linux/mm/ksm.c
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   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/memory.h>
  33#include <linux/mmu_notifier.h>
  34#include <linux/swap.h>
  35#include <linux/ksm.h>
  36#include <linux/hash.h>
  37#include <linux/freezer.h>
  38#include <linux/oom.h>
  39
  40#include <asm/tlbflush.h>
  41#include "internal.h"
  42
  43/*
  44 * A few notes about the KSM scanning process,
  45 * to make it easier to understand the data structures below:
  46 *
  47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
  48 * contents into a data structure that holds pointers to the pages' locations.
  49 *
  50 * Since the contents of the pages may change at any moment, KSM cannot just
  51 * insert the pages into a normal sorted tree and expect it to find anything.
  52 * Therefore KSM uses two data structures - the stable and the unstable tree.
  53 *
  54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  55 * by their contents.  Because each such page is write-protected, searching on
  56 * this tree is fully assured to be working (except when pages are unmapped),
  57 * and therefore this tree is called the stable tree.
  58 *
  59 * In addition to the stable tree, KSM uses a second data structure called the
  60 * unstable tree: this tree holds pointers to pages which have been found to
  61 * be "unchanged for a period of time".  The unstable tree sorts these pages
  62 * by their contents, but since they are not write-protected, KSM cannot rely
  63 * upon the unstable tree to work correctly - the unstable tree is liable to
  64 * be corrupted as its contents are modified, and so it is called unstable.
  65 *
  66 * KSM solves this problem by several techniques:
  67 *
  68 * 1) The unstable tree is flushed every time KSM completes scanning all
  69 *    memory areas, and then the tree is rebuilt again from the beginning.
  70 * 2) KSM will only insert into the unstable tree, pages whose hash value
  71 *    has not changed since the previous scan of all memory areas.
  72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
  73 *    colors of the nodes and not on their contents, assuring that even when
  74 *    the tree gets "corrupted" it won't get out of balance, so scanning time
  75 *    remains the same (also, searching and inserting nodes in an rbtree uses
  76 *    the same algorithm, so we have no overhead when we flush and rebuild).
  77 * 4) KSM never flushes the stable tree, which means that even if it were to
  78 *    take 10 attempts to find a page in the unstable tree, once it is found,
  79 *    it is secured in the stable tree.  (When we scan a new page, we first
  80 *    compare it against the stable tree, and then against the unstable tree.)
  81 */
  82
  83/**
  84 * struct mm_slot - ksm information per mm that is being scanned
  85 * @link: link to the mm_slots hash list
  86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
  87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
  88 * @mm: the mm that this information is valid for
  89 */
  90struct mm_slot {
  91        struct hlist_node link;
  92        struct list_head mm_list;
  93        struct rmap_item *rmap_list;
  94        struct mm_struct *mm;
  95};
  96
  97/**
  98 * struct ksm_scan - cursor for scanning
  99 * @mm_slot: the current mm_slot we are scanning
 100 * @address: the next address inside that to be scanned
 101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
 102 * @seqnr: count of completed full scans (needed when removing unstable node)
 103 *
 104 * There is only the one ksm_scan instance of this cursor structure.
 105 */
 106struct ksm_scan {
 107        struct mm_slot *mm_slot;
 108        unsigned long address;
 109        struct rmap_item **rmap_list;
 110        unsigned long seqnr;
 111};
 112
 113/**
 114 * struct stable_node - node of the stable rbtree
 115 * @node: rb node of this ksm page in the stable tree
 116 * @hlist: hlist head of rmap_items using this ksm page
 117 * @kpfn: page frame number of this ksm page
 118 */
 119struct stable_node {
 120        struct rb_node node;
 121        struct hlist_head hlist;
 122        unsigned long kpfn;
 123};
 124
 125/**
 126 * struct rmap_item - reverse mapping item for virtual addresses
 127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 129 * @mm: the memory structure this rmap_item is pointing into
 130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 131 * @oldchecksum: previous checksum of the page at that virtual address
 132 * @node: rb node of this rmap_item in the unstable tree
 133 * @head: pointer to stable_node heading this list in the stable tree
 134 * @hlist: link into hlist of rmap_items hanging off that stable_node
 135 */
 136struct rmap_item {
 137        struct rmap_item *rmap_list;
 138        struct anon_vma *anon_vma;      /* when stable */
 139        struct mm_struct *mm;
 140        unsigned long address;          /* + low bits used for flags below */
 141        unsigned int oldchecksum;       /* when unstable */
 142        union {
 143                struct rb_node node;    /* when node of unstable tree */
 144                struct {                /* when listed from stable tree */
 145                        struct stable_node *head;
 146                        struct hlist_node hlist;
 147                };
 148        };
 149};
 150
 151#define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
 152#define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
 153#define STABLE_FLAG     0x200   /* is listed from the stable tree */
 154
 155/* The stable and unstable tree heads */
 156static struct rb_root root_stable_tree = RB_ROOT;
 157static struct rb_root root_unstable_tree = RB_ROOT;
 158
 159#define MM_SLOTS_HASH_SHIFT 10
 160#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
 161static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
 162
 163static struct mm_slot ksm_mm_head = {
 164        .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
 165};
 166static struct ksm_scan ksm_scan = {
 167        .mm_slot = &ksm_mm_head,
 168};
 169
 170static struct kmem_cache *rmap_item_cache;
 171static struct kmem_cache *stable_node_cache;
 172static struct kmem_cache *mm_slot_cache;
 173
 174/* The number of nodes in the stable tree */
 175static unsigned long ksm_pages_shared;
 176
 177/* The number of page slots additionally sharing those nodes */
 178static unsigned long ksm_pages_sharing;
 179
 180/* The number of nodes in the unstable tree */
 181static unsigned long ksm_pages_unshared;
 182
 183/* The number of rmap_items in use: to calculate pages_volatile */
 184static unsigned long ksm_rmap_items;
 185
 186/* Number of pages ksmd should scan in one batch */
 187static unsigned int ksm_thread_pages_to_scan = 100;
 188
 189/* Milliseconds ksmd should sleep between batches */
 190static unsigned int ksm_thread_sleep_millisecs = 20;
 191
 192#define KSM_RUN_STOP    0
 193#define KSM_RUN_MERGE   1
 194#define KSM_RUN_UNMERGE 2
 195static unsigned int ksm_run = KSM_RUN_STOP;
 196
 197static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 198static DEFINE_MUTEX(ksm_thread_mutex);
 199static DEFINE_SPINLOCK(ksm_mmlist_lock);
 200
 201#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
 202                sizeof(struct __struct), __alignof__(struct __struct),\
 203                (__flags), NULL)
 204
 205static int __init ksm_slab_init(void)
 206{
 207        rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
 208        if (!rmap_item_cache)
 209                goto out;
 210
 211        stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
 212        if (!stable_node_cache)
 213                goto out_free1;
 214
 215        mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
 216        if (!mm_slot_cache)
 217                goto out_free2;
 218
 219        return 0;
 220
 221out_free2:
 222        kmem_cache_destroy(stable_node_cache);
 223out_free1:
 224        kmem_cache_destroy(rmap_item_cache);
 225out:
 226        return -ENOMEM;
 227}
 228
 229static void __init ksm_slab_free(void)
 230{
 231        kmem_cache_destroy(mm_slot_cache);
 232        kmem_cache_destroy(stable_node_cache);
 233        kmem_cache_destroy(rmap_item_cache);
 234        mm_slot_cache = NULL;
 235}
 236
 237static inline struct rmap_item *alloc_rmap_item(void)
 238{
 239        struct rmap_item *rmap_item;
 240
 241        rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
 242        if (rmap_item)
 243                ksm_rmap_items++;
 244        return rmap_item;
 245}
 246
 247static inline void free_rmap_item(struct rmap_item *rmap_item)
 248{
 249        ksm_rmap_items--;
 250        rmap_item->mm = NULL;   /* debug safety */
 251        kmem_cache_free(rmap_item_cache, rmap_item);
 252}
 253
 254static inline struct stable_node *alloc_stable_node(void)
 255{
 256        return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
 257}
 258
 259static inline void free_stable_node(struct stable_node *stable_node)
 260{
 261        kmem_cache_free(stable_node_cache, stable_node);
 262}
 263
 264static inline struct mm_slot *alloc_mm_slot(void)
 265{
 266        if (!mm_slot_cache)     /* initialization failed */
 267                return NULL;
 268        return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 269}
 270
 271static inline void free_mm_slot(struct mm_slot *mm_slot)
 272{
 273        kmem_cache_free(mm_slot_cache, mm_slot);
 274}
 275
 276static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 277{
 278        struct mm_slot *mm_slot;
 279        struct hlist_head *bucket;
 280        struct hlist_node *node;
 281
 282        bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 283        hlist_for_each_entry(mm_slot, node, bucket, link) {
 284                if (mm == mm_slot->mm)
 285                        return mm_slot;
 286        }
 287        return NULL;
 288}
 289
 290static void insert_to_mm_slots_hash(struct mm_struct *mm,
 291                                    struct mm_slot *mm_slot)
 292{
 293        struct hlist_head *bucket;
 294
 295        bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 296        mm_slot->mm = mm;
 297        hlist_add_head(&mm_slot->link, bucket);
 298}
 299
 300static inline int in_stable_tree(struct rmap_item *rmap_item)
 301{
 302        return rmap_item->address & STABLE_FLAG;
 303}
 304
 305/*
 306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 307 * page tables after it has passed through ksm_exit() - which, if necessary,
 308 * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
 309 * a special flag: they can just back out as soon as mm_users goes to zero.
 310 * ksm_test_exit() is used throughout to make this test for exit: in some
 311 * places for correctness, in some places just to avoid unnecessary work.
 312 */
 313static inline bool ksm_test_exit(struct mm_struct *mm)
 314{
 315        return atomic_read(&mm->mm_users) == 0;
 316}
 317
 318/*
 319 * We use break_ksm to break COW on a ksm page: it's a stripped down
 320 *
 321 *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 322 *              put_page(page);
 323 *
 324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 325 * in case the application has unmapped and remapped mm,addr meanwhile.
 326 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 328 */
 329static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 330{
 331        struct page *page;
 332        int ret = 0;
 333
 334        do {
 335                cond_resched();
 336                page = follow_page(vma, addr, FOLL_GET);
 337                if (IS_ERR_OR_NULL(page))
 338                        break;
 339                if (PageKsm(page))
 340                        ret = handle_mm_fault(vma->vm_mm, vma, addr,
 341                                                        FAULT_FLAG_WRITE);
 342                else
 343                        ret = VM_FAULT_WRITE;
 344                put_page(page);
 345        } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
 346        /*
 347         * We must loop because handle_mm_fault() may back out if there's
 348         * any difficulty e.g. if pte accessed bit gets updated concurrently.
 349         *
 350         * VM_FAULT_WRITE is what we have been hoping for: it indicates that
 351         * COW has been broken, even if the vma does not permit VM_WRITE;
 352         * but note that a concurrent fault might break PageKsm for us.
 353         *
 354         * VM_FAULT_SIGBUS could occur if we race with truncation of the
 355         * backing file, which also invalidates anonymous pages: that's
 356         * okay, that truncation will have unmapped the PageKsm for us.
 357         *
 358         * VM_FAULT_OOM: at the time of writing (late July 2009), setting
 359         * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
 360         * current task has TIF_MEMDIE set, and will be OOM killed on return
 361         * to user; and ksmd, having no mm, would never be chosen for that.
 362         *
 363         * But if the mm is in a limited mem_cgroup, then the fault may fail
 364         * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
 365         * even ksmd can fail in this way - though it's usually breaking ksm
 366         * just to undo a merge it made a moment before, so unlikely to oom.
 367         *
 368         * That's a pity: we might therefore have more kernel pages allocated
 369         * than we're counting as nodes in the stable tree; but ksm_do_scan
 370         * will retry to break_cow on each pass, so should recover the page
 371         * in due course.  The important thing is to not let VM_MERGEABLE
 372         * be cleared while any such pages might remain in the area.
 373         */
 374        return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 375}
 376
 377static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
 378                unsigned long addr)
 379{
 380        struct vm_area_struct *vma;
 381        if (ksm_test_exit(mm))
 382                return NULL;
 383        vma = find_vma(mm, addr);
 384        if (!vma || vma->vm_start > addr)
 385                return NULL;
 386        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 387                return NULL;
 388        return vma;
 389}
 390
 391static void break_cow(struct rmap_item *rmap_item)
 392{
 393        struct mm_struct *mm = rmap_item->mm;
 394        unsigned long addr = rmap_item->address;
 395        struct vm_area_struct *vma;
 396
 397        /*
 398         * It is not an accident that whenever we want to break COW
 399         * to undo, we also need to drop a reference to the anon_vma.
 400         */
 401        put_anon_vma(rmap_item->anon_vma);
 402
 403        down_read(&mm->mmap_sem);
 404        vma = find_mergeable_vma(mm, addr);
 405        if (vma)
 406                break_ksm(vma, addr);
 407        up_read(&mm->mmap_sem);
 408}
 409
 410static struct page *page_trans_compound_anon(struct page *page)
 411{
 412        if (PageTransCompound(page)) {
 413                struct page *head = compound_trans_head(page);
 414                /*
 415                 * head may actually be splitted and freed from under
 416                 * us but it's ok here.
 417                 */
 418                if (PageAnon(head))
 419                        return head;
 420        }
 421        return NULL;
 422}
 423
 424static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 425{
 426        struct mm_struct *mm = rmap_item->mm;
 427        unsigned long addr = rmap_item->address;
 428        struct vm_area_struct *vma;
 429        struct page *page;
 430
 431        down_read(&mm->mmap_sem);
 432        vma = find_mergeable_vma(mm, addr);
 433        if (!vma)
 434                goto out;
 435
 436        page = follow_page(vma, addr, FOLL_GET);
 437        if (IS_ERR_OR_NULL(page))
 438                goto out;
 439        if (PageAnon(page) || page_trans_compound_anon(page)) {
 440                flush_anon_page(vma, page, addr);
 441                flush_dcache_page(page);
 442        } else {
 443                put_page(page);
 444out:            page = NULL;
 445        }
 446        up_read(&mm->mmap_sem);
 447        return page;
 448}
 449
 450static void remove_node_from_stable_tree(struct stable_node *stable_node)
 451{
 452        struct rmap_item *rmap_item;
 453        struct hlist_node *hlist;
 454
 455        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
 456                if (rmap_item->hlist.next)
 457                        ksm_pages_sharing--;
 458                else
 459                        ksm_pages_shared--;
 460                put_anon_vma(rmap_item->anon_vma);
 461                rmap_item->address &= PAGE_MASK;
 462                cond_resched();
 463        }
 464
 465        rb_erase(&stable_node->node, &root_stable_tree);
 466        free_stable_node(stable_node);
 467}
 468
 469/*
 470 * get_ksm_page: checks if the page indicated by the stable node
 471 * is still its ksm page, despite having held no reference to it.
 472 * In which case we can trust the content of the page, and it
 473 * returns the gotten page; but if the page has now been zapped,
 474 * remove the stale node from the stable tree and return NULL.
 475 *
 476 * You would expect the stable_node to hold a reference to the ksm page.
 477 * But if it increments the page's count, swapping out has to wait for
 478 * ksmd to come around again before it can free the page, which may take
 479 * seconds or even minutes: much too unresponsive.  So instead we use a
 480 * "keyhole reference": access to the ksm page from the stable node peeps
 481 * out through its keyhole to see if that page still holds the right key,
 482 * pointing back to this stable node.  This relies on freeing a PageAnon
 483 * page to reset its page->mapping to NULL, and relies on no other use of
 484 * a page to put something that might look like our key in page->mapping.
 485 *
 486 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
 487 * but this is different - made simpler by ksm_thread_mutex being held, but
 488 * interesting for assuming that no other use of the struct page could ever
 489 * put our expected_mapping into page->mapping (or a field of the union which
 490 * coincides with page->mapping).  The RCU calls are not for KSM at all, but
 491 * to keep the page_count protocol described with page_cache_get_speculative.
 492 *
 493 * Note: it is possible that get_ksm_page() will return NULL one moment,
 494 * then page the next, if the page is in between page_freeze_refs() and
 495 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
 496 * is on its way to being freed; but it is an anomaly to bear in mind.
 497 */
 498static struct page *get_ksm_page(struct stable_node *stable_node)
 499{
 500        struct page *page;
 501        void *expected_mapping;
 502
 503        page = pfn_to_page(stable_node->kpfn);
 504        expected_mapping = (void *)stable_node +
 505                                (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 506        rcu_read_lock();
 507        if (page->mapping != expected_mapping)
 508                goto stale;
 509        if (!get_page_unless_zero(page))
 510                goto stale;
 511        if (page->mapping != expected_mapping) {
 512                put_page(page);
 513                goto stale;
 514        }
 515        rcu_read_unlock();
 516        return page;
 517stale:
 518        rcu_read_unlock();
 519        remove_node_from_stable_tree(stable_node);
 520        return NULL;
 521}
 522
 523/*
 524 * Removing rmap_item from stable or unstable tree.
 525 * This function will clean the information from the stable/unstable tree.
 526 */
 527static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 528{
 529        if (rmap_item->address & STABLE_FLAG) {
 530                struct stable_node *stable_node;
 531                struct page *page;
 532
 533                stable_node = rmap_item->head;
 534                page = get_ksm_page(stable_node);
 535                if (!page)
 536                        goto out;
 537
 538                lock_page(page);
 539                hlist_del(&rmap_item->hlist);
 540                unlock_page(page);
 541                put_page(page);
 542
 543                if (stable_node->hlist.first)
 544                        ksm_pages_sharing--;
 545                else
 546                        ksm_pages_shared--;
 547
 548                put_anon_vma(rmap_item->anon_vma);
 549                rmap_item->address &= PAGE_MASK;
 550
 551        } else if (rmap_item->address & UNSTABLE_FLAG) {
 552                unsigned char age;
 553                /*
 554                 * Usually ksmd can and must skip the rb_erase, because
 555                 * root_unstable_tree was already reset to RB_ROOT.
 556                 * But be careful when an mm is exiting: do the rb_erase
 557                 * if this rmap_item was inserted by this scan, rather
 558                 * than left over from before.
 559                 */
 560                age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 561                BUG_ON(age > 1);
 562                if (!age)
 563                        rb_erase(&rmap_item->node, &root_unstable_tree);
 564
 565                ksm_pages_unshared--;
 566                rmap_item->address &= PAGE_MASK;
 567        }
 568out:
 569        cond_resched();         /* we're called from many long loops */
 570}
 571
 572static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 573                                       struct rmap_item **rmap_list)
 574{
 575        while (*rmap_list) {
 576                struct rmap_item *rmap_item = *rmap_list;
 577                *rmap_list = rmap_item->rmap_list;
 578                remove_rmap_item_from_tree(rmap_item);
 579                free_rmap_item(rmap_item);
 580        }
 581}
 582
 583/*
 584 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 585 * than check every pte of a given vma, the locking doesn't quite work for
 586 * that - an rmap_item is assigned to the stable tree after inserting ksm
 587 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 588 * rmap_items from parent to child at fork time (so as not to waste time
 589 * if exit comes before the next scan reaches it).
 590 *
 591 * Similarly, although we'd like to remove rmap_items (so updating counts
 592 * and freeing memory) when unmerging an area, it's easier to leave that
 593 * to the next pass of ksmd - consider, for example, how ksmd might be
 594 * in cmp_and_merge_page on one of the rmap_items we would be removing.
 595 */
 596static int unmerge_ksm_pages(struct vm_area_struct *vma,
 597                             unsigned long start, unsigned long end)
 598{
 599        unsigned long addr;
 600        int err = 0;
 601
 602        for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
 603                if (ksm_test_exit(vma->vm_mm))
 604                        break;
 605                if (signal_pending(current))
 606                        err = -ERESTARTSYS;
 607                else
 608                        err = break_ksm(vma, addr);
 609        }
 610        return err;
 611}
 612
 613#ifdef CONFIG_SYSFS
 614/*
 615 * Only called through the sysfs control interface:
 616 */
 617static int unmerge_and_remove_all_rmap_items(void)
 618{
 619        struct mm_slot *mm_slot;
 620        struct mm_struct *mm;
 621        struct vm_area_struct *vma;
 622        int err = 0;
 623
 624        spin_lock(&ksm_mmlist_lock);
 625        ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
 626                                                struct mm_slot, mm_list);
 627        spin_unlock(&ksm_mmlist_lock);
 628
 629        for (mm_slot = ksm_scan.mm_slot;
 630                        mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
 631                mm = mm_slot->mm;
 632                down_read(&mm->mmap_sem);
 633                for (vma = mm->mmap; vma; vma = vma->vm_next) {
 634                        if (ksm_test_exit(mm))
 635                                break;
 636                        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 637                                continue;
 638                        err = unmerge_ksm_pages(vma,
 639                                                vma->vm_start, vma->vm_end);
 640                        if (err)
 641                                goto error;
 642                }
 643
 644                remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
 645
 646                spin_lock(&ksm_mmlist_lock);
 647                ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
 648                                                struct mm_slot, mm_list);
 649                if (ksm_test_exit(mm)) {
 650                        hlist_del(&mm_slot->link);
 651                        list_del(&mm_slot->mm_list);
 652                        spin_unlock(&ksm_mmlist_lock);
 653
 654                        free_mm_slot(mm_slot);
 655                        clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 656                        up_read(&mm->mmap_sem);
 657                        mmdrop(mm);
 658                } else {
 659                        spin_unlock(&ksm_mmlist_lock);
 660                        up_read(&mm->mmap_sem);
 661                }
 662        }
 663
 664        ksm_scan.seqnr = 0;
 665        return 0;
 666
 667error:
 668        up_read(&mm->mmap_sem);
 669        spin_lock(&ksm_mmlist_lock);
 670        ksm_scan.mm_slot = &ksm_mm_head;
 671        spin_unlock(&ksm_mmlist_lock);
 672        return err;
 673}
 674#endif /* CONFIG_SYSFS */
 675
 676static u32 calc_checksum(struct page *page)
 677{
 678        u32 checksum;
 679        void *addr = kmap_atomic(page);
 680        checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 681        kunmap_atomic(addr);
 682        return checksum;
 683}
 684
 685static int memcmp_pages(struct page *page1, struct page *page2)
 686{
 687        char *addr1, *addr2;
 688        int ret;
 689
 690        addr1 = kmap_atomic(page1);
 691        addr2 = kmap_atomic(page2);
 692        ret = memcmp(addr1, addr2, PAGE_SIZE);
 693        kunmap_atomic(addr2);
 694        kunmap_atomic(addr1);
 695        return ret;
 696}
 697
 698static inline int pages_identical(struct page *page1, struct page *page2)
 699{
 700        return !memcmp_pages(page1, page2);
 701}
 702
 703static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 704                              pte_t *orig_pte)
 705{
 706        struct mm_struct *mm = vma->vm_mm;
 707        unsigned long addr;
 708        pte_t *ptep;
 709        spinlock_t *ptl;
 710        int swapped;
 711        int err = -EFAULT;
 712        unsigned long mmun_start;       /* For mmu_notifiers */
 713        unsigned long mmun_end;         /* For mmu_notifiers */
 714
 715        addr = page_address_in_vma(page, vma);
 716        if (addr == -EFAULT)
 717                goto out;
 718
 719        BUG_ON(PageTransCompound(page));
 720
 721        mmun_start = addr;
 722        mmun_end   = addr + PAGE_SIZE;
 723        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 724
 725        ptep = page_check_address(page, mm, addr, &ptl, 0);
 726        if (!ptep)
 727                goto out_mn;
 728
 729        if (pte_write(*ptep) || pte_dirty(*ptep)) {
 730                pte_t entry;
 731
 732                swapped = PageSwapCache(page);
 733                flush_cache_page(vma, addr, page_to_pfn(page));
 734                /*
 735                 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 736                 * take any lock, therefore the check that we are going to make
 737                 * with the pagecount against the mapcount is racey and
 738                 * O_DIRECT can happen right after the check.
 739                 * So we clear the pte and flush the tlb before the check
 740                 * this assure us that no O_DIRECT can happen after the check
 741                 * or in the middle of the check.
 742                 */
 743                entry = ptep_clear_flush(vma, addr, ptep);
 744                /*
 745                 * Check that no O_DIRECT or similar I/O is in progress on the
 746                 * page
 747                 */
 748                if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 749                        set_pte_at(mm, addr, ptep, entry);
 750                        goto out_unlock;
 751                }
 752                if (pte_dirty(entry))
 753                        set_page_dirty(page);
 754                entry = pte_mkclean(pte_wrprotect(entry));
 755                set_pte_at_notify(mm, addr, ptep, entry);
 756        }
 757        *orig_pte = *ptep;
 758        err = 0;
 759
 760out_unlock:
 761        pte_unmap_unlock(ptep, ptl);
 762out_mn:
 763        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 764out:
 765        return err;
 766}
 767
 768/**
 769 * replace_page - replace page in vma by new ksm page
 770 * @vma:      vma that holds the pte pointing to page
 771 * @page:     the page we are replacing by kpage
 772 * @kpage:    the ksm page we replace page by
 773 * @orig_pte: the original value of the pte
 774 *
 775 * Returns 0 on success, -EFAULT on failure.
 776 */
 777static int replace_page(struct vm_area_struct *vma, struct page *page,
 778                        struct page *kpage, pte_t orig_pte)
 779{
 780        struct mm_struct *mm = vma->vm_mm;
 781        pmd_t *pmd;
 782        pte_t *ptep;
 783        spinlock_t *ptl;
 784        unsigned long addr;
 785        int err = -EFAULT;
 786        unsigned long mmun_start;       /* For mmu_notifiers */
 787        unsigned long mmun_end;         /* For mmu_notifiers */
 788
 789        addr = page_address_in_vma(page, vma);
 790        if (addr == -EFAULT)
 791                goto out;
 792
 793        pmd = mm_find_pmd(mm, addr);
 794        if (!pmd)
 795                goto out;
 796        BUG_ON(pmd_trans_huge(*pmd));
 797
 798        mmun_start = addr;
 799        mmun_end   = addr + PAGE_SIZE;
 800        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 801
 802        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 803        if (!pte_same(*ptep, orig_pte)) {
 804                pte_unmap_unlock(ptep, ptl);
 805                goto out_mn;
 806        }
 807
 808        get_page(kpage);
 809        page_add_anon_rmap(kpage, vma, addr);
 810
 811        flush_cache_page(vma, addr, pte_pfn(*ptep));
 812        ptep_clear_flush(vma, addr, ptep);
 813        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 814
 815        page_remove_rmap(page);
 816        if (!page_mapped(page))
 817                try_to_free_swap(page);
 818        put_page(page);
 819
 820        pte_unmap_unlock(ptep, ptl);
 821        err = 0;
 822out_mn:
 823        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 824out:
 825        return err;
 826}
 827
 828static int page_trans_compound_anon_split(struct page *page)
 829{
 830        int ret = 0;
 831        struct page *transhuge_head = page_trans_compound_anon(page);
 832        if (transhuge_head) {
 833                /* Get the reference on the head to split it. */
 834                if (get_page_unless_zero(transhuge_head)) {
 835                        /*
 836                         * Recheck we got the reference while the head
 837                         * was still anonymous.
 838                         */
 839                        if (PageAnon(transhuge_head))
 840                                ret = split_huge_page(transhuge_head);
 841                        else
 842                                /*
 843                                 * Retry later if split_huge_page run
 844                                 * from under us.
 845                                 */
 846                                ret = 1;
 847                        put_page(transhuge_head);
 848                } else
 849                        /* Retry later if split_huge_page run from under us. */
 850                        ret = 1;
 851        }
 852        return ret;
 853}
 854
 855/*
 856 * try_to_merge_one_page - take two pages and merge them into one
 857 * @vma: the vma that holds the pte pointing to page
 858 * @page: the PageAnon page that we want to replace with kpage
 859 * @kpage: the PageKsm page that we want to map instead of page,
 860 *         or NULL the first time when we want to use page as kpage.
 861 *
 862 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 863 */
 864static int try_to_merge_one_page(struct vm_area_struct *vma,
 865                                 struct page *page, struct page *kpage)
 866{
 867        pte_t orig_pte = __pte(0);
 868        int err = -EFAULT;
 869
 870        if (page == kpage)                      /* ksm page forked */
 871                return 0;
 872
 873        if (!(vma->vm_flags & VM_MERGEABLE))
 874                goto out;
 875        if (PageTransCompound(page) && page_trans_compound_anon_split(page))
 876                goto out;
 877        BUG_ON(PageTransCompound(page));
 878        if (!PageAnon(page))
 879                goto out;
 880
 881        /*
 882         * We need the page lock to read a stable PageSwapCache in
 883         * write_protect_page().  We use trylock_page() instead of
 884         * lock_page() because we don't want to wait here - we
 885         * prefer to continue scanning and merging different pages,
 886         * then come back to this page when it is unlocked.
 887         */
 888        if (!trylock_page(page))
 889                goto out;
 890        /*
 891         * If this anonymous page is mapped only here, its pte may need
 892         * to be write-protected.  If it's mapped elsewhere, all of its
 893         * ptes are necessarily already write-protected.  But in either
 894         * case, we need to lock and check page_count is not raised.
 895         */
 896        if (write_protect_page(vma, page, &orig_pte) == 0) {
 897                if (!kpage) {
 898                        /*
 899                         * While we hold page lock, upgrade page from
 900                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
 901                         * stable_tree_insert() will update stable_node.
 902                         */
 903                        set_page_stable_node(page, NULL);
 904                        mark_page_accessed(page);
 905                        err = 0;
 906                } else if (pages_identical(page, kpage))
 907                        err = replace_page(vma, page, kpage, orig_pte);
 908        }
 909
 910        if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
 911                munlock_vma_page(page);
 912                if (!PageMlocked(kpage)) {
 913                        unlock_page(page);
 914                        lock_page(kpage);
 915                        mlock_vma_page(kpage);
 916                        page = kpage;           /* for final unlock */
 917                }
 918        }
 919
 920        unlock_page(page);
 921out:
 922        return err;
 923}
 924
 925/*
 926 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 927 * but no new kernel page is allocated: kpage must already be a ksm page.
 928 *
 929 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 930 */
 931static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
 932                                      struct page *page, struct page *kpage)
 933{
 934        struct mm_struct *mm = rmap_item->mm;
 935        struct vm_area_struct *vma;
 936        int err = -EFAULT;
 937
 938        down_read(&mm->mmap_sem);
 939        if (ksm_test_exit(mm))
 940                goto out;
 941        vma = find_vma(mm, rmap_item->address);
 942        if (!vma || vma->vm_start > rmap_item->address)
 943                goto out;
 944
 945        err = try_to_merge_one_page(vma, page, kpage);
 946        if (err)
 947                goto out;
 948
 949        /* Must get reference to anon_vma while still holding mmap_sem */
 950        rmap_item->anon_vma = vma->anon_vma;
 951        get_anon_vma(vma->anon_vma);
 952out:
 953        up_read(&mm->mmap_sem);
 954        return err;
 955}
 956
 957/*
 958 * try_to_merge_two_pages - take two identical pages and prepare them
 959 * to be merged into one page.
 960 *
 961 * This function returns the kpage if we successfully merged two identical
 962 * pages into one ksm page, NULL otherwise.
 963 *
 964 * Note that this function upgrades page to ksm page: if one of the pages
 965 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 966 */
 967static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 968                                           struct page *page,
 969                                           struct rmap_item *tree_rmap_item,
 970                                           struct page *tree_page)
 971{
 972        int err;
 973
 974        err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
 975        if (!err) {
 976                err = try_to_merge_with_ksm_page(tree_rmap_item,
 977                                                        tree_page, page);
 978                /*
 979                 * If that fails, we have a ksm page with only one pte
 980                 * pointing to it: so break it.
 981                 */
 982                if (err)
 983                        break_cow(rmap_item);
 984        }
 985        return err ? NULL : page;
 986}
 987
 988/*
 989 * stable_tree_search - search for page inside the stable tree
 990 *
 991 * This function checks if there is a page inside the stable tree
 992 * with identical content to the page that we are scanning right now.
 993 *
 994 * This function returns the stable tree node of identical content if found,
 995 * NULL otherwise.
 996 */
 997static struct page *stable_tree_search(struct page *page)
 998{
 999        struct rb_node *node = root_stable_tree.rb_node;
1000        struct stable_node *stable_node;
1001
1002        stable_node = page_stable_node(page);
1003        if (stable_node) {                      /* ksm page forked */
1004                get_page(page);
1005                return page;
1006        }
1007
1008        while (node) {
1009                struct page *tree_page;
1010                int ret;
1011
1012                cond_resched();
1013                stable_node = rb_entry(node, struct stable_node, node);
1014                tree_page = get_ksm_page(stable_node);
1015                if (!tree_page)
1016                        return NULL;
1017
1018                ret = memcmp_pages(page, tree_page);
1019
1020                if (ret < 0) {
1021                        put_page(tree_page);
1022                        node = node->rb_left;
1023                } else if (ret > 0) {
1024                        put_page(tree_page);
1025                        node = node->rb_right;
1026                } else
1027                        return tree_page;
1028        }
1029
1030        return NULL;
1031}
1032
1033/*
1034 * stable_tree_insert - insert rmap_item pointing to new ksm page
1035 * into the stable tree.
1036 *
1037 * This function returns the stable tree node just allocated on success,
1038 * NULL otherwise.
1039 */
1040static struct stable_node *stable_tree_insert(struct page *kpage)
1041{
1042        struct rb_node **new = &root_stable_tree.rb_node;
1043        struct rb_node *parent = NULL;
1044        struct stable_node *stable_node;
1045
1046        while (*new) {
1047                struct page *tree_page;
1048                int ret;
1049
1050                cond_resched();
1051                stable_node = rb_entry(*new, struct stable_node, node);
1052                tree_page = get_ksm_page(stable_node);
1053                if (!tree_page)
1054                        return NULL;
1055
1056                ret = memcmp_pages(kpage, tree_page);
1057                put_page(tree_page);
1058
1059                parent = *new;
1060                if (ret < 0)
1061                        new = &parent->rb_left;
1062                else if (ret > 0)
1063                        new = &parent->rb_right;
1064                else {
1065                        /*
1066                         * It is not a bug that stable_tree_search() didn't
1067                         * find this node: because at that time our page was
1068                         * not yet write-protected, so may have changed since.
1069                         */
1070                        return NULL;
1071                }
1072        }
1073
1074        stable_node = alloc_stable_node();
1075        if (!stable_node)
1076                return NULL;
1077
1078        rb_link_node(&stable_node->node, parent, new);
1079        rb_insert_color(&stable_node->node, &root_stable_tree);
1080
1081        INIT_HLIST_HEAD(&stable_node->hlist);
1082
1083        stable_node->kpfn = page_to_pfn(kpage);
1084        set_page_stable_node(kpage, stable_node);
1085
1086        return stable_node;
1087}
1088
1089/*
1090 * unstable_tree_search_insert - search for identical page,
1091 * else insert rmap_item into the unstable tree.
1092 *
1093 * This function searches for a page in the unstable tree identical to the
1094 * page currently being scanned; and if no identical page is found in the
1095 * tree, we insert rmap_item as a new object into the unstable tree.
1096 *
1097 * This function returns pointer to rmap_item found to be identical
1098 * to the currently scanned page, NULL otherwise.
1099 *
1100 * This function does both searching and inserting, because they share
1101 * the same walking algorithm in an rbtree.
1102 */
1103static
1104struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1105                                              struct page *page,
1106                                              struct page **tree_pagep)
1107
1108{
1109        struct rb_node **new = &root_unstable_tree.rb_node;
1110        struct rb_node *parent = NULL;
1111
1112        while (*new) {
1113                struct rmap_item *tree_rmap_item;
1114                struct page *tree_page;
1115                int ret;
1116
1117                cond_resched();
1118                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1119                tree_page = get_mergeable_page(tree_rmap_item);
1120                if (IS_ERR_OR_NULL(tree_page))
1121                        return NULL;
1122
1123                /*
1124                 * Don't substitute a ksm page for a forked page.
1125                 */
1126                if (page == tree_page) {
1127                        put_page(tree_page);
1128                        return NULL;
1129                }
1130
1131                ret = memcmp_pages(page, tree_page);
1132
1133                parent = *new;
1134                if (ret < 0) {
1135                        put_page(tree_page);
1136                        new = &parent->rb_left;
1137                } else if (ret > 0) {
1138                        put_page(tree_page);
1139                        new = &parent->rb_right;
1140                } else {
1141                        *tree_pagep = tree_page;
1142                        return tree_rmap_item;
1143                }
1144        }
1145
1146        rmap_item->address |= UNSTABLE_FLAG;
1147        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1148        rb_link_node(&rmap_item->node, parent, new);
1149        rb_insert_color(&rmap_item->node, &root_unstable_tree);
1150
1151        ksm_pages_unshared++;
1152        return NULL;
1153}
1154
1155/*
1156 * stable_tree_append - add another rmap_item to the linked list of
1157 * rmap_items hanging off a given node of the stable tree, all sharing
1158 * the same ksm page.
1159 */
1160static void stable_tree_append(struct rmap_item *rmap_item,
1161                               struct stable_node *stable_node)
1162{
1163        rmap_item->head = stable_node;
1164        rmap_item->address |= STABLE_FLAG;
1165        hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1166
1167        if (rmap_item->hlist.next)
1168                ksm_pages_sharing++;
1169        else
1170                ksm_pages_shared++;
1171}
1172
1173/*
1174 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1175 * if not, compare checksum to previous and if it's the same, see if page can
1176 * be inserted into the unstable tree, or merged with a page already there and
1177 * both transferred to the stable tree.
1178 *
1179 * @page: the page that we are searching identical page to.
1180 * @rmap_item: the reverse mapping into the virtual address of this page
1181 */
1182static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1183{
1184        struct rmap_item *tree_rmap_item;
1185        struct page *tree_page = NULL;
1186        struct stable_node *stable_node;
1187        struct page *kpage;
1188        unsigned int checksum;
1189        int err;
1190
1191        remove_rmap_item_from_tree(rmap_item);
1192
1193        /* We first start with searching the page inside the stable tree */
1194        kpage = stable_tree_search(page);
1195        if (kpage) {
1196                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1197                if (!err) {
1198                        /*
1199                         * The page was successfully merged:
1200                         * add its rmap_item to the stable tree.
1201                         */
1202                        lock_page(kpage);
1203                        stable_tree_append(rmap_item, page_stable_node(kpage));
1204                        unlock_page(kpage);
1205                }
1206                put_page(kpage);
1207                return;
1208        }
1209
1210        /*
1211         * If the hash value of the page has changed from the last time
1212         * we calculated it, this page is changing frequently: therefore we
1213         * don't want to insert it in the unstable tree, and we don't want
1214         * to waste our time searching for something identical to it there.
1215         */
1216        checksum = calc_checksum(page);
1217        if (rmap_item->oldchecksum != checksum) {
1218                rmap_item->oldchecksum = checksum;
1219                return;
1220        }
1221
1222        tree_rmap_item =
1223                unstable_tree_search_insert(rmap_item, page, &tree_page);
1224        if (tree_rmap_item) {
1225                kpage = try_to_merge_two_pages(rmap_item, page,
1226                                                tree_rmap_item, tree_page);
1227                put_page(tree_page);
1228                /*
1229                 * As soon as we merge this page, we want to remove the
1230                 * rmap_item of the page we have merged with from the unstable
1231                 * tree, and insert it instead as new node in the stable tree.
1232                 */
1233                if (kpage) {
1234                        remove_rmap_item_from_tree(tree_rmap_item);
1235
1236                        lock_page(kpage);
1237                        stable_node = stable_tree_insert(kpage);
1238                        if (stable_node) {
1239                                stable_tree_append(tree_rmap_item, stable_node);
1240                                stable_tree_append(rmap_item, stable_node);
1241                        }
1242                        unlock_page(kpage);
1243
1244                        /*
1245                         * If we fail to insert the page into the stable tree,
1246                         * we will have 2 virtual addresses that are pointing
1247                         * to a ksm page left outside the stable tree,
1248                         * in which case we need to break_cow on both.
1249                         */
1250                        if (!stable_node) {
1251                                break_cow(tree_rmap_item);
1252                                break_cow(rmap_item);
1253                        }
1254                }
1255        }
1256}
1257
1258static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1259                                            struct rmap_item **rmap_list,
1260                                            unsigned long addr)
1261{
1262        struct rmap_item *rmap_item;
1263
1264        while (*rmap_list) {
1265                rmap_item = *rmap_list;
1266                if ((rmap_item->address & PAGE_MASK) == addr)
1267                        return rmap_item;
1268                if (rmap_item->address > addr)
1269                        break;
1270                *rmap_list = rmap_item->rmap_list;
1271                remove_rmap_item_from_tree(rmap_item);
1272                free_rmap_item(rmap_item);
1273        }
1274
1275        rmap_item = alloc_rmap_item();
1276        if (rmap_item) {
1277                /* It has already been zeroed */
1278                rmap_item->mm = mm_slot->mm;
1279                rmap_item->address = addr;
1280                rmap_item->rmap_list = *rmap_list;
1281                *rmap_list = rmap_item;
1282        }
1283        return rmap_item;
1284}
1285
1286static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1287{
1288        struct mm_struct *mm;
1289        struct mm_slot *slot;
1290        struct vm_area_struct *vma;
1291        struct rmap_item *rmap_item;
1292
1293        if (list_empty(&ksm_mm_head.mm_list))
1294                return NULL;
1295
1296        slot = ksm_scan.mm_slot;
1297        if (slot == &ksm_mm_head) {
1298                /*
1299                 * A number of pages can hang around indefinitely on per-cpu
1300                 * pagevecs, raised page count preventing write_protect_page
1301                 * from merging them.  Though it doesn't really matter much,
1302                 * it is puzzling to see some stuck in pages_volatile until
1303                 * other activity jostles them out, and they also prevented
1304                 * LTP's KSM test from succeeding deterministically; so drain
1305                 * them here (here rather than on entry to ksm_do_scan(),
1306                 * so we don't IPI too often when pages_to_scan is set low).
1307                 */
1308                lru_add_drain_all();
1309
1310                root_unstable_tree = RB_ROOT;
1311
1312                spin_lock(&ksm_mmlist_lock);
1313                slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1314                ksm_scan.mm_slot = slot;
1315                spin_unlock(&ksm_mmlist_lock);
1316                /*
1317                 * Although we tested list_empty() above, a racing __ksm_exit
1318                 * of the last mm on the list may have removed it since then.
1319                 */
1320                if (slot == &ksm_mm_head)
1321                        return NULL;
1322next_mm:
1323                ksm_scan.address = 0;
1324                ksm_scan.rmap_list = &slot->rmap_list;
1325        }
1326
1327        mm = slot->mm;
1328        down_read(&mm->mmap_sem);
1329        if (ksm_test_exit(mm))
1330                vma = NULL;
1331        else
1332                vma = find_vma(mm, ksm_scan.address);
1333
1334        for (; vma; vma = vma->vm_next) {
1335                if (!(vma->vm_flags & VM_MERGEABLE))
1336                        continue;
1337                if (ksm_scan.address < vma->vm_start)
1338                        ksm_scan.address = vma->vm_start;
1339                if (!vma->anon_vma)
1340                        ksm_scan.address = vma->vm_end;
1341
1342                while (ksm_scan.address < vma->vm_end) {
1343                        if (ksm_test_exit(mm))
1344                                break;
1345                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1346                        if (IS_ERR_OR_NULL(*page)) {
1347                                ksm_scan.address += PAGE_SIZE;
1348                                cond_resched();
1349                                continue;
1350                        }
1351                        if (PageAnon(*page) ||
1352                            page_trans_compound_anon(*page)) {
1353                                flush_anon_page(vma, *page, ksm_scan.address);
1354                                flush_dcache_page(*page);
1355                                rmap_item = get_next_rmap_item(slot,
1356                                        ksm_scan.rmap_list, ksm_scan.address);
1357                                if (rmap_item) {
1358                                        ksm_scan.rmap_list =
1359                                                        &rmap_item->rmap_list;
1360                                        ksm_scan.address += PAGE_SIZE;
1361                                } else
1362                                        put_page(*page);
1363                                up_read(&mm->mmap_sem);
1364                                return rmap_item;
1365                        }
1366                        put_page(*page);
1367                        ksm_scan.address += PAGE_SIZE;
1368                        cond_resched();
1369                }
1370        }
1371
1372        if (ksm_test_exit(mm)) {
1373                ksm_scan.address = 0;
1374                ksm_scan.rmap_list = &slot->rmap_list;
1375        }
1376        /*
1377         * Nuke all the rmap_items that are above this current rmap:
1378         * because there were no VM_MERGEABLE vmas with such addresses.
1379         */
1380        remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1381
1382        spin_lock(&ksm_mmlist_lock);
1383        ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1384                                                struct mm_slot, mm_list);
1385        if (ksm_scan.address == 0) {
1386                /*
1387                 * We've completed a full scan of all vmas, holding mmap_sem
1388                 * throughout, and found no VM_MERGEABLE: so do the same as
1389                 * __ksm_exit does to remove this mm from all our lists now.
1390                 * This applies either when cleaning up after __ksm_exit
1391                 * (but beware: we can reach here even before __ksm_exit),
1392                 * or when all VM_MERGEABLE areas have been unmapped (and
1393                 * mmap_sem then protects against race with MADV_MERGEABLE).
1394                 */
1395                hlist_del(&slot->link);
1396                list_del(&slot->mm_list);
1397                spin_unlock(&ksm_mmlist_lock);
1398
1399                free_mm_slot(slot);
1400                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1401                up_read(&mm->mmap_sem);
1402                mmdrop(mm);
1403        } else {
1404                spin_unlock(&ksm_mmlist_lock);
1405                up_read(&mm->mmap_sem);
1406        }
1407
1408        /* Repeat until we've completed scanning the whole list */
1409        slot = ksm_scan.mm_slot;
1410        if (slot != &ksm_mm_head)
1411                goto next_mm;
1412
1413        ksm_scan.seqnr++;
1414        return NULL;
1415}
1416
1417/**
1418 * ksm_do_scan  - the ksm scanner main worker function.
1419 * @scan_npages - number of pages we want to scan before we return.
1420 */
1421static void ksm_do_scan(unsigned int scan_npages)
1422{
1423        struct rmap_item *rmap_item;
1424        struct page *uninitialized_var(page);
1425
1426        while (scan_npages-- && likely(!freezing(current))) {
1427                cond_resched();
1428                rmap_item = scan_get_next_rmap_item(&page);
1429                if (!rmap_item)
1430                        return;
1431                if (!PageKsm(page) || !in_stable_tree(rmap_item))
1432                        cmp_and_merge_page(page, rmap_item);
1433                put_page(page);
1434        }
1435}
1436
1437static int ksmd_should_run(void)
1438{
1439        return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1440}
1441
1442static int ksm_scan_thread(void *nothing)
1443{
1444        set_freezable();
1445        set_user_nice(current, 5);
1446
1447        while (!kthread_should_stop()) {
1448                mutex_lock(&ksm_thread_mutex);
1449                if (ksmd_should_run())
1450                        ksm_do_scan(ksm_thread_pages_to_scan);
1451                mutex_unlock(&ksm_thread_mutex);
1452
1453                try_to_freeze();
1454
1455                if (ksmd_should_run()) {
1456                        schedule_timeout_interruptible(
1457                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
1458                } else {
1459                        wait_event_freezable(ksm_thread_wait,
1460                                ksmd_should_run() || kthread_should_stop());
1461                }
1462        }
1463        return 0;
1464}
1465
1466int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1467                unsigned long end, int advice, unsigned long *vm_flags)
1468{
1469        struct mm_struct *mm = vma->vm_mm;
1470        int err;
1471
1472        switch (advice) {
1473        case MADV_MERGEABLE:
1474                /*
1475                 * Be somewhat over-protective for now!
1476                 */
1477                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1478                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1479                                 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
1480                        return 0;               /* just ignore the advice */
1481
1482#ifdef VM_SAO
1483                if (*vm_flags & VM_SAO)
1484                        return 0;
1485#endif
1486
1487                if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1488                        err = __ksm_enter(mm);
1489                        if (err)
1490                                return err;
1491                }
1492
1493                *vm_flags |= VM_MERGEABLE;
1494                break;
1495
1496        case MADV_UNMERGEABLE:
1497                if (!(*vm_flags & VM_MERGEABLE))
1498                        return 0;               /* just ignore the advice */
1499
1500                if (vma->anon_vma) {
1501                        err = unmerge_ksm_pages(vma, start, end);
1502                        if (err)
1503                                return err;
1504                }
1505
1506                *vm_flags &= ~VM_MERGEABLE;
1507                break;
1508        }
1509
1510        return 0;
1511}
1512
1513int __ksm_enter(struct mm_struct *mm)
1514{
1515        struct mm_slot *mm_slot;
1516        int needs_wakeup;
1517
1518        mm_slot = alloc_mm_slot();
1519        if (!mm_slot)
1520                return -ENOMEM;
1521
1522        /* Check ksm_run too?  Would need tighter locking */
1523        needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1524
1525        spin_lock(&ksm_mmlist_lock);
1526        insert_to_mm_slots_hash(mm, mm_slot);
1527        /*
1528         * Insert just behind the scanning cursor, to let the area settle
1529         * down a little; when fork is followed by immediate exec, we don't
1530         * want ksmd to waste time setting up and tearing down an rmap_list.
1531         */
1532        list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1533        spin_unlock(&ksm_mmlist_lock);
1534
1535        set_bit(MMF_VM_MERGEABLE, &mm->flags);
1536        atomic_inc(&mm->mm_count);
1537
1538        if (needs_wakeup)
1539                wake_up_interruptible(&ksm_thread_wait);
1540
1541        return 0;
1542}
1543
1544void __ksm_exit(struct mm_struct *mm)
1545{
1546        struct mm_slot *mm_slot;
1547        int easy_to_free = 0;
1548
1549        /*
1550         * This process is exiting: if it's straightforward (as is the
1551         * case when ksmd was never running), free mm_slot immediately.
1552         * But if it's at the cursor or has rmap_items linked to it, use
1553         * mmap_sem to synchronize with any break_cows before pagetables
1554         * are freed, and leave the mm_slot on the list for ksmd to free.
1555         * Beware: ksm may already have noticed it exiting and freed the slot.
1556         */
1557
1558        spin_lock(&ksm_mmlist_lock);
1559        mm_slot = get_mm_slot(mm);
1560        if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1561                if (!mm_slot->rmap_list) {
1562                        hlist_del(&mm_slot->link);
1563                        list_del(&mm_slot->mm_list);
1564                        easy_to_free = 1;
1565                } else {
1566                        list_move(&mm_slot->mm_list,
1567                                  &ksm_scan.mm_slot->mm_list);
1568                }
1569        }
1570        spin_unlock(&ksm_mmlist_lock);
1571
1572        if (easy_to_free) {
1573                free_mm_slot(mm_slot);
1574                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1575                mmdrop(mm);
1576        } else if (mm_slot) {
1577                down_write(&mm->mmap_sem);
1578                up_write(&mm->mmap_sem);
1579        }
1580}
1581
1582struct page *ksm_does_need_to_copy(struct page *page,
1583                        struct vm_area_struct *vma, unsigned long address)
1584{
1585        struct page *new_page;
1586
1587        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1588        if (new_page) {
1589                copy_user_highpage(new_page, page, address, vma);
1590
1591                SetPageDirty(new_page);
1592                __SetPageUptodate(new_page);
1593                SetPageSwapBacked(new_page);
1594                __set_page_locked(new_page);
1595
1596                if (!mlocked_vma_newpage(vma, new_page))
1597                        lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1598                else
1599                        add_page_to_unevictable_list(new_page);
1600        }
1601
1602        return new_page;
1603}
1604
1605int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1606                        unsigned long *vm_flags)
1607{
1608        struct stable_node *stable_node;
1609        struct rmap_item *rmap_item;
1610        struct hlist_node *hlist;
1611        unsigned int mapcount = page_mapcount(page);
1612        int referenced = 0;
1613        int search_new_forks = 0;
1614
1615        VM_BUG_ON(!PageKsm(page));
1616        VM_BUG_ON(!PageLocked(page));
1617
1618        stable_node = page_stable_node(page);
1619        if (!stable_node)
1620                return 0;
1621again:
1622        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1623                struct anon_vma *anon_vma = rmap_item->anon_vma;
1624                struct anon_vma_chain *vmac;
1625                struct vm_area_struct *vma;
1626
1627                anon_vma_lock_read(anon_vma);
1628                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1629                                               0, ULONG_MAX) {
1630                        vma = vmac->vma;
1631                        if (rmap_item->address < vma->vm_start ||
1632                            rmap_item->address >= vma->vm_end)
1633                                continue;
1634                        /*
1635                         * Initially we examine only the vma which covers this
1636                         * rmap_item; but later, if there is still work to do,
1637                         * we examine covering vmas in other mms: in case they
1638                         * were forked from the original since ksmd passed.
1639                         */
1640                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1641                                continue;
1642
1643                        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1644                                continue;
1645
1646                        referenced += page_referenced_one(page, vma,
1647                                rmap_item->address, &mapcount, vm_flags);
1648                        if (!search_new_forks || !mapcount)
1649                                break;
1650                }
1651                anon_vma_unlock_read(anon_vma);
1652                if (!mapcount)
1653                        goto out;
1654        }
1655        if (!search_new_forks++)
1656                goto again;
1657out:
1658        return referenced;
1659}
1660
1661int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1662{
1663        struct stable_node *stable_node;
1664        struct hlist_node *hlist;
1665        struct rmap_item *rmap_item;
1666        int ret = SWAP_AGAIN;
1667        int search_new_forks = 0;
1668
1669        VM_BUG_ON(!PageKsm(page));
1670        VM_BUG_ON(!PageLocked(page));
1671
1672        stable_node = page_stable_node(page);
1673        if (!stable_node)
1674                return SWAP_FAIL;
1675again:
1676        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1677                struct anon_vma *anon_vma = rmap_item->anon_vma;
1678                struct anon_vma_chain *vmac;
1679                struct vm_area_struct *vma;
1680
1681                anon_vma_lock_read(anon_vma);
1682                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1683                                               0, ULONG_MAX) {
1684                        vma = vmac->vma;
1685                        if (rmap_item->address < vma->vm_start ||
1686                            rmap_item->address >= vma->vm_end)
1687                                continue;
1688                        /*
1689                         * Initially we examine only the vma which covers this
1690                         * rmap_item; but later, if there is still work to do,
1691                         * we examine covering vmas in other mms: in case they
1692                         * were forked from the original since ksmd passed.
1693                         */
1694                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1695                                continue;
1696
1697                        ret = try_to_unmap_one(page, vma,
1698                                        rmap_item->address, flags);
1699                        if (ret != SWAP_AGAIN || !page_mapped(page)) {
1700                                anon_vma_unlock_read(anon_vma);
1701                                goto out;
1702                        }
1703                }
1704                anon_vma_unlock_read(anon_vma);
1705        }
1706        if (!search_new_forks++)
1707                goto again;
1708out:
1709        return ret;
1710}
1711
1712#ifdef CONFIG_MIGRATION
1713int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1714                  struct vm_area_struct *, unsigned long, void *), void *arg)
1715{
1716        struct stable_node *stable_node;
1717        struct hlist_node *hlist;
1718        struct rmap_item *rmap_item;
1719        int ret = SWAP_AGAIN;
1720        int search_new_forks = 0;
1721
1722        VM_BUG_ON(!PageKsm(page));
1723        VM_BUG_ON(!PageLocked(page));
1724
1725        stable_node = page_stable_node(page);
1726        if (!stable_node)
1727                return ret;
1728again:
1729        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1730                struct anon_vma *anon_vma = rmap_item->anon_vma;
1731                struct anon_vma_chain *vmac;
1732                struct vm_area_struct *vma;
1733
1734                anon_vma_lock_read(anon_vma);
1735                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1736                                               0, ULONG_MAX) {
1737                        vma = vmac->vma;
1738                        if (rmap_item->address < vma->vm_start ||
1739                            rmap_item->address >= vma->vm_end)
1740                                continue;
1741                        /*
1742                         * Initially we examine only the vma which covers this
1743                         * rmap_item; but later, if there is still work to do,
1744                         * we examine covering vmas in other mms: in case they
1745                         * were forked from the original since ksmd passed.
1746                         */
1747                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1748                                continue;
1749
1750                        ret = rmap_one(page, vma, rmap_item->address, arg);
1751                        if (ret != SWAP_AGAIN) {
1752                                anon_vma_unlock_read(anon_vma);
1753                                goto out;
1754                        }
1755                }
1756                anon_vma_unlock_read(anon_vma);
1757        }
1758        if (!search_new_forks++)
1759                goto again;
1760out:
1761        return ret;
1762}
1763
1764void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1765{
1766        struct stable_node *stable_node;
1767
1768        VM_BUG_ON(!PageLocked(oldpage));
1769        VM_BUG_ON(!PageLocked(newpage));
1770        VM_BUG_ON(newpage->mapping != oldpage->mapping);
1771
1772        stable_node = page_stable_node(newpage);
1773        if (stable_node) {
1774                VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1775                stable_node->kpfn = page_to_pfn(newpage);
1776        }
1777}
1778#endif /* CONFIG_MIGRATION */
1779
1780#ifdef CONFIG_MEMORY_HOTREMOVE
1781static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1782                                                 unsigned long end_pfn)
1783{
1784        struct rb_node *node;
1785
1786        for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1787                struct stable_node *stable_node;
1788
1789                stable_node = rb_entry(node, struct stable_node, node);
1790                if (stable_node->kpfn >= start_pfn &&
1791                    stable_node->kpfn < end_pfn)
1792                        return stable_node;
1793        }
1794        return NULL;
1795}
1796
1797static int ksm_memory_callback(struct notifier_block *self,
1798                               unsigned long action, void *arg)
1799{
1800        struct memory_notify *mn = arg;
1801        struct stable_node *stable_node;
1802
1803        switch (action) {
1804        case MEM_GOING_OFFLINE:
1805                /*
1806                 * Keep it very simple for now: just lock out ksmd and
1807                 * MADV_UNMERGEABLE while any memory is going offline.
1808                 * mutex_lock_nested() is necessary because lockdep was alarmed
1809                 * that here we take ksm_thread_mutex inside notifier chain
1810                 * mutex, and later take notifier chain mutex inside
1811                 * ksm_thread_mutex to unlock it.   But that's safe because both
1812                 * are inside mem_hotplug_mutex.
1813                 */
1814                mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1815                break;
1816
1817        case MEM_OFFLINE:
1818                /*
1819                 * Most of the work is done by page migration; but there might
1820                 * be a few stable_nodes left over, still pointing to struct
1821                 * pages which have been offlined: prune those from the tree.
1822                 */
1823                while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1824                                        mn->start_pfn + mn->nr_pages)) != NULL)
1825                        remove_node_from_stable_tree(stable_node);
1826                /* fallthrough */
1827
1828        case MEM_CANCEL_OFFLINE:
1829                mutex_unlock(&ksm_thread_mutex);
1830                break;
1831        }
1832        return NOTIFY_OK;
1833}
1834#endif /* CONFIG_MEMORY_HOTREMOVE */
1835
1836#ifdef CONFIG_SYSFS
1837/*
1838 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1839 */
1840
1841#define KSM_ATTR_RO(_name) \
1842        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1843#define KSM_ATTR(_name) \
1844        static struct kobj_attribute _name##_attr = \
1845                __ATTR(_name, 0644, _name##_show, _name##_store)
1846
1847static ssize_t sleep_millisecs_show(struct kobject *kobj,
1848                                    struct kobj_attribute *attr, char *buf)
1849{
1850        return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1851}
1852
1853static ssize_t sleep_millisecs_store(struct kobject *kobj,
1854                                     struct kobj_attribute *attr,
1855                                     const char *buf, size_t count)
1856{
1857        unsigned long msecs;
1858        int err;
1859
1860        err = strict_strtoul(buf, 10, &msecs);
1861        if (err || msecs > UINT_MAX)
1862                return -EINVAL;
1863
1864        ksm_thread_sleep_millisecs = msecs;
1865
1866        return count;
1867}
1868KSM_ATTR(sleep_millisecs);
1869
1870static ssize_t pages_to_scan_show(struct kobject *kobj,
1871                                  struct kobj_attribute *attr, char *buf)
1872{
1873        return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1874}
1875
1876static ssize_t pages_to_scan_store(struct kobject *kobj,
1877                                   struct kobj_attribute *attr,
1878                                   const char *buf, size_t count)
1879{
1880        int err;
1881        unsigned long nr_pages;
1882
1883        err = strict_strtoul(buf, 10, &nr_pages);
1884        if (err || nr_pages > UINT_MAX)
1885                return -EINVAL;
1886
1887        ksm_thread_pages_to_scan = nr_pages;
1888
1889        return count;
1890}
1891KSM_ATTR(pages_to_scan);
1892
1893static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1894                        char *buf)
1895{
1896        return sprintf(buf, "%u\n", ksm_run);
1897}
1898
1899static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1900                         const char *buf, size_t count)
1901{
1902        int err;
1903        unsigned long flags;
1904
1905        err = strict_strtoul(buf, 10, &flags);
1906        if (err || flags > UINT_MAX)
1907                return -EINVAL;
1908        if (flags > KSM_RUN_UNMERGE)
1909                return -EINVAL;
1910
1911        /*
1912         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1913         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1914         * breaking COW to free the pages_shared (but leaves mm_slots
1915         * on the list for when ksmd may be set running again).
1916         */
1917
1918        mutex_lock(&ksm_thread_mutex);
1919        if (ksm_run != flags) {
1920                ksm_run = flags;
1921                if (flags & KSM_RUN_UNMERGE) {
1922                        set_current_oom_origin();
1923                        err = unmerge_and_remove_all_rmap_items();
1924                        clear_current_oom_origin();
1925                        if (err) {
1926                                ksm_run = KSM_RUN_STOP;
1927                                count = err;
1928                        }
1929                }
1930        }
1931        mutex_unlock(&ksm_thread_mutex);
1932
1933        if (flags & KSM_RUN_MERGE)
1934                wake_up_interruptible(&ksm_thread_wait);
1935
1936        return count;
1937}
1938KSM_ATTR(run);
1939
1940static ssize_t pages_shared_show(struct kobject *kobj,
1941                                 struct kobj_attribute *attr, char *buf)
1942{
1943        return sprintf(buf, "%lu\n", ksm_pages_shared);
1944}
1945KSM_ATTR_RO(pages_shared);
1946
1947static ssize_t pages_sharing_show(struct kobject *kobj,
1948                                  struct kobj_attribute *attr, char *buf)
1949{
1950        return sprintf(buf, "%lu\n", ksm_pages_sharing);
1951}
1952KSM_ATTR_RO(pages_sharing);
1953
1954static ssize_t pages_unshared_show(struct kobject *kobj,
1955                                   struct kobj_attribute *attr, char *buf)
1956{
1957        return sprintf(buf, "%lu\n", ksm_pages_unshared);
1958}
1959KSM_ATTR_RO(pages_unshared);
1960
1961static ssize_t pages_volatile_show(struct kobject *kobj,
1962                                   struct kobj_attribute *attr, char *buf)
1963{
1964        long ksm_pages_volatile;
1965
1966        ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1967                                - ksm_pages_sharing - ksm_pages_unshared;
1968        /*
1969         * It was not worth any locking to calculate that statistic,
1970         * but it might therefore sometimes be negative: conceal that.
1971         */
1972        if (ksm_pages_volatile < 0)
1973                ksm_pages_volatile = 0;
1974        return sprintf(buf, "%ld\n", ksm_pages_volatile);
1975}
1976KSM_ATTR_RO(pages_volatile);
1977
1978static ssize_t full_scans_show(struct kobject *kobj,
1979                               struct kobj_attribute *attr, char *buf)
1980{
1981        return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1982}
1983KSM_ATTR_RO(full_scans);
1984
1985static struct attribute *ksm_attrs[] = {
1986        &sleep_millisecs_attr.attr,
1987        &pages_to_scan_attr.attr,
1988        &run_attr.attr,
1989        &pages_shared_attr.attr,
1990        &pages_sharing_attr.attr,
1991        &pages_unshared_attr.attr,
1992        &pages_volatile_attr.attr,
1993        &full_scans_attr.attr,
1994        NULL,
1995};
1996
1997static struct attribute_group ksm_attr_group = {
1998        .attrs = ksm_attrs,
1999        .name = "ksm",
2000};
2001#endif /* CONFIG_SYSFS */
2002
2003static int __init ksm_init(void)
2004{
2005        struct task_struct *ksm_thread;
2006        int err;
2007
2008        err = ksm_slab_init();
2009        if (err)
2010                goto out;
2011
2012        ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2013        if (IS_ERR(ksm_thread)) {
2014                printk(KERN_ERR "ksm: creating kthread failed\n");
2015                err = PTR_ERR(ksm_thread);
2016                goto out_free;
2017        }
2018
2019#ifdef CONFIG_SYSFS
2020        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2021        if (err) {
2022                printk(KERN_ERR "ksm: register sysfs failed\n");
2023                kthread_stop(ksm_thread);
2024                goto out_free;
2025        }
2026#else
2027        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2028
2029#endif /* CONFIG_SYSFS */
2030
2031#ifdef CONFIG_MEMORY_HOTREMOVE
2032        /*
2033         * Choose a high priority since the callback takes ksm_thread_mutex:
2034         * later callbacks could only be taking locks which nest within that.
2035         */
2036        hotplug_memory_notifier(ksm_memory_callback, 100);
2037#endif
2038        return 0;
2039
2040out_free:
2041        ksm_slab_free();
2042out:
2043        return err;
2044}
2045module_init(ksm_init)
2046
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