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 void break_cow(struct rmap_item *rmap_item)
 378{
 379        struct mm_struct *mm = rmap_item->mm;
 380        unsigned long addr = rmap_item->address;
 381        struct vm_area_struct *vma;
 382
 383        /*
 384         * It is not an accident that whenever we want to break COW
 385         * to undo, we also need to drop a reference to the anon_vma.
 386         */
 387        put_anon_vma(rmap_item->anon_vma);
 388
 389        down_read(&mm->mmap_sem);
 390        if (ksm_test_exit(mm))
 391                goto out;
 392        vma = find_vma(mm, addr);
 393        if (!vma || vma->vm_start > addr)
 394                goto out;
 395        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 396                goto out;
 397        break_ksm(vma, addr);
 398out:
 399        up_read(&mm->mmap_sem);
 400}
 401
 402static struct page *page_trans_compound_anon(struct page *page)
 403{
 404        if (PageTransCompound(page)) {
 405                struct page *head = compound_trans_head(page);
 406                /*
 407                 * head may actually be splitted and freed from under
 408                 * us but it's ok here.
 409                 */
 410                if (PageAnon(head))
 411                        return head;
 412        }
 413        return NULL;
 414}
 415
 416static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 417{
 418        struct mm_struct *mm = rmap_item->mm;
 419        unsigned long addr = rmap_item->address;
 420        struct vm_area_struct *vma;
 421        struct page *page;
 422
 423        down_read(&mm->mmap_sem);
 424        if (ksm_test_exit(mm))
 425                goto out;
 426        vma = find_vma(mm, addr);
 427        if (!vma || vma->vm_start > addr)
 428                goto out;
 429        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 430                goto out;
 431
 432        page = follow_page(vma, addr, FOLL_GET);
 433        if (IS_ERR_OR_NULL(page))
 434                goto out;
 435        if (PageAnon(page) || page_trans_compound_anon(page)) {
 436                flush_anon_page(vma, page, addr);
 437                flush_dcache_page(page);
 438        } else {
 439                put_page(page);
 440out:            page = NULL;
 441        }
 442        up_read(&mm->mmap_sem);
 443        return page;
 444}
 445
 446static void remove_node_from_stable_tree(struct stable_node *stable_node)
 447{
 448        struct rmap_item *rmap_item;
 449        struct hlist_node *hlist;
 450
 451        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
 452                if (rmap_item->hlist.next)
 453                        ksm_pages_sharing--;
 454                else
 455                        ksm_pages_shared--;
 456                put_anon_vma(rmap_item->anon_vma);
 457                rmap_item->address &= PAGE_MASK;
 458                cond_resched();
 459        }
 460
 461        rb_erase(&stable_node->node, &root_stable_tree);
 462        free_stable_node(stable_node);
 463}
 464
 465/*
 466 * get_ksm_page: checks if the page indicated by the stable node
 467 * is still its ksm page, despite having held no reference to it.
 468 * In which case we can trust the content of the page, and it
 469 * returns the gotten page; but if the page has now been zapped,
 470 * remove the stale node from the stable tree and return NULL.
 471 *
 472 * You would expect the stable_node to hold a reference to the ksm page.
 473 * But if it increments the page's count, swapping out has to wait for
 474 * ksmd to come around again before it can free the page, which may take
 475 * seconds or even minutes: much too unresponsive.  So instead we use a
 476 * "keyhole reference": access to the ksm page from the stable node peeps
 477 * out through its keyhole to see if that page still holds the right key,
 478 * pointing back to this stable node.  This relies on freeing a PageAnon
 479 * page to reset its page->mapping to NULL, and relies on no other use of
 480 * a page to put something that might look like our key in page->mapping.
 481 *
 482 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
 483 * but this is different - made simpler by ksm_thread_mutex being held, but
 484 * interesting for assuming that no other use of the struct page could ever
 485 * put our expected_mapping into page->mapping (or a field of the union which
 486 * coincides with page->mapping).  The RCU calls are not for KSM at all, but
 487 * to keep the page_count protocol described with page_cache_get_speculative.
 488 *
 489 * Note: it is possible that get_ksm_page() will return NULL one moment,
 490 * then page the next, if the page is in between page_freeze_refs() and
 491 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
 492 * is on its way to being freed; but it is an anomaly to bear in mind.
 493 */
 494static struct page *get_ksm_page(struct stable_node *stable_node)
 495{
 496        struct page *page;
 497        void *expected_mapping;
 498
 499        page = pfn_to_page(stable_node->kpfn);
 500        expected_mapping = (void *)stable_node +
 501                                (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 502        rcu_read_lock();
 503        if (page->mapping != expected_mapping)
 504                goto stale;
 505        if (!get_page_unless_zero(page))
 506                goto stale;
 507        if (page->mapping != expected_mapping) {
 508                put_page(page);
 509                goto stale;
 510        }
 511        rcu_read_unlock();
 512        return page;
 513stale:
 514        rcu_read_unlock();
 515        remove_node_from_stable_tree(stable_node);
 516        return NULL;
 517}
 518
 519/*
 520 * Removing rmap_item from stable or unstable tree.
 521 * This function will clean the information from the stable/unstable tree.
 522 */
 523static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 524{
 525        if (rmap_item->address & STABLE_FLAG) {
 526                struct stable_node *stable_node;
 527                struct page *page;
 528
 529                stable_node = rmap_item->head;
 530                page = get_ksm_page(stable_node);
 531                if (!page)
 532                        goto out;
 533
 534                lock_page(page);
 535                hlist_del(&rmap_item->hlist);
 536                unlock_page(page);
 537                put_page(page);
 538
 539                if (stable_node->hlist.first)
 540                        ksm_pages_sharing--;
 541                else
 542                        ksm_pages_shared--;
 543
 544                put_anon_vma(rmap_item->anon_vma);
 545                rmap_item->address &= PAGE_MASK;
 546
 547        } else if (rmap_item->address & UNSTABLE_FLAG) {
 548                unsigned char age;
 549                /*
 550                 * Usually ksmd can and must skip the rb_erase, because
 551                 * root_unstable_tree was already reset to RB_ROOT.
 552                 * But be careful when an mm is exiting: do the rb_erase
 553                 * if this rmap_item was inserted by this scan, rather
 554                 * than left over from before.
 555                 */
 556                age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 557                BUG_ON(age > 1);
 558                if (!age)
 559                        rb_erase(&rmap_item->node, &root_unstable_tree);
 560
 561                ksm_pages_unshared--;
 562                rmap_item->address &= PAGE_MASK;
 563        }
 564out:
 565        cond_resched();         /* we're called from many long loops */
 566}
 567
 568static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 569                                       struct rmap_item **rmap_list)
 570{
 571        while (*rmap_list) {
 572                struct rmap_item *rmap_item = *rmap_list;
 573                *rmap_list = rmap_item->rmap_list;
 574                remove_rmap_item_from_tree(rmap_item);
 575                free_rmap_item(rmap_item);
 576        }
 577}
 578
 579/*
 580 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 581 * than check every pte of a given vma, the locking doesn't quite work for
 582 * that - an rmap_item is assigned to the stable tree after inserting ksm
 583 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 584 * rmap_items from parent to child at fork time (so as not to waste time
 585 * if exit comes before the next scan reaches it).
 586 *
 587 * Similarly, although we'd like to remove rmap_items (so updating counts
 588 * and freeing memory) when unmerging an area, it's easier to leave that
 589 * to the next pass of ksmd - consider, for example, how ksmd might be
 590 * in cmp_and_merge_page on one of the rmap_items we would be removing.
 591 */
 592static int unmerge_ksm_pages(struct vm_area_struct *vma,
 593                             unsigned long start, unsigned long end)
 594{
 595        unsigned long addr;
 596        int err = 0;
 597
 598        for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
 599                if (ksm_test_exit(vma->vm_mm))
 600                        break;
 601                if (signal_pending(current))
 602                        err = -ERESTARTSYS;
 603                else
 604                        err = break_ksm(vma, addr);
 605        }
 606        return err;
 607}
 608
 609#ifdef CONFIG_SYSFS
 610/*
 611 * Only called through the sysfs control interface:
 612 */
 613static int unmerge_and_remove_all_rmap_items(void)
 614{
 615        struct mm_slot *mm_slot;
 616        struct mm_struct *mm;
 617        struct vm_area_struct *vma;
 618        int err = 0;
 619
 620        spin_lock(&ksm_mmlist_lock);
 621        ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
 622                                                struct mm_slot, mm_list);
 623        spin_unlock(&ksm_mmlist_lock);
 624
 625        for (mm_slot = ksm_scan.mm_slot;
 626                        mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
 627                mm = mm_slot->mm;
 628                down_read(&mm->mmap_sem);
 629                for (vma = mm->mmap; vma; vma = vma->vm_next) {
 630                        if (ksm_test_exit(mm))
 631                                break;
 632                        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 633                                continue;
 634                        err = unmerge_ksm_pages(vma,
 635                                                vma->vm_start, vma->vm_end);
 636                        if (err)
 637                                goto error;
 638                }
 639
 640                remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
 641
 642                spin_lock(&ksm_mmlist_lock);
 643                ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
 644                                                struct mm_slot, mm_list);
 645                if (ksm_test_exit(mm)) {
 646                        hlist_del(&mm_slot->link);
 647                        list_del(&mm_slot->mm_list);
 648                        spin_unlock(&ksm_mmlist_lock);
 649
 650                        free_mm_slot(mm_slot);
 651                        clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 652                        up_read(&mm->mmap_sem);
 653                        mmdrop(mm);
 654                } else {
 655                        spin_unlock(&ksm_mmlist_lock);
 656                        up_read(&mm->mmap_sem);
 657                }
 658        }
 659
 660        ksm_scan.seqnr = 0;
 661        return 0;
 662
 663error:
 664        up_read(&mm->mmap_sem);
 665        spin_lock(&ksm_mmlist_lock);
 666        ksm_scan.mm_slot = &ksm_mm_head;
 667        spin_unlock(&ksm_mmlist_lock);
 668        return err;
 669}
 670#endif /* CONFIG_SYSFS */
 671
 672static u32 calc_checksum(struct page *page)
 673{
 674        u32 checksum;
 675        void *addr = kmap_atomic(page, KM_USER0);
 676        checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 677        kunmap_atomic(addr, KM_USER0);
 678        return checksum;
 679}
 680
 681static int memcmp_pages(struct page *page1, struct page *page2)
 682{
 683        char *addr1, *addr2;
 684        int ret;
 685
 686        addr1 = kmap_atomic(page1, KM_USER0);
 687        addr2 = kmap_atomic(page2, KM_USER1);
 688        ret = memcmp(addr1, addr2, PAGE_SIZE);
 689        kunmap_atomic(addr2, KM_USER1);
 690        kunmap_atomic(addr1, KM_USER0);
 691        return ret;
 692}
 693
 694static inline int pages_identical(struct page *page1, struct page *page2)
 695{
 696        return !memcmp_pages(page1, page2);
 697}
 698
 699static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 700                              pte_t *orig_pte)
 701{
 702        struct mm_struct *mm = vma->vm_mm;
 703        unsigned long addr;
 704        pte_t *ptep;
 705        spinlock_t *ptl;
 706        int swapped;
 707        int err = -EFAULT;
 708
 709        addr = page_address_in_vma(page, vma);
 710        if (addr == -EFAULT)
 711                goto out;
 712
 713        BUG_ON(PageTransCompound(page));
 714        ptep = page_check_address(page, mm, addr, &ptl, 0);
 715        if (!ptep)
 716                goto out;
 717
 718        if (pte_write(*ptep) || pte_dirty(*ptep)) {
 719                pte_t entry;
 720
 721                swapped = PageSwapCache(page);
 722                flush_cache_page(vma, addr, page_to_pfn(page));
 723                /*
 724                 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 725                 * take any lock, therefore the check that we are going to make
 726                 * with the pagecount against the mapcount is racey and
 727                 * O_DIRECT can happen right after the check.
 728                 * So we clear the pte and flush the tlb before the check
 729                 * this assure us that no O_DIRECT can happen after the check
 730                 * or in the middle of the check.
 731                 */
 732                entry = ptep_clear_flush(vma, addr, ptep);
 733                /*
 734                 * Check that no O_DIRECT or similar I/O is in progress on the
 735                 * page
 736                 */
 737                if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 738                        set_pte_at(mm, addr, ptep, entry);
 739                        goto out_unlock;
 740                }
 741                if (pte_dirty(entry))
 742                        set_page_dirty(page);
 743                entry = pte_mkclean(pte_wrprotect(entry));
 744                set_pte_at_notify(mm, addr, ptep, entry);
 745        }
 746        *orig_pte = *ptep;
 747        err = 0;
 748
 749out_unlock:
 750        pte_unmap_unlock(ptep, ptl);
 751out:
 752        return err;
 753}
 754
 755/**
 756 * replace_page - replace page in vma by new ksm page
 757 * @vma:      vma that holds the pte pointing to page
 758 * @page:     the page we are replacing by kpage
 759 * @kpage:    the ksm page we replace page by
 760 * @orig_pte: the original value of the pte
 761 *
 762 * Returns 0 on success, -EFAULT on failure.
 763 */
 764static int replace_page(struct vm_area_struct *vma, struct page *page,
 765                        struct page *kpage, pte_t orig_pte)
 766{
 767        struct mm_struct *mm = vma->vm_mm;
 768        pgd_t *pgd;
 769        pud_t *pud;
 770        pmd_t *pmd;
 771        pte_t *ptep;
 772        spinlock_t *ptl;
 773        unsigned long addr;
 774        int err = -EFAULT;
 775
 776        addr = page_address_in_vma(page, vma);
 777        if (addr == -EFAULT)
 778                goto out;
 779
 780        pgd = pgd_offset(mm, addr);
 781        if (!pgd_present(*pgd))
 782                goto out;
 783
 784        pud = pud_offset(pgd, addr);
 785        if (!pud_present(*pud))
 786                goto out;
 787
 788        pmd = pmd_offset(pud, addr);
 789        BUG_ON(pmd_trans_huge(*pmd));
 790        if (!pmd_present(*pmd))
 791                goto out;
 792
 793        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 794        if (!pte_same(*ptep, orig_pte)) {
 795                pte_unmap_unlock(ptep, ptl);
 796                goto out;
 797        }
 798
 799        get_page(kpage);
 800        page_add_anon_rmap(kpage, vma, addr);
 801
 802        flush_cache_page(vma, addr, pte_pfn(*ptep));
 803        ptep_clear_flush(vma, addr, ptep);
 804        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 805
 806        page_remove_rmap(page);
 807        if (!page_mapped(page))
 808                try_to_free_swap(page);
 809        put_page(page);
 810
 811        pte_unmap_unlock(ptep, ptl);
 812        err = 0;
 813out:
 814        return err;
 815}
 816
 817static int page_trans_compound_anon_split(struct page *page)
 818{
 819        int ret = 0;
 820        struct page *transhuge_head = page_trans_compound_anon(page);
 821        if (transhuge_head) {
 822                /* Get the reference on the head to split it. */
 823                if (get_page_unless_zero(transhuge_head)) {
 824                        /*
 825                         * Recheck we got the reference while the head
 826                         * was still anonymous.
 827                         */
 828                        if (PageAnon(transhuge_head))
 829                                ret = split_huge_page(transhuge_head);
 830                        else
 831                                /*
 832                                 * Retry later if split_huge_page run
 833                                 * from under us.
 834                                 */
 835                                ret = 1;
 836                        put_page(transhuge_head);
 837                } else
 838                        /* Retry later if split_huge_page run from under us. */
 839                        ret = 1;
 840        }
 841        return ret;
 842}
 843
 844/*
 845 * try_to_merge_one_page - take two pages and merge them into one
 846 * @vma: the vma that holds the pte pointing to page
 847 * @page: the PageAnon page that we want to replace with kpage
 848 * @kpage: the PageKsm page that we want to map instead of page,
 849 *         or NULL the first time when we want to use page as kpage.
 850 *
 851 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 852 */
 853static int try_to_merge_one_page(struct vm_area_struct *vma,
 854                                 struct page *page, struct page *kpage)
 855{
 856        pte_t orig_pte = __pte(0);
 857        int err = -EFAULT;
 858
 859        if (page == kpage)                      /* ksm page forked */
 860                return 0;
 861
 862        if (!(vma->vm_flags & VM_MERGEABLE))
 863                goto out;
 864        if (PageTransCompound(page) && page_trans_compound_anon_split(page))
 865                goto out;
 866        BUG_ON(PageTransCompound(page));
 867        if (!PageAnon(page))
 868                goto out;
 869
 870        /*
 871         * We need the page lock to read a stable PageSwapCache in
 872         * write_protect_page().  We use trylock_page() instead of
 873         * lock_page() because we don't want to wait here - we
 874         * prefer to continue scanning and merging different pages,
 875         * then come back to this page when it is unlocked.
 876         */
 877        if (!trylock_page(page))
 878                goto out;
 879        /*
 880         * If this anonymous page is mapped only here, its pte may need
 881         * to be write-protected.  If it's mapped elsewhere, all of its
 882         * ptes are necessarily already write-protected.  But in either
 883         * case, we need to lock and check page_count is not raised.
 884         */
 885        if (write_protect_page(vma, page, &orig_pte) == 0) {
 886                if (!kpage) {
 887                        /*
 888                         * While we hold page lock, upgrade page from
 889                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
 890                         * stable_tree_insert() will update stable_node.
 891                         */
 892                        set_page_stable_node(page, NULL);
 893                        mark_page_accessed(page);
 894                        err = 0;
 895                } else if (pages_identical(page, kpage))
 896                        err = replace_page(vma, page, kpage, orig_pte);
 897        }
 898
 899        if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
 900                munlock_vma_page(page);
 901                if (!PageMlocked(kpage)) {
 902                        unlock_page(page);
 903                        lock_page(kpage);
 904                        mlock_vma_page(kpage);
 905                        page = kpage;           /* for final unlock */
 906                }
 907        }
 908
 909        unlock_page(page);
 910out:
 911        return err;
 912}
 913
 914/*
 915 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 916 * but no new kernel page is allocated: kpage must already be a ksm page.
 917 *
 918 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 919 */
 920static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
 921                                      struct page *page, struct page *kpage)
 922{
 923        struct mm_struct *mm = rmap_item->mm;
 924        struct vm_area_struct *vma;
 925        int err = -EFAULT;
 926
 927        down_read(&mm->mmap_sem);
 928        if (ksm_test_exit(mm))
 929                goto out;
 930        vma = find_vma(mm, rmap_item->address);
 931        if (!vma || vma->vm_start > rmap_item->address)
 932                goto out;
 933
 934        err = try_to_merge_one_page(vma, page, kpage);
 935        if (err)
 936                goto out;
 937
 938        /* Must get reference to anon_vma while still holding mmap_sem */
 939        rmap_item->anon_vma = vma->anon_vma;
 940        get_anon_vma(vma->anon_vma);
 941out:
 942        up_read(&mm->mmap_sem);
 943        return err;
 944}
 945
 946/*
 947 * try_to_merge_two_pages - take two identical pages and prepare them
 948 * to be merged into one page.
 949 *
 950 * This function returns the kpage if we successfully merged two identical
 951 * pages into one ksm page, NULL otherwise.
 952 *
 953 * Note that this function upgrades page to ksm page: if one of the pages
 954 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 955 */
 956static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 957                                           struct page *page,
 958                                           struct rmap_item *tree_rmap_item,
 959                                           struct page *tree_page)
 960{
 961        int err;
 962
 963        err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
 964        if (!err) {
 965                err = try_to_merge_with_ksm_page(tree_rmap_item,
 966                                                        tree_page, page);
 967                /*
 968                 * If that fails, we have a ksm page with only one pte
 969                 * pointing to it: so break it.
 970                 */
 971                if (err)
 972                        break_cow(rmap_item);
 973        }
 974        return err ? NULL : page;
 975}
 976
 977/*
 978 * stable_tree_search - search for page inside the stable tree
 979 *
 980 * This function checks if there is a page inside the stable tree
 981 * with identical content to the page that we are scanning right now.
 982 *
 983 * This function returns the stable tree node of identical content if found,
 984 * NULL otherwise.
 985 */
 986static struct page *stable_tree_search(struct page *page)
 987{
 988        struct rb_node *node = root_stable_tree.rb_node;
 989        struct stable_node *stable_node;
 990
 991        stable_node = page_stable_node(page);
 992        if (stable_node) {                      /* ksm page forked */
 993                get_page(page);
 994                return page;
 995        }
 996
 997        while (node) {
 998                struct page *tree_page;
 999                int ret;
1000
1001                cond_resched();
1002                stable_node = rb_entry(node, struct stable_node, node);
1003                tree_page = get_ksm_page(stable_node);
1004                if (!tree_page)
1005                        return NULL;
1006
1007                ret = memcmp_pages(page, tree_page);
1008
1009                if (ret < 0) {
1010                        put_page(tree_page);
1011                        node = node->rb_left;
1012                } else if (ret > 0) {
1013                        put_page(tree_page);
1014                        node = node->rb_right;
1015                } else
1016                        return tree_page;
1017        }
1018
1019        return NULL;
1020}
1021
1022/*
1023 * stable_tree_insert - insert rmap_item pointing to new ksm page
1024 * into the stable tree.
1025 *
1026 * This function returns the stable tree node just allocated on success,
1027 * NULL otherwise.
1028 */
1029static struct stable_node *stable_tree_insert(struct page *kpage)
1030{
1031        struct rb_node **new = &root_stable_tree.rb_node;
1032        struct rb_node *parent = NULL;
1033        struct stable_node *stable_node;
1034
1035        while (*new) {
1036                struct page *tree_page;
1037                int ret;
1038
1039                cond_resched();
1040                stable_node = rb_entry(*new, struct stable_node, node);
1041                tree_page = get_ksm_page(stable_node);
1042                if (!tree_page)
1043                        return NULL;
1044
1045                ret = memcmp_pages(kpage, tree_page);
1046                put_page(tree_page);
1047
1048                parent = *new;
1049                if (ret < 0)
1050                        new = &parent->rb_left;
1051                else if (ret > 0)
1052                        new = &parent->rb_right;
1053                else {
1054                        /*
1055                         * It is not a bug that stable_tree_search() didn't
1056                         * find this node: because at that time our page was
1057                         * not yet write-protected, so may have changed since.
1058                         */
1059                        return NULL;
1060                }
1061        }
1062
1063        stable_node = alloc_stable_node();
1064        if (!stable_node)
1065                return NULL;
1066
1067        rb_link_node(&stable_node->node, parent, new);
1068        rb_insert_color(&stable_node->node, &root_stable_tree);
1069
1070        INIT_HLIST_HEAD(&stable_node->hlist);
1071
1072        stable_node->kpfn = page_to_pfn(kpage);
1073        set_page_stable_node(kpage, stable_node);
1074
1075        return stable_node;
1076}
1077
1078/*
1079 * unstable_tree_search_insert - search for identical page,
1080 * else insert rmap_item into the unstable tree.
1081 *
1082 * This function searches for a page in the unstable tree identical to the
1083 * page currently being scanned; and if no identical page is found in the
1084 * tree, we insert rmap_item as a new object into the unstable tree.
1085 *
1086 * This function returns pointer to rmap_item found to be identical
1087 * to the currently scanned page, NULL otherwise.
1088 *
1089 * This function does both searching and inserting, because they share
1090 * the same walking algorithm in an rbtree.
1091 */
1092static
1093struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1094                                              struct page *page,
1095                                              struct page **tree_pagep)
1096
1097{
1098        struct rb_node **new = &root_unstable_tree.rb_node;
1099        struct rb_node *parent = NULL;
1100
1101        while (*new) {
1102                struct rmap_item *tree_rmap_item;
1103                struct page *tree_page;
1104                int ret;
1105
1106                cond_resched();
1107                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1108                tree_page = get_mergeable_page(tree_rmap_item);
1109                if (IS_ERR_OR_NULL(tree_page))
1110                        return NULL;
1111
1112                /*
1113                 * Don't substitute a ksm page for a forked page.
1114                 */
1115                if (page == tree_page) {
1116                        put_page(tree_page);
1117                        return NULL;
1118                }
1119
1120                ret = memcmp_pages(page, tree_page);
1121
1122                parent = *new;
1123                if (ret < 0) {
1124                        put_page(tree_page);
1125                        new = &parent->rb_left;
1126                } else if (ret > 0) {
1127                        put_page(tree_page);
1128                        new = &parent->rb_right;
1129                } else {
1130                        *tree_pagep = tree_page;
1131                        return tree_rmap_item;
1132                }
1133        }
1134
1135        rmap_item->address |= UNSTABLE_FLAG;
1136        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1137        rb_link_node(&rmap_item->node, parent, new);
1138        rb_insert_color(&rmap_item->node, &root_unstable_tree);
1139
1140        ksm_pages_unshared++;
1141        return NULL;
1142}
1143
1144/*
1145 * stable_tree_append - add another rmap_item to the linked list of
1146 * rmap_items hanging off a given node of the stable tree, all sharing
1147 * the same ksm page.
1148 */
1149static void stable_tree_append(struct rmap_item *rmap_item,
1150                               struct stable_node *stable_node)
1151{
1152        rmap_item->head = stable_node;
1153        rmap_item->address |= STABLE_FLAG;
1154        hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1155
1156        if (rmap_item->hlist.next)
1157                ksm_pages_sharing++;
1158        else
1159                ksm_pages_shared++;
1160}
1161
1162/*
1163 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1164 * if not, compare checksum to previous and if it's the same, see if page can
1165 * be inserted into the unstable tree, or merged with a page already there and
1166 * both transferred to the stable tree.
1167 *
1168 * @page: the page that we are searching identical page to.
1169 * @rmap_item: the reverse mapping into the virtual address of this page
1170 */
1171static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1172{
1173        struct rmap_item *tree_rmap_item;
1174        struct page *tree_page = NULL;
1175        struct stable_node *stable_node;
1176        struct page *kpage;
1177        unsigned int checksum;
1178        int err;
1179
1180        remove_rmap_item_from_tree(rmap_item);
1181
1182        /* We first start with searching the page inside the stable tree */
1183        kpage = stable_tree_search(page);
1184        if (kpage) {
1185                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1186                if (!err) {
1187                        /*
1188                         * The page was successfully merged:
1189                         * add its rmap_item to the stable tree.
1190                         */
1191                        lock_page(kpage);
1192                        stable_tree_append(rmap_item, page_stable_node(kpage));
1193                        unlock_page(kpage);
1194                }
1195                put_page(kpage);
1196                return;
1197        }
1198
1199        /*
1200         * If the hash value of the page has changed from the last time
1201         * we calculated it, this page is changing frequently: therefore we
1202         * don't want to insert it in the unstable tree, and we don't want
1203         * to waste our time searching for something identical to it there.
1204         */
1205        checksum = calc_checksum(page);
1206        if (rmap_item->oldchecksum != checksum) {
1207                rmap_item->oldchecksum = checksum;
1208                return;
1209        }
1210
1211        tree_rmap_item =
1212                unstable_tree_search_insert(rmap_item, page, &tree_page);
1213        if (tree_rmap_item) {
1214                kpage = try_to_merge_two_pages(rmap_item, page,
1215                                                tree_rmap_item, tree_page);
1216                put_page(tree_page);
1217                /*
1218                 * As soon as we merge this page, we want to remove the
1219                 * rmap_item of the page we have merged with from the unstable
1220                 * tree, and insert it instead as new node in the stable tree.
1221                 */
1222                if (kpage) {
1223                        remove_rmap_item_from_tree(tree_rmap_item);
1224
1225                        lock_page(kpage);
1226                        stable_node = stable_tree_insert(kpage);
1227                        if (stable_node) {
1228                                stable_tree_append(tree_rmap_item, stable_node);
1229                                stable_tree_append(rmap_item, stable_node);
1230                        }
1231                        unlock_page(kpage);
1232
1233                        /*
1234                         * If we fail to insert the page into the stable tree,
1235                         * we will have 2 virtual addresses that are pointing
1236                         * to a ksm page left outside the stable tree,
1237                         * in which case we need to break_cow on both.
1238                         */
1239                        if (!stable_node) {
1240                                break_cow(tree_rmap_item);
1241                                break_cow(rmap_item);
1242                        }
1243                }
1244        }
1245}
1246
1247static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1248                                            struct rmap_item **rmap_list,
1249                                            unsigned long addr)
1250{
1251        struct rmap_item *rmap_item;
1252
1253        while (*rmap_list) {
1254                rmap_item = *rmap_list;
1255                if ((rmap_item->address & PAGE_MASK) == addr)
1256                        return rmap_item;
1257                if (rmap_item->address > addr)
1258                        break;
1259                *rmap_list = rmap_item->rmap_list;
1260                remove_rmap_item_from_tree(rmap_item);
1261                free_rmap_item(rmap_item);
1262        }
1263
1264        rmap_item = alloc_rmap_item();
1265        if (rmap_item) {
1266                /* It has already been zeroed */
1267                rmap_item->mm = mm_slot->mm;
1268                rmap_item->address = addr;
1269                rmap_item->rmap_list = *rmap_list;
1270                *rmap_list = rmap_item;
1271        }
1272        return rmap_item;
1273}
1274
1275static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1276{
1277        struct mm_struct *mm;
1278        struct mm_slot *slot;
1279        struct vm_area_struct *vma;
1280        struct rmap_item *rmap_item;
1281
1282        if (list_empty(&ksm_mm_head.mm_list))
1283                return NULL;
1284
1285        slot = ksm_scan.mm_slot;
1286        if (slot == &ksm_mm_head) {
1287                /*
1288                 * A number of pages can hang around indefinitely on per-cpu
1289                 * pagevecs, raised page count preventing write_protect_page
1290                 * from merging them.  Though it doesn't really matter much,
1291                 * it is puzzling to see some stuck in pages_volatile until
1292                 * other activity jostles them out, and they also prevented
1293                 * LTP's KSM test from succeeding deterministically; so drain
1294                 * them here (here rather than on entry to ksm_do_scan(),
1295                 * so we don't IPI too often when pages_to_scan is set low).
1296                 */
1297                lru_add_drain_all();
1298
1299                root_unstable_tree = RB_ROOT;
1300
1301                spin_lock(&ksm_mmlist_lock);
1302                slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1303                ksm_scan.mm_slot = slot;
1304                spin_unlock(&ksm_mmlist_lock);
1305                /*
1306                 * Although we tested list_empty() above, a racing __ksm_exit
1307                 * of the last mm on the list may have removed it since then.
1308                 */
1309                if (slot == &ksm_mm_head)
1310                        return NULL;
1311next_mm:
1312                ksm_scan.address = 0;
1313                ksm_scan.rmap_list = &slot->rmap_list;
1314        }
1315
1316        mm = slot->mm;
1317        down_read(&mm->mmap_sem);
1318        if (ksm_test_exit(mm))
1319                vma = NULL;
1320        else
1321                vma = find_vma(mm, ksm_scan.address);
1322
1323        for (; vma; vma = vma->vm_next) {
1324                if (!(vma->vm_flags & VM_MERGEABLE))
1325                        continue;
1326                if (ksm_scan.address < vma->vm_start)
1327                        ksm_scan.address = vma->vm_start;
1328                if (!vma->anon_vma)
1329                        ksm_scan.address = vma->vm_end;
1330
1331                while (ksm_scan.address < vma->vm_end) {
1332                        if (ksm_test_exit(mm))
1333                                break;
1334                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1335                        if (IS_ERR_OR_NULL(*page)) {
1336                                ksm_scan.address += PAGE_SIZE;
1337                                cond_resched();
1338                                continue;
1339                        }
1340                        if (PageAnon(*page) ||
1341                            page_trans_compound_anon(*page)) {
1342                                flush_anon_page(vma, *page, ksm_scan.address);
1343                                flush_dcache_page(*page);
1344                                rmap_item = get_next_rmap_item(slot,
1345                                        ksm_scan.rmap_list, ksm_scan.address);
1346                                if (rmap_item) {
1347                                        ksm_scan.rmap_list =
1348                                                        &rmap_item->rmap_list;
1349                                        ksm_scan.address += PAGE_SIZE;
1350                                } else
1351                                        put_page(*page);
1352                                up_read(&mm->mmap_sem);
1353                                return rmap_item;
1354                        }
1355                        put_page(*page);
1356                        ksm_scan.address += PAGE_SIZE;
1357                        cond_resched();
1358                }
1359        }
1360
1361        if (ksm_test_exit(mm)) {
1362                ksm_scan.address = 0;
1363                ksm_scan.rmap_list = &slot->rmap_list;
1364        }
1365        /*
1366         * Nuke all the rmap_items that are above this current rmap:
1367         * because there were no VM_MERGEABLE vmas with such addresses.
1368         */
1369        remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1370
1371        spin_lock(&ksm_mmlist_lock);
1372        ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1373                                                struct mm_slot, mm_list);
1374        if (ksm_scan.address == 0) {
1375                /*
1376                 * We've completed a full scan of all vmas, holding mmap_sem
1377                 * throughout, and found no VM_MERGEABLE: so do the same as
1378                 * __ksm_exit does to remove this mm from all our lists now.
1379                 * This applies either when cleaning up after __ksm_exit
1380                 * (but beware: we can reach here even before __ksm_exit),
1381                 * or when all VM_MERGEABLE areas have been unmapped (and
1382                 * mmap_sem then protects against race with MADV_MERGEABLE).
1383                 */
1384                hlist_del(&slot->link);
1385                list_del(&slot->mm_list);
1386                spin_unlock(&ksm_mmlist_lock);
1387
1388                free_mm_slot(slot);
1389                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1390                up_read(&mm->mmap_sem);
1391                mmdrop(mm);
1392        } else {
1393                spin_unlock(&ksm_mmlist_lock);
1394                up_read(&mm->mmap_sem);
1395        }
1396
1397        /* Repeat until we've completed scanning the whole list */
1398        slot = ksm_scan.mm_slot;
1399        if (slot != &ksm_mm_head)
1400                goto next_mm;
1401
1402        ksm_scan.seqnr++;
1403        return NULL;
1404}
1405
1406/**
1407 * ksm_do_scan  - the ksm scanner main worker function.
1408 * @scan_npages - number of pages we want to scan before we return.
1409 */
1410static void ksm_do_scan(unsigned int scan_npages)
1411{
1412        struct rmap_item *rmap_item;
1413        struct page *uninitialized_var(page);
1414
1415        while (scan_npages-- && likely(!freezing(current))) {
1416                cond_resched();
1417                rmap_item = scan_get_next_rmap_item(&page);
1418                if (!rmap_item)
1419                        return;
1420                if (!PageKsm(page) || !in_stable_tree(rmap_item))
1421                        cmp_and_merge_page(page, rmap_item);
1422                put_page(page);
1423        }
1424}
1425
1426static int ksmd_should_run(void)
1427{
1428        return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1429}
1430
1431static int ksm_scan_thread(void *nothing)
1432{
1433        set_freezable();
1434        set_user_nice(current, 5);
1435
1436        while (!kthread_should_stop()) {
1437                mutex_lock(&ksm_thread_mutex);
1438                if (ksmd_should_run())
1439                        ksm_do_scan(ksm_thread_pages_to_scan);
1440                mutex_unlock(&ksm_thread_mutex);
1441
1442                try_to_freeze();
1443
1444                if (ksmd_should_run()) {
1445                        schedule_timeout_interruptible(
1446                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
1447                } else {
1448                        wait_event_freezable(ksm_thread_wait,
1449                                ksmd_should_run() || kthread_should_stop());
1450                }
1451        }
1452        return 0;
1453}
1454
1455int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1456                unsigned long end, int advice, unsigned long *vm_flags)
1457{
1458        struct mm_struct *mm = vma->vm_mm;
1459        int err;
1460
1461        switch (advice) {
1462        case MADV_MERGEABLE:
1463                /*
1464                 * Be somewhat over-protective for now!
1465                 */
1466                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1467                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1468                                 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1469                                 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1470                        return 0;               /* just ignore the advice */
1471
1472                if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1473                        err = __ksm_enter(mm);
1474                        if (err)
1475                                return err;
1476                }
1477
1478                *vm_flags |= VM_MERGEABLE;
1479                break;
1480
1481        case MADV_UNMERGEABLE:
1482                if (!(*vm_flags & VM_MERGEABLE))
1483                        return 0;               /* just ignore the advice */
1484
1485                if (vma->anon_vma) {
1486                        err = unmerge_ksm_pages(vma, start, end);
1487                        if (err)
1488                                return err;
1489                }
1490
1491                *vm_flags &= ~VM_MERGEABLE;
1492                break;
1493        }
1494
1495        return 0;
1496}
1497
1498int __ksm_enter(struct mm_struct *mm)
1499{
1500        struct mm_slot *mm_slot;
1501        int needs_wakeup;
1502
1503        mm_slot = alloc_mm_slot();
1504        if (!mm_slot)
1505                return -ENOMEM;
1506
1507        /* Check ksm_run too?  Would need tighter locking */
1508        needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1509
1510        spin_lock(&ksm_mmlist_lock);
1511        insert_to_mm_slots_hash(mm, mm_slot);
1512        /*
1513         * Insert just behind the scanning cursor, to let the area settle
1514         * down a little; when fork is followed by immediate exec, we don't
1515         * want ksmd to waste time setting up and tearing down an rmap_list.
1516         */
1517        list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1518        spin_unlock(&ksm_mmlist_lock);
1519
1520        set_bit(MMF_VM_MERGEABLE, &mm->flags);
1521        atomic_inc(&mm->mm_count);
1522
1523        if (needs_wakeup)
1524                wake_up_interruptible(&ksm_thread_wait);
1525
1526        return 0;
1527}
1528
1529void __ksm_exit(struct mm_struct *mm)
1530{
1531        struct mm_slot *mm_slot;
1532        int easy_to_free = 0;
1533
1534        /*
1535         * This process is exiting: if it's straightforward (as is the
1536         * case when ksmd was never running), free mm_slot immediately.
1537         * But if it's at the cursor or has rmap_items linked to it, use
1538         * mmap_sem to synchronize with any break_cows before pagetables
1539         * are freed, and leave the mm_slot on the list for ksmd to free.
1540         * Beware: ksm may already have noticed it exiting and freed the slot.
1541         */
1542
1543        spin_lock(&ksm_mmlist_lock);
1544        mm_slot = get_mm_slot(mm);
1545        if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1546                if (!mm_slot->rmap_list) {
1547                        hlist_del(&mm_slot->link);
1548                        list_del(&mm_slot->mm_list);
1549                        easy_to_free = 1;
1550                } else {
1551                        list_move(&mm_slot->mm_list,
1552                                  &ksm_scan.mm_slot->mm_list);
1553                }
1554        }
1555        spin_unlock(&ksm_mmlist_lock);
1556
1557        if (easy_to_free) {
1558                free_mm_slot(mm_slot);
1559                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1560                mmdrop(mm);
1561        } else if (mm_slot) {
1562                down_write(&mm->mmap_sem);
1563                up_write(&mm->mmap_sem);
1564        }
1565}
1566
1567struct page *ksm_does_need_to_copy(struct page *page,
1568                        struct vm_area_struct *vma, unsigned long address)
1569{
1570        struct page *new_page;
1571
1572        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1573        if (new_page) {
1574                copy_user_highpage(new_page, page, address, vma);
1575
1576                SetPageDirty(new_page);
1577                __SetPageUptodate(new_page);
1578                SetPageSwapBacked(new_page);
1579                __set_page_locked(new_page);
1580
1581                if (page_evictable(new_page, vma))
1582                        lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1583                else
1584                        add_page_to_unevictable_list(new_page);
1585        }
1586
1587        return new_page;
1588}
1589
1590int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1591                        unsigned long *vm_flags)
1592{
1593        struct stable_node *stable_node;
1594        struct rmap_item *rmap_item;
1595        struct hlist_node *hlist;
1596        unsigned int mapcount = page_mapcount(page);
1597        int referenced = 0;
1598        int search_new_forks = 0;
1599
1600        VM_BUG_ON(!PageKsm(page));
1601        VM_BUG_ON(!PageLocked(page));
1602
1603        stable_node = page_stable_node(page);
1604        if (!stable_node)
1605                return 0;
1606again:
1607        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1608                struct anon_vma *anon_vma = rmap_item->anon_vma;
1609                struct anon_vma_chain *vmac;
1610                struct vm_area_struct *vma;
1611
1612                anon_vma_lock(anon_vma);
1613                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1614                        vma = vmac->vma;
1615                        if (rmap_item->address < vma->vm_start ||
1616                            rmap_item->address >= vma->vm_end)
1617                                continue;
1618                        /*
1619                         * Initially we examine only the vma which covers this
1620                         * rmap_item; but later, if there is still work to do,
1621                         * we examine covering vmas in other mms: in case they
1622                         * were forked from the original since ksmd passed.
1623                         */
1624                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1625                                continue;
1626
1627                        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1628                                continue;
1629
1630                        referenced += page_referenced_one(page, vma,
1631                                rmap_item->address, &mapcount, vm_flags);
1632                        if (!search_new_forks || !mapcount)
1633                                break;
1634                }
1635                anon_vma_unlock(anon_vma);
1636                if (!mapcount)
1637                        goto out;
1638        }
1639        if (!search_new_forks++)
1640                goto again;
1641out:
1642        return referenced;
1643}
1644
1645int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1646{
1647        struct stable_node *stable_node;
1648        struct hlist_node *hlist;
1649        struct rmap_item *rmap_item;
1650        int ret = SWAP_AGAIN;
1651        int search_new_forks = 0;
1652
1653        VM_BUG_ON(!PageKsm(page));
1654        VM_BUG_ON(!PageLocked(page));
1655
1656        stable_node = page_stable_node(page);
1657        if (!stable_node)
1658                return SWAP_FAIL;
1659again:
1660        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1661                struct anon_vma *anon_vma = rmap_item->anon_vma;
1662                struct anon_vma_chain *vmac;
1663                struct vm_area_struct *vma;
1664
1665                anon_vma_lock(anon_vma);
1666                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1667                        vma = vmac->vma;
1668                        if (rmap_item->address < vma->vm_start ||
1669                            rmap_item->address >= vma->vm_end)
1670                                continue;
1671                        /*
1672                         * Initially we examine only the vma which covers this
1673                         * rmap_item; but later, if there is still work to do,
1674                         * we examine covering vmas in other mms: in case they
1675                         * were forked from the original since ksmd passed.
1676                         */
1677                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1678                                continue;
1679
1680                        ret = try_to_unmap_one(page, vma,
1681                                        rmap_item->address, flags);
1682                        if (ret != SWAP_AGAIN || !page_mapped(page)) {
1683                                anon_vma_unlock(anon_vma);
1684                                goto out;
1685                        }
1686                }
1687                anon_vma_unlock(anon_vma);
1688        }
1689        if (!search_new_forks++)
1690                goto again;
1691out:
1692        return ret;
1693}
1694
1695#ifdef CONFIG_MIGRATION
1696int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1697                  struct vm_area_struct *, unsigned long, void *), void *arg)
1698{
1699        struct stable_node *stable_node;
1700        struct hlist_node *hlist;
1701        struct rmap_item *rmap_item;
1702        int ret = SWAP_AGAIN;
1703        int search_new_forks = 0;
1704
1705        VM_BUG_ON(!PageKsm(page));
1706        VM_BUG_ON(!PageLocked(page));
1707
1708        stable_node = page_stable_node(page);
1709        if (!stable_node)
1710                return ret;
1711again:
1712        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1713                struct anon_vma *anon_vma = rmap_item->anon_vma;
1714                struct anon_vma_chain *vmac;
1715                struct vm_area_struct *vma;
1716
1717                anon_vma_lock(anon_vma);
1718                list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1719                        vma = vmac->vma;
1720                        if (rmap_item->address < vma->vm_start ||
1721                            rmap_item->address >= vma->vm_end)
1722                                continue;
1723                        /*
1724                         * Initially we examine only the vma which covers this
1725                         * rmap_item; but later, if there is still work to do,
1726                         * we examine covering vmas in other mms: in case they
1727                         * were forked from the original since ksmd passed.
1728                         */
1729                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1730                                continue;
1731
1732                        ret = rmap_one(page, vma, rmap_item->address, arg);
1733                        if (ret != SWAP_AGAIN) {
1734                                anon_vma_unlock(anon_vma);
1735                                goto out;
1736                        }
1737                }
1738                anon_vma_unlock(anon_vma);
1739        }
1740        if (!search_new_forks++)
1741                goto again;
1742out:
1743        return ret;
1744}
1745
1746void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1747{
1748        struct stable_node *stable_node;
1749
1750        VM_BUG_ON(!PageLocked(oldpage));
1751        VM_BUG_ON(!PageLocked(newpage));
1752        VM_BUG_ON(newpage->mapping != oldpage->mapping);
1753
1754        stable_node = page_stable_node(newpage);
1755        if (stable_node) {
1756                VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1757                stable_node->kpfn = page_to_pfn(newpage);
1758        }
1759}
1760#endif /* CONFIG_MIGRATION */
1761
1762#ifdef CONFIG_MEMORY_HOTREMOVE
1763static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1764                                                 unsigned long end_pfn)
1765{
1766        struct rb_node *node;
1767
1768        for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1769                struct stable_node *stable_node;
1770
1771                stable_node = rb_entry(node, struct stable_node, node);
1772                if (stable_node->kpfn >= start_pfn &&
1773                    stable_node->kpfn < end_pfn)
1774                        return stable_node;
1775        }
1776        return NULL;
1777}
1778
1779static int ksm_memory_callback(struct notifier_block *self,
1780                               unsigned long action, void *arg)
1781{
1782        struct memory_notify *mn = arg;
1783        struct stable_node *stable_node;
1784
1785        switch (action) {
1786        case MEM_GOING_OFFLINE:
1787                /*
1788                 * Keep it very simple for now: just lock out ksmd and
1789                 * MADV_UNMERGEABLE while any memory is going offline.
1790                 * mutex_lock_nested() is necessary because lockdep was alarmed
1791                 * that here we take ksm_thread_mutex inside notifier chain
1792                 * mutex, and later take notifier chain mutex inside
1793                 * ksm_thread_mutex to unlock it.   But that's safe because both
1794                 * are inside mem_hotplug_mutex.
1795                 */
1796                mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1797                break;
1798
1799        case MEM_OFFLINE:
1800                /*
1801                 * Most of the work is done by page migration; but there might
1802                 * be a few stable_nodes left over, still pointing to struct
1803                 * pages which have been offlined: prune those from the tree.
1804                 */
1805                while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1806                                        mn->start_pfn + mn->nr_pages)) != NULL)
1807                        remove_node_from_stable_tree(stable_node);
1808                /* fallthrough */
1809
1810        case MEM_CANCEL_OFFLINE:
1811                mutex_unlock(&ksm_thread_mutex);
1812                break;
1813        }
1814        return NOTIFY_OK;
1815}
1816#endif /* CONFIG_MEMORY_HOTREMOVE */
1817
1818#ifdef CONFIG_SYSFS
1819/*
1820 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1821 */
1822
1823#define KSM_ATTR_RO(_name) \
1824        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1825#define KSM_ATTR(_name) \
1826        static struct kobj_attribute _name##_attr = \
1827                __ATTR(_name, 0644, _name##_show, _name##_store)
1828
1829static ssize_t sleep_millisecs_show(struct kobject *kobj,
1830                                    struct kobj_attribute *attr, char *buf)
1831{
1832        return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1833}
1834
1835static ssize_t sleep_millisecs_store(struct kobject *kobj,
1836                                     struct kobj_attribute *attr,
1837                                     const char *buf, size_t count)
1838{
1839        unsigned long msecs;
1840        int err;
1841
1842        err = strict_strtoul(buf, 10, &msecs);
1843        if (err || msecs > UINT_MAX)
1844                return -EINVAL;
1845
1846        ksm_thread_sleep_millisecs = msecs;
1847
1848        return count;
1849}
1850KSM_ATTR(sleep_millisecs);
1851
1852static ssize_t pages_to_scan_show(struct kobject *kobj,
1853                                  struct kobj_attribute *attr, char *buf)
1854{
1855        return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1856}
1857
1858static ssize_t pages_to_scan_store(struct kobject *kobj,
1859                                   struct kobj_attribute *attr,
1860                                   const char *buf, size_t count)
1861{
1862        int err;
1863        unsigned long nr_pages;
1864
1865        err = strict_strtoul(buf, 10, &nr_pages);
1866        if (err || nr_pages > UINT_MAX)
1867                return -EINVAL;
1868
1869        ksm_thread_pages_to_scan = nr_pages;
1870
1871        return count;
1872}
1873KSM_ATTR(pages_to_scan);
1874
1875static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1876                        char *buf)
1877{
1878        return sprintf(buf, "%u\n", ksm_run);
1879}
1880
1881static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1882                         const char *buf, size_t count)
1883{
1884        int err;
1885        unsigned long flags;
1886
1887        err = strict_strtoul(buf, 10, &flags);
1888        if (err || flags > UINT_MAX)
1889                return -EINVAL;
1890        if (flags > KSM_RUN_UNMERGE)
1891                return -EINVAL;
1892
1893        /*
1894         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1895         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1896         * breaking COW to free the pages_shared (but leaves mm_slots
1897         * on the list for when ksmd may be set running again).
1898         */
1899
1900        mutex_lock(&ksm_thread_mutex);
1901        if (ksm_run != flags) {
1902                ksm_run = flags;
1903                if (flags & KSM_RUN_UNMERGE) {
1904                        int oom_score_adj;
1905
1906                        oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1907                        err = unmerge_and_remove_all_rmap_items();
1908                        test_set_oom_score_adj(oom_score_adj);
1909                        if (err) {
1910                                ksm_run = KSM_RUN_STOP;
1911                                count = err;
1912                        }
1913                }
1914        }
1915        mutex_unlock(&ksm_thread_mutex);
1916
1917        if (flags & KSM_RUN_MERGE)
1918                wake_up_interruptible(&ksm_thread_wait);
1919
1920        return count;
1921}
1922KSM_ATTR(run);
1923
1924static ssize_t pages_shared_show(struct kobject *kobj,
1925                                 struct kobj_attribute *attr, char *buf)
1926{
1927        return sprintf(buf, "%lu\n", ksm_pages_shared);
1928}
1929KSM_ATTR_RO(pages_shared);
1930
1931static ssize_t pages_sharing_show(struct kobject *kobj,
1932                                  struct kobj_attribute *attr, char *buf)
1933{
1934        return sprintf(buf, "%lu\n", ksm_pages_sharing);
1935}
1936KSM_ATTR_RO(pages_sharing);
1937
1938static ssize_t pages_unshared_show(struct kobject *kobj,
1939                                   struct kobj_attribute *attr, char *buf)
1940{
1941        return sprintf(buf, "%lu\n", ksm_pages_unshared);
1942}
1943KSM_ATTR_RO(pages_unshared);
1944
1945static ssize_t pages_volatile_show(struct kobject *kobj,
1946                                   struct kobj_attribute *attr, char *buf)
1947{
1948        long ksm_pages_volatile;
1949
1950        ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1951                                - ksm_pages_sharing - ksm_pages_unshared;
1952        /*
1953         * It was not worth any locking to calculate that statistic,
1954         * but it might therefore sometimes be negative: conceal that.
1955         */
1956        if (ksm_pages_volatile < 0)
1957                ksm_pages_volatile = 0;
1958        return sprintf(buf, "%ld\n", ksm_pages_volatile);
1959}
1960KSM_ATTR_RO(pages_volatile);
1961
1962static ssize_t full_scans_show(struct kobject *kobj,
1963                               struct kobj_attribute *attr, char *buf)
1964{
1965        return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1966}
1967KSM_ATTR_RO(full_scans);
1968
1969static struct attribute *ksm_attrs[] = {
1970        &sleep_millisecs_attr.attr,
1971        &pages_to_scan_attr.attr,
1972        &run_attr.attr,
1973        &pages_shared_attr.attr,
1974        &pages_sharing_attr.attr,
1975        &pages_unshared_attr.attr,
1976        &pages_volatile_attr.attr,
1977        &full_scans_attr.attr,
1978        NULL,
1979};
1980
1981static struct attribute_group ksm_attr_group = {
1982        .attrs = ksm_attrs,
1983        .name = "ksm",
1984};
1985#endif /* CONFIG_SYSFS */
1986
1987static int __init ksm_init(void)
1988{
1989        struct task_struct *ksm_thread;
1990        int err;
1991
1992        err = ksm_slab_init();
1993        if (err)
1994                goto out;
1995
1996        ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1997        if (IS_ERR(ksm_thread)) {
1998                printk(KERN_ERR "ksm: creating kthread failed\n");
1999                err = PTR_ERR(ksm_thread);
2000                goto out_free;
2001        }
2002
2003#ifdef CONFIG_SYSFS
2004        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2005        if (err) {
2006                printk(KERN_ERR "ksm: register sysfs failed\n");
2007                kthread_stop(ksm_thread);
2008                goto out_free;
2009        }
2010#else
2011        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2012
2013#endif /* CONFIG_SYSFS */
2014
2015#ifdef CONFIG_MEMORY_HOTREMOVE
2016        /*
2017         * Choose a high priority since the callback takes ksm_thread_mutex:
2018         * later callbacks could only be taking locks which nest within that.
2019         */
2020        hotplug_memory_notifier(ksm_memory_callback, 100);
2021#endif
2022        return 0;
2023
2024out_free:
2025        ksm_slab_free();
2026out:
2027        return err;
2028}
2029module_init(ksm_init)
2030
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