /**
  92  * struct ksm_scan - cursor for scanning
  93  * @mm_slot: the current mm_slot we are scanning
  94  * @address: the next address inside that to be scanned
  95  * @rmap_item: the current rmap that we are scanning inside the rmap_list
  96  * @seqnr: count of completed full scans (needed when removing unstable node)
  97  *
  98  * There is only the one ksm_scan instance of this cursor structure.
  99  */
 100 struct ksm_scan {
 101         struct mm_slot *mm_slot;
 102         unsigned long address;
 103         struct rmap_item *rmap_item;
 104         unsigned long seqnr;
 105 };
 106
 107 /**
 108  * struct rmap_item - reverse mapping item for virtual addresses
 109  * @link: link into mm_slot's rmap_list (rmap_list is per mm)
 110  * @mm: the memory structure this rmap_item is pointing into
 111  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 112  * @oldchecksum: previous checksum of the page at that virtual address
 113  * @node: rb_node of this rmap_item in either unstable or stable tree
 114  * @next: next rmap_item hanging off the same node of the stable tree
 115  * @prev: previous rmap_item hanging off the same node of the stable tree
 116  */
 117 struct rmap_item {
 118         struct list_head link;
 119         struct mm_struct *mm;
 120         unsigned long address;          /* + low bits used for flags below */
 121         union {
 122                 unsigned int oldchecksum;               /* when unstable */
 123                 struct rmap_item *next;                 /* when stable */
 124         };
 125         union {
 126                 struct rb_node node;                    /* when tree node */
 127                 struct rmap_item *prev;                 /* in stable list */
 128         };
 129 };
 130
 131 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
 132 #define NODE_FLAG       0x100   /* is a node of unstable or stable tree */
 133 #define STABLE_FLAG     0x200   /* is a node or list item of stable tree */
 134
 135 /* The stable and unstable tree heads */
 136 static struct rb_root root_stable_tree = RB_ROOT;
 137 static struct rb_root root_unstable_tree = RB_ROOT;
 138
 139 #define MM_SLOTS_HASH_HEADS 1024
 140 static struct hlist_head *mm_slots_hash;
 141
 142 static struct mm_slot ksm_mm_head = {
 143         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
 144 };
 145 static struct ksm_scan ksm_scan = {
 146         .mm_slot = &ksm_mm_head,
 147 };
 148
 149 static struct kmem_cache *rmap_item_cache;
 150 static struct kmem_cache *mm_slot_cache;
 151
 152 /* The number of nodes in the stable tree */
 153 static unsigned long ksm_pages_shared;
 154
 155 /* The number of page slots additionally sharing those nodes */
 156 static unsigned long ksm_pages_sharing;
 157
 158 /* The number of nodes in the unstable tree */
 159 static unsigned long ksm_pages_unshared;
 160
 161 /* The number of rmap_items in use: to calculate pages_volatile */
 162 static unsigned long ksm_rmap_items;
 163
 164 /* Limit on the number of unswappable pages used */
 165 static unsigned long ksm_max_kernel_pages;
 166
 167 /* Number of pages ksmd should scan in one batch */
 168 static unsigned int ksm_thread_pages_to_scan;
 169
 170 /* Milliseconds ksmd should sleep between batches */
 171 static unsigned int ksm_thread_sleep_millisecs;
 172
 173 #define KSM_RUN_STOP    0
 174 #define KSM_RUN_MERGE   1
 175 #define KSM_RUN_UNMERGE 2
 176 static unsigned int ksm_run;
 177
 178 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 179 static DEFINE_MUTEX(ksm_thread_mutex);
 180 static DEFINE_SPINLOCK(ksm_mmlist_lock);
 181
 182 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
 183                 sizeof(struct __struct), __alignof__(struct __struct),\
 184                 (__flags), NULL)
 185
 186 static int __init ksm_slab_init(void)
 187 {
 188         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
 189         if (!rmap_item_cache)
 190                 goto out;
 191
 192         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
 193         if (!mm_slot_cache)
 194                 goto out_free;
 195
 196         return 0;
 197
 198 out_free:
 199         kmem_cache_destroy(rmap_item_cache);
 200 out:
 201         return -ENOMEM;
 202 }
 203
 204 static void __init ksm_slab_free(void)
 205 {
 206         kmem_cache_destroy(mm_slot_cache);
 207         kmem_cache_destroy(rmap_item_cache);
 208         mm_slot_cache = NULL;
 209 }
 210
 211 static inline struct rmap_item *alloc_rmap_item(void)
 212 {
 213         struct rmap_item *rmap_item;
 214
 215         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
 216         if (rmap_item)
 217                 ksm_rmap_items++;
 218         return rmap_item;
 219 }
 220
 221 static inline void free_rmap_item(struct rmap_item *rmap_item)
 222 {
 223         ksm_rmap_items--;
 224         rmap_item->mm = NULL;   /* debug safety */
 225         kmem_cache_free(rmap_item_cache, rmap_item);
 226 }
 227
 228 static inline struct mm_slot *alloc_mm_slot(void)
 229 {
 230         if (!mm_slot_cache)     /* initialization failed */
 231                 return NULL;
 232         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 233 }
 234
 235 static inline void free_mm_slot(struct mm_slot *mm_slot)
 236 {
 237         kmem_cache_free(mm_slot_cache, mm_slot);
 238 }
 239
 240 static int __init mm_slots_hash_init(void)
 241 {
 242         mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
 243                                 GFP_KERNEL);
 244         if (!mm_slots_hash)
 245                 return -ENOMEM;
 246         return 0;
 247 }
 248
 249 static void __init mm_slots_hash_free(void)
 250 {
 251         kfree(mm_slots_hash);
 252 }
 253
 254 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 255 {
 256         struct mm_slot *mm_slot;
 257         struct hlist_head *bucket;
 258         struct hlist_node *node;
 259
 260         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
 261                                 % MM_SLOTS_HASH_HEADS];
 262         hlist_for_each_entry(mm_slot, node, bucket, link) {
 263                 if (mm == mm_slot->mm)
 264                         return mm_slot;
 265         }
 266         return NULL;
 267 }
 268
 269 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 270                                     struct mm_slot *mm_slot)
 271 {
 272         struct hlist_head *bucket;
 273
 274         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
 275                                 % MM_SLOTS_HASH_HEADS];
 276         mm_slot->mm = mm;
 277         INIT_LIST_HEAD(&mm_slot->rmap_list);
 278         hlist_add_head(&mm_slot->link, bucket);
 279 }
 280
 281 static inline int in_stable_tree(struct rmap_item *rmap_item)
 282 {
 283         return rmap_item->address & STABLE_FLAG;
 284 }
 285
 286 /*
 287  * We use break_ksm to break COW on a ksm page: it's a stripped down
 288  *
 289  *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 290  *              put_page(page);
 291  *
 292  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 293  * in case the application has unmapped and remapped mm,addr meanwhile.
 294  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 295  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 296  */
 297 static void break_ksm(struct vm_area_struct *vma, unsigned long addr)
 298 {
 299         struct page *page;
 300         int ret;
 301
 302         do {
 303                 cond_resched();
 304                 page = follow_page(vma, addr, FOLL_GET);
 305                 if (!page)
 306                         break;
 307                 if (PageKsm(page))
 308                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
 309                                                         FAULT_FLAG_WRITE);
 310                 else
 311                         ret = VM_FAULT_WRITE;
 312                 put_page(page);
 313         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS)));
 314
 315         /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */
 316 }
 317
 318 static void break_cow(struct mm_struct *mm, unsigned long addr)
 319 {
 320         struct vm_area_struct *vma;
 321
 322         down_read(&mm->mmap_sem);
 323         vma = find_vma(mm, addr);
 324         if (!vma || vma->vm_start > addr)
 325                 goto out;
 326         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 327                 goto out;
 328         break_ksm(vma, addr);
 329 out:
 330         up_read(&mm->mmap_sem);
 331 }
 332
 333 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 334 {
 335         struct mm_struct *mm = rmap_item->mm;
 336         unsigned long addr = rmap_item->address;
 337         struct vm_area_struct *vma;
 338         struct page *page;
 339
 340         down_read(&mm->mmap_sem);
 341         vma = find_vma(mm, addr);
 342         if (!vma || vma->vm_start > addr)
 343                 goto out;
 344         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 345                 goto out;
 346
 347         page = follow_page(vma, addr, FOLL_GET);
 348         if (!page)
 349                 goto out;
 350         if (PageAnon(page)) {
 351                 flush_anon_page(vma, page, addr);
 352                 flush_dcache_page(page);
 353         } else {
 354                 put_page(page);
 355 out:            page = NULL;
 356         }
 357         up_read(&mm->mmap_sem);
 358         return page;
 359 }
 360
 361 /*
 362  * get_ksm_page: checks if the page at the virtual address in rmap_item
 363  * is still PageKsm, in which case we can trust the content of the page,
 364  * and it returns the gotten page; but NULL if the page has been zapped.
 365  */
 366 static struct page *get_ksm_page(struct rmap_item *rmap_item)
 367 {
 368         struct page *page;
 369
 370         page = get_mergeable_page(rmap_item);
 371         if (page && !PageKsm(page)) {
 372                 put_page(page);
 373                 page = NULL;
 374         }
 375         return page;
 376 }
 377
 378 /*
 379  * Removing rmap_item from stable or unstable tree.
 380  * This function will clean the information from the stable/unstable tree.
 381  */
 382 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 383 {
 384         if (in_stable_tree(rmap_item)) {
 385                 struct rmap_item *next_item = rmap_item->next;
 386
 387                 if (rmap_item->address & NODE_FLAG) {
 388                         if (next_item) {
 389                                 rb_replace_node(&rmap_item->node,
 390                                                 &next_item->node,
 391                                                 &root_stable_tree);
 392                                 next_item->address |= NODE_FLAG;
 393                                 ksm_pages_sharing--;
 394                         } else {
 395                                 rb_erase(&rmap_item->node, &root_stable_tree);
 396                                 ksm_pages_shared--;
 397                         }
 398                 } else {
 399                         struct rmap_item *prev_item = rmap_item->prev;
 400
 401                         BUG_ON(prev_item->next != rmap_item);
 402                         prev_item->next = next_item;
 403                         if (next_item) {
 404                                 BUG_ON(next_item->prev != rmap_item);
 405                                 next_item->prev = rmap_item->prev;
 406                         }
 407                         ksm_pages_sharing--;
 408                 }
 409
 410                 rmap_item->next = NULL;
 411
 412         } else if (rmap_item->address & NODE_FLAG) {
 413                 unsigned char age;
 414                 /*
 415                  * ksm_thread can and must skip the rb_erase, because
 416                  * root_unstable_tree was already reset to RB_ROOT.
 417                  * But __ksm_exit has to be careful: do the rb_erase
 418                  * if it's interrupting a scan, and this rmap_item was
 419                  * inserted by this scan rather than left from before.
 420                  *
 421                  * Because of the case in which remove_mm_from_lists
 422                  * increments seqnr before removing rmaps, unstable_nr
 423                  * may even be 2 behind seqnr, but should never be
 424                  * further behind.  Yes, I did have trouble with this!
 425                  */
 426                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 427                 BUG_ON(age > 2);
 428                 if (!age)
 429                         rb_erase(&rmap_item->node, &root_unstable_tree);
 430                 ksm_pages_unshared--;
 431         }
 432
 433         rmap_item->address &= PAGE_MASK;
 434
 435         cond_resched();         /* we're called from many long loops */
 436 }
 437
 438 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 439                                        struct list_head *cur)
 440 {
 441         struct rmap_item *rmap_item;
 442
 443         while (cur != &mm_slot->rmap_list) {
 444                 rmap_item = list_entry(cur, struct rmap_item, link);
 445                 cur = cur->next;
 446                 remove_rmap_item_from_tree(rmap_item);
 447                 list_del(&rmap_item->link);
 448                 free_rmap_item(rmap_item);
 449         }
 450 }
 451
 452 /*
 453  * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 454  * than check every pte of a given vma, the locking doesn't quite work for
 455  * that - an rmap_item is assigned to the stable tree after inserting ksm
 456  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 457  * rmap_items from parent to child at fork time (so as not to waste time
 458  * if exit comes before the next scan reaches it).
 459  *
 460  * Similarly, although we'd like to remove rmap_items (so updating counts
 461  * and freeing memory) when unmerging an area, it's easier to leave that
 462  * to the next pass of ksmd - consider, for example, how ksmd might be
 463  * in cmp_and_merge_page on one of the rmap_items we would be removing.
 464  */
 465 static void unmerge_ksm_pages(struct vm_area_struct *vma,
 466                               unsigned long start, unsigned long end)
 467 {
 468         unsigned long addr;
 469
 470         for (addr = start; addr < end; addr += PAGE_SIZE)
 471                 break_ksm(vma, addr);
 472 }
 473
 474 static void unmerge_and_remove_all_rmap_items(void)
 475 {
 476         struct mm_slot *mm_slot;
 477         struct mm_struct *mm;
 478         struct vm_area_struct *vma;
 479
 480         list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) {
 481                 mm = mm_slot->mm;
 482                 down_read(&mm->mmap_sem);
 483                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
 484                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 485                                 continue;
 486                         unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
 487                 }
 488                 remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
 489                 up_read(&mm->mmap_sem);
 490         }
 491
 492         spin_lock(&ksm_mmlist_lock);
 493         if (ksm_scan.mm_slot != &ksm_mm_head) {
 494                 ksm_scan.mm_slot = &ksm_mm_head;
 495                 ksm_scan.seqnr++;
 496         }
 497         spin_unlock(&ksm_mmlist_lock);
 498 }
 499
 500 static void remove_mm_from_lists(struct mm_struct *mm)
 501 {
 502         struct mm_slot *mm_slot;
 503
 504         spin_lock(&ksm_mmlist_lock);
 505         mm_slot = get_mm_slot(mm);
 506
 507         /*
 508          * This mm_slot is always at the scanning cursor when we're
 509          * called from scan_get_next_rmap_item; but it's a special
 510          * case when we're called from __ksm_exit.
 511          */
 512         if (ksm_scan.mm_slot == mm_slot) {
 513                 ksm_scan.mm_slot = list_entry(
 514                         mm_slot->mm_list.next, struct mm_slot, mm_list);
 515                 ksm_scan.address = 0;
 516                 ksm_scan.rmap_item = list_entry(
 517                         &ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
 518                 if (ksm_scan.mm_slot == &ksm_mm_head)
 519                         ksm_scan.seqnr++;
 520         }
 521
 522         hlist_del(&mm_slot->link);
 523         list_del(&mm_slot->mm_list);
 524         spin_unlock(&ksm_mmlist_lock);
 525
 526         remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
 527         free_mm_slot(mm_slot);
 528         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 529 }
 530
 531 static u32 calc_checksum(struct page *page)
 532 {
 533         u32 checksum;
 534         void *addr = kmap_atomic(page, KM_USER0);
 535         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 536         kunmap_atomic(addr, KM_USER0);
 537         return checksum;
 538 }
 539
 540 static int memcmp_pages(struct page *page1, struct page *page2)
 541 {
 542         char *addr1, *addr2;
 543         int ret;
 544
 545         addr1 = kmap_atomic(page1, KM_USER0);
 546         addr2 = kmap_atomic(page2, KM_USER1);
 547         ret = memcmp(addr1, addr2, PAGE_SIZE);
 548         kunmap_atomic(addr2, KM_USER1);
 549         kunmap_atomic(addr1, KM_USER0);
 550         return ret;
 551 }
 552
 553 static inline int pages_identical(struct page *page1, struct page *page2)
 554 {
 555         return !memcmp_pages(page1, page2);
 556 }
 557
 558 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 559                               pte_t *orig_pte)
 560 {
 561         struct mm_struct *mm = vma->vm_mm;
 562         unsigned long addr;
 563         pte_t *ptep;
 564         spinlock_t *ptl;
 565         int swapped;
 566         int err = -EFAULT;
 567
 568         addr = page_address_in_vma(page, vma);
 569         if (addr == -EFAULT)
 570                 goto out;
 571
 572         ptep = page_check_address(page, mm, addr, &ptl, 0);
 573         if (!ptep)
 574                 goto out;
 575
 576         if (pte_write(*ptep)) {
 577                 pte_t entry;
 578
 579                 swapped = PageSwapCache(page);
 580                 flush_cache_page(vma, addr, page_to_pfn(page));
 581                 /*
 582                  * Ok this is tricky, when get_user_pages_fast() run it doesnt
 583                  * take any lock, therefore the check that we are going to make
 584                  * with the pagecount against the mapcount is racey and
 585                  * O_DIRECT can happen right after the check.
 586                  * So we clear the pte and flush the tlb before the check
 587                  * this assure us that no O_DIRECT can happen after the check
 588                  * or in the middle of the check.
 589                  */
 590                 entry = ptep_clear_flush(vma, addr, ptep);
 591                 /*
 592                  * Check that no O_DIRECT or similar I/O is in progress on the
 593                  * page
 594                  */
 595                 if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
 596                         set_pte_at_notify(mm, addr, ptep, entry);
 597                         goto out_unlock;
 598                 }
 599                 entry = pte_wrprotect(entry);
 600                 set_pte_at_notify(mm, addr, ptep, entry);
 601         }
 602         *orig_pte = *ptep;
 603         err = 0;
 604
 605 out_unlock:
 606         pte_unmap_unlock(ptep, ptl);
 607 out:
 608         return err;
 609 }
 610
 611 /**
 612  * replace_page - replace page in vma by new ksm page
 613  * @vma:      vma that holds the pte pointing to oldpage
 614  * @oldpage:  the page we are replacing by newpage
 615  * @newpage:  the ksm page we replace oldpage by
 616  * @orig_pte: the original value of the pte
 617  *
 618  * Returns 0 on success, -EFAULT on failure.
 619  */
 620 static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
 621                         struct page *newpage, pte_t orig_pte)
 622 {
 623         struct mm_struct *mm = vma->vm_mm;
 624         pgd_t *pgd;
 625         pud_t *pud;
 626         pmd_t *pmd;
 627         pte_t *ptep;
 628         spinlock_t *ptl;
 629         unsigned long addr;
 630         pgprot_t prot;
 631         int err = -EFAULT;
 632
 633         prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
 634
 635         addr = page_address_in_vma(oldpage, vma);
 636         if (addr == -EFAULT)
 637                 goto out;
 638
 639         pgd = pgd_offset(mm, addr);
 640         if (!pgd_present(*pgd))
 641                 goto out;
 642
 643         pud = pud_offset(pgd, addr);
 644         if (!pud_present(*pud))
 645                 goto out;
 646
 647         pmd = pmd_offset(pud, addr);
 648         if (!pmd_present(*pmd))
 649                 goto out;
 650
 651         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 652         if (!pte_same(*ptep, orig_pte)) {
 653                 pte_unmap_unlock(ptep, ptl);
 654                 goto out;
 655         }
 656
 657         get_page(newpage);
 658         page_add_ksm_rmap(newpage);
 659
 660         flush_cache_page(vma, addr, pte_pfn(*ptep));
 661         ptep_clear_flush(vma, addr, ptep);
 662         set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
 663
 664         page_remove_rmap(oldpage);
 665         put_page(oldpage);
 666
 667         pte_unmap_unlock(ptep, ptl);
 668         err = 0;
 669 out:
 670         return err;
 671 }
 672
 673 /*
 674  * try_to_merge_one_page - take two pages and merge them into one
 675  * @vma: the vma that hold the pte pointing into oldpage
 676  * @oldpage: the page that we want to replace with newpage
 677  * @newpage: the page that we want to map instead of oldpage
 678  *
 679  * Note:
 680  * oldpage should be a PageAnon page, while newpage should be a PageKsm page,
 681  * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
 682  *
 683  * This function returns 0 if the pages were merged, -EFAULT otherwise.
 684  */
 685 static int try_to_merge_one_page(struct vm_area_struct *vma,
 686                                  struct page *oldpage,
 687                                  struct page *newpage)
 688 {
 689         pte_t orig_pte = __pte(0);
 690         int err = -EFAULT;
 691
 692         if (!(vma->vm_flags & VM_MERGEABLE))
 693                 goto out;
 694
 695         if (!PageAnon(oldpage))
 696                 goto out;
 697
 698         get_page(newpage);
 699         get_page(oldpage);
 700
 701         /*
 702          * We need the page lock to read a stable PageSwapCache in
 703          * write_protect_page().  We use trylock_page() instead of
 704          * lock_page() because we don't want to wait here - we
 705          * prefer to continue scanning and merging different pages,
 706          * then come back to this page when it is unlocked.
 707          */
 708         if (!trylock_page(oldpage))
 709                 goto out_putpage;
 710         /*
 711          * If this anonymous page is mapped only here, its pte may need
 712          * to be write-protected.  If it's mapped elsewhere, all of its
 713          * ptes are necessarily already write-protected.  But in either
 714          * case, we need to lock and check page_count is not raised.
 715          */
 716         if (write_protect_page(vma, oldpage, &orig_pte)) {
 717                 unlock_page(oldpage);
 718                 goto out_putpage;
 719         }
 720         unlock_page(oldpage);
 721
 722         if (pages_identical(oldpage, newpage))
 723                 err = replace_page(vma, oldpage, newpage, orig_pte);
 724
 725 out_putpage:
 726         put_page(oldpage);
 727         put_page(newpage);
 728 out:
 729         return err;
 730 }
 731
 732 /*
 733  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 734  * but no new kernel page is allocated: kpage must already be a ksm page.
 735  */
 736 static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
 737                                       unsigned long addr1,
 738                                       struct page *page1,
 739                                       struct page *kpage)
 740 {
 741         struct vm_area_struct *vma;
 742         int err = -EFAULT;
 743
 744         down_read(&mm1->mmap_sem);
 745         vma = find_vma(mm1, addr1);
 746         if (!vma || vma->vm_start > addr1)
 747                 goto out;
 748
 749         err = try_to_merge_one_page(vma, page1, kpage);
 750 out:
 751         up_read(&mm1->mmap_sem);
 752         return err;
 753 }
 754
 755 /*
 756  * try_to_merge_two_pages - take two identical pages and prepare them
 757  * to be merged into one page.
 758  *
 759  * This function returns 0 if we successfully mapped two identical pages
 760  * into one page, -EFAULT otherwise.
 761  *
 762  * Note that this function allocates a new kernel page: if one of the pages
 763  * is already a ksm page, try_to_merge_with_ksm_page should be used.
 764  */
 765 static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
 766                                   struct page *page1, struct mm_struct *mm2,
 767                                   unsigned long addr2, struct page *page2)
 768 {
 769         struct vm_area_struct *vma;
 770         struct page *kpage;
 771         int err = -EFAULT;
 772
 773         /*
 774          * The number of nodes in the stable tree
 775          * is the number of kernel pages that we hold.
 776          */
 777         if (ksm_max_kernel_pages &&
 778             ksm_max_kernel_pages <= ksm_pages_shared)
 779                 return err;
 780
 781         kpage = alloc_page(GFP_HIGHUSER);
 782         if (!kpage)
 783                 return err;
 784
 785         down_read(&mm1->mmap_sem);
 786         vma = find_vma(mm1, addr1);
 787         if (!vma || vma->vm_start > addr1) {
 788                 up_read(&mm1->mmap_sem);
 789                 goto out;
 790         }
 791
 792         copy_user_highpage(kpage, page1, addr1, vma);
 793         err = try_to_merge_one_page(vma, page1, kpage);
 794         up_read(&mm1->mmap_sem);
 795
 796         if (!err) {
 797                 err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
 798                 /*
 799                  * If that fails, we have a ksm page with only one pte
 800                  * pointing to it: so break it.
 801                  */
 802                 if (err)
 803                         break_cow(mm1, addr1);
 804         }
 805 out:
 806         put_page(kpage);
 807         return err;
 808 }
 809
 810 /*
 811  * stable_tree_search - search page inside the stable tree
 812  * @page: the page that we are searching identical pages to.
 813  * @page2: pointer into identical page that we are holding inside the stable
 814  *         tree that we have found.
 815  * @rmap_item: the reverse mapping item
 816  *
 817  * This function checks if there is a page inside the stable tree
 818  * with identical content to the page that we are scanning right now.
 819  *
 820  * This function return rmap_item pointer to the identical item if found,
 821  * NULL otherwise.
 822  */
 823 static struct rmap_item *stable_tree_search(struct page *page,
 824                                             struct page **page2,
 825                                             struct rmap_item *rmap_item)
 826 {
 827         struct rb_node *node = root_stable_tree.rb_node;
 828
 829         while (node) {
 830                 struct rmap_item *tree_rmap_item, *next_rmap_item;
 831                 int ret;
 832
 833                 tree_rmap_item = rb_entry(node, struct rmap_item, node);
 834                 while (tree_rmap_item) {
 835                         BUG_ON(!in_stable_tree(tree_rmap_item));
 836                         cond_resched();
 837                         page2[0] = get_ksm_page(tree_rmap_item);
 838                         if (page2[0])
 839                                 break;
 840                         next_rmap_item = tree_rmap_item->next;
 841                         remove_rmap_item_from_tree(tree_rmap_item);
 842                         tree_rmap_item = next_rmap_item;
 843                 }
 844                 if (!tree_rmap_item)
 845                         return NULL;
 846
 847                 ret = memcmp_pages(page, page2[0]);
 848
 849                 if (ret < 0) {
 850                         put_page(page2[0]);
 851                         node = node->rb_left;
 852                 } else if (ret > 0) {
 853                         put_page(page2[0]);
 854                         node = node->rb_right;
 855                 } else {
 856                         return tree_rmap_item;
 857                 }
 858         }
 859
 860         return NULL;
 861 }
 862
 863 /*
 864  * stable_tree_insert - insert rmap_item pointing to new ksm page
 865  * into the stable tree.
 866  *
 867  * @page: the page that we are searching identical page to inside the stable
 868  *        tree.
 869  * @rmap_item: pointer to the reverse mapping item.
 870  *
 871  * This function returns rmap_item if success, NULL otherwise.
 872  */
 873 static struct rmap_item *stable_tree_insert(struct page *page,
 874                                             struct rmap_item *rmap_item)
 875 {
 876         struct rb_node **new = &root_stable_tree.rb_node;
 877         struct rb_node *parent = NULL;
 878
 879         while (*new) {
 880                 struct rmap_item *tree_rmap_item, *next_rmap_item;
 881                 struct page *tree_page;
 882                 int ret;
 883
 884                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
 885                 while (tree_rmap_item) {
 886                         BUG_ON(!in_stable_tree(tree_rmap_item));
 887                         cond_resched();
 888                         tree_page = get_ksm_page(tree_rmap_item);
 889                         if (tree_page)
 890                                 break;
 891                         next_rmap_item = tree_rmap_item->next;
 892                         remove_rmap_item_from_tree(tree_rmap_item);
 893                         tree_rmap_item = next_rmap_item;
 894                 }
 895                 if (!tree_rmap_item)
 896                         return NULL;
 897
 898                 ret = memcmp_pages(page, tree_page);
 899                 put_page(tree_page);
 900
 901                 parent = *new;
 902                 if (ret < 0)
 903                         new = &parent->rb_left;
 904                 else if (ret > 0)
 905                         new = &parent->rb_right;
 906                 else {
 907                         /*
 908                          * It is not a bug that stable_tree_search() didn't
 909                          * find this node: because at that time our page was
 910                          * not yet write-protected, so may have changed since.
 911                          */
 912                         return NULL;
 913                 }
 914         }
 915
 916         rmap_item->address |= NODE_FLAG | STABLE_FLAG;
 917         rmap_item->next = NULL;
 918         rb_link_node(&rmap_item->node, parent, new);
 919         rb_insert_color(&rmap_item->node, &root_stable_tree);
 920
 921         ksm_pages_shared++;
 922         return rmap_item;
 923 }
 924
 925 /*
 926  * unstable_tree_search_insert - search and insert items into the unstable tree.
 927  *
 928  * @page: the page that we are going to search for identical page or to insert
 929  *        into the unstable tree
 930  * @page2: pointer into identical page that was found inside the unstable tree
 931  * @rmap_item: the reverse mapping item of page
 932  *
 933  * This function searches for a page in the unstable tree identical to the
 934  * page currently being scanned; and if no identical page is found in the
 935  * tree, we insert rmap_item as a new object into the unstable tree.
 936  *
 937  * This function returns pointer to rmap_item found to be identical
 938  * to the currently scanned page, NULL otherwise.
 939  *
 940  * This function does both searching and inserting, because they share
 941  * the same walking algorithm in an rbtree.
 942  */
 943 static struct rmap_item *unstable_tree_search_insert(struct page *page,
 944                                                 struct page **page2,
 945                                                 struct rmap_item *rmap_item)
 946 {
 947         struct rb_node **new = &root_unstable_tree.rb_node;
 948         struct rb_node *parent = NULL;
 949
 950         while (*new) {
 951                 struct rmap_item *tree_rmap_item;
 952                 int ret;
 953
 954                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
 955                 page2[0] = get_mergeable_page(tree_rmap_item);
 956                 if (!page2[0])
 957                         return NULL;
 958
 959                 /*
 960                  * Don't substitute an unswappable ksm page
 961                  * just for one good swappable forked page.
 962                  */
 963                 if (page == page2[0]) {
 964                         put_page(page2[0]);
 965                         return NULL;
 966                 }
 967
 968                 ret = memcmp_pages(page, page2[0]);
 969
 970                 parent = *new;
 971                 if (ret < 0) {
 972                         put_page(page2[0]);
 973                         new = &parent->rb_left;
 974                 } else if (ret > 0) {
 975                         put_page(page2[0]);
 976                         new = &parent->rb_right;
 977                 } else {
 978                         return tree_rmap_item;
 979                 }
 980         }
 981
 982         rmap_item->address |= NODE_FLAG;
 983         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
 984         rb_link_node(&rmap_item->node, parent, new);
 985         rb_insert_color(&rmap_item->node, &root_unstable_tree);
 986
 987         ksm_pages_unshared++;
 988         return NULL;
 989 }
 990
 991 /*
 992  * stable_tree_append - add another rmap_item to the linked list of
 993  * rmap_items hanging off a given node of the stable tree, all sharing
 994  * the same ksm page.
 995  */
 996 static void stable_tree_append(struct rmap_item *rmap_item,
 997                                struct rmap_item *tree_rmap_item)
 998 {
 999         rmap_item->next = tree_rmap_item->next;
1000         rmap_item->prev = tree_rmap_item;
1001
1002         if (tree_rmap_item->next)
1003                 tree_rmap_item->next->prev = rmap_item;
1004
1005         tree_rmap_item->next = rmap_item;
1006         rmap_item->address |= STABLE_FLAG;
1007
1008         ksm_pages_sharing++;
1009 }
1010
1011 /*
1012  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1013  * if not, compare checksum to previous and if it's the same, see if page can
1014  * be inserted into the unstable tree, or merged with a page already there and
1015  * both transferred to the stable tree.
1016  *
1017  * @page: the page that we are searching identical page to.
1018  * @rmap_item: the reverse mapping into the virtual address of this page
1019  */
1020 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1021 {
1022         struct page *page2[1];
1023         struct rmap_item *tree_rmap_item;
1024         unsigned int checksum;
1025         int err;
1026
1027         if (in_stable_tree(rmap_item))
1028                 remove_rmap_item_from_tree(rmap_item);
1029
1030         /* We first start with searching the page inside the stable tree */
1031         tree_rmap_item = stable_tree_search(page, page2, rmap_item);
1032         if (tree_rmap_item) {
1033                 if (page == page2[0])                   /* forked */
1034                         err = 0;
1035                 else
1036                         err = try_to_merge_with_ksm_page(rmap_item->mm,
1037                                                          rmap_item->address,
1038                                                          page, page2[0]);
1039                 put_page(page2[0]);
1040
1041                 if (!err) {
1042                         /*
1043                          * The page was successfully merged:
1044                          * add its rmap_item to the stable tree.
1045                          */
1046                         stable_tree_append(rmap_item, tree_rmap_item);
1047                 }
1048                 return;
1049         }
1050
1051         /*
1052          * A ksm page might have got here by fork, but its other
1053          * references have already been removed from the stable tree.
1054          */
1055         if (PageKsm(page))
1056                 break_cow(rmap_item->mm, rmap_item->address);
1057
1058         /*
1059          * In case the hash value of the page was changed from the last time we
1060          * have calculated it, this page to be changed frequely, therefore we
1061          * don't want to insert it to the unstable tree, and we don't want to
1062          * waste our time to search if there is something identical to it there.
1063          */
1064         checksum = calc_checksum(page);
1065         if (rmap_item->oldchecksum != checksum) {
1066                 rmap_item->oldchecksum = checksum;
1067                 return;
1068         }
1069
1070         tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
1071         if (tree_rmap_item) {
1072                 err = try_to_merge_two_pages(rmap_item->mm,
1073                                              rmap_item->address, page,
1074                                              tree_rmap_item->mm,
1075                                              tree_rmap_item->address, page2[0]);
1076                 /*
1077                  * As soon as we merge this page, we want to remove the
1078                  * rmap_item of the page we have merged with from the unstable
1079                  * tree, and insert it instead as new node in the stable tree.
1080                  */
1081                 if (!err) {
1082                         rb_erase(&tree_rmap_item->node, &root_unstable_tree);
1083                         tree_rmap_item->address &= ~NODE_FLAG;
1084                         ksm_pages_unshared--;
1085
1086                         /*
1087                          * If we fail to insert the page into the stable tree,
1088                          * we will have 2 virtual addresses that are pointing
1089                          * to a ksm page left outside the stable tree,
1090                          * in which case we need to break_cow on both.
1091                          */
1092                         if (stable_tree_insert(page2[0], tree_rmap_item))
1093                                 stable_tree_append(rmap_item, tree_rmap_item);
1094                         else {
1095                                 break_cow(tree_rmap_item->mm,
1096                                                 tree_rmap_item->address);
1097                                 break_cow(rmap_item->mm, rmap_item->address);
1098                         }
1099                 }
1100
1101                 put_page(page2[0]);
1102         }
1103 }
1104
1105 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1106                                             struct list_head *cur,
1107                                             unsigned long addr)
1108 {
1109         struct rmap_item *rmap_item;
1110
1111         while (cur != &mm_slot->rmap_list) {
1112                 rmap_item = list_entry(cur, struct rmap_item, link);
1113                 if ((rmap_item->address & PAGE_MASK) == addr) {
1114                         if (!in_stable_tree(rmap_item))
1115                                 remove_rmap_item_from_tree(rmap_item);
1116                         return rmap_item;
1117                 }
1118                 if (rmap_item->address > addr)
1119                         break;
1120                 cur = cur->next;
1121                 remove_rmap_item_from_tree(rmap_item);
1122                 list_del(&rmap_item->link);
1123                 free_rmap_item(rmap_item);
1124         }
1125
1126         rmap_item = alloc_rmap_item();
1127         if (rmap_item) {
1128                 /* It has already been zeroed */
1129                 rmap_item->mm = mm_slot->mm;
1130                 rmap_item->address = addr;
1131                 list_add_tail(&rmap_item->link, cur);
1132         }
1133         return rmap_item;
1134 }
1135
1136 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1137 {
1138         struct mm_struct *mm;
1139         struct mm_slot *slot;
1140         struct vm_area_struct *vma;
1141         struct rmap_item *rmap_item;
1142
1143         if (list_empty(&ksm_mm_head.mm_list))
1144                 return NULL;
1145
1146         slot = ksm_scan.mm_slot;
1147         if (slot == &ksm_mm_head) {
1148                 root_unstable_tree = RB_ROOT;
1149
1150                 spin_lock(&ksm_mmlist_lock);
1151                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1152                 ksm_scan.mm_slot = slot;
1153                 spin_unlock(&ksm_mmlist_lock);
1154 next_mm:
1155                 ksm_scan.address = 0;
1156                 ksm_scan.rmap_item = list_entry(&slot->rmap_list,
1157                                                 struct rmap_item, link);
1158         }
1159
1160         mm = slot->mm;
1161         down_read(&mm->mmap_sem);
1162         for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) {
1163                 if (!(vma->vm_flags & VM_MERGEABLE))
1164                         continue;
1165                 if (ksm_scan.address < vma->vm_start)
1166                         ksm_scan.address = vma->vm_start;
1167                 if (!vma->anon_vma)
1168                         ksm_scan.address = vma->vm_end;
1169
1170                 while (ksm_scan.address < vma->vm_end) {
1171                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1172                         if (*page && PageAnon(*page)) {
1173                                 flush_anon_page(vma, *page, ksm_scan.address);
1174                                 flush_dcache_page(*page);
1175                                 rmap_item = get_next_rmap_item(slot,
1176                                         ksm_scan.rmap_item->link.next,
1177                                         ksm_scan.address);
1178                                 if (rmap_item) {
1179                                         ksm_scan.rmap_item = rmap_item;
1180                                         ksm_scan.address += PAGE_SIZE;
1181                                 } else
1182                                         put_page(*page);
1183                                 up_read(&mm->mmap_sem);
1184                                 return rmap_item;
1185                         }
1186                         if (*page)
1187                                 put_page(*page);
1188                         ksm_scan.address += PAGE_SIZE;
1189                         cond_resched();
1190                 }
1191         }
1192
1193         if (!ksm_scan.address) {
1194                 /*
1195                  * We've completed a full scan of all vmas, holding mmap_sem
1196                  * throughout, and found no VM_MERGEABLE: so do the same as
1197                  * __ksm_exit does to remove this mm from all our lists now.
1198                  */
1199                 remove_mm_from_lists(mm);
1200                 up_read(&mm->mmap_sem);
1201                 slot = ksm_scan.mm_slot;
1202                 if (slot != &ksm_mm_head)
1203                         goto next_mm;
1204                 return NULL;
1205         }
1206
1207         /*
1208          * Nuke all the rmap_items that are above this current rmap:
1209          * because there were no VM_MERGEABLE vmas with such addresses.
1210          */
1211         remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
1212         up_read(&mm->mmap_sem);
1213
1214         spin_lock(&ksm_mmlist_lock);
1215         slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1216         ksm_scan.mm_slot = slot;
1217         spin_unlock(&ksm_mmlist_lock);
1218
1219         /* Repeat until we've completed scanning the whole list */
1220         if (slot != &ksm_mm_head)
1221                 goto next_mm;
1222
1223         /*
1224          * Bump seqnr here rather than at top, so that __ksm_exit
1225          * can skip rb_erase on unstable tree until we run again.
1226          */
1227         ksm_scan.seqnr++;
1228         return NULL;
1229 }
1230
1231 /**
1232  * ksm_do_scan  - the ksm scanner main worker function.
1233  * @scan_npages - number of pages we want to scan before we return.
1234  */
1235 static void ksm_do_scan(unsigned int scan_npages)
1236 {
1237         struct rmap_item *rmap_item;
1238         struct page *page;
1239
1240         while (scan_npages--) {
1241                 cond_resched();
1242                 rmap_item = scan_get_next_rmap_item(&page);
1243                 if (!rmap_item)
1244                         return;
1245                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1246                         cmp_and_merge_page(page, rmap_item);
1247                 else if (page_mapcount(page) == 1) {
1248                         /*
1249                          * Replace now-unshared ksm page by ordinary page.
1250                          */
1251                         break_cow(rmap_item->mm, rmap_item->address);
1252                         remove_rmap_item_from_tree(rmap_item);
1253                         rmap_item->oldchecksum = calc_checksum(page);
1254                 }
1255                 put_page(page);
1256         }
1257 }
1258
1259 static int ksmd_should_run(void)
1260 {
1261         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1262 }
1263
1264 static int ksm_scan_thread(void *nothing)
1265 {
1266         set_user_nice(current, 5);
1267
1268         while (!kthread_should_stop()) {
1269                 mutex_lock(&ksm_thread_mutex);
1270                 if (ksmd_should_run())
1271                         ksm_do_scan(ksm_thread_pages_to_scan);
1272                 mutex_unlock(&ksm_thread_mutex);
1273
1274                 if (ksmd_should_run()) {
1275                         schedule_timeout_interruptible(
1276                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1277                 } else {
1278                         wait_event_interruptible(ksm_thread_wait,
1279                                 ksmd_should_run() || kthread_should_stop());
1280                 }
1281         }
1282         return 0;
1283 }
1284
1285 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1286                 unsigned long end, int advice, unsigned long *vm_flags)
1287 {
1288         struct mm_struct *mm = vma->vm_mm;
1289
1290         switch (advice) {
1291         case MADV_MERGEABLE:
1292                 /*
1293                  * Be somewhat over-protective for now!
1294                  */
1295                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1296                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1297                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1298                                  VM_MIXEDMAP  | VM_SAO))
1299                         return 0;               /* just ignore the advice */
1300
1301                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
1302                         if (__ksm_enter(mm) < 0)
1303                                 return -EAGAIN;
1304
1305                 *vm_flags |= VM_MERGEABLE;
1306                 break;
1307
1308         case MADV_UNMERGEABLE:
1309                 if (!(*vm_flags & VM_MERGEABLE))
1310                         return 0;               /* just ignore the advice */
1311
1312                 if (vma->anon_vma)
1313                         unmerge_ksm_pages(vma, start, end);
1314
1315                 *vm_flags &= ~VM_MERGEABLE;
1316                 break;
1317         }
1318
1319         return 0;
1320 }
1321
1322 int __ksm_enter(struct mm_struct *mm)
1323 {
1324         struct mm_slot *mm_slot;
1325         int needs_wakeup;
1326
1327         mm_slot = alloc_mm_slot();
1328         if (!mm_slot)
1329                 return -ENOMEM;
1330
1331         /* Check ksm_run too?  Would need tighter locking */
1332         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1333
1334         spin_lock(&ksm_mmlist_lock);
1335         insert_to_mm_slots_hash(mm, mm_slot);
1336         /*
1337          * Insert just behind the scanning cursor, to let the area settle
1338          * down a little; when fork is followed by immediate exec, we don't
1339          * want ksmd to waste time setting up and tearing down an rmap_list.
1340          */
1341         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1342         spin_unlock(&ksm_mmlist_lock);
1343
1344         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1345
1346         if (needs_wakeup)
1347                 wake_up_interruptible(&ksm_thread_wait);
1348
1349         return 0;
1350 }
1351
1352 void __ksm_exit(struct mm_struct *mm)
1353 {
1354         /*
1355          * This process is exiting: doesn't hold and doesn't need mmap_sem;
1356          * but we do need to exclude ksmd and other exiters while we modify
1357          * the various lists and trees.
1358          */
1359         mutex_lock(&ksm_thread_mutex);
1360         remove_mm_from_lists(mm);
1361         mutex_unlock(&ksm_thread_mutex);
1362 }
1363
1364 #define KSM_ATTR_RO(_name) \
1365         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1366 #define KSM_ATTR(_name) \
1367         static struct kobj_attribute _name##_attr = \
1368                 __ATTR(_name, 0644, _name##_show, _name##_store)
1369
1370 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1371                                     struct kobj_attribute *attr, char *buf)
1372 {
1373         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1374 }
1375
1376 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1377                                      struct kobj_attribute *attr,
1378                                      const char *buf, size_t count)
1379 {
1380         unsigned long msecs;
1381         int err;
1382
1383         err = strict_strtoul(buf, 10, &msecs);
1384         if (err || msecs > UINT_MAX)
1385                 return -EINVAL;
1386
1387         ksm_thread_sleep_millisecs = msecs;
1388
1389         return count;
1390 }
1391 KSM_ATTR(sleep_millisecs);
1392
1393 static ssize_t pages_to_scan_show(struct kobject *kobj,
1394                                   struct kobj_attribute *attr, char *buf)
1395 {
1396         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1397 }
1398
1399 static ssize_t pages_to_scan_store(struct kobject *kobj,
1400                                    struct kobj_attribute *attr,
1401                                    const char *buf, size_t count)
1402 {
1403         int err;
1404         unsigned long nr_pages;
1405
1406         err = strict_strtoul(buf, 10, &nr_pages);
1407         if (err || nr_pages > UINT_MAX)
1408                 return -EINVAL;
1409
1410         ksm_thread_pages_to_scan = nr_pages;
1411
1412         return count;
1413 }
1414 KSM_ATTR(pages_to_scan);
1415
1416 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1417                         char *buf)
1418 {
1419         return sprintf(buf, "%u\n", ksm_run);
1420 }
1421
1422 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1423                          const char *buf, size_t count)
1424 {
1425         int err;
1426         unsigned long flags;
1427
1428         err = strict_strtoul(buf, 10, &flags);
1429         if (err || flags > UINT_MAX)
1430                 return -EINVAL;
1431         if (flags > KSM_RUN_UNMERGE)
1432                 return -EINVAL;
1433
1434         /*
1435          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1436          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1437          * breaking COW to free the unswappable pages_shared (but leaves
1438          * mm_slots on the list for when ksmd may be set running again).
1439          */
1440
1441         mutex_lock(&ksm_thread_mutex);
1442         if (ksm_run != flags) {
1443                 ksm_run = flags;
1444                 if (flags & KSM_RUN_UNMERGE)
1445                         unmerge_and_remove_all_rmap_items();
1446         }
1447         mutex_unlock(&ksm_thread_mutex);
1448
1449         if (flags & KSM_RUN_MERGE)
1450                 wake_up_interruptible(&ksm_thread_wait);
1451
1452         return count;
1453 }
1454 KSM_ATTR(run);
1455
1456 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1457                                       struct kobj_attribute *attr,
1458                                       const char *buf, size_t count)
1459 {
1460         int err;
1461         unsigned long nr_pages;
1462
1463         err = strict_strtoul(buf, 10, &nr_pages);
1464         if (err)
1465                 return -EINVAL;
1466
1467         ksm_max_kernel_pages = nr_pages;
1468
1469         return count;
1470 }
1471
1472 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1473                                      struct kobj_attribute *attr, char *buf)
1474 {
1475         return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1476 }
1477 KSM_ATTR(max_kernel_pages);
1478
1479 static ssize_t pages_shared_show(struct kobject *kobj,
1480                                  struct kobj_attribute *attr, char *buf)
1481 {
1482         return sprintf(buf, "%lu\n", ksm_pages_shared);
1483 }
1484 KSM_ATTR_RO(pages_shared);
1485
1486 static ssize_t pages_sharing_show(struct kobject *kobj,
1487                                   struct kobj_attribute *attr, char *buf)
1488 {
1489         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1490 }
1491 KSM_ATTR_RO(pages_sharing);
1492
1493 static ssize_t pages_unshared_show(struct kobject *kobj,
1494                                    struct kobj_attribute *attr, char *buf)
1495 {
1496         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1497 }
1498 KSM_ATTR_RO(pages_unshared);
1499
1500 static ssize_t pages_volatile_show(struct kobject *kobj,
1501                                    struct kobj_attribute *attr, char *buf)
1502 {
1503         long ksm_pages_volatile;
1504
1505         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1506                                 - ksm_pages_sharing - ksm_pages_unshared;
1507         /*
1508          * It was not worth any locking to calculate that statistic,
1509          * but it might therefore sometimes be negative: conceal that.
1510          */
1511         if (ksm_pages_volatile < 0)
1512                 ksm_pages_volatile = 0;
1513         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1514 }
1515 KSM_ATTR_RO(pages_volatile);
1516
1517 static ssize_t full_scans_show(struct kobject *kobj,
1518                                struct kobj_attribute *attr, char *buf)
1519 {
1520         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1521 }
1522 KSM_ATTR_RO(full_scans);
1523
1524 static struct attribute *ksm_attrs[] = {
1525         &sleep_millisecs_attr.attr,
1526         &pages_to_scan_attr.attr,
1527         &run_attr.attr,
1528         &max_kernel_pages_attr.attr,
1529         &pages_shared_attr.attr,
1530         &pages_sharing_attr.attr,
1531         &pages_unshared_attr.attr,
1532         &pages_volatile_attr.attr,
1533         &full_scans_attr.attr,
1534         NULL,
1535 };
1536
1537 static struct attribute_group ksm_attr_group = {
1538         .attrs = ksm_attrs,
1539         .name = "ksm",
1540 };
1541
1542 static int __init ksm_init(void)
1543 {
1544         struct task_struct *ksm_thread;
1545         int err;
1546
1547         err = ksm_slab_init();
1548         if (err)
1549                 goto out;
1550
1551         err = mm_slots_hash_init();
1552         if (err)
1553                 goto out_free1;
1554
1555         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1556         if (IS_ERR(ksm_thread)) {
1557                 printk(KERN_ERR "ksm: creating kthread failed\n");
1558                 err = PTR_ERR(ksm_thread);
1559                 goto out_free2;
1560         }
1561
1562         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1563         if (err) {
1564                 printk(KERN_ERR "ksm: register sysfs failed\n");
1565                 goto out_free3;
1566         }
1567
1568         return 0;
1569
1570 out_free3:
1571         kthread_stop(ksm_thread);
1572 out_free2:
1573         mm_slots_hash_free();
1574 out_free1:
1575         ksm_slab_free();
1576 out:
1577         return err;
1578 }
1579 module_init(ksm_init)