linux/mm/ksm.c
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   1/*
   2 * Memory merging support.
   3 *
   4 * This code enables dynamic sharing of identical pages found in different
   5 * memory areas, even if they are not shared by fork()
   6 *
   7 * Copyright (C) 2008-2009 Red Hat, Inc.
   8 * Authors:
   9 *      Izik Eidus
  10 *      Andrea Arcangeli
  11 *      Chris Wright
  12 *      Hugh Dickins
  13 *
  14 * This work is licensed under the terms of the GNU GPL, version 2.
  15 */
  16
  17#include <linux/errno.h>
  18#include <linux/mm.h>
  19#include <linux/fs.h>
  20#include <linux/mman.h>
  21#include <linux/sched.h>
  22#include <linux/rwsem.h>
  23#include <linux/pagemap.h>
  24#include <linux/rmap.h>
  25#include <linux/spinlock.h>
  26#include <linux/jhash.h>
  27#include <linux/delay.h>
  28#include <linux/kthread.h>
  29#include <linux/wait.h>
  30#include <linux/slab.h>
  31#include <linux/rbtree.h>
  32#include <linux/memory.h>
  33#include <linux/mmu_notifier.h>
  34#include <linux/swap.h>
  35#include <linux/ksm.h>
  36#include <linux/hash.h>
  37#include <linux/freezer.h>
  38#include <linux/oom.h>
  39
  40#include <asm/tlbflush.h>
  41#include "internal.h"
  42
  43/*
  44 * A few notes about the KSM scanning process,
  45 * to make it easier to understand the data structures below:
  46 *
  47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
  48 * contents into a data structure that holds pointers to the pages' locations.
  49 *
  50 * Since the contents of the pages may change at any moment, KSM cannot just
  51 * insert the pages into a normal sorted tree and expect it to find anything.
  52 * Therefore KSM uses two data structures - the stable and the unstable tree.
  53 *
  54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  55 * by their contents.  Because each such page is write-protected, searching on
  56 * this tree is fully assured to be working (except when pages are unmapped),
  57 * and therefore this tree is called the stable tree.
  58 *
  59 * In addition to the stable tree, KSM uses a second data structure called the
  60 * unstable tree: this tree holds pointers to pages which have been found to
  61 * be "unchanged for a period of time".  The unstable tree sorts these pages
  62 * by their contents, but since they are not write-protected, KSM cannot rely
  63 * upon the unstable tree to work correctly - the unstable tree is liable to
  64 * be corrupted as its contents are modified, and so it is called unstable.
  65 *
  66 * KSM solves this problem by several techniques:
  67 *
  68 * 1) The unstable tree is flushed every time KSM completes scanning all
  69 *    memory areas, and then the tree is rebuilt again from the beginning.
  70 * 2) KSM will only insert into the unstable tree, pages whose hash value
  71 *    has not changed since the previous scan of all memory areas.
  72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
  73 *    colors of the nodes and not on their contents, assuring that even when
  74 *    the tree gets "corrupted" it won't get out of balance, so scanning time
  75 *    remains the same (also, searching and inserting nodes in an rbtree uses
  76 *    the same algorithm, so we have no overhead when we flush and rebuild).
  77 * 4) KSM never flushes the stable tree, which means that even if it were to
  78 *    take 10 attempts to find a page in the unstable tree, once it is found,
  79 *    it is secured in the stable tree.  (When we scan a new page, we first
  80 *    compare it against the stable tree, and then against the unstable tree.)
  81 */
  82
  83/**
  84 * struct mm_slot - ksm information per mm that is being scanned
  85 * @link: link to the mm_slots hash list
  86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
  87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
  88 * @mm: the mm that this information is valid for
  89 */
  90struct mm_slot {
  91        struct hlist_node link;
  92        struct list_head mm_list;
  93        struct rmap_item *rmap_list;
  94        struct mm_struct *mm;
  95};
  96
  97/**
  98 * struct ksm_scan - cursor for scanning
  99 * @mm_slot: the current mm_slot we are scanning
 100 * @address: the next address inside that to be scanned
 101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
 102 * @seqnr: count of completed full scans (needed when removing unstable node)
 103 *
 104 * There is only the one ksm_scan instance of this cursor structure.
 105 */
 106struct ksm_scan {
 107        struct mm_slot *mm_slot;
 108        unsigned long address;
 109        struct rmap_item **rmap_list;
 110        unsigned long seqnr;
 111};
 112
 113/**
 114 * struct stable_node - node of the stable rbtree
 115 * @node: rb node of this ksm page in the stable tree
 116 * @hlist: hlist head of rmap_items using this ksm page
 117 * @kpfn: page frame number of this ksm page
 118 */
 119struct stable_node {
 120        struct rb_node node;
 121        struct hlist_head hlist;
 122        unsigned long kpfn;
 123};
 124
 125/**
 126 * struct rmap_item - reverse mapping item for virtual addresses
 127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 129 * @mm: the memory structure this rmap_item is pointing into
 130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 131 * @oldchecksum: previous checksum of the page at that virtual address
 132 * @node: rb node of this rmap_item in the unstable tree
 133 * @head: pointer to stable_node heading this list in the stable tree
 134 * @hlist: link into hlist of rmap_items hanging off that stable_node
 135 */
 136struct rmap_item {
 137        struct rmap_item *rmap_list;
 138        struct anon_vma *anon_vma;      /* when stable */
 139        struct mm_struct *mm;
 140        unsigned long address;          /* + low bits used for flags below */
 141        unsigned int oldchecksum;       /* when unstable */
 142        union {
 143                struct rb_node node;    /* when node of unstable tree */
 144                struct {                /* when listed from stable tree */
 145                        struct stable_node *head;
 146                        struct hlist_node hlist;
 147                };
 148        };
 149};
 150
 151#define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
 152#define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
 153#define STABLE_FLAG     0x200   /* is listed from the stable tree */
 154
 155/* The stable and unstable tree heads */
 156static struct rb_root root_stable_tree = RB_ROOT;
 157static struct rb_root root_unstable_tree = RB_ROOT;
 158
 159#define MM_SLOTS_HASH_SHIFT 10
 160#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
 161static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
 162
 163static struct mm_slot ksm_mm_head = {
 164        .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
 165};
 166static struct ksm_scan ksm_scan = {
 167        .mm_slot = &ksm_mm_head,
 168};
 169
 170static struct kmem_cache *rmap_item_cache;
 171static struct kmem_cache *stable_node_cache;
 172static struct kmem_cache *mm_slot_cache;
 173
 174/* The number of nodes in the stable tree */
 175static unsigned long ksm_pages_shared;
 176
 177/* The number of page slots additionally sharing those nodes */
 178static unsigned long ksm_pages_sharing;
 179
 180/* The number of nodes in the unstable tree */
 181static unsigned long ksm_pages_unshared;
 182
 183/* The number of rmap_items in use: to calculate pages_volatile */
 184static unsigned long ksm_rmap_items;
 185
 186/* Number of pages ksmd should scan in one batch */
 187static unsigned int ksm_thread_pages_to_scan = 100;
 188
 189/* Milliseconds ksmd should sleep between batches */
 190static unsigned int ksm_thread_sleep_millisecs = 20;
 191
 192#define KSM_RUN_STOP    0
 193#define KSM_RUN_MERGE   1
 194#define KSM_RUN_UNMERGE 2
 195static unsigned int ksm_run = KSM_RUN_STOP;
 196
 197static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 198static DEFINE_MUTEX(ksm_thread_mutex);
 199static DEFINE_SPINLOCK(ksm_mmlist_lock);
 200
 201#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
 202                sizeof(struct __struct), __alignof__(struct __struct),\
 203                (__flags), NULL)
 204
 205static int __init ksm_slab_init(void)
 206{
 207        rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
 208        if (!rmap_item_cache)
 209                goto out;
 210
 211        stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
 212        if (!stable_node_cache)
 213                goto out_free1;
 214
 215        mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
 216        if (!mm_slot_cache)
 217                goto out_free2;
 218
 219        return 0;
 220
 221out_free2:
 222        kmem_cache_destroy(stable_node_cache);
 223out_free1:
 224        kmem_cache_destroy(rmap_item_cache);
 225out:
 226        return -ENOMEM;
 227}
 228
 229static void __init ksm_slab_free(void)
 230{
 231        kmem_cache_destroy(mm_slot_cache);
 232        kmem_cache_destroy(stable_node_cache);
 233        kmem_cache_destroy(rmap_item_cache);
 234        mm_slot_cache = NULL;
 235}
 236
 237static inline struct rmap_item *alloc_rmap_item(void)
 238{
 239        struct rmap_item *rmap_item;
 240
 241        rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
 242        if (rmap_item)
 243                ksm_rmap_items++;
 244        return rmap_item;
 245}
 246
 247static inline void free_rmap_item(struct rmap_item *rmap_item)
 248{
 249        ksm_rmap_items--;
 250        rmap_item->mm = NULL;   /* debug safety */
 251        kmem_cache_free(rmap_item_cache, rmap_item);
 252}
 253
 254static inline struct stable_node *alloc_stable_node(void)
 255{
 256        return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
 257}
 258
 259static inline void free_stable_node(struct stable_node *stable_node)
 260{
 261        kmem_cache_free(stable_node_cache, stable_node);
 262}
 263
 264static inline struct mm_slot *alloc_mm_slot(void)
 265{
 266        if (!mm_slot_cache)     /* initialization failed */
 267                return NULL;
 268        return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 269}
 270
 271static inline void free_mm_slot(struct mm_slot *mm_slot)
 272{
 273        kmem_cache_free(mm_slot_cache, mm_slot);
 274}
 275
 276static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 277{
 278        struct mm_slot *mm_slot;
 279        struct hlist_head *bucket;
 280        struct hlist_node *node;
 281
 282        bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 283        hlist_for_each_entry(mm_slot, node, bucket, link) {
 284                if (mm == mm_slot->mm)
 285                        return mm_slot;
 286        }
 287        return NULL;
 288}
 289
 290static void insert_to_mm_slots_hash(struct mm_struct *mm,
 291                                    struct mm_slot *mm_slot)
 292{
 293        struct hlist_head *bucket;
 294
 295        bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 296        mm_slot->mm = mm;
 297        hlist_add_head(&mm_slot->link, bucket);
 298}
 299
 300static inline int in_stable_tree(struct rmap_item *rmap_item)
 301{
 302        return rmap_item->address & STABLE_FLAG;
 303}
 304
 305/*
 306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 307 * page tables after it has passed through ksm_exit() - which, if necessary,
 308 * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
 309 * a special flag: they can just back out as soon as mm_users goes to zero.
 310 * ksm_test_exit() is used throughout to make this test for exit: in some
 311 * places for correctness, in some places just to avoid unnecessary work.
 312 */
 313static inline bool ksm_test_exit(struct mm_struct *mm)
 314{
 315        return atomic_read(&mm->mm_users) == 0;
 316}
 317
 318/*
 319 * We use break_ksm to break COW on a ksm page: it's a stripped down
 320 *
 321 *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 322 *              put_page(page);
 323 *
 324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 325 * in case the application has unmapped and remapped mm,addr meanwhile.
 326 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 328 */
 329static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 330{
 331        struct page *page;
 332        int ret = 0;
 333
 334        do {
 335                cond_resched();
 336                page = follow_page(vma, addr, FOLL_GET);
 337                if (IS_ERR_OR_NULL(page))
 338                        break;
 339                if (PageKsm(page))
 340                        ret = handle_mm_fault(vma->vm_mm, vma, addr,
 341                                                        FAULT_FLAG_WRITE);
 342                else
 343                        ret = VM_FAULT_WRITE;
 344                put_page(page);
 345        } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
 346        /*
 347         * We must loop because handle_mm_fault() may back out if there's
 348         * any difficulty e.g. if pte accessed bit gets updated concurrently.
 349         *
 350         * VM_FAULT_WRITE is what we have been hoping for: it indicates that
 351         * COW has been broken, even if the vma does not permit VM_WRITE;
 352         * but note that a concurrent fault might break PageKsm for us.
 353         *
 354         * VM_FAULT_SIGBUS could occur if we race with truncation of the
 355         * backing file, which also invalidates anonymous pages: that's
 356         * okay, that truncation will have unmapped the PageKsm for us.
 357         *
 358         * VM_FAULT_OOM: at the time of writing (late July 2009), setting
 359         * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
 360         * current task has TIF_MEMDIE set, and will be OOM killed on return
 361         * to user; and ksmd, having no mm, would never be chosen for that.
 362         *
 363         * But if the mm is in a limited mem_cgroup, then the fault may fail
 364         * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
 365         * even ksmd can fail in this way - though it's usually breaking ksm
 366         * just to undo a merge it made a moment before, so unlikely to oom.
 367         *
 368         * That's a pity: we might therefore have more kernel pages allocated
 369         * than we're counting as nodes in the stable tree; but ksm_do_scan
 370         * will retry to break_cow on each pass, so should recover the page
 371         * in due course.  The important thing is to not let VM_MERGEABLE
 372         * be cleared while any such pages might remain in the area.
 373         */
 374        return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 375}
 376
 377static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
 378                unsigned long addr)
 379{
 380        struct vm_area_struct *vma;
 381        if (ksm_test_exit(mm))
 382                return NULL;
 383        vma = find_vma(mm, addr);
 384        if (!vma || vma->vm_start > addr)
 385                return NULL;
 386        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 387                return NULL;
 388        return vma;
 389}
 390
 391static void break_cow(struct rmap_item *rmap_item)
 392{
 393        struct mm_struct *mm = rmap_item->mm;
 394        unsigned long addr = rmap_item->address;
 395        struct vm_area_struct *vma;
 396
 397        /*
 398         * It is not an accident that whenever we want to break COW
 399         * to undo, we also need to drop a reference to the anon_vma.
 400         */
 401        put_anon_vma(rmap_item->anon_vma);
 402
 403        down_read(&mm->mmap_sem);
 404        vma = find_mergeable_vma(mm, addr);
 405        if (vma)
 406                break_ksm(vma, addr);
 407        up_read(&mm->mmap_sem);
 408}
 409
 410static struct page *page_trans_compound_anon(struct page *page)
 411{
 412        if (PageTransCompound(page)) {
 413                struct page *head = compound_trans_head(page);
 414                /*
 415                 * head may actually be splitted and freed from under
 416                 * us but it's ok here.
 417                 */
 418                if (PageAnon(head))
 419                        return head;
 420        }
 421        return NULL;
 422}
 423
 424static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 425{
 426        struct mm_struct *mm = rmap_item->mm;
 427        unsigned long addr = rmap_item->address;
 428        struct vm_area_struct *vma;
 429        struct page *page;
 430
 431        down_read(&mm->mmap_sem);
 432        vma = find_mergeable_vma(mm, addr);
 433        if (!vma)
 434                goto out;
 435
 436        page = follow_page(vma, addr, FOLL_GET);
 437        if (IS_ERR_OR_NULL(page))
 438                goto out;
 439        if (PageAnon(page) || page_trans_compound_anon(page)) {
 440                flush_anon_page(vma, page, addr);
 441                flush_dcache_page(page);
 442        } else {
 443                put_page(page);
 444out:            page = NULL;
 445        }
 446        up_read(&mm->mmap_sem);
 447        return page;
 448}
 449
 450static void remove_node_from_stable_tree(struct stable_node *stable_node)
 451{
 452        struct rmap_item *rmap_item;
 453        struct hlist_node *hlist;
 454
 455        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
 456                if (rmap_item->hlist.next)
 457                        ksm_pages_sharing--;
 458                else
 459                        ksm_pages_shared--;
 460                put_anon_vma(rmap_item->anon_vma);
 461                rmap_item->address &= PAGE_MASK;
 462                cond_resched();
 463        }
 464
 465        rb_erase(&stable_node->node, &root_stable_tree);
 466        free_stable_node(stable_node);
 467}
 468
 469/*
 470 * get_ksm_page: checks if the page indicated by the stable node
 471 * is still its ksm page, despite having held no reference to it.
 472 * In which case we can trust the content of the page, and it
 473 * returns the gotten page; but if the page has now been zapped,
 474 * remove the stale node from the stable tree and return NULL.
 475 *
 476 * You would expect the stable_node to hold a reference to the ksm page.
 477 * But if it increments the page's count, swapping out has to wait for
 478 * ksmd to come around again before it can free the page, which may take
 479 * seconds or even minutes: much too unresponsive.  So instead we use a
 480 * "keyhole reference": access to the ksm page from the stable node peeps
 481 * out through its keyhole to see if that page still holds the right key,
 482 * pointing back to this stable node.  This relies on freeing a PageAnon
 483 * page to reset its page->mapping to NULL, and relies on no other use of
 484 * a page to put something that might look like our key in page->mapping.
 485 *
 486 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
 487 * but this is different - made simpler by ksm_thread_mutex being held, but
 488 * interesting for assuming that no other use of the struct page could ever
 489 * put our expected_mapping into page->mapping (or a field of the union which
 490 * coincides with page->mapping).  The RCU calls are not for KSM at all, but
 491 * to keep the page_count protocol described with page_cache_get_speculative.
 492 *
 493 * Note: it is possible that get_ksm_page() will return NULL one moment,
 494 * then page the next, if the page is in between page_freeze_refs() and
 495 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
 496 * is on its way to being freed; but it is an anomaly to bear in mind.
 497 */
 498static struct page *get_ksm_page(struct stable_node *stable_node)
 499{
 500        struct page *page;
 501        void *expected_mapping;
 502
 503        page = pfn_to_page(stable_node->kpfn);
 504        expected_mapping = (void *)stable_node +
 505                                (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 506        rcu_read_lock();
 507        if (page->mapping != expected_mapping)
 508                goto stale;
 509        if (!get_page_unless_zero(page))
 510                goto stale;
 511        if (page->mapping != expected_mapping) {
 512                put_page(page);
 513                goto stale;
 514        }
 515        rcu_read_unlock();
 516        return page;
 517stale:
 518        rcu_read_unlock();
 519        remove_node_from_stable_tree(stable_node);
 520        return NULL;
 521}
 522
 523/*
 524 * Removing rmap_item from stable or unstable tree.
 525 * This function will clean the information from the stable/unstable tree.
 526 */
 527static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 528{
 529        if (rmap_item->address & STABLE_FLAG) {
 530                struct stable_node *stable_node;
 531                struct page *page;
 532
 533                stable_node = rmap_item->head;
 534                page = get_ksm_page(stable_node);
 535                if (!page)
 536                        goto out;
 537
 538                lock_page(page);
 539                hlist_del(&rmap_item->hlist);
 540                unlock_page(page);
 541                put_page(page);
 542
 543                if (stable_node->hlist.first)
 544                        ksm_pages_sharing--;
 545                else
 546                        ksm_pages_shared--;
 547
 548                put_anon_vma(rmap_item->anon_vma);
 549                rmap_item->address &= PAGE_MASK;
 550
 551        } else if (rmap_item->address & UNSTABLE_FLAG) {
 552                unsigned char age;
 553                /*
 554                 * Usually ksmd can and must skip the rb_erase, because
 555                 * root_unstable_tree was already reset to RB_ROOT.
 556                 * But be careful when an mm is exiting: do the rb_erase
 557                 * if this rmap_item was inserted by this scan, rather
 558                 * than left over from before.
 559                 */
 560                age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 561                BUG_ON(age > 1);
 562                if (!age)
 563                        rb_erase(&rmap_item->node, &root_unstable_tree);
 564
 565                ksm_pages_unshared--;
 566                rmap_item->address &= PAGE_MASK;
 567        }
 568out:
 569        cond_resched();         /* we're called from many long loops */
 570}
 571
 572static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 573                                       struct rmap_item **rmap_list)
 574{
 575        while (*rmap_list) {
 576                struct rmap_item *rmap_item = *rmap_list;
 577                *rmap_list = rmap_item->rmap_list;
 578                remove_rmap_item_from_tree(rmap_item);
 579                free_rmap_item(rmap_item);
 580        }
 581}
 582
 583/*
 584 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 585 * than check every pte of a given vma, the locking doesn't quite work for
 586 * that - an rmap_item is assigned to the stable tree after inserting ksm
 587 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 588 * rmap_items from parent to child at fork time (so as not to waste time
 589 * if exit comes before the next scan reaches it).
 590 *
 591 * Similarly, although we'd like to remove rmap_items (so updating counts
 592 * and freeing memory) when unmerging an area, it's easier to leave that
 593 * to the next pass of ksmd - consider, for example, how ksmd might be
 594 * in cmp_and_merge_page on one of the rmap_items we would be removing.
 595 */
 596static int unmerge_ksm_pages(struct vm_area_struct *vma,
 597                             unsigned long start, unsigned long end)
 598{
 599        unsigned long addr;
 600        int err = 0;
 601
 602        for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
 603                if (ksm_test_exit(vma->vm_mm))
 604                        break;
 605                if (signal_pending(current))
 606                        err = -ERESTARTSYS;
 607                else
 608                        err = break_ksm(vma, addr);
 609        }
 610        return err;
 611}
 612
 613#ifdef CONFIG_SYSFS
 614/*
 615 * Only called through the sysfs control interface:
 616 */
 617static int unmerge_and_remove_all_rmap_items(void)
 618{
 619        struct mm_slot *mm_slot;
 620        struct mm_struct *mm;
 621        struct vm_area_struct *vma;
 622        int err = 0;
 623
 624        spin_lock(&ksm_mmlist_lock);
 625        ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
 626                                                struct mm_slot, mm_list);
 627        spin_unlock(&ksm_mmlist_lock);
 628
 629        for (mm_slot = ksm_scan.mm_slot;
 630                        mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
 631                mm = mm_slot->mm;
 632                down_read(&mm->mmap_sem);
 633                for (vma = mm->mmap; vma; vma = vma->vm_next) {
 634                        if (ksm_test_exit(mm))
 635                                break;
 636                        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 637                                continue;
 638                        err = unmerge_ksm_pages(vma,
 639                                                vma->vm_start, vma->vm_end);
 640                        if (err)
 641                                goto error;
 642                }
 643
 644                remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
 645
 646                spin_lock(&ksm_mmlist_lock);
 647                ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
 648                                                struct mm_slot, mm_list);
 649                if (ksm_test_exit(mm)) {
 650                        hlist_del(&mm_slot->link);
 651                        list_del(&mm_slot->mm_list);
 652                        spin_unlock(&ksm_mmlist_lock);
 653
 654                        free_mm_slot(mm_slot);
 655                        clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 656                        up_read(&mm->mmap_sem);
 657                        mmdrop(mm);
 658                } else {
 659                        spin_unlock(&ksm_mmlist_lock);
 660                        up_read(&mm->mmap_sem);
 661                }
 662        }
 663
 664        ksm_scan.seqnr = 0;
 665        return 0;
 666
 667error:
 668        up_read(&mm->mmap_sem);
 669        spin_lock(&ksm_mmlist_lock);
 670        ksm_scan.mm_slot = &ksm_mm_head;
 671        spin_unlock(&ksm_mmlist_lock);
 672        return err;
 673}
 674#endif /* CONFIG_SYSFS */
 675
 676static u32 calc_checksum(struct page *page)
 677{
 678        u32 checksum;
 679        void *addr = kmap_atomic(page);
 680        checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 681        kunmap_atomic(addr);
 682        return checksum;
 683}
 684
 685static int memcmp_pages(struct page *page1, struct page *page2)
 686{
 687        char *addr1, *addr2;
 688        int ret;
 689
 690        addr1 = kmap_atomic(page1);
 691        addr2 = kmap_atomic(page2);
 692        ret = memcmp(addr1, addr2, PAGE_SIZE);
 693        kunmap_atomic(addr2);
 694        kunmap_atomic(addr1);
 695        return ret;
 696}
 697
 698static inline int pages_identical(struct page *page1, struct page *page2)
 699{
 700        return !memcmp_pages(page1, page2);
 701}
 702
 703static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 704                              pte_t *orig_pte)
 705{
 706        struct mm_struct *mm = vma->vm_mm;
 707        unsigned long addr;
 708        pte_t *ptep;
 709        spinlock_t *ptl;
 710        int swapped;
 711        int err = -EFAULT;
 712        unsigned long mmun_start;       /* For mmu_notifiers */
 713        unsigned long mmun_end;         /* For mmu_notifiers */
 714
 715        addr = page_address_in_vma(page, vma);
 716        if (addr == -EFAULT)
 717                goto out;
 718
 719        BUG_ON(PageTransCompound(page));
 720
 721        mmun_start = addr;
 722        mmun_end   = addr + PAGE_SIZE;
 723        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 724
 725        ptep = page_check_address(page, mm, addr, &ptl, 0);
 726        if (!ptep)
 727                goto out_mn;
 728
 729        if (pte_write(*ptep) || pte_dirty(*ptep)) {
 730                pte_t entry;
 731
 732                swapped = PageSwapCache(page);
 733                flush_cache_page(vma, addr, page_to_pfn(page));
 734                /*
 735                 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 736                 * take any lock, therefore the check that we are going to make
 737                 * with the pagecount against the mapcount is racey and
 738                 * O_DIRECT can happen right after the check.
 739                 * So we clear the pte and flush the tlb before the check
 740                 * this assure us that no O_DIRECT can happen after the check
 741                 * or in the middle of the check.
 742                 */
 743                entry = ptep_clear_flush(vma, addr, ptep);
 744                /*
 745                 * Check that no O_DIRECT or similar I/O is in progress on the
 746                 * page
 747                 */
 748                if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 749                        set_pte_at(mm, addr, ptep, entry);
 750                        goto out_unlock;
 751                }
 752                if (pte_dirty(entry))
 753                        set_page_dirty(page);
 754                entry = pte_mkclean(pte_wrprotect(entry));
 755                set_pte_at_notify(mm, addr, ptep, entry);
 756        }
 757        *orig_pte = *ptep;
 758        err = 0;
 759
 760out_unlock:
 761        pte_unmap_unlock(ptep, ptl);
 762out_mn:
 763        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 764out:
 765        return err;
 766}
 767
 768/**
 769 * replace_page - replace page in vma by new ksm page
 770 * @vma:      vma that holds the pte pointing to page
 771 * @page:     the page we are replacing by kpage
 772 * @kpage:    the ksm page we replace page by
 773 * @orig_pte: the original value of the pte
 774 *
 775 * Returns 0 on success, -EFAULT on failure.
 776 */
 777static int replace_page(struct vm_area_struct *vma, struct page *page,
 778                        struct page *kpage, pte_t orig_pte)
 779{
 780        struct mm_struct *mm = vma->vm_mm;
 781        pgd_t *pgd;
 782        pud_t *pud;
 783        pmd_t *pmd;
 784        pte_t *ptep;
 785        spinlock_t *ptl;
 786        unsigned long addr;
 787        int err = -EFAULT;
 788        unsigned long mmun_start;       /* For mmu_notifiers */
 789        unsigned long mmun_end;         /* For mmu_notifiers */
 790
 791        addr = page_address_in_vma(page, vma);
 792        if (addr == -EFAULT)
 793                goto out;
 794
 795        pgd = pgd_offset(mm, addr);
 796        if (!pgd_present(*pgd))
 797                goto out;
 798
 799        pud = pud_offset(pgd, addr);
 800        if (!pud_present(*pud))
 801                goto out;
 802
 803        pmd = pmd_offset(pud, addr);
 804        BUG_ON(pmd_trans_huge(*pmd));
 805        if (!pmd_present(*pmd))
 806                goto out;
 807
 808        mmun_start = addr;
 809        mmun_end   = addr + PAGE_SIZE;
 810        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 811
 812        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 813        if (!pte_same(*ptep, orig_pte)) {
 814                pte_unmap_unlock(ptep, ptl);
 815                goto out_mn;
 816        }
 817
 818        get_page(kpage);
 819        page_add_anon_rmap(kpage, vma, addr);
 820
 821        flush_cache_page(vma, addr, pte_pfn(*ptep));
 822        ptep_clear_flush(vma, addr, ptep);
 823        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 824
 825        page_remove_rmap(page);
 826        if (!page_mapped(page))
 827                try_to_free_swap(page);
 828        put_page(page);
 829
 830        pte_unmap_unlock(ptep, ptl);
 831        err = 0;
 832out_mn:
 833        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 834out:
 835        return err;
 836}
 837
 838static int page_trans_compound_anon_split(struct page *page)
 839{
 840        int ret = 0;
 841        struct page *transhuge_head = page_trans_compound_anon(page);
 842        if (transhuge_head) {
 843                /* Get the reference on the head to split it. */
 844                if (get_page_unless_zero(transhuge_head)) {
 845                        /*
 846                         * Recheck we got the reference while the head
 847                         * was still anonymous.
 848                         */
 849                        if (PageAnon(transhuge_head))
 850                                ret = split_huge_page(transhuge_head);
 851                        else
 852                                /*
 853                                 * Retry later if split_huge_page run
 854                                 * from under us.
 855                                 */
 856                                ret = 1;
 857                        put_page(transhuge_head);
 858                } else
 859                        /* Retry later if split_huge_page run from under us. */
 860                        ret = 1;
 861        }
 862        return ret;
 863}
 864
 865/*
 866 * try_to_merge_one_page - take two pages and merge them into one
 867 * @vma: the vma that holds the pte pointing to page
 868 * @page: the PageAnon page that we want to replace with kpage
 869 * @kpage: the PageKsm page that we want to map instead of page,
 870 *         or NULL the first time when we want to use page as kpage.
 871 *
 872 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 873 */
 874static int try_to_merge_one_page(struct vm_area_struct *vma,
 875                                 struct page *page, struct page *kpage)
 876{
 877        pte_t orig_pte = __pte(0);
 878        int err = -EFAULT;
 879
 880        if (page == kpage)                      /* ksm page forked */
 881                return 0;
 882
 883        if (!(vma->vm_flags & VM_MERGEABLE))
 884                goto out;
 885        if (PageTransCompound(page) && page_trans_compound_anon_split(page))
 886                goto out;
 887        BUG_ON(PageTransCompound(page));
 888        if (!PageAnon(page))
 889                goto out;
 890
 891        /*
 892         * We need the page lock to read a stable PageSwapCache in
 893         * write_protect_page().  We use trylock_page() instead of
 894         * lock_page() because we don't want to wait here - we
 895         * prefer to continue scanning and merging different pages,
 896         * then come back to this page when it is unlocked.
 897         */
 898        if (!trylock_page(page))
 899                goto out;
 900        /*
 901         * If this anonymous page is mapped only here, its pte may need
 902         * to be write-protected.  If it's mapped elsewhere, all of its
 903         * ptes are necessarily already write-protected.  But in either
 904         * case, we need to lock and check page_count is not raised.
 905         */
 906        if (write_protect_page(vma, page, &orig_pte) == 0) {
 907                if (!kpage) {
 908                        /*
 909                         * While we hold page lock, upgrade page from
 910                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
 911                         * stable_tree_insert() will update stable_node.
 912                         */
 913                        set_page_stable_node(page, NULL);
 914                        mark_page_accessed(page);
 915                        err = 0;
 916                } else if (pages_identical(page, kpage))
 917                        err = replace_page(vma, page, kpage, orig_pte);
 918        }
 919
 920        if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
 921                munlock_vma_page(page);
 922                if (!PageMlocked(kpage)) {
 923                        unlock_page(page);
 924                        lock_page(kpage);
 925                        mlock_vma_page(kpage);
 926                        page = kpage;           /* for final unlock */
 927                }
 928        }
 929
 930        unlock_page(page);
 931out:
 932        return err;
 933}
 934
 935/*
 936 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 937 * but no new kernel page is allocated: kpage must already be a ksm page.
 938 *
 939 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 940 */
 941static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
 942                                      struct page *page, struct page *kpage)
 943{
 944        struct mm_struct *mm = rmap_item->mm;
 945        struct vm_area_struct *vma;
 946        int err = -EFAULT;
 947
 948        down_read(&mm->mmap_sem);
 949        if (ksm_test_exit(mm))
 950                goto out;
 951        vma = find_vma(mm, rmap_item->address);
 952        if (!vma || vma->vm_start > rmap_item->address)
 953                goto out;
 954
 955        err = try_to_merge_one_page(vma, page, kpage);
 956        if (err)
 957                goto out;
 958
 959        /* Must get reference to anon_vma while still holding mmap_sem */
 960        rmap_item->anon_vma = vma->anon_vma;
 961        get_anon_vma(vma->anon_vma);
 962out:
 963        up_read(&mm->mmap_sem);
 964        return err;
 965}
 966
 967/*
 968 * try_to_merge_two_pages - take two identical pages and prepare them
 969 * to be merged into one page.
 970 *
 971 * This function returns the kpage if we successfully merged two identical
 972 * pages into one ksm page, NULL otherwise.
 973 *
 974 * Note that this function upgrades page to ksm page: if one of the pages
 975 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 976 */
 977static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 978                                           struct page *page,
 979                                           struct rmap_item *tree_rmap_item,
 980                                           struct page *tree_page)
 981{
 982        int err;
 983
 984        err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
 985        if (!err) {
 986                err = try_to_merge_with_ksm_page(tree_rmap_item,
 987                                                        tree_page, page);
 988                /*
 989                 * If that fails, we have a ksm page with only one pte
 990                 * pointing to it: so break it.
 991                 */
 992                if (err)
 993                        break_cow(rmap_item);
 994        }
 995        return err ? NULL : page;
 996}
 997
 998/*
 999 * stable_tree_search - search for page inside the stable tree
1000 *
1001 * This function checks if there is a page inside the stable tree
1002 * with identical content to the page that we are scanning right now.
1003 *
1004 * This function returns the stable tree node of identical content if found,
1005 * NULL otherwise.
1006 */
1007static struct page *stable_tree_search(struct page *page)
1008{
1009        struct rb_node *node = root_stable_tree.rb_node;
1010        struct stable_node *stable_node;
1011
1012        stable_node = page_stable_node(page);
1013        if (stable_node) {                      /* ksm page forked */
1014                get_page(page);
1015                return page;
1016        }
1017
1018        while (node) {
1019                struct page *tree_page;
1020                int ret;
1021
1022                cond_resched();
1023                stable_node = rb_entry(node, struct stable_node, node);
1024                tree_page = get_ksm_page(stable_node);
1025                if (!tree_page)
1026                        return NULL;
1027
1028                ret = memcmp_pages(page, tree_page);
1029
1030                if (ret < 0) {
1031                        put_page(tree_page);
1032                        node = node->rb_left;
1033                } else if (ret > 0) {
1034                        put_page(tree_page);
1035                        node = node->rb_right;
1036                } else
1037                        return tree_page;
1038        }
1039
1040        return NULL;
1041}
1042
1043/*
1044 * stable_tree_insert - insert rmap_item pointing to new ksm page
1045 * into the stable tree.
1046 *
1047 * This function returns the stable tree node just allocated on success,
1048 * NULL otherwise.
1049 */
1050static struct stable_node *stable_tree_insert(struct page *kpage)
1051{
1052        struct rb_node **new = &root_stable_tree.rb_node;
1053        struct rb_node *parent = NULL;
1054        struct stable_node *stable_node;
1055
1056        while (*new) {
1057                struct page *tree_page;
1058                int ret;
1059
1060                cond_resched();
1061                stable_node = rb_entry(*new, struct stable_node, node);
1062                tree_page = get_ksm_page(stable_node);
1063                if (!tree_page)
1064                        return NULL;
1065
1066                ret = memcmp_pages(kpage, tree_page);
1067                put_page(tree_page);
1068
1069                parent = *new;
1070                if (ret < 0)
1071                        new = &parent->rb_left;
1072                else if (ret > 0)
1073                        new = &parent->rb_right;
1074                else {
1075                        /*
1076                         * It is not a bug that stable_tree_search() didn't
1077                         * find this node: because at that time our page was
1078                         * not yet write-protected, so may have changed since.
1079                         */
1080                        return NULL;
1081                }
1082        }
1083
1084        stable_node = alloc_stable_node();
1085        if (!stable_node)
1086                return NULL;
1087
1088        rb_link_node(&stable_node->node, parent, new);
1089        rb_insert_color(&stable_node->node, &root_stable_tree);
1090
1091        INIT_HLIST_HEAD(&stable_node->hlist);
1092
1093        stable_node->kpfn = page_to_pfn(kpage);
1094        set_page_stable_node(kpage, stable_node);
1095
1096        return stable_node;
1097}
1098
1099/*
1100 * unstable_tree_search_insert - search for identical page,
1101 * else insert rmap_item into the unstable tree.
1102 *
1103 * This function searches for a page in the unstable tree identical to the
1104 * page currently being scanned; and if no identical page is found in the
1105 * tree, we insert rmap_item as a new object into the unstable tree.
1106 *
1107 * This function returns pointer to rmap_item found to be identical
1108 * to the currently scanned page, NULL otherwise.
1109 *
1110 * This function does both searching and inserting, because they share
1111 * the same walking algorithm in an rbtree.
1112 */
1113static
1114struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1115                                              struct page *page,
1116                                              struct page **tree_pagep)
1117
1118{
1119        struct rb_node **new = &root_unstable_tree.rb_node;
1120        struct rb_node *parent = NULL;
1121
1122        while (*new) {
1123                struct rmap_item *tree_rmap_item;
1124                struct page *tree_page;
1125                int ret;
1126
1127                cond_resched();
1128                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1129                tree_page = get_mergeable_page(tree_rmap_item);
1130                if (IS_ERR_OR_NULL(tree_page))
1131                        return NULL;
1132
1133                /*
1134                 * Don't substitute a ksm page for a forked page.
1135                 */
1136                if (page == tree_page) {
1137                        put_page(tree_page);
1138                        return NULL;
1139                }
1140
1141                ret = memcmp_pages(page, tree_page);
1142
1143                parent = *new;
1144                if (ret < 0) {
1145                        put_page(tree_page);
1146                        new = &parent->rb_left;
1147                } else if (ret > 0) {
1148                        put_page(tree_page);
1149                        new = &parent->rb_right;
1150                } else {
1151                        *tree_pagep = tree_page;
1152                        return tree_rmap_item;
1153                }
1154        }
1155
1156        rmap_item->address |= UNSTABLE_FLAG;
1157        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1158        rb_link_node(&rmap_item->node, parent, new);
1159        rb_insert_color(&rmap_item->node, &root_unstable_tree);
1160
1161        ksm_pages_unshared++;
1162        return NULL;
1163}
1164
1165/*
1166 * stable_tree_append - add another rmap_item to the linked list of
1167 * rmap_items hanging off a given node of the stable tree, all sharing
1168 * the same ksm page.
1169 */
1170static void stable_tree_append(struct rmap_item *rmap_item,
1171                               struct stable_node *stable_node)
1172{
1173        rmap_item->head = stable_node;
1174        rmap_item->address |= STABLE_FLAG;
1175        hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1176
1177        if (rmap_item->hlist.next)
1178                ksm_pages_sharing++;
1179        else
1180                ksm_pages_shared++;
1181}
1182
1183/*
1184 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1185 * if not, compare checksum to previous and if it's the same, see if page can
1186 * be inserted into the unstable tree, or merged with a page already there and
1187 * both transferred to the stable tree.
1188 *
1189 * @page: the page that we are searching identical page to.
1190 * @rmap_item: the reverse mapping into the virtual address of this page
1191 */
1192static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1193{
1194        struct rmap_item *tree_rmap_item;
1195        struct page *tree_page = NULL;
1196        struct stable_node *stable_node;
1197        struct page *kpage;
1198        unsigned int checksum;
1199        int err;
1200
1201        remove_rmap_item_from_tree(rmap_item);
1202
1203        /* We first start with searching the page inside the stable tree */
1204        kpage = stable_tree_search(page);
1205        if (kpage) {
1206                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1207                if (!err) {
1208                        /*
1209                         * The page was successfully merged:
1210                         * add its rmap_item to the stable tree.
1211                         */
1212                        lock_page(kpage);
1213                        stable_tree_append(rmap_item, page_stable_node(kpage));
1214                        unlock_page(kpage);
1215                }
1216                put_page(kpage);
1217                return;
1218        }
1219
1220        /*
1221         * If the hash value of the page has changed from the last time
1222         * we calculated it, this page is changing frequently: therefore we
1223         * don't want to insert it in the unstable tree, and we don't want
1224         * to waste our time searching for something identical to it there.
1225         */
1226        checksum = calc_checksum(page);
1227        if (rmap_item->oldchecksum != checksum) {
1228                rmap_item->oldchecksum = checksum;
1229                return;
1230        }
1231
1232        tree_rmap_item =
1233                unstable_tree_search_insert(rmap_item, page, &tree_page);
1234        if (tree_rmap_item) {
1235                kpage = try_to_merge_two_pages(rmap_item, page,
1236                                                tree_rmap_item, tree_page);
1237                put_page(tree_page);
1238                /*
1239                 * As soon as we merge this page, we want to remove the
1240                 * rmap_item of the page we have merged with from the unstable
1241                 * tree, and insert it instead as new node in the stable tree.
1242                 */
1243                if (kpage) {
1244                        remove_rmap_item_from_tree(tree_rmap_item);
1245
1246                        lock_page(kpage);
1247                        stable_node = stable_tree_insert(kpage);
1248                        if (stable_node) {
1249                                stable_tree_append(tree_rmap_item, stable_node);
1250                                stable_tree_append(rmap_item, stable_node);
1251                        }
1252                        unlock_page(kpage);
1253
1254                        /*
1255                         * If we fail to insert the page into the stable tree,
1256                         * we will have 2 virtual addresses that are pointing
1257                         * to a ksm page left outside the stable tree,
1258                         * in which case we need to break_cow on both.
1259                         */
1260                        if (!stable_node) {
1261                                break_cow(tree_rmap_item);
1262                                break_cow(rmap_item);
1263                        }
1264                }
1265        }
1266}
1267
1268static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1269                                            struct rmap_item **rmap_list,
1270                                            unsigned long addr)
1271{
1272        struct rmap_item *rmap_item;
1273
1274        while (*rmap_list) {
1275                rmap_item = *rmap_list;
1276                if ((rmap_item->address & PAGE_MASK) == addr)
1277                        return rmap_item;
1278                if (rmap_item->address > addr)
1279                        break;
1280                *rmap_list = rmap_item->rmap_list;
1281                remove_rmap_item_from_tree(rmap_item);
1282                free_rmap_item(rmap_item);
1283        }
1284
1285        rmap_item = alloc_rmap_item();
1286        if (rmap_item) {
1287                /* It has already been zeroed */
1288                rmap_item->mm = mm_slot->mm;
1289                rmap_item->address = addr;
1290                rmap_item->rmap_list = *rmap_list;
1291                *rmap_list = rmap_item;
1292        }
1293        return rmap_item;
1294}
1295
1296static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1297{
1298        struct mm_struct *mm;
1299        struct mm_slot *slot;
1300        struct vm_area_struct *vma;
1301        struct rmap_item *rmap_item;
1302
1303        if (list_empty(&ksm_mm_head.mm_list))
1304                return NULL;
1305
1306        slot = ksm_scan.mm_slot;
1307        if (slot == &ksm_mm_head) {
1308                /*
1309                 * A number of pages can hang around indefinitely on per-cpu
1310                 * pagevecs, raised page count preventing write_protect_page
1311                 * from merging them.  Though it doesn't really matter much,
1312                 * it is puzzling to see some stuck in pages_volatile until
1313                 * other activity jostles them out, and they also prevented
1314                 * LTP's KSM test from succeeding deterministically; so drain
1315                 * them here (here rather than on entry to ksm_do_scan(),
1316                 * so we don't IPI too often when pages_to_scan is set low).
1317                 */
1318                lru_add_drain_all();
1319
1320                root_unstable_tree = RB_ROOT;
1321
1322                spin_lock(&ksm_mmlist_lock);
1323                slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1324                ksm_scan.mm_slot = slot;
1325                spin_unlock(&ksm_mmlist_lock);
1326                /*
1327                 * Although we tested list_empty() above, a racing __ksm_exit
1328                 * of the last mm on the list may have removed it since then.
1329                 */
1330                if (slot == &ksm_mm_head)
1331                        return NULL;
1332next_mm:
1333                ksm_scan.address = 0;
1334                ksm_scan.rmap_list = &slot->rmap_list;
1335        }
1336
1337        mm = slot->mm;
1338        down_read(&mm->mmap_sem);
1339        if (ksm_test_exit(mm))
1340                vma = NULL;
1341        else
1342                vma = find_vma(mm, ksm_scan.address);
1343
1344        for (; vma; vma = vma->vm_next) {
1345                if (!(vma->vm_flags & VM_MERGEABLE))
1346                        continue;
1347                if (ksm_scan.address < vma->vm_start)
1348                        ksm_scan.address = vma->vm_start;
1349                if (!vma->anon_vma)
1350                        ksm_scan.address = vma->vm_end;
1351
1352                while (ksm_scan.address < vma->vm_end) {
1353                        if (ksm_test_exit(mm))
1354                                break;
1355                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1356                        if (IS_ERR_OR_NULL(*page)) {
1357                                ksm_scan.address += PAGE_SIZE;
1358                                cond_resched();
1359                                continue;
1360                        }
1361                        if (PageAnon(*page) ||
1362                            page_trans_compound_anon(*page)) {
1363                                flush_anon_page(vma, *page, ksm_scan.address);
1364                                flush_dcache_page(*page);
1365                                rmap_item = get_next_rmap_item(slot,
1366                                        ksm_scan.rmap_list, ksm_scan.address);
1367                                if (rmap_item) {
1368                                        ksm_scan.rmap_list =
1369                                                        &rmap_item->rmap_list;
1370                                        ksm_scan.address += PAGE_SIZE;
1371                                } else
1372                                        put_page(*page);
1373                                up_read(&mm->mmap_sem);
1374                                return rmap_item;
1375                        }
1376                        put_page(*page);
1377                        ksm_scan.address += PAGE_SIZE;
1378                        cond_resched();
1379                }
1380        }
1381
1382        if (ksm_test_exit(mm)) {
1383                ksm_scan.address = 0;
1384                ksm_scan.rmap_list = &slot->rmap_list;
1385        }
1386        /*
1387         * Nuke all the rmap_items that are above this current rmap:
1388         * because there were no VM_MERGEABLE vmas with such addresses.
1389         */
1390        remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1391
1392        spin_lock(&ksm_mmlist_lock);
1393        ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1394                                                struct mm_slot, mm_list);
1395        if (ksm_scan.address == 0) {
1396                /*
1397                 * We've completed a full scan of all vmas, holding mmap_sem
1398                 * throughout, and found no VM_MERGEABLE: so do the same as
1399                 * __ksm_exit does to remove this mm from all our lists now.
1400                 * This applies either when cleaning up after __ksm_exit
1401                 * (but beware: we can reach here even before __ksm_exit),
1402                 * or when all VM_MERGEABLE areas have been unmapped (and
1403                 * mmap_sem then protects against race with MADV_MERGEABLE).
1404                 */
1405                hlist_del(&slot->link);
1406                list_del(&slot->mm_list);
1407                spin_unlock(&ksm_mmlist_lock);
1408
1409                free_mm_slot(slot);
1410                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1411                up_read(&mm->mmap_sem);
1412                mmdrop(mm);
1413        } else {
1414                spin_unlock(&ksm_mmlist_lock);
1415                up_read(&mm->mmap_sem);
1416        }
1417
1418        /* Repeat until we've completed scanning the whole list */
1419        slot = ksm_scan.mm_slot;
1420        if (slot != &ksm_mm_head)
1421                goto next_mm;
1422
1423        ksm_scan.seqnr++;
1424        return NULL;
1425}
1426
1427/**
1428 * ksm_do_scan  - the ksm scanner main worker function.
1429 * @scan_npages - number of pages we want to scan before we return.
1430 */
1431static void ksm_do_scan(unsigned int scan_npages)
1432{
1433        struct rmap_item *rmap_item;
1434        struct page *uninitialized_var(page);
1435
1436        while (scan_npages-- && likely(!freezing(current))) {
1437                cond_resched();
1438                rmap_item = scan_get_next_rmap_item(&page);
1439                if (!rmap_item)
1440                        return;
1441                if (!PageKsm(page) || !in_stable_tree(rmap_item))
1442                        cmp_and_merge_page(page, rmap_item);
1443                put_page(page);
1444        }
1445}
1446
1447static int ksmd_should_run(void)
1448{
1449        return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1450}
1451
1452static int ksm_scan_thread(void *nothing)
1453{
1454        set_freezable();
1455        set_user_nice(current, 5);
1456
1457        while (!kthread_should_stop()) {
1458                mutex_lock(&ksm_thread_mutex);
1459                if (ksmd_should_run())
1460                        ksm_do_scan(ksm_thread_pages_to_scan);
1461                mutex_unlock(&ksm_thread_mutex);
1462
1463                try_to_freeze();
1464
1465                if (ksmd_should_run()) {
1466                        schedule_timeout_interruptible(
1467                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
1468                } else {
1469                        wait_event_freezable(ksm_thread_wait,
1470                                ksmd_should_run() || kthread_should_stop());
1471                }
1472        }
1473        return 0;
1474}
1475
1476int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1477                unsigned long end, int advice, unsigned long *vm_flags)
1478{
1479        struct mm_struct *mm = vma->vm_mm;
1480        int err;
1481
1482        switch (advice) {
1483        case MADV_MERGEABLE:
1484                /*
1485                 * Be somewhat over-protective for now!
1486                 */
1487                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1488                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1489                                 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
1490                        return 0;               /* just ignore the advice */
1491
1492#ifdef VM_SAO
1493                if (*vm_flags & VM_SAO)
1494                        return 0;
1495#endif
1496
1497                if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1498                        err = __ksm_enter(mm);
1499                        if (err)
1500                                return err;
1501                }
1502
1503                *vm_flags |= VM_MERGEABLE;
1504                break;
1505
1506        case MADV_UNMERGEABLE:
1507                if (!(*vm_flags & VM_MERGEABLE))
1508                        return 0;               /* just ignore the advice */
1509
1510                if (vma->anon_vma) {
1511                        err = unmerge_ksm_pages(vma, start, end);
1512                        if (err)
1513                                return err;
1514                }
1515
1516                *vm_flags &= ~VM_MERGEABLE;
1517                break;
1518        }
1519
1520        return 0;
1521}
1522
1523int __ksm_enter(struct mm_struct *mm)
1524{
1525        struct mm_slot *mm_slot;
1526        int needs_wakeup;
1527
1528        mm_slot = alloc_mm_slot();
1529        if (!mm_slot)
1530                return -ENOMEM;
1531
1532        /* Check ksm_run too?  Would need tighter locking */
1533        needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1534
1535        spin_lock(&ksm_mmlist_lock);
1536        insert_to_mm_slots_hash(mm, mm_slot);
1537        /*
1538         * Insert just behind the scanning cursor, to let the area settle
1539         * down a little; when fork is followed by immediate exec, we don't
1540         * want ksmd to waste time setting up and tearing down an rmap_list.
1541         */
1542        list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1543        spin_unlock(&ksm_mmlist_lock);
1544
1545        set_bit(MMF_VM_MERGEABLE, &mm->flags);
1546        atomic_inc(&mm->mm_count);
1547
1548        if (needs_wakeup)
1549                wake_up_interruptible(&ksm_thread_wait);
1550
1551        return 0;
1552}
1553
1554void __ksm_exit(struct mm_struct *mm)
1555{
1556        struct mm_slot *mm_slot;
1557        int easy_to_free = 0;
1558
1559        /*
1560         * This process is exiting: if it's straightforward (as is the
1561         * case when ksmd was never running), free mm_slot immediately.
1562         * But if it's at the cursor or has rmap_items linked to it, use
1563         * mmap_sem to synchronize with any break_cows before pagetables
1564         * are freed, and leave the mm_slot on the list for ksmd to free.
1565         * Beware: ksm may already have noticed it exiting and freed the slot.
1566         */
1567
1568        spin_lock(&ksm_mmlist_lock);
1569        mm_slot = get_mm_slot(mm);
1570        if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1571                if (!mm_slot->rmap_list) {
1572                        hlist_del(&mm_slot->link);
1573                        list_del(&mm_slot->mm_list);
1574                        easy_to_free = 1;
1575                } else {
1576                        list_move(&mm_slot->mm_list,
1577                                  &ksm_scan.mm_slot->mm_list);
1578                }
1579        }
1580        spin_unlock(&ksm_mmlist_lock);
1581
1582        if (easy_to_free) {
1583                free_mm_slot(mm_slot);
1584                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1585                mmdrop(mm);
1586        } else if (mm_slot) {
1587                down_write(&mm->mmap_sem);
1588                up_write(&mm->mmap_sem);
1589        }
1590}
1591
1592struct page *ksm_does_need_to_copy(struct page *page,
1593                        struct vm_area_struct *vma, unsigned long address)
1594{
1595        struct page *new_page;
1596
1597        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1598        if (new_page) {
1599                copy_user_highpage(new_page, page, address, vma);
1600
1601                SetPageDirty(new_page);
1602                __SetPageUptodate(new_page);
1603                SetPageSwapBacked(new_page);
1604                __set_page_locked(new_page);
1605
1606                if (!mlocked_vma_newpage(vma, new_page))
1607                        lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1608                else
1609                        add_page_to_unevictable_list(new_page);
1610        }
1611
1612        return new_page;
1613}
1614
1615int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1616                        unsigned long *vm_flags)
1617{
1618        struct stable_node *stable_node;
1619        struct rmap_item *rmap_item;
1620        struct hlist_node *hlist;
1621        unsigned int mapcount = page_mapcount(page);
1622        int referenced = 0;
1623        int search_new_forks = 0;
1624
1625        VM_BUG_ON(!PageKsm(page));
1626        VM_BUG_ON(!PageLocked(page));
1627
1628        stable_node = page_stable_node(page);
1629        if (!stable_node)
1630                return 0;
1631again:
1632        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1633                struct anon_vma *anon_vma = rmap_item->anon_vma;
1634                struct anon_vma_chain *vmac;
1635                struct vm_area_struct *vma;
1636
1637                anon_vma_lock(anon_vma);
1638                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1639                                               0, ULONG_MAX) {
1640                        vma = vmac->vma;
1641                        if (rmap_item->address < vma->vm_start ||
1642                            rmap_item->address >= vma->vm_end)
1643                                continue;
1644                        /*
1645                         * Initially we examine only the vma which covers this
1646                         * rmap_item; but later, if there is still work to do,
1647                         * we examine covering vmas in other mms: in case they
1648                         * were forked from the original since ksmd passed.
1649                         */
1650                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1651                                continue;
1652
1653                        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1654                                continue;
1655
1656                        referenced += page_referenced_one(page, vma,
1657                                rmap_item->address, &mapcount, vm_flags);
1658                        if (!search_new_forks || !mapcount)
1659                                break;
1660                }
1661                anon_vma_unlock(anon_vma);
1662                if (!mapcount)
1663                        goto out;
1664        }
1665        if (!search_new_forks++)
1666                goto again;
1667out:
1668        return referenced;
1669}
1670
1671int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1672{
1673        struct stable_node *stable_node;
1674        struct hlist_node *hlist;
1675        struct rmap_item *rmap_item;
1676        int ret = SWAP_AGAIN;
1677        int search_new_forks = 0;
1678
1679        VM_BUG_ON(!PageKsm(page));
1680        VM_BUG_ON(!PageLocked(page));
1681
1682        stable_node = page_stable_node(page);
1683        if (!stable_node)
1684                return SWAP_FAIL;
1685again:
1686        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1687                struct anon_vma *anon_vma = rmap_item->anon_vma;
1688                struct anon_vma_chain *vmac;
1689                struct vm_area_struct *vma;
1690
1691                anon_vma_lock(anon_vma);
1692                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1693                                               0, ULONG_MAX) {
1694                        vma = vmac->vma;
1695                        if (rmap_item->address < vma->vm_start ||
1696                            rmap_item->address >= vma->vm_end)
1697                                continue;
1698                        /*
1699                         * Initially we examine only the vma which covers this
1700                         * rmap_item; but later, if there is still work to do,
1701                         * we examine covering vmas in other mms: in case they
1702                         * were forked from the original since ksmd passed.
1703                         */
1704                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1705                                continue;
1706
1707                        ret = try_to_unmap_one(page, vma,
1708                                        rmap_item->address, flags);
1709                        if (ret != SWAP_AGAIN || !page_mapped(page)) {
1710                                anon_vma_unlock(anon_vma);
1711                                goto out;
1712                        }
1713                }
1714                anon_vma_unlock(anon_vma);
1715        }
1716        if (!search_new_forks++)
1717                goto again;
1718out:
1719        return ret;
1720}
1721
1722#ifdef CONFIG_MIGRATION
1723int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1724                  struct vm_area_struct *, unsigned long, void *), void *arg)
1725{
1726        struct stable_node *stable_node;
1727        struct hlist_node *hlist;
1728        struct rmap_item *rmap_item;
1729        int ret = SWAP_AGAIN;
1730        int search_new_forks = 0;
1731
1732        VM_BUG_ON(!PageKsm(page));
1733        VM_BUG_ON(!PageLocked(page));
1734
1735        stable_node = page_stable_node(page);
1736        if (!stable_node)
1737                return ret;
1738again:
1739        hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1740                struct anon_vma *anon_vma = rmap_item->anon_vma;
1741                struct anon_vma_chain *vmac;
1742                struct vm_area_struct *vma;
1743
1744                anon_vma_lock(anon_vma);
1745                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1746                                               0, ULONG_MAX) {
1747                        vma = vmac->vma;
1748                        if (rmap_item->address < vma->vm_start ||
1749                            rmap_item->address >= vma->vm_end)
1750                                continue;
1751                        /*
1752                         * Initially we examine only the vma which covers this
1753                         * rmap_item; but later, if there is still work to do,
1754                         * we examine covering vmas in other mms: in case they
1755                         * were forked from the original since ksmd passed.
1756                         */
1757                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1758                                continue;
1759
1760                        ret = rmap_one(page, vma, rmap_item->address, arg);
1761                        if (ret != SWAP_AGAIN) {
1762                                anon_vma_unlock(anon_vma);
1763                                goto out;
1764                        }
1765                }
1766                anon_vma_unlock(anon_vma);
1767        }
1768        if (!search_new_forks++)
1769                goto again;
1770out:
1771        return ret;
1772}
1773
1774void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1775{
1776        struct stable_node *stable_node;
1777
1778        VM_BUG_ON(!PageLocked(oldpage));
1779        VM_BUG_ON(!PageLocked(newpage));
1780        VM_BUG_ON(newpage->mapping != oldpage->mapping);
1781
1782        stable_node = page_stable_node(newpage);
1783        if (stable_node) {
1784                VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1785                stable_node->kpfn = page_to_pfn(newpage);
1786        }
1787}
1788#endif /* CONFIG_MIGRATION */
1789
1790#ifdef CONFIG_MEMORY_HOTREMOVE
1791static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1792                                                 unsigned long end_pfn)
1793{
1794        struct rb_node *node;
1795
1796        for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1797                struct stable_node *stable_node;
1798
1799                stable_node = rb_entry(node, struct stable_node, node);
1800                if (stable_node->kpfn >= start_pfn &&
1801                    stable_node->kpfn < end_pfn)
1802                        return stable_node;
1803        }
1804        return NULL;
1805}
1806
1807static int ksm_memory_callback(struct notifier_block *self,
1808                               unsigned long action, void *arg)
1809{
1810        struct memory_notify *mn = arg;
1811        struct stable_node *stable_node;
1812
1813        switch (action) {
1814        case MEM_GOING_OFFLINE:
1815                /*
1816                 * Keep it very simple for now: just lock out ksmd and
1817                 * MADV_UNMERGEABLE while any memory is going offline.
1818                 * mutex_lock_nested() is necessary because lockdep was alarmed
1819                 * that here we take ksm_thread_mutex inside notifier chain
1820                 * mutex, and later take notifier chain mutex inside
1821                 * ksm_thread_mutex to unlock it.   But that's safe because both
1822                 * are inside mem_hotplug_mutex.
1823                 */
1824                mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1825                break;
1826
1827        case MEM_OFFLINE:
1828                /*
1829                 * Most of the work is done by page migration; but there might
1830                 * be a few stable_nodes left over, still pointing to struct
1831                 * pages which have been offlined: prune those from the tree.
1832                 */
1833                while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1834                                        mn->start_pfn + mn->nr_pages)) != NULL)
1835                        remove_node_from_stable_tree(stable_node);
1836                /* fallthrough */
1837
1838        case MEM_CANCEL_OFFLINE:
1839                mutex_unlock(&ksm_thread_mutex);
1840                break;
1841        }
1842        return NOTIFY_OK;
1843}
1844#endif /* CONFIG_MEMORY_HOTREMOVE */
1845
1846#ifdef CONFIG_SYSFS
1847/*
1848 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1849 */
1850
1851#define KSM_ATTR_RO(_name) \
1852        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1853#define KSM_ATTR(_name) \
1854        static struct kobj_attribute _name##_attr = \
1855                __ATTR(_name, 0644, _name##_show, _name##_store)
1856
1857static ssize_t sleep_millisecs_show(struct kobject *kobj,
1858                                    struct kobj_attribute *attr, char *buf)
1859{
1860        return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1861}
1862
1863static ssize_t sleep_millisecs_store(struct kobject *kobj,
1864                                     struct kobj_attribute *attr,
1865                                     const char *buf, size_t count)
1866{
1867        unsigned long msecs;
1868        int err;
1869
1870        err = strict_strtoul(buf, 10, &msecs);
1871        if (err || msecs > UINT_MAX)
1872                return -EINVAL;
1873
1874        ksm_thread_sleep_millisecs = msecs;
1875
1876        return count;
1877}
1878KSM_ATTR(sleep_millisecs);
1879
1880static ssize_t pages_to_scan_show(struct kobject *kobj,
1881                                  struct kobj_attribute *attr, char *buf)
1882{
1883        return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1884}
1885
1886static ssize_t pages_to_scan_store(struct kobject *kobj,
1887                                   struct kobj_attribute *attr,
1888                                   const char *buf, size_t count)
1889{
1890        int err;
1891        unsigned long nr_pages;
1892
1893        err = strict_strtoul(buf, 10, &nr_pages);
1894        if (err || nr_pages > UINT_MAX)
1895                return -EINVAL;
1896
1897        ksm_thread_pages_to_scan = nr_pages;
1898
1899        return count;
1900}
1901KSM_ATTR(pages_to_scan);
1902
1903static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1904                        char *buf)
1905{
1906        return sprintf(buf, "%u\n", ksm_run);
1907}
1908
1909static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1910                         const char *buf, size_t count)
1911{
1912        int err;
1913        unsigned long flags;
1914
1915        err = strict_strtoul(buf, 10, &flags);
1916        if (err || flags > UINT_MAX)
1917                return -EINVAL;
1918        if (flags > KSM_RUN_UNMERGE)
1919                return -EINVAL;
1920
1921        /*
1922         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1923         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1924         * breaking COW to free the pages_shared (but leaves mm_slots
1925         * on the list for when ksmd may be set running again).
1926         */
1927
1928        mutex_lock(&ksm_thread_mutex);
1929        if (ksm_run != flags) {
1930                ksm_run = flags;
1931                if (flags & KSM_RUN_UNMERGE) {
1932                        int oom_score_adj;
1933
1934                        oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1935                        err = unmerge_and_remove_all_rmap_items();
1936                        compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1937                                                                oom_score_adj);
1938                        if (err) {
1939                                ksm_run = KSM_RUN_STOP;
1940                                count = err;
1941                        }
1942                }
1943        }
1944        mutex_unlock(&ksm_thread_mutex);
1945
1946        if (flags & KSM_RUN_MERGE)
1947                wake_up_interruptible(&ksm_thread_wait);
1948
1949        return count;
1950}
1951KSM_ATTR(run);
1952
1953static ssize_t pages_shared_show(struct kobject *kobj,
1954                                 struct kobj_attribute *attr, char *buf)
1955{
1956        return sprintf(buf, "%lu\n", ksm_pages_shared);
1957}
1958KSM_ATTR_RO(pages_shared);
1959
1960static ssize_t pages_sharing_show(struct kobject *kobj,
1961                                  struct kobj_attribute *attr, char *buf)
1962{
1963        return sprintf(buf, "%lu\n", ksm_pages_sharing);
1964}
1965KSM_ATTR_RO(pages_sharing);
1966
1967static ssize_t pages_unshared_show(struct kobject *kobj,
1968                                   struct kobj_attribute *attr, char *buf)
1969{
1970        return sprintf(buf, "%lu\n", ksm_pages_unshared);
1971}
1972KSM_ATTR_RO(pages_unshared);
1973
1974static ssize_t pages_volatile_show(struct kobject *kobj,
1975                                   struct kobj_attribute *attr, char *buf)
1976{
1977        long ksm_pages_volatile;
1978
1979        ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1980                                - ksm_pages_sharing - ksm_pages_unshared;
1981        /*
1982         * It was not worth any locking to calculate that statistic,
1983         * but it might therefore sometimes be negative: conceal that.
1984         */
1985        if (ksm_pages_volatile < 0)
1986                ksm_pages_volatile = 0;
1987        return sprintf(buf, "%ld\n", ksm_pages_volatile);
1988}
1989KSM_ATTR_RO(pages_volatile);
1990
1991static ssize_t full_scans_show(struct kobject *kobj,
1992                               struct kobj_attribute *attr, char *buf)
1993{
1994        return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1995}
1996KSM_ATTR_RO(full_scans);
1997
1998static struct attribute *ksm_attrs[] = {
1999        &sleep_millisecs_attr.attr,
2000        &pages_to_scan_attr.attr,
2001        &run_attr.attr,
2002        &pages_shared_attr.attr,
2003        &pages_sharing_attr.attr,
2004        &pages_unshared_attr.attr,
2005        &pages_volatile_attr.attr,
2006        &full_scans_attr.attr,
2007        NULL,
2008};
2009
2010static struct attribute_group ksm_attr_group = {
2011        .attrs = ksm_attrs,
2012        .name = "ksm",
2013};
2014#endif /* CONFIG_SYSFS */
2015
2016static int __init ksm_init(void)
2017{
2018        struct task_struct *ksm_thread;
2019        int err;
2020
2021        err = ksm_slab_init();
2022        if (err)
2023                goto out;
2024
2025        ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2026        if (IS_ERR(ksm_thread)) {
2027                printk(KERN_ERR "ksm: creating kthread failed\n");
2028                err = PTR_ERR(ksm_thread);
2029                goto out_free;
2030        }
2031
2032#ifdef CONFIG_SYSFS
2033        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2034        if (err) {
2035                printk(KERN_ERR "ksm: register sysfs failed\n");
2036                kthread_stop(ksm_thread);
2037                goto out_free;
2038        }
2039#else
2040        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2041
2042#endif /* CONFIG_SYSFS */
2043
2044#ifdef CONFIG_MEMORY_HOTREMOVE
2045        /*
2046         * Choose a high priority since the callback takes ksm_thread_mutex:
2047         * later callbacks could only be taking locks which nest within that.
2048         */
2049        hotplug_memory_notifier(ksm_memory_callback, 100);
2050#endif
2051        return 0;
2052
2053out_free:
2054        ksm_slab_free();
2055out:
2056        return err;
2057}
2058module_init(ksm_init)
2059
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