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
 713        addr = page_address_in_vma(page, vma);
 714        if (addr == -EFAULT)
 715                goto out;
 716
 717        BUG_ON(PageTransCompound(page));
 718        ptep = page_check_address(page, mm, addr, &ptl, 0);
 719        if (!ptep)
 720                goto out;
 721
 722        if (pte_write(*ptep) || pte_dirty(*ptep)) {
 723                pte_t entry;
 724
 725                swapped = PageSwapCache(page);
 726                flush_cache_page(vma, addr, page_to_pfn(page));
 727                /*
 728                 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 729                 * take any lock, therefore the check that we are going to make
 730                 * with the pagecount against the mapcount is racey and
 731                 * O_DIRECT can happen right after the check.
 732                 * So we clear the pte and flush the tlb before the check
 733                 * this assure us that no O_DIRECT can happen after the check
 734                 * or in the middle of the check.
 735                 */
 736                entry = ptep_clear_flush(vma, addr, ptep);
 737                /*
 738                 * Check that no O_DIRECT or similar I/O is in progress on the
 739                 * page
 740                 */
 741                if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 742                        set_pte_at(mm, addr, ptep, entry);
 743                        goto out_unlock;
 744                }
 745                if (pte_dirty(entry))
 746                        set_page_dirty(page);
 747                entry = pte_mkclean(pte_wrprotect(entry));
 748                set_pte_at_notify(mm, addr, ptep, entry);
 749        }
 750        *orig_pte = *ptep;
 751        err = 0;
 752
 753out_unlock:
 754        pte_unmap_unlock(ptep, ptl);
 755out:
 756        return err;
 757}
 758
 759/**
 760 * replace_page - replace page in vma by new ksm page
 761 * @vma:      vma that holds the pte pointing to page
 762 * @page:     the page we are replacing by kpage
 763 * @kpage:    the ksm page we replace page by
 764 * @orig_pte: the original value of the pte
 765 *
 766 * Returns 0 on success, -EFAULT on failure.
 767 */
 768static int replace_page(struct vm_area_struct *vma, struct page *page,
 769                        struct page *kpage, pte_t orig_pte)
 770{
 771        struct mm_struct *mm = vma->vm_mm;
 772        pgd_t *pgd;
 773        pud_t *pud;
 774        pmd_t *pmd;
 775        pte_t *ptep;
 776        spinlock_t *ptl;
 777        unsigned long addr;
 778        int err = -EFAULT;
 779
 780        addr = page_address_in_vma(page, vma);
 781        if (addr == -EFAULT)
 782                goto out;
 783
 784        pgd = pgd_offset(mm, addr);
 785        if (!pgd_present(*pgd))
 786                goto out;
 787
 788        pud = pud_offset(pgd, addr);
 789        if (!pud_present(*pud))
 790                goto out;
 791
 792        pmd = pmd_offset(pud, addr);
 793        BUG_ON(pmd_trans_huge(*pmd));
 794        if (!pmd_present(*pmd))
 795                goto out;
 796
 797        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 798        if (!pte_same(*ptep, orig_pte)) {
 799                pte_unmap_unlock(ptep, ptl);
 800                goto out;
 801        }
 802
 803        get_page(kpage);
 804        page_add_anon_rmap(kpage, vma, addr);
 805
 806        flush_cache_page(vma, addr, pte_pfn(*ptep));
 807        ptep_clear_flush(vma, addr, ptep);
 808        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 809
 810        page_remove_rmap(page);
 811        if (!page_mapped(page))
 812                try_to_free_swap(page);
 813        put_page(page);
 814
 815        pte_unmap_unlock(ptep, ptl);
 816        err = 0;
 817out:
 818        return err;
 819}
 820
 821static int page_trans_compound_anon_split(struct page *page)
 822{
 823        int ret = 0;
 824        struct page *transhuge_head = page_trans_compound_anon(page);
 825        if (transhuge_head) {
 826                /* Get the reference on the head to split it. */
 827                if (get_page_unless_zero(transhuge_head)) {
 828                        /*
 829                         * Recheck we got the reference while the head
 830                         * was still anonymous.
 831                         */
 832                        if (PageAnon(transhuge_head))
 833                                ret = split_huge_page(transhuge_head);
 834                        else
 835                                /*
 836                                 * Retry later if split_huge_page run
 837                                 * from under us.
 838                                 */
 839                                ret = 1;
 840                        put_page(transhuge_head);
 841                } else
 842                        /* Retry later if split_huge_page run from under us. */
 843                        ret = 1;
 844        }
 845        return ret;
 846}
 847
 848/*
 849 * try_to_merge_one_page - take two pages and merge them into one
 850 * @vma: the vma that holds the pte pointing to page
 851 * @page: the PageAnon page that we want to replace with kpage
 852 * @kpage: the PageKsm page that we want to map instead of page,
 853 *         or NULL the first time when we want to use page as kpage.
 854 *
 855 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 856 */
 857static int try_to_merge_one_page(struct vm_area_struct *vma,
 858                                 struct page *page, struct page *kpage)
 859{
 860        pte_t orig_pte = __pte(0);
 861        int err = -EFAULT;
 862
 863        if (page == kpage)                      /* ksm page forked */
 864                return 0;
 865
 866        if (!(vma->vm_flags & VM_MERGEABLE))
 867                goto out;
 868        if (PageTransCompound(page) && page_trans_compound_anon_split(page))
 869                goto out;
 870        BUG_ON(PageTransCompound(page));
 871        if (!PageAnon(page))
 872                goto out;
 873
 874        /*
 875         * We need the page lock to read a stable PageSwapCache in
 876         * write_protect_page().  We use trylock_page() instead of
 877         * lock_page() because we don't want to wait here - we
 878         * prefer to continue scanning and merging different pages,
 879         * then come back to this page when it is unlocked.
 880         */
 881        if (!trylock_page(page))
 882                goto out;
 883        /*
 884         * If this anonymous page is mapped only here, its pte may need
 885         * to be write-protected.  If it's mapped elsewhere, all of its
 886         * ptes are necessarily already write-protected.  But in either
 887         * case, we need to lock and check page_count is not raised.
 888         */
 889        if (write_protect_page(vma, page, &orig_pte) == 0) {
 890                if (!kpage) {
 891                        /*
 892                         * While we hold page lock, upgrade page from
 893                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
 894                         * stable_tree_insert() will update stable_node.
 895                         */
 896                        set_page_stable_node(page, NULL);
 897                        mark_page_accessed(page);
 898                        err = 0;
 899                } else if (pages_identical(page, kpage))
 900                        err = replace_page(vma, page, kpage, orig_pte);
 901        }
 902
 903        if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
 904                munlock_vma_page(page);
 905                if (!PageMlocked(kpage)) {
 906                        unlock_page(page);
 907                        lock_page(kpage);
 908                        mlock_vma_page(kpage);
 909                        page = kpage;           /* for final unlock */
 910                }
 911        }
 912
 913        unlock_page(page);
 914out:
 915        return err;
 916}
 917
 918/*
 919 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 920 * but no new kernel page is allocated: kpage must already be a ksm page.
 921 *
 922 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 923 */
 924static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
 925                                      struct page *page, struct page *kpage)
 926{
 927        struct mm_struct *mm = rmap_item->mm;
 928        struct vm_area_struct *vma;
 929        int err = -EFAULT;
 930
 931        down_read(&mm->mmap_sem);
 932        if (ksm_test_exit(mm))
 933                goto out;
 934        vma = find_vma(mm, rmap_item->address);
 935        if (!vma || vma->vm_start > rmap_item->address)
 936                goto out;
 937
 938        err = try_to_merge_one_page(vma, page, kpage);
 939        if (err)
 940                goto out;
 941
 942        /* Must get reference to anon_vma while still holding mmap_sem */
 943        rmap_item->anon_vma = vma->anon_vma;
 944        get_anon_vma(vma->anon_vma);
 945out:
 946        up_read(&mm->mmap_sem);
 947        return err;
 948}
 949
 950/*
 951 * try_to_merge_two_pages - take two identical pages and prepare them
 952 * to be merged into one page.
 953 *
 954 * This function returns the kpage if we successfully merged two identical
 955 * pages into one ksm page, NULL otherwise.
 956 *
 957 * Note that this function upgrades page to ksm page: if one of the pages
 958 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 959 */
 960static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 961                                           struct page *page,
 962                                           struct rmap_item *tree_rmap_item,
 963                                           struct page *tree_page)
 964{
 965        int err;
 966
 967        err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
 968        if (!err) {
 969                err = try_to_merge_with_ksm_page(tree_rmap_item,
 970                                                        tree_page, page);
 971                /*
 972                 * If that fails, we have a ksm page with only one pte
 973                 * pointing to it: so break it.
 974                 */
 975                if (err)
 976                        break_cow(rmap_item);
 977        }
 978        return err ? NULL : page;
 979}
 980
 981/*
 982 * stable_tree_search - search for page inside the stable tree
 983 *
 984 * This function checks if there is a page inside the stable tree
 985 * with identical content to the page that we are scanning right now.
 986 *
 987 * This function returns the stable tree node of identical content if found,
 988 * NULL otherwise.
 989 */
 990static struct page *stable_tree_search(struct page *page)
 991{
 992        struct rb_node *node = root_stable_tree.rb_node;
 993        struct stable_node *stable_node;
 994
 995        stable_node = page_stable_node(page);
 996        if (stable_node) {                      /* ksm page forked */
 997                get_page(page);
 998                return page;
 999        }
1000
1001        while (node) {
1002                struct page *tree_page;
1003                int ret;
1004
1005                cond_resched();
1006                stable_node = rb_entry(node, struct stable_node, node);
1007                tree_page = get_ksm_page(stable_node);
1008                if (!tree_page)
1009                        return NULL;
1010
1011                ret = memcmp_pages(page, tree_page);
1012
1013                if (ret < 0) {
1014                        put_page(tree_page);
1015                        node = node->rb_left;
1016                } else if (ret > 0) {
1017                        put_page(tree_page);
1018                        node = node->rb_right;
1019                } else
1020                        return tree_page;
1021        }
1022
1023        return NULL;
1024}
1025
1026/*
1027 * stable_tree_insert - insert rmap_item pointing to new ksm page
1028 * into the stable tree.
1029 *
1030 * This function returns the stable tree node just allocated on success,
1031 * NULL otherwise.
1032 */
1033static struct stable_node *stable_tree_insert(struct page *kpage)
1034{
1035        struct rb_node **new = &root_stable_tree.rb_node;
1036        struct rb_node *parent = NULL;
1037        struct stable_node *stable_node;
1038
1039        while (*new) {
1040                struct page *tree_page;
1041                int ret;
1042
1043                cond_resched();
1044                stable_node = rb_entry(*new, struct stable_node, node);
1045                tree_page = get_ksm_page(stable_node);
1046                if (!tree_page)
1047                        return NULL;
1048
1049                ret = memcmp_pages(kpage, tree_page);
1050                put_page(tree_page);
1051
1052                parent = *new;
1053                if (ret < 0)
1054                        new = &parent->rb_left;
1055                else if (ret > 0)
1056                        new = &parent->rb_right;
1057                else {
1058                        /*
1059                         * It is not a bug that stable_tree_search() didn't
1060                         * find this node: because at that time our page was
1061                         * not yet write-protected, so may have changed since.
1062                         */
1063                        return NULL;
1064                }
1065        }
1066
1067        stable_node = alloc_stable_node();
1068        if (!stable_node)
1069                return NULL;
1070
1071        rb_link_node(&stable_node->node, parent, new);
1072        rb_insert_color(&stable_node->node, &root_stable_tree);
1073
1074        INIT_HLIST_HEAD(&stable_node->hlist);
1075
1076        stable_node->kpfn = page_to_pfn(kpage);
1077        set_page_stable_node(kpage, stable_node);
1078
1079        return stable_node;
1080}
1081
1082/*
1083 * unstable_tree_search_insert - search for identical page,
1084 * else insert rmap_item into the unstable tree.
1085 *
1086 * This function searches for a page in the unstable tree identical to the
1087 * page currently being scanned; and if no identical page is found in the
1088 * tree, we insert rmap_item as a new object into the unstable tree.
1089 *
1090 * This function returns pointer to rmap_item found to be identical
1091 * to the currently scanned page, NULL otherwise.
1092 *
1093 * This function does both searching and inserting, because they share
1094 * the same walking algorithm in an rbtree.
1095 */
1096static
1097struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1098                                              struct page *page,
1099                                              struct page **tree_pagep)
1100
1101{
1102        struct rb_node **new = &root_unstable_tree.rb_node;
1103        struct rb_node *parent = NULL;
1104
1105        while (*new) {
1106                struct rmap_item *tree_rmap_item;
1107                struct page *tree_page;
1108                int ret;
1109
1110                cond_resched();
1111                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1112                tree_page = get_mergeable_page(tree_rmap_item);
1113                if (IS_ERR_OR_NULL(tree_page))
1114                        return NULL;
1115
1116                /*
1117                 * Don't substitute a ksm page for a forked page.
1118                 */
1119                if (page == tree_page) {
1120                        put_page(tree_page);
1121                        return NULL;
1122                }
1123
1124                ret = memcmp_pages(page, tree_page);
1125
1126                parent = *new;
1127                if (ret < 0) {
1128                        put_page(tree_page);
1129                        new = &parent->rb_left;
1130                } else if (ret > 0) {
1131                        put_page(tree_page);
1132                        new = &parent->rb_right;
1133                } else {
1134                        *tree_pagep = tree_page;
1135                        return tree_rmap_item;
1136                }
1137        }
1138
1139        rmap_item->address |= UNSTABLE_FLAG;
1140        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1141        rb_link_node(&rmap_item->node, parent, new);
1142        rb_insert_color(&rmap_item->node, &root_unstable_tree);
1143
1144        ksm_pages_unshared++;
1145        return NULL;
1146}
1147
1148/*
1149 * stable_tree_append - add another rmap_item to the linked list of
1150 * rmap_items hanging off a given node of the stable tree, all sharing
1151 * the same ksm page.
1152 */
1153static void stable_tree_append(struct rmap_item *rmap_item,
1154                               struct stable_node *stable_node)
1155{
1156        rmap_item->head = stable_node;
1157        rmap_item->address |= STABLE_FLAG;
1158        hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1159
1160        if (rmap_item->hlist.next)
1161                ksm_pages_sharing++;
1162        else
1163                ksm_pages_shared++;
1164}
1165
1166/*
1167 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1168 * if not, compare checksum to previous and if it's the same, see if page can
1169 * be inserted into the unstable tree, or merged with a page already there and
1170 * both transferred to the stable tree.
1171 *
1172 * @page: the page that we are searching identical page to.
1173 * @rmap_item: the reverse mapping into the virtual address of this page
1174 */
1175static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1176{
1177        struct rmap_item *tree_rmap_item;
1178        struct page *tree_page = NULL;
1179        struct stable_node *stable_node;
1180        struct page *kpage;
1181        unsigned int checksum;
1182        int err;
1183
1184        remove_rmap_item_from_tree(rmap_item);
1185
1186        /* We first start with searching the page inside the stable tree */
1187        kpage = stable_tree_search(page);
1188        if (kpage) {
1189                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1190                if (!err) {
1191                        /*
1192                         * The page was successfully merged:
1193                         * add its rmap_item to the stable tree.
1194                         */
1195                        lock_page(kpage);
1196                        stable_tree_append(rmap_item, page_stable_node(kpage));
1197                        unlock_page(kpage);
1198                }
1199                put_page(kpage);
1200                return;
1201        }
1202
1203        /*
1204         * If the hash value of the page has changed from the last time
1205         * we calculated it, this page is changing frequently: therefore we
1206         * don't want to insert it in the unstable tree, and we don't want
1207         * to waste our time searching for something identical to it there.
1208         */
1209        checksum = calc_checksum(page);
1210        if (rmap_item->oldchecksum != checksum) {
1211                rmap_item->oldchecksum = checksum;
1212                return;
1213        }
1214
1215        tree_rmap_item =
1216                unstable_tree_search_insert(rmap_item, page, &tree_page);
1217        if (tree_rmap_item) {
1218                kpage = try_to_merge_two_pages(rmap_item, page,
1219                                                tree_rmap_item, tree_page);
1220                put_page(tree_page);
1221                /*
1222                 * As soon as we merge this page, we want to remove the
1223                 * rmap_item of the page we have merged with from the unstable
1224                 * tree, and insert it instead as new node in the stable tree.
1225                 */
1226                if (kpage) {
1227                        remove_rmap_item_from_tree(tree_rmap_item);
1228
1229                        lock_page(kpage);
1230                        stable_node = stable_tree_insert(kpage);
1231                        if (stable_node) {
1232                                stable_tree_append(tree_rmap_item, stable_node);
1233                                stable_tree_append(rmap_item, stable_node);
1234                        }
1235                        unlock_page(kpage);
1236
1237                        /*
1238                         * If we fail to insert the page into the stable tree,
1239                         * we will have 2 virtual addresses that are pointing
1240                         * to a ksm page left outside the stable tree,
1241                         * in which case we need to break_cow on both.
1242                         */
1243                        if (!stable_node) {
1244                                break_cow(tree_rmap_item);
1245                                break_cow(rmap_item);
1246                        }
1247                }
1248        }
1249}
1250
1251static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1252                                            struct rmap_item **rmap_list,
1253                                            unsigned long addr)
1254{
1255        struct rmap_item *rmap_item;
1256
1257        while (*rmap_list) {
1258                rmap_item = *rmap_list;
1259                if ((rmap_item->address & PAGE_MASK) == addr)
1260                        return rmap_item;
1261                if (rmap_item->address > addr)
1262                        break;
1263                *rmap_list = rmap_item->rmap_list;
1264                remove_rmap_item_from_tree(rmap_item);
1265                free_rmap_item(rmap_item);
1266        }
1267
1268        rmap_item = alloc_rmap_item();
1269        if (rmap_item) {
1270                /* It has already been zeroed */
1271                rmap_item->mm = mm_slot->mm;
1272                rmap_item->address = addr;
1273                rmap_item->rmap_list = *rmap_list;
1274                *rmap_list = rmap_item;
1275        }
1276        return rmap_item;
1277}
1278
1279static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1280{
1281        struct mm_struct *mm;
1282        struct mm_slot *slot;
1283        struct vm_area_struct *vma;
1284        struct rmap_item *rmap_item;
1285
1286        if (list_empty(&ksm_mm_head.mm_list))
1287                return NULL;
1288
1289        slot = ksm_scan.mm_slot;
1290        if (slot == &ksm_mm_head) {
1291                /*
1292                 * A number of pages can hang around indefinitely on per-cpu
1293                 * pagevecs, raised page count preventing write_protect_page
1294                 * from merging them.  Though it doesn't really matter much,
1295                 * it is puzzling to see some stuck in pages_volatile until
1296                 * other activity jostles them out, and they also prevented
1297                 * LTP's KSM test from succeeding deterministically; so drain
1298                 * them here (here rather than on entry to ksm_do_scan(),
1299                 * so we don't IPI too often when pages_to_scan is set low).
1300                 */
1301                lru_add_drain_all();
1302
1303                root_unstable_tree = RB_ROOT;
1304
1305                spin_lock(&ksm_mmlist_lock);
1306                slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1307                ksm_scan.mm_slot = slot;
1308                spin_unlock(&ksm_mmlist_lock);
1309                /*
1310                 * Although we tested list_empty() above, a racing __ksm_exit
1311                 * of the last mm on the list may have removed it since then.
1312                 */
1313                if (slot == &ksm_mm_head)
1314                        return NULL;
1315next_mm:
1316                ksm_scan.address = 0;
1317                ksm_scan.rmap_list = &slot->rmap_list;
1318        }
1319
1320        mm = slot->mm;
1321        down_read(&mm->mmap_sem);
1322        if (ksm_test_exit(mm))
1323                vma = NULL;
1324        else
1325                vma = find_vma(mm, ksm_scan.address);
1326
1327        for (; vma; vma = vma->vm_next) {
1328                if (!(vma->vm_flags & VM_MERGEABLE))
1329                        continue;
1330                if (ksm_scan.address < vma->vm_start)
1331                        ksm_scan.address = vma->vm_start;
1332                if (!vma->anon_vma)
1333                        ksm_scan.address = vma->vm_end;
1334
1335                while (ksm_scan.address < vma->vm_end) {
1336                        if (ksm_test_exit(mm))
1337                                break;
1338                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1339                        if (IS_ERR_OR_NULL(*page)) {
1340                                ksm_scan.address += PAGE_SIZE;
1341                                cond_resched();
1342                                continue;
1343                        }
1344                        if (PageAnon(*page) ||
1345                            page_trans_compound_anon(*page)) {
1346                                flush_anon_page(vma, *page, ksm_scan.address);
1347                                flush_dcache_page(*page);
1348                                rmap_item = get_next_rmap_item(slot,
1349                                        ksm_scan.rmap_list, ksm_scan.address);
1350                                if (rmap_item) {
1351                                        ksm_scan.rmap_list =
1352                                                        &rmap_item->rmap_list;
1353                                        ksm_scan.address += PAGE_SIZE;
1354                                } else
1355                                        put_page(*page);
1356                                up_read(&mm->mmap_sem);
1357                                return rmap_item;
1358                        }
1359                        put_page(*page);
1360                        ksm_scan.address += PAGE_SIZE;
1361                        cond_resched();
1362                }
1363        }
1364
1365        if (ksm_test_exit(mm)) {
1366                ksm_scan.address = 0;
1367                ksm_scan.rmap_list = &slot->rmap_list;
1368        }
1369        /*
1370         * Nuke all the rmap_items that are above this current rmap:
1371         * because there were no VM_MERGEABLE vmas with such addresses.
1372         */
1373        remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1374
1375        spin_lock(&ksm_mmlist_lock);
1376        ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1377                                                struct mm_slot, mm_list);
1378        if (ksm_scan.address == 0) {
1379                /*
1380                 * We've completed a full scan of all vmas, holding mmap_sem
1381                 * throughout, and found no VM_MERGEABLE: so do the same as
1382                 * __ksm_exit does to remove this mm from all our lists now.
1383                 * This applies either when cleaning up after __ksm_exit
1384                 * (but beware: we can reach here even before __ksm_exit),
1385                 * or when all VM_MERGEABLE areas have been unmapped (and
1386                 * mmap_sem then protects against race with MADV_MERGEABLE).
1387                 */
1388                hlist_del(&slot->link);
1389                list_del(&slot->mm_list);
1390                spin_unlock(&ksm_mmlist_lock);
1391
1392                free_mm_slot(slot);
1393                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1394                up_read(&mm->mmap_sem);
1395                mmdrop(mm);
1396        } else {
1397                spin_unlock(&ksm_mmlist_lock);
1398                up_read(&mm->mmap_sem);
1399        }
1400
1401        /* Repeat until we've completed scanning the whole list */
1402        slot = ksm_scan.mm_slot;
1403        if (slot != &ksm_mm_head)
1404                goto next_mm;
1405
1406        ksm_scan.seqnr++;
1407        return NULL;
1408}
1409
1410/**
1411 * ksm_do_scan  - the ksm scanner main worker function.
1412 * @scan_npages - number of pages we want to scan before we return.
1413 */
1414static void ksm_do_scan(unsigned int scan_npages)
1415{
1416        struct rmap_item *rmap_item;
1417        struct page *uninitialized_var(page);
1418
1419        while (scan_npages-- && likely(!freezing(current))) {
1420                cond_resched();
1421                rmap_item = scan_get_next_rmap_item(&page);
1422                if (!rmap_item)
1423                        return;
1424                if (!PageKsm(page) || !in_stable_tree(rmap_item))
1425                        cmp_and_merge_page(page, rmap_item);
1426                put_page(page);
1427        }
1428}
1429
1430static int ksmd_should_run(void)
1431{
1432        return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1433}
1434
1435static int ksm_scan_thread(void *nothing)
1436{
1437        set_freezable();
1438        set_user_nice(current, 5);
1439
1440        while (!kthread_should_stop()) {
1441                mutex_lock(&ksm_thread_mutex);
1442                if (ksmd_should_run())
1443                        ksm_do_scan(ksm_thread_pages_to_scan);
1444                mutex_unlock(&ksm_thread_mutex);
1445
1446                try_to_freeze();
1447
1448                if (ksmd_should_run()) {
1449                        schedule_timeout_interruptible(
1450                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
1451                } else {
1452                        wait_event_freezable(ksm_thread_wait,
1453                                ksmd_should_run() || kthread_should_stop());
1454                }
1455        }
1456        return 0;
1457}
1458
1459int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1460                unsigned long end, int advice, unsigned long *vm_flags)
1461{
1462        struct mm_struct *mm = vma->vm_mm;
1463        int err;
1464
1465        switch (advice) {
1466        case MADV_MERGEABLE:
1467                /*
1468                 * Be somewhat over-protective for now!
1469                 */
1470                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1471                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1472                                 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1473                                 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1474                        return 0;               /* just ignore the advice */
1475
1476                if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1477                        err = __ksm_enter(mm);
1478                        if (err)
1479                                return err;
1480                }
1481
1482                *vm_flags |= VM_MERGEABLE;
1483                break;
1484
1485        case MADV_UNMERGEABLE:
1486                if (!(*vm_flags & VM_MERGEABLE))
1487                        return 0;               /* just ignore the advice */
1488
1489                if (vma->anon_vma) {
1490                        err = unmerge_ksm_pages(vma, start, end);
1491                        if (err)
1492                                return err;
1493                }
1494
1495                *vm_flags &= ~VM_MERGEABLE;
1496                break;
1497        }
1498
1499        return 0;
1500}
1501
1502int __ksm_enter(struct mm_struct *mm)
1503{
1504        struct mm_slot *mm_slot;
1505        int needs_wakeup;
1506
1507        mm_slot = alloc_mm_slot();
1508        if (!mm_slot)
1509                return -ENOMEM;
1510
1511        /* Check ksm_run too?  Would need tighter locking */
1512        needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1513
1514        spin_lock(&ksm_mmlist_lock);
1515        insert_to_mm_slots_hash(mm, mm_slot);
1516        /*
1517         * Insert just behind the scanning cursor, to let the area settle
1518         * down a little; when fork is followed by immediate exec, we don't
1519         * want ksmd to waste time setting up and tearing down an rmap_list.
1520         */
1521        list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1522        spin_unlock(&ksm_mmlist_lock);
1523
1524        set_bit(MMF_VM_MERGEABLE, &mm->flags);
1525        atomic_inc(&mm->mm_count);
1526
1527        if (needs_wakeup)
1528                wake_up_interruptible(&ksm_thread_wait);
1529
1530        return 0;
1531}
1532
1533void __ksm_exit(struct mm_struct *mm)
1534{
1535        struct mm_slot *mm_slot;
1536        int easy_to_free = 0;
1537
1538        /*
1539         * This process is exiting: if it's straightforward (as is the
1540         * case when ksmd was never running), free mm_slot immediately.
1541         * But if it's at the cursor or has rmap_items linked to it, use
1542         * mmap_sem to synchronize with any break_cows before pagetables
1543         * are freed, and leave the mm_slot on the list for ksmd to free.
1544         * Beware: ksm may already have noticed it exiting and freed the slot.
1545         */
1546
1547        spin_lock(&ksm_mmlist_lock);
1548        mm_slot = get_mm_slot(mm);
1549        if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1550                if (!mm_slot->rmap_list) {
1551                        hlist_del(&mm_slot->link);
1552                        list_del(&mm_slot->mm_list);
1553                        easy_to_free = 1;
1554                } else {
1555                        list_move(&mm_slot->mm_list,
1556                                  &ksm_scan.mm_slot->mm_list);
1557                }
1558        }
1559        spin_unlock(&ksm_mmlist_lock);
1560
1561        if (easy_to_free) {
1562                free_mm_slot(mm_slot);
1563                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1564                mmdrop(mm);
1565        } else if (mm_slot) {
1566                down_write(&mm->mmap_sem);
1567                up_write(&mm->mmap_sem);
1568        }
1569}
1570
1571struct page *ksm_does_need_to_copy(struct page *page,
1572                        struct vm_area_struct *vma, unsigned long address)
1573{
1574        struct page *new_page;
1575
1576        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1577        if (new_page) {
1578                copy_user_highpage(new_page, page, address, vma);
1579
1580                SetPageDirty(new_page);
1581                __SetPageUptodate(new_page);
1582                SetPageSwapBacked(new_page);
1583                __set_page_locked(new_page);
1584
1585                if (page_evictable(new_page, vma))
1586                        lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1587                else
1588                        add_page_to_unevictable_list(new_page);
1589        }
1590
1591        return new_page;
1592}
1593
1594int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1595                        unsigned long *vm_flags)
1596{
1597        struct stable_node *stable_node;
1598        struct rmap_item *rmap_item;
1599        struct hlist_node *hlist;
1600        unsigned int mapcount = page_mapcount(page);
1601        int referenced = 0;
1602        int search_new_forks = 0;
1603
1604        VM_BUG_ON(!PageKsm(page));
1605        VM_BUG_ON(!PageLocked(page));
1606
1607        stable_node = page_stable_node(page);
1608        if (!stable_node)
1609                return 0;
1610again:
1611        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1612                struct anon_vma *anon_vma = rmap_item->anon_vma;
1613                struct anon_vma_chain *vmac;
1614                struct vm_area_struct *vma;
1615
1616                anon_vma_lock(anon_vma);
1617                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1618                        vma = vmac->vma;
1619                        if (rmap_item->address < vma->vm_start ||
1620                            rmap_item->address >= vma->vm_end)
1621                                continue;
1622                        /*
1623                         * Initially we examine only the vma which covers this
1624                         * rmap_item; but later, if there is still work to do,
1625                         * we examine covering vmas in other mms: in case they
1626                         * were forked from the original since ksmd passed.
1627                         */
1628                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1629                                continue;
1630
1631                        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1632                                continue;
1633
1634                        referenced += page_referenced_one(page, vma,
1635                                rmap_item->address, &mapcount, vm_flags);
1636                        if (!search_new_forks || !mapcount)
1637                                break;
1638                }
1639                anon_vma_unlock(anon_vma);
1640                if (!mapcount)
1641                        goto out;
1642        }
1643        if (!search_new_forks++)
1644                goto again;
1645out:
1646        return referenced;
1647}
1648
1649int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1650{
1651        struct stable_node *stable_node;
1652        struct hlist_node *hlist;
1653        struct rmap_item *rmap_item;
1654        int ret = SWAP_AGAIN;
1655        int search_new_forks = 0;
1656
1657        VM_BUG_ON(!PageKsm(page));
1658        VM_BUG_ON(!PageLocked(page));
1659
1660        stable_node = page_stable_node(page);
1661        if (!stable_node)
1662                return SWAP_FAIL;
1663again:
1664        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1665                struct anon_vma *anon_vma = rmap_item->anon_vma;
1666                struct anon_vma_chain *vmac;
1667                struct vm_area_struct *vma;
1668
1669                anon_vma_lock(anon_vma);
1670                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1671                        vma = vmac->vma;
1672                        if (rmap_item->address < vma->vm_start ||
1673                            rmap_item->address >= vma->vm_end)
1674                                continue;
1675                        /*
1676                         * Initially we examine only the vma which covers this
1677                         * rmap_item; but later, if there is still work to do,
1678                         * we examine covering vmas in other mms: in case they
1679                         * were forked from the original since ksmd passed.
1680                         */
1681                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1682                                continue;
1683
1684                        ret = try_to_unmap_one(page, vma,
1685                                        rmap_item->address, flags);
1686                        if (ret != SWAP_AGAIN || !page_mapped(page)) {
1687                                anon_vma_unlock(anon_vma);
1688                                goto out;
1689                        }
1690                }
1691                anon_vma_unlock(anon_vma);
1692        }
1693        if (!search_new_forks++)
1694                goto again;
1695out:
1696        return ret;
1697}
1698
1699#ifdef CONFIG_MIGRATION
1700int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1701                  struct vm_area_struct *, unsigned long, void *), void *arg)
1702{
1703        struct stable_node *stable_node;
1704        struct hlist_node *hlist;
1705        struct rmap_item *rmap_item;
1706        int ret = SWAP_AGAIN;
1707        int search_new_forks = 0;
1708
1709        VM_BUG_ON(!PageKsm(page));
1710        VM_BUG_ON(!PageLocked(page));
1711
1712        stable_node = page_stable_node(page);
1713        if (!stable_node)
1714                return ret;
1715again:
1716        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1717                struct anon_vma *anon_vma = rmap_item->anon_vma;
1718                struct anon_vma_chain *vmac;
1719                struct vm_area_struct *vma;
1720
1721                anon_vma_lock(anon_vma);
1722                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1723                        vma = vmac->vma;
1724                        if (rmap_item->address < vma->vm_start ||
1725                            rmap_item->address >= vma->vm_end)
1726                                continue;
1727                        /*
1728                         * Initially we examine only the vma which covers this
1729                         * rmap_item; but later, if there is still work to do,
1730                         * we examine covering vmas in other mms: in case they
1731                         * were forked from the original since ksmd passed.
1732                         */
1733                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1734                                continue;
1735
1736                        ret = rmap_one(page, vma, rmap_item->address, arg);
1737                        if (ret != SWAP_AGAIN) {
1738                                anon_vma_unlock(anon_vma);
1739                                goto out;
1740                        }
1741                }
1742                anon_vma_unlock(anon_vma);
1743        }
1744        if (!search_new_forks++)
1745                goto again;
1746out:
1747        return ret;
1748}
1749
1750void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1751{
1752        struct stable_node *stable_node;
1753
1754        VM_BUG_ON(!PageLocked(oldpage));
1755        VM_BUG_ON(!PageLocked(newpage));
1756        VM_BUG_ON(newpage->mapping != oldpage->mapping);
1757
1758        stable_node = page_stable_node(newpage);
1759        if (stable_node) {
1760                VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1761                stable_node->kpfn = page_to_pfn(newpage);
1762        }
1763}
1764#endif /* CONFIG_MIGRATION */
1765
1766#ifdef CONFIG_MEMORY_HOTREMOVE
1767static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1768                                                 unsigned long end_pfn)
1769{
1770        struct rb_node *node;
1771
1772        for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1773                struct stable_node *stable_node;
1774
1775                stable_node = rb_entry(node, struct stable_node, node);
1776                if (stable_node->kpfn >= start_pfn &&
1777                    stable_node->kpfn < end_pfn)
1778                        return stable_node;
1779        }
1780        return NULL;
1781}
1782
1783static int ksm_memory_callback(struct notifier_block *self,
1784                               unsigned long action, void *arg)
1785{
1786        struct memory_notify *mn = arg;
1787        struct stable_node *stable_node;
1788
1789        switch (action) {
1790        case MEM_GOING_OFFLINE:
1791                /*
1792                 * Keep it very simple for now: just lock out ksmd and
1793                 * MADV_UNMERGEABLE while any memory is going offline.
1794                 * mutex_lock_nested() is necessary because lockdep was alarmed
1795                 * that here we take ksm_thread_mutex inside notifier chain
1796                 * mutex, and later take notifier chain mutex inside
1797                 * ksm_thread_mutex to unlock it.   But that's safe because both
1798                 * are inside mem_hotplug_mutex.
1799                 */
1800                mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1801                break;
1802
1803        case MEM_OFFLINE:
1804                /*
1805                 * Most of the work is done by page migration; but there might
1806                 * be a few stable_nodes left over, still pointing to struct
1807                 * pages which have been offlined: prune those from the tree.
1808                 */
1809                while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1810                                        mn->start_pfn + mn->nr_pages)) != NULL)
1811                        remove_node_from_stable_tree(stable_node);
1812                /* fallthrough */
1813
1814        case MEM_CANCEL_OFFLINE:
1815                mutex_unlock(&ksm_thread_mutex);
1816                break;
1817        }
1818        return NOTIFY_OK;
1819}
1820#endif /* CONFIG_MEMORY_HOTREMOVE */
1821
1822#ifdef CONFIG_SYSFS
1823/*
1824 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1825 */
1826
1827#define KSM_ATTR_RO(_name) \
1828        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1829#define KSM_ATTR(_name) \
1830        static struct kobj_attribute _name##_attr = \
1831                __ATTR(_name, 0644, _name##_show, _name##_store)
1832
1833static ssize_t sleep_millisecs_show(struct kobject *kobj,
1834                                    struct kobj_attribute *attr, char *buf)
1835{
1836        return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1837}
1838
1839static ssize_t sleep_millisecs_store(struct kobject *kobj,
1840                                     struct kobj_attribute *attr,
1841                                     const char *buf, size_t count)
1842{
1843        unsigned long msecs;
1844        int err;
1845
1846        err = strict_strtoul(buf, 10, &msecs);
1847        if (err || msecs > UINT_MAX)
1848                return -EINVAL;
1849
1850        ksm_thread_sleep_millisecs = msecs;
1851
1852        return count;
1853}
1854KSM_ATTR(sleep_millisecs);
1855
1856static ssize_t pages_to_scan_show(struct kobject *kobj,
1857                                  struct kobj_attribute *attr, char *buf)
1858{
1859        return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1860}
1861
1862static ssize_t pages_to_scan_store(struct kobject *kobj,
1863                                   struct kobj_attribute *attr,
1864                                   const char *buf, size_t count)
1865{
1866        int err;
1867        unsigned long nr_pages;
1868
1869        err = strict_strtoul(buf, 10, &nr_pages);
1870        if (err || nr_pages > UINT_MAX)
1871                return -EINVAL;
1872
1873        ksm_thread_pages_to_scan = nr_pages;
1874
1875        return count;
1876}
1877KSM_ATTR(pages_to_scan);
1878
1879static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1880                        char *buf)
1881{
1882        return sprintf(buf, "%u\n", ksm_run);
1883}
1884
1885static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1886                         const char *buf, size_t count)
1887{
1888        int err;
1889        unsigned long flags;
1890
1891        err = strict_strtoul(buf, 10, &flags);
1892        if (err || flags > UINT_MAX)
1893                return -EINVAL;
1894        if (flags > KSM_RUN_UNMERGE)
1895                return -EINVAL;
1896
1897        /*
1898         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1899         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1900         * breaking COW to free the pages_shared (but leaves mm_slots
1901         * on the list for when ksmd may be set running again).
1902         */
1903
1904        mutex_lock(&ksm_thread_mutex);
1905        if (ksm_run != flags) {
1906                ksm_run = flags;
1907                if (flags & KSM_RUN_UNMERGE) {
1908                        int oom_score_adj;
1909
1910                        oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1911                        err = unmerge_and_remove_all_rmap_items();
1912                        compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1913                                                                oom_score_adj);
1914                        if (err) {
1915                                ksm_run = KSM_RUN_STOP;
1916                                count = err;
1917                        }
1918                }
1919        }
1920        mutex_unlock(&ksm_thread_mutex);
1921
1922        if (flags & KSM_RUN_MERGE)
1923                wake_up_interruptible(&ksm_thread_wait);
1924
1925        return count;
1926}
1927KSM_ATTR(run);
1928
1929static ssize_t pages_shared_show(struct kobject *kobj,
1930                                 struct kobj_attribute *attr, char *buf)
1931{
1932        return sprintf(buf, "%lu\n", ksm_pages_shared);
1933}
1934KSM_ATTR_RO(pages_shared);
1935
1936static ssize_t pages_sharing_show(struct kobject *kobj,
1937                                  struct kobj_attribute *attr, char *buf)
1938{
1939        return sprintf(buf, "%lu\n", ksm_pages_sharing);
1940}
1941KSM_ATTR_RO(pages_sharing);
1942
1943static ssize_t pages_unshared_show(struct kobject *kobj,
1944                                   struct kobj_attribute *attr, char *buf)
1945{
1946        return sprintf(buf, "%lu\n", ksm_pages_unshared);
1947}
1948KSM_ATTR_RO(pages_unshared);
1949
1950static ssize_t pages_volatile_show(struct kobject *kobj,
1951                                   struct kobj_attribute *attr, char *buf)
1952{
1953        long ksm_pages_volatile;
1954
1955        ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1956                                - ksm_pages_sharing - ksm_pages_unshared;
1957        /*
1958         * It was not worth any locking to calculate that statistic,
1959         * but it might therefore sometimes be negative: conceal that.
1960         */
1961        if (ksm_pages_volatile < 0)
1962                ksm_pages_volatile = 0;
1963        return sprintf(buf, "%ld\n", ksm_pages_volatile);
1964}
1965KSM_ATTR_RO(pages_volatile);
1966
1967static ssize_t full_scans_show(struct kobject *kobj,
1968                               struct kobj_attribute *attr, char *buf)
1969{
1970        return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1971}
1972KSM_ATTR_RO(full_scans);
1973
1974static struct attribute *ksm_attrs[] = {
1975        &sleep_millisecs_attr.attr,
1976        &pages_to_scan_attr.attr,
1977        &run_attr.attr,
1978        &pages_shared_attr.attr,
1979        &pages_sharing_attr.attr,
1980        &pages_unshared_attr.attr,
1981        &pages_volatile_attr.attr,
1982        &full_scans_attr.attr,
1983        NULL,
1984};
1985
1986static struct attribute_group ksm_attr_group = {
1987        .attrs = ksm_attrs,
1988        .name = "ksm",
1989};
1990#endif /* CONFIG_SYSFS */
1991
1992static int __init ksm_init(void)
1993{
1994        struct task_struct *ksm_thread;
1995        int err;
1996
1997        err = ksm_slab_init();
1998        if (err)
1999                goto out;
2000
2001        ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2002        if (IS_ERR(ksm_thread)) {
2003                printk(KERN_ERR "ksm: creating kthread failed\n");
2004                err = PTR_ERR(ksm_thread);
2005                goto out_free;
2006        }
2007
2008#ifdef CONFIG_SYSFS
2009        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2010        if (err) {
2011                printk(KERN_ERR "ksm: register sysfs failed\n");
2012                kthread_stop(ksm_thread);
2013                goto out_free;
2014        }
2015#else
2016        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2017
2018#endif /* CONFIG_SYSFS */
2019
2020#ifdef CONFIG_MEMORY_HOTREMOVE
2021        /*
2022         * Choose a high priority since the callback takes ksm_thread_mutex:
2023         * later callbacks could only be taking locks which nest within that.
2024         */
2025        hotplug_memory_notifier(ksm_memory_callback, 100);
2026#endif
2027        return 0;
2028
2029out_free:
2030        ksm_slab_free();
2031out:
2032        return err;
2033}
2034module_init(ksm_init)
2035
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