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/hashtable.h>
  37#include <linux/freezer.h>
  38#include <linux/oom.h>
  39#include <linux/numa.h>
  40
  41#include <asm/tlbflush.h>
  42#include "internal.h"
  43
  44#ifdef CONFIG_NUMA
  45#define NUMA(x)         (x)
  46#define DO_NUMA(x)      do { (x); } while (0)
  47#else
  48#define NUMA(x)         (0)
  49#define DO_NUMA(x)      do { } while (0)
  50#endif
  51
  52/*
  53 * A few notes about the KSM scanning process,
  54 * to make it easier to understand the data structures below:
  55 *
  56 * In order to reduce excessive scanning, KSM sorts the memory pages by their
  57 * contents into a data structure that holds pointers to the pages' locations.
  58 *
  59 * Since the contents of the pages may change at any moment, KSM cannot just
  60 * insert the pages into a normal sorted tree and expect it to find anything.
  61 * Therefore KSM uses two data structures - the stable and the unstable tree.
  62 *
  63 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  64 * by their contents.  Because each such page is write-protected, searching on
  65 * this tree is fully assured to be working (except when pages are unmapped),
  66 * and therefore this tree is called the stable tree.
  67 *
  68 * In addition to the stable tree, KSM uses a second data structure called the
  69 * unstable tree: this tree holds pointers to pages which have been found to
  70 * be "unchanged for a period of time".  The unstable tree sorts these pages
  71 * by their contents, but since they are not write-protected, KSM cannot rely
  72 * upon the unstable tree to work correctly - the unstable tree is liable to
  73 * be corrupted as its contents are modified, and so it is called unstable.
  74 *
  75 * KSM solves this problem by several techniques:
  76 *
  77 * 1) The unstable tree is flushed every time KSM completes scanning all
  78 *    memory areas, and then the tree is rebuilt again from the beginning.
  79 * 2) KSM will only insert into the unstable tree, pages whose hash value
  80 *    has not changed since the previous scan of all memory areas.
  81 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
  82 *    colors of the nodes and not on their contents, assuring that even when
  83 *    the tree gets "corrupted" it won't get out of balance, so scanning time
  84 *    remains the same (also, searching and inserting nodes in an rbtree uses
  85 *    the same algorithm, so we have no overhead when we flush and rebuild).
  86 * 4) KSM never flushes the stable tree, which means that even if it were to
  87 *    take 10 attempts to find a page in the unstable tree, once it is found,
  88 *    it is secured in the stable tree.  (When we scan a new page, we first
  89 *    compare it against the stable tree, and then against the unstable tree.)
  90 *
  91 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
  92 * stable trees and multiple unstable trees: one of each for each NUMA node.
  93 */
  94
  95/**
  96 * struct mm_slot - ksm information per mm that is being scanned
  97 * @link: link to the mm_slots hash list
  98 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
  99 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
 100 * @mm: the mm that this information is valid for
 101 */
 102struct mm_slot {
 103        struct hlist_node link;
 104        struct list_head mm_list;
 105        struct rmap_item *rmap_list;
 106        struct mm_struct *mm;
 107};
 108
 109/**
 110 * struct ksm_scan - cursor for scanning
 111 * @mm_slot: the current mm_slot we are scanning
 112 * @address: the next address inside that to be scanned
 113 * @rmap_list: link to the next rmap to be scanned in the rmap_list
 114 * @seqnr: count of completed full scans (needed when removing unstable node)
 115 *
 116 * There is only the one ksm_scan instance of this cursor structure.
 117 */
 118struct ksm_scan {
 119        struct mm_slot *mm_slot;
 120        unsigned long address;
 121        struct rmap_item **rmap_list;
 122        unsigned long seqnr;
 123};
 124
 125/**
 126 * struct stable_node - node of the stable rbtree
 127 * @node: rb node of this ksm page in the stable tree
 128 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
 129 * @list: linked into migrate_nodes, pending placement in the proper node tree
 130 * @hlist: hlist head of rmap_items using this ksm page
 131 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
 132 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
 133 */
 134struct stable_node {
 135        union {
 136                struct rb_node node;    /* when node of stable tree */
 137                struct {                /* when listed for migration */
 138                        struct list_head *head;
 139                        struct list_head list;
 140                };
 141        };
 142        struct hlist_head hlist;
 143        unsigned long kpfn;
 144#ifdef CONFIG_NUMA
 145        int nid;
 146#endif
 147};
 148
 149/**
 150 * struct rmap_item - reverse mapping item for virtual addresses
 151 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 152 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
 154 * @mm: the memory structure this rmap_item is pointing into
 155 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 156 * @oldchecksum: previous checksum of the page at that virtual address
 157 * @node: rb node of this rmap_item in the unstable tree
 158 * @head: pointer to stable_node heading this list in the stable tree
 159 * @hlist: link into hlist of rmap_items hanging off that stable_node
 160 */
 161struct rmap_item {
 162        struct rmap_item *rmap_list;
 163        union {
 164                struct anon_vma *anon_vma;      /* when stable */
 165#ifdef CONFIG_NUMA
 166                int nid;                /* when node of unstable tree */
 167#endif
 168        };
 169        struct mm_struct *mm;
 170        unsigned long address;          /* + low bits used for flags below */
 171        unsigned int oldchecksum;       /* when unstable */
 172        union {
 173                struct rb_node node;    /* when node of unstable tree */
 174                struct {                /* when listed from stable tree */
 175                        struct stable_node *head;
 176                        struct hlist_node hlist;
 177                };
 178        };
 179};
 180
 181#define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
 182#define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
 183#define STABLE_FLAG     0x200   /* is listed from the stable tree */
 184
 185/* The stable and unstable tree heads */
 186static struct rb_root one_stable_tree[1] = { RB_ROOT };
 187static struct rb_root one_unstable_tree[1] = { RB_ROOT };
 188static struct rb_root *root_stable_tree = one_stable_tree;
 189static struct rb_root *root_unstable_tree = one_unstable_tree;
 190
 191/* Recently migrated nodes of stable tree, pending proper placement */
 192static LIST_HEAD(migrate_nodes);
 193
 194#define MM_SLOTS_HASH_BITS 10
 195static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
 196
 197static struct mm_slot ksm_mm_head = {
 198        .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
 199};
 200static struct ksm_scan ksm_scan = {
 201        .mm_slot = &ksm_mm_head,
 202};
 203
 204static struct kmem_cache *rmap_item_cache;
 205static struct kmem_cache *stable_node_cache;
 206static struct kmem_cache *mm_slot_cache;
 207
 208/* The number of nodes in the stable tree */
 209static unsigned long ksm_pages_shared;
 210
 211/* The number of page slots additionally sharing those nodes */
 212static unsigned long ksm_pages_sharing;
 213
 214/* The number of nodes in the unstable tree */
 215static unsigned long ksm_pages_unshared;
 216
 217/* The number of rmap_items in use: to calculate pages_volatile */
 218static unsigned long ksm_rmap_items;
 219
 220/* Number of pages ksmd should scan in one batch */
 221static unsigned int ksm_thread_pages_to_scan = 100;
 222
 223/* Milliseconds ksmd should sleep between batches */
 224static unsigned int ksm_thread_sleep_millisecs = 20;
 225
 226#ifdef CONFIG_NUMA
 227/* Zeroed when merging across nodes is not allowed */
 228static unsigned int ksm_merge_across_nodes = 1;
 229static int ksm_nr_node_ids = 1;
 230#else
 231#define ksm_merge_across_nodes  1U
 232#define ksm_nr_node_ids         1
 233#endif
 234
 235#define KSM_RUN_STOP    0
 236#define KSM_RUN_MERGE   1
 237#define KSM_RUN_UNMERGE 2
 238#define KSM_RUN_OFFLINE 4
 239static unsigned long ksm_run = KSM_RUN_STOP;
 240static void wait_while_offlining(void);
 241
 242static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 243static DEFINE_MUTEX(ksm_thread_mutex);
 244static DEFINE_SPINLOCK(ksm_mmlist_lock);
 245
 246#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
 247                sizeof(struct __struct), __alignof__(struct __struct),\
 248                (__flags), NULL)
 249
 250static int __init ksm_slab_init(void)
 251{
 252        rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
 253        if (!rmap_item_cache)
 254                goto out;
 255
 256        stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
 257        if (!stable_node_cache)
 258                goto out_free1;
 259
 260        mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
 261        if (!mm_slot_cache)
 262                goto out_free2;
 263
 264        return 0;
 265
 266out_free2:
 267        kmem_cache_destroy(stable_node_cache);
 268out_free1:
 269        kmem_cache_destroy(rmap_item_cache);
 270out:
 271        return -ENOMEM;
 272}
 273
 274static void __init ksm_slab_free(void)
 275{
 276        kmem_cache_destroy(mm_slot_cache);
 277        kmem_cache_destroy(stable_node_cache);
 278        kmem_cache_destroy(rmap_item_cache);
 279        mm_slot_cache = NULL;
 280}
 281
 282static inline struct rmap_item *alloc_rmap_item(void)
 283{
 284        struct rmap_item *rmap_item;
 285
 286        rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
 287        if (rmap_item)
 288                ksm_rmap_items++;
 289        return rmap_item;
 290}
 291
 292static inline void free_rmap_item(struct rmap_item *rmap_item)
 293{
 294        ksm_rmap_items--;
 295        rmap_item->mm = NULL;   /* debug safety */
 296        kmem_cache_free(rmap_item_cache, rmap_item);
 297}
 298
 299static inline struct stable_node *alloc_stable_node(void)
 300{
 301        return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
 302}
 303
 304static inline void free_stable_node(struct stable_node *stable_node)
 305{
 306        kmem_cache_free(stable_node_cache, stable_node);
 307}
 308
 309static inline struct mm_slot *alloc_mm_slot(void)
 310{
 311        if (!mm_slot_cache)     /* initialization failed */
 312                return NULL;
 313        return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 314}
 315
 316static inline void free_mm_slot(struct mm_slot *mm_slot)
 317{
 318        kmem_cache_free(mm_slot_cache, mm_slot);
 319}
 320
 321static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 322{
 323        struct mm_slot *slot;
 324
 325        hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
 326                if (slot->mm == mm)
 327                        return slot;
 328
 329        return NULL;
 330}
 331
 332static void insert_to_mm_slots_hash(struct mm_struct *mm,
 333                                    struct mm_slot *mm_slot)
 334{
 335        mm_slot->mm = mm;
 336        hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
 337}
 338
 339/*
 340 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 341 * page tables after it has passed through ksm_exit() - which, if necessary,
 342 * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
 343 * a special flag: they can just back out as soon as mm_users goes to zero.
 344 * ksm_test_exit() is used throughout to make this test for exit: in some
 345 * places for correctness, in some places just to avoid unnecessary work.
 346 */
 347static inline bool ksm_test_exit(struct mm_struct *mm)
 348{
 349        return atomic_read(&mm->mm_users) == 0;
 350}
 351
 352/*
 353 * We use break_ksm to break COW on a ksm page: it's a stripped down
 354 *
 355 *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 356 *              put_page(page);
 357 *
 358 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 359 * in case the application has unmapped and remapped mm,addr meanwhile.
 360 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 361 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 362 */
 363static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 364{
 365        struct page *page;
 366        int ret = 0;
 367
 368        do {
 369                cond_resched();
 370                page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
 371                if (IS_ERR_OR_NULL(page))
 372                        break;
 373                if (PageKsm(page))
 374                        ret = handle_mm_fault(vma->vm_mm, vma, addr,
 375                                                        FAULT_FLAG_WRITE);
 376                else
 377                        ret = VM_FAULT_WRITE;
 378                put_page(page);
 379        } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
 380        /*
 381         * We must loop because handle_mm_fault() may back out if there's
 382         * any difficulty e.g. if pte accessed bit gets updated concurrently.
 383         *
 384         * VM_FAULT_WRITE is what we have been hoping for: it indicates that
 385         * COW has been broken, even if the vma does not permit VM_WRITE;
 386         * but note that a concurrent fault might break PageKsm for us.
 387         *
 388         * VM_FAULT_SIGBUS could occur if we race with truncation of the
 389         * backing file, which also invalidates anonymous pages: that's
 390         * okay, that truncation will have unmapped the PageKsm for us.
 391         *
 392         * VM_FAULT_OOM: at the time of writing (late July 2009), setting
 393         * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
 394         * current task has TIF_MEMDIE set, and will be OOM killed on return
 395         * to user; and ksmd, having no mm, would never be chosen for that.
 396         *
 397         * But if the mm is in a limited mem_cgroup, then the fault may fail
 398         * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
 399         * even ksmd can fail in this way - though it's usually breaking ksm
 400         * just to undo a merge it made a moment before, so unlikely to oom.
 401         *
 402         * That's a pity: we might therefore have more kernel pages allocated
 403         * than we're counting as nodes in the stable tree; but ksm_do_scan
 404         * will retry to break_cow on each pass, so should recover the page
 405         * in due course.  The important thing is to not let VM_MERGEABLE
 406         * be cleared while any such pages might remain in the area.
 407         */
 408        return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 409}
 410
 411static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
 412                unsigned long addr)
 413{
 414        struct vm_area_struct *vma;
 415        if (ksm_test_exit(mm))
 416                return NULL;
 417        vma = find_vma(mm, addr);
 418        if (!vma || vma->vm_start > addr)
 419                return NULL;
 420        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 421                return NULL;
 422        return vma;
 423}
 424
 425static void break_cow(struct rmap_item *rmap_item)
 426{
 427        struct mm_struct *mm = rmap_item->mm;
 428        unsigned long addr = rmap_item->address;
 429        struct vm_area_struct *vma;
 430
 431        /*
 432         * It is not an accident that whenever we want to break COW
 433         * to undo, we also need to drop a reference to the anon_vma.
 434         */
 435        put_anon_vma(rmap_item->anon_vma);
 436
 437        down_read(&mm->mmap_sem);
 438        vma = find_mergeable_vma(mm, addr);
 439        if (vma)
 440                break_ksm(vma, addr);
 441        up_read(&mm->mmap_sem);
 442}
 443
 444static struct page *page_trans_compound_anon(struct page *page)
 445{
 446        if (PageTransCompound(page)) {
 447                struct page *head = compound_trans_head(page);
 448                /*
 449                 * head may actually be splitted and freed from under
 450                 * us but it's ok here.
 451                 */
 452                if (PageAnon(head))
 453                        return head;
 454        }
 455        return NULL;
 456}
 457
 458static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 459{
 460        struct mm_struct *mm = rmap_item->mm;
 461        unsigned long addr = rmap_item->address;
 462        struct vm_area_struct *vma;
 463        struct page *page;
 464
 465        down_read(&mm->mmap_sem);
 466        vma = find_mergeable_vma(mm, addr);
 467        if (!vma)
 468                goto out;
 469
 470        page = follow_page(vma, addr, FOLL_GET);
 471        if (IS_ERR_OR_NULL(page))
 472                goto out;
 473        if (PageAnon(page) || page_trans_compound_anon(page)) {
 474                flush_anon_page(vma, page, addr);
 475                flush_dcache_page(page);
 476        } else {
 477                put_page(page);
 478out:            page = NULL;
 479        }
 480        up_read(&mm->mmap_sem);
 481        return page;
 482}
 483
 484/*
 485 * This helper is used for getting right index into array of tree roots.
 486 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
 487 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
 488 * every node has its own stable and unstable tree.
 489 */
 490static inline int get_kpfn_nid(unsigned long kpfn)
 491{
 492        return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
 493}
 494
 495static void remove_node_from_stable_tree(struct stable_node *stable_node)
 496{
 497        struct rmap_item *rmap_item;
 498
 499        hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
 500                if (rmap_item->hlist.next)
 501                        ksm_pages_sharing--;
 502                else
 503                        ksm_pages_shared--;
 504                put_anon_vma(rmap_item->anon_vma);
 505                rmap_item->address &= PAGE_MASK;
 506                cond_resched();
 507        }
 508
 509        if (stable_node->head == &migrate_nodes)
 510                list_del(&stable_node->list);
 511        else
 512                rb_erase(&stable_node->node,
 513                         root_stable_tree + NUMA(stable_node->nid));
 514        free_stable_node(stable_node);
 515}
 516
 517/*
 518 * get_ksm_page: checks if the page indicated by the stable node
 519 * is still its ksm page, despite having held no reference to it.
 520 * In which case we can trust the content of the page, and it
 521 * returns the gotten page; but if the page has now been zapped,
 522 * remove the stale node from the stable tree and return NULL.
 523 * But beware, the stable node's page might be being migrated.
 524 *
 525 * You would expect the stable_node to hold a reference to the ksm page.
 526 * But if it increments the page's count, swapping out has to wait for
 527 * ksmd to come around again before it can free the page, which may take
 528 * seconds or even minutes: much too unresponsive.  So instead we use a
 529 * "keyhole reference": access to the ksm page from the stable node peeps
 530 * out through its keyhole to see if that page still holds the right key,
 531 * pointing back to this stable node.  This relies on freeing a PageAnon
 532 * page to reset its page->mapping to NULL, and relies on no other use of
 533 * a page to put something that might look like our key in page->mapping.
 534 * is on its way to being freed; but it is an anomaly to bear in mind.
 535 */
 536static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
 537{
 538        struct page *page;
 539        void *expected_mapping;
 540        unsigned long kpfn;
 541
 542        expected_mapping = (void *)stable_node +
 543                                (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 544again:
 545        kpfn = ACCESS_ONCE(stable_node->kpfn);
 546        page = pfn_to_page(kpfn);
 547
 548        /*
 549         * page is computed from kpfn, so on most architectures reading
 550         * page->mapping is naturally ordered after reading node->kpfn,
 551         * but on Alpha we need to be more careful.
 552         */
 553        smp_read_barrier_depends();
 554        if (ACCESS_ONCE(page->mapping) != expected_mapping)
 555                goto stale;
 556
 557        /*
 558         * We cannot do anything with the page while its refcount is 0.
 559         * Usually 0 means free, or tail of a higher-order page: in which
 560         * case this node is no longer referenced, and should be freed;
 561         * however, it might mean that the page is under page_freeze_refs().
 562         * The __remove_mapping() case is easy, again the node is now stale;
 563         * but if page is swapcache in migrate_page_move_mapping(), it might
 564         * still be our page, in which case it's essential to keep the node.
 565         */
 566        while (!get_page_unless_zero(page)) {
 567                /*
 568                 * Another check for page->mapping != expected_mapping would
 569                 * work here too.  We have chosen the !PageSwapCache test to
 570                 * optimize the common case, when the page is or is about to
 571                 * be freed: PageSwapCache is cleared (under spin_lock_irq)
 572                 * in the freeze_refs section of __remove_mapping(); but Anon
 573                 * page->mapping reset to NULL later, in free_pages_prepare().
 574                 */
 575                if (!PageSwapCache(page))
 576                        goto stale;
 577                cpu_relax();
 578        }
 579
 580        if (ACCESS_ONCE(page->mapping) != expected_mapping) {
 581                put_page(page);
 582                goto stale;
 583        }
 584
 585        if (lock_it) {
 586                lock_page(page);
 587                if (ACCESS_ONCE(page->mapping) != expected_mapping) {
 588                        unlock_page(page);
 589                        put_page(page);
 590                        goto stale;
 591                }
 592        }
 593        return page;
 594
 595stale:
 596        /*
 597         * We come here from above when page->mapping or !PageSwapCache
 598         * suggests that the node is stale; but it might be under migration.
 599         * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
 600         * before checking whether node->kpfn has been changed.
 601         */
 602        smp_rmb();
 603        if (ACCESS_ONCE(stable_node->kpfn) != kpfn)
 604                goto again;
 605        remove_node_from_stable_tree(stable_node);
 606        return NULL;
 607}
 608
 609/*
 610 * Removing rmap_item from stable or unstable tree.
 611 * This function will clean the information from the stable/unstable tree.
 612 */
 613static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 614{
 615        if (rmap_item->address & STABLE_FLAG) {
 616                struct stable_node *stable_node;
 617                struct page *page;
 618
 619                stable_node = rmap_item->head;
 620                page = get_ksm_page(stable_node, true);
 621                if (!page)
 622                        goto out;
 623
 624                hlist_del(&rmap_item->hlist);
 625                unlock_page(page);
 626                put_page(page);
 627
 628                if (stable_node->hlist.first)
 629                        ksm_pages_sharing--;
 630                else
 631                        ksm_pages_shared--;
 632
 633                put_anon_vma(rmap_item->anon_vma);
 634                rmap_item->address &= PAGE_MASK;
 635
 636        } else if (rmap_item->address & UNSTABLE_FLAG) {
 637                unsigned char age;
 638                /*
 639                 * Usually ksmd can and must skip the rb_erase, because
 640                 * root_unstable_tree was already reset to RB_ROOT.
 641                 * But be careful when an mm is exiting: do the rb_erase
 642                 * if this rmap_item was inserted by this scan, rather
 643                 * than left over from before.
 644                 */
 645                age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 646                BUG_ON(age > 1);
 647                if (!age)
 648                        rb_erase(&rmap_item->node,
 649                                 root_unstable_tree + NUMA(rmap_item->nid));
 650                ksm_pages_unshared--;
 651                rmap_item->address &= PAGE_MASK;
 652        }
 653out:
 654        cond_resched();         /* we're called from many long loops */
 655}
 656
 657static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 658                                       struct rmap_item **rmap_list)
 659{
 660        while (*rmap_list) {
 661                struct rmap_item *rmap_item = *rmap_list;
 662                *rmap_list = rmap_item->rmap_list;
 663                remove_rmap_item_from_tree(rmap_item);
 664                free_rmap_item(rmap_item);
 665        }
 666}
 667
 668/*
 669 * Though it's very tempting to unmerge rmap_items from stable tree rather
 670 * than check every pte of a given vma, the locking doesn't quite work for
 671 * that - an rmap_item is assigned to the stable tree after inserting ksm
 672 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 673 * rmap_items from parent to child at fork time (so as not to waste time
 674 * if exit comes before the next scan reaches it).
 675 *
 676 * Similarly, although we'd like to remove rmap_items (so updating counts
 677 * and freeing memory) when unmerging an area, it's easier to leave that
 678 * to the next pass of ksmd - consider, for example, how ksmd might be
 679 * in cmp_and_merge_page on one of the rmap_items we would be removing.
 680 */
 681static int unmerge_ksm_pages(struct vm_area_struct *vma,
 682                             unsigned long start, unsigned long end)
 683{
 684        unsigned long addr;
 685        int err = 0;
 686
 687        for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
 688                if (ksm_test_exit(vma->vm_mm))
 689                        break;
 690                if (signal_pending(current))
 691                        err = -ERESTARTSYS;
 692                else
 693                        err = break_ksm(vma, addr);
 694        }
 695        return err;
 696}
 697
 698#ifdef CONFIG_SYSFS
 699/*
 700 * Only called through the sysfs control interface:
 701 */
 702static int remove_stable_node(struct stable_node *stable_node)
 703{
 704        struct page *page;
 705        int err;
 706
 707        page = get_ksm_page(stable_node, true);
 708        if (!page) {
 709                /*
 710                 * get_ksm_page did remove_node_from_stable_tree itself.
 711                 */
 712                return 0;
 713        }
 714
 715        if (WARN_ON_ONCE(page_mapped(page))) {
 716                /*
 717                 * This should not happen: but if it does, just refuse to let
 718                 * merge_across_nodes be switched - there is no need to panic.
 719                 */
 720                err = -EBUSY;
 721        } else {
 722                /*
 723                 * The stable node did not yet appear stale to get_ksm_page(),
 724                 * since that allows for an unmapped ksm page to be recognized
 725                 * right up until it is freed; but the node is safe to remove.
 726                 * This page might be in a pagevec waiting to be freed,
 727                 * or it might be PageSwapCache (perhaps under writeback),
 728                 * or it might have been removed from swapcache a moment ago.
 729                 */
 730                set_page_stable_node(page, NULL);
 731                remove_node_from_stable_tree(stable_node);
 732                err = 0;
 733        }
 734
 735        unlock_page(page);
 736        put_page(page);
 737        return err;
 738}
 739
 740static int remove_all_stable_nodes(void)
 741{
 742        struct stable_node *stable_node;
 743        struct list_head *this, *next;
 744        int nid;
 745        int err = 0;
 746
 747        for (nid = 0; nid < ksm_nr_node_ids; nid++) {
 748                while (root_stable_tree[nid].rb_node) {
 749                        stable_node = rb_entry(root_stable_tree[nid].rb_node,
 750                                                struct stable_node, node);
 751                        if (remove_stable_node(stable_node)) {
 752                                err = -EBUSY;
 753                                break;  /* proceed to next nid */
 754                        }
 755                        cond_resched();
 756                }
 757        }
 758        list_for_each_safe(this, next, &migrate_nodes) {
 759                stable_node = list_entry(this, struct stable_node, list);
 760                if (remove_stable_node(stable_node))
 761                        err = -EBUSY;
 762                cond_resched();
 763        }
 764        return err;
 765}
 766
 767static int unmerge_and_remove_all_rmap_items(void)
 768{
 769        struct mm_slot *mm_slot;
 770        struct mm_struct *mm;
 771        struct vm_area_struct *vma;
 772        int err = 0;
 773
 774        spin_lock(&ksm_mmlist_lock);
 775        ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
 776                                                struct mm_slot, mm_list);
 777        spin_unlock(&ksm_mmlist_lock);
 778
 779        for (mm_slot = ksm_scan.mm_slot;
 780                        mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
 781                mm = mm_slot->mm;
 782                down_read(&mm->mmap_sem);
 783                for (vma = mm->mmap; vma; vma = vma->vm_next) {
 784                        if (ksm_test_exit(mm))
 785                                break;
 786                        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 787                                continue;
 788                        err = unmerge_ksm_pages(vma,
 789                                                vma->vm_start, vma->vm_end);
 790                        if (err)
 791                                goto error;
 792                }
 793
 794                remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
 795
 796                spin_lock(&ksm_mmlist_lock);
 797                ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
 798                                                struct mm_slot, mm_list);
 799                if (ksm_test_exit(mm)) {
 800                        hash_del(&mm_slot->link);
 801                        list_del(&mm_slot->mm_list);
 802                        spin_unlock(&ksm_mmlist_lock);
 803
 804                        free_mm_slot(mm_slot);
 805                        clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 806                        up_read(&mm->mmap_sem);
 807                        mmdrop(mm);
 808                } else {
 809                        spin_unlock(&ksm_mmlist_lock);
 810                        up_read(&mm->mmap_sem);
 811                }
 812        }
 813
 814        /* Clean up stable nodes, but don't worry if some are still busy */
 815        remove_all_stable_nodes();
 816        ksm_scan.seqnr = 0;
 817        return 0;
 818
 819error:
 820        up_read(&mm->mmap_sem);
 821        spin_lock(&ksm_mmlist_lock);
 822        ksm_scan.mm_slot = &ksm_mm_head;
 823        spin_unlock(&ksm_mmlist_lock);
 824        return err;
 825}
 826#endif /* CONFIG_SYSFS */
 827
 828static u32 calc_checksum(struct page *page)
 829{
 830        u32 checksum;
 831        void *addr = kmap_atomic(page);
 832        checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 833        kunmap_atomic(addr);
 834        return checksum;
 835}
 836
 837static int memcmp_pages(struct page *page1, struct page *page2)
 838{
 839        char *addr1, *addr2;
 840        int ret;
 841
 842        addr1 = kmap_atomic(page1);
 843        addr2 = kmap_atomic(page2);
 844        ret = memcmp(addr1, addr2, PAGE_SIZE);
 845        kunmap_atomic(addr2);
 846        kunmap_atomic(addr1);
 847        return ret;
 848}
 849
 850static inline int pages_identical(struct page *page1, struct page *page2)
 851{
 852        return !memcmp_pages(page1, page2);
 853}
 854
 855static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 856                              pte_t *orig_pte)
 857{
 858        struct mm_struct *mm = vma->vm_mm;
 859        unsigned long addr;
 860        pte_t *ptep;
 861        spinlock_t *ptl;
 862        int swapped;
 863        int err = -EFAULT;
 864        unsigned long mmun_start;       /* For mmu_notifiers */
 865        unsigned long mmun_end;         /* For mmu_notifiers */
 866
 867        addr = page_address_in_vma(page, vma);
 868        if (addr == -EFAULT)
 869                goto out;
 870
 871        BUG_ON(PageTransCompound(page));
 872
 873        mmun_start = addr;
 874        mmun_end   = addr + PAGE_SIZE;
 875        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 876
 877        ptep = page_check_address(page, mm, addr, &ptl, 0);
 878        if (!ptep)
 879                goto out_mn;
 880
 881        if (pte_write(*ptep) || pte_dirty(*ptep)) {
 882                pte_t entry;
 883
 884                swapped = PageSwapCache(page);
 885                flush_cache_page(vma, addr, page_to_pfn(page));
 886                /*
 887                 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 888                 * take any lock, therefore the check that we are going to make
 889                 * with the pagecount against the mapcount is racey and
 890                 * O_DIRECT can happen right after the check.
 891                 * So we clear the pte and flush the tlb before the check
 892                 * this assure us that no O_DIRECT can happen after the check
 893                 * or in the middle of the check.
 894                 */
 895                entry = ptep_clear_flush(vma, addr, ptep);
 896                /*
 897                 * Check that no O_DIRECT or similar I/O is in progress on the
 898                 * page
 899                 */
 900                if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 901                        set_pte_at(mm, addr, ptep, entry);
 902                        goto out_unlock;
 903                }
 904                if (pte_dirty(entry))
 905                        set_page_dirty(page);
 906                entry = pte_mkclean(pte_wrprotect(entry));
 907                set_pte_at_notify(mm, addr, ptep, entry);
 908        }
 909        *orig_pte = *ptep;
 910        err = 0;
 911
 912out_unlock:
 913        pte_unmap_unlock(ptep, ptl);
 914out_mn:
 915        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 916out:
 917        return err;
 918}
 919
 920/**
 921 * replace_page - replace page in vma by new ksm page
 922 * @vma:      vma that holds the pte pointing to page
 923 * @page:     the page we are replacing by kpage
 924 * @kpage:    the ksm page we replace page by
 925 * @orig_pte: the original value of the pte
 926 *
 927 * Returns 0 on success, -EFAULT on failure.
 928 */
 929static int replace_page(struct vm_area_struct *vma, struct page *page,
 930                        struct page *kpage, pte_t orig_pte)
 931{
 932        struct mm_struct *mm = vma->vm_mm;
 933        pmd_t *pmd;
 934        pte_t *ptep;
 935        spinlock_t *ptl;
 936        unsigned long addr;
 937        int err = -EFAULT;
 938        unsigned long mmun_start;       /* For mmu_notifiers */
 939        unsigned long mmun_end;         /* For mmu_notifiers */
 940
 941        addr = page_address_in_vma(page, vma);
 942        if (addr == -EFAULT)
 943                goto out;
 944
 945        pmd = mm_find_pmd(mm, addr);
 946        if (!pmd)
 947                goto out;
 948        BUG_ON(pmd_trans_huge(*pmd));
 949
 950        mmun_start = addr;
 951        mmun_end   = addr + PAGE_SIZE;
 952        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 953
 954        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 955        if (!pte_same(*ptep, orig_pte)) {
 956                pte_unmap_unlock(ptep, ptl);
 957                goto out_mn;
 958        }
 959
 960        get_page(kpage);
 961        page_add_anon_rmap(kpage, vma, addr);
 962
 963        flush_cache_page(vma, addr, pte_pfn(*ptep));
 964        ptep_clear_flush(vma, addr, ptep);
 965        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 966
 967        page_remove_rmap(page);
 968        if (!page_mapped(page))
 969                try_to_free_swap(page);
 970        put_page(page);
 971
 972        pte_unmap_unlock(ptep, ptl);
 973        err = 0;
 974out_mn:
 975        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 976out:
 977        return err;
 978}
 979
 980static int page_trans_compound_anon_split(struct page *page)
 981{
 982        int ret = 0;
 983        struct page *transhuge_head = page_trans_compound_anon(page);
 984        if (transhuge_head) {
 985                /* Get the reference on the head to split it. */
 986                if (get_page_unless_zero(transhuge_head)) {
 987                        /*
 988                         * Recheck we got the reference while the head
 989                         * was still anonymous.
 990                         */
 991                        if (PageAnon(transhuge_head))
 992                                ret = split_huge_page(transhuge_head);
 993                        else
 994                                /*
 995                                 * Retry later if split_huge_page run
 996                                 * from under us.
 997                                 */
 998                                ret = 1;
 999                        put_page(transhuge_head);
1000                } else
1001                        /* Retry later if split_huge_page run from under us. */
1002                        ret = 1;
1003        }
1004        return ret;
1005}
1006
1007/*
1008 * try_to_merge_one_page - take two pages and merge them into one
1009 * @vma: the vma that holds the pte pointing to page
1010 * @page: the PageAnon page that we want to replace with kpage
1011 * @kpage: the PageKsm page that we want to map instead of page,
1012 *         or NULL the first time when we want to use page as kpage.
1013 *
1014 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1015 */
1016static int try_to_merge_one_page(struct vm_area_struct *vma,
1017                                 struct page *page, struct page *kpage)
1018{
1019        pte_t orig_pte = __pte(0);
1020        int err = -EFAULT;
1021
1022        if (page == kpage)                      /* ksm page forked */
1023                return 0;
1024
1025        if (!(vma->vm_flags & VM_MERGEABLE))
1026                goto out;
1027        if (PageTransCompound(page) && page_trans_compound_anon_split(page))
1028                goto out;
1029        BUG_ON(PageTransCompound(page));
1030        if (!PageAnon(page))
1031                goto out;
1032
1033        /*
1034         * We need the page lock to read a stable PageSwapCache in
1035         * write_protect_page().  We use trylock_page() instead of
1036         * lock_page() because we don't want to wait here - we
1037         * prefer to continue scanning and merging different pages,
1038         * then come back to this page when it is unlocked.
1039         */
1040        if (!trylock_page(page))
1041                goto out;
1042        /*
1043         * If this anonymous page is mapped only here, its pte may need
1044         * to be write-protected.  If it's mapped elsewhere, all of its
1045         * ptes are necessarily already write-protected.  But in either
1046         * case, we need to lock and check page_count is not raised.
1047         */
1048        if (write_protect_page(vma, page, &orig_pte) == 0) {
1049                if (!kpage) {
1050                        /*
1051                         * While we hold page lock, upgrade page from
1052                         * PageAnon+anon_vma to PageKsm+NULL stable_node:
1053                         * stable_tree_insert() will update stable_node.
1054                         */
1055                        set_page_stable_node(page, NULL);
1056                        mark_page_accessed(page);
1057                        err = 0;
1058                } else if (pages_identical(page, kpage))
1059                        err = replace_page(vma, page, kpage, orig_pte);
1060        }
1061
1062        if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1063                munlock_vma_page(page);
1064                if (!PageMlocked(kpage)) {
1065                        unlock_page(page);
1066                        lock_page(kpage);
1067                        mlock_vma_page(kpage);
1068                        page = kpage;           /* for final unlock */
1069                }
1070        }
1071
1072        unlock_page(page);
1073out:
1074        return err;
1075}
1076
1077/*
1078 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1079 * but no new kernel page is allocated: kpage must already be a ksm page.
1080 *
1081 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1082 */
1083static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1084                                      struct page *page, struct page *kpage)
1085{
1086        struct mm_struct *mm = rmap_item->mm;
1087        struct vm_area_struct *vma;
1088        int err = -EFAULT;
1089
1090        down_read(&mm->mmap_sem);
1091        if (ksm_test_exit(mm))
1092                goto out;
1093        vma = find_vma(mm, rmap_item->address);
1094        if (!vma || vma->vm_start > rmap_item->address)
1095                goto out;
1096
1097        err = try_to_merge_one_page(vma, page, kpage);
1098        if (err)
1099                goto out;
1100
1101        /* Unstable nid is in union with stable anon_vma: remove first */
1102        remove_rmap_item_from_tree(rmap_item);
1103
1104        /* Must get reference to anon_vma while still holding mmap_sem */
1105        rmap_item->anon_vma = vma->anon_vma;
1106        get_anon_vma(vma->anon_vma);
1107out:
1108        up_read(&mm->mmap_sem);
1109        return err;
1110}
1111
1112/*
1113 * try_to_merge_two_pages - take two identical pages and prepare them
1114 * to be merged into one page.
1115 *
1116 * This function returns the kpage if we successfully merged two identical
1117 * pages into one ksm page, NULL otherwise.
1118 *
1119 * Note that this function upgrades page to ksm page: if one of the pages
1120 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1121 */
1122static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1123                                           struct page *page,
1124                                           struct rmap_item *tree_rmap_item,
1125                                           struct page *tree_page)
1126{
1127        int err;
1128
1129        err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1130        if (!err) {
1131                err = try_to_merge_with_ksm_page(tree_rmap_item,
1132                                                        tree_page, page);
1133                /*
1134                 * If that fails, we have a ksm page with only one pte
1135                 * pointing to it: so break it.
1136                 */
1137                if (err)
1138                        break_cow(rmap_item);
1139        }
1140        return err ? NULL : page;
1141}
1142
1143/*
1144 * stable_tree_search - search for page inside the stable tree
1145 *
1146 * This function checks if there is a page inside the stable tree
1147 * with identical content to the page that we are scanning right now.
1148 *
1149 * This function returns the stable tree node of identical content if found,
1150 * NULL otherwise.
1151 */
1152static struct page *stable_tree_search(struct page *page)
1153{
1154        int nid;
1155        struct rb_root *root;
1156        struct rb_node **new;
1157        struct rb_node *parent;
1158        struct stable_node *stable_node;
1159        struct stable_node *page_node;
1160
1161        page_node = page_stable_node(page);
1162        if (page_node && page_node->head != &migrate_nodes) {
1163                /* ksm page forked */
1164                get_page(page);
1165                return page;
1166        }
1167
1168        nid = get_kpfn_nid(page_to_pfn(page));
1169        root = root_stable_tree + nid;
1170again:
1171        new = &root->rb_node;
1172        parent = NULL;
1173
1174        while (*new) {
1175                struct page *tree_page;
1176                int ret;
1177
1178                cond_resched();
1179                stable_node = rb_entry(*new, struct stable_node, node);
1180                tree_page = get_ksm_page(stable_node, false);
1181                if (!tree_page)
1182                        return NULL;
1183
1184                ret = memcmp_pages(page, tree_page);
1185                put_page(tree_page);
1186
1187                parent = *new;
1188                if (ret < 0)
1189                        new = &parent->rb_left;
1190                else if (ret > 0)
1191                        new = &parent->rb_right;
1192                else {
1193                        /*
1194                         * Lock and unlock the stable_node's page (which
1195                         * might already have been migrated) so that page
1196                         * migration is sure to notice its raised count.
1197                         * It would be more elegant to return stable_node
1198                         * than kpage, but that involves more changes.
1199                         */
1200                        tree_page = get_ksm_page(stable_node, true);
1201                        if (tree_page) {
1202                                unlock_page(tree_page);
1203                                if (get_kpfn_nid(stable_node->kpfn) !=
1204                                                NUMA(stable_node->nid)) {
1205                                        put_page(tree_page);
1206                                        goto replace;
1207                                }
1208                                return tree_page;
1209                        }
1210                        /*
1211                         * There is now a place for page_node, but the tree may
1212                         * have been rebalanced, so re-evaluate parent and new.
1213                         */
1214                        if (page_node)
1215                                goto again;
1216                        return NULL;
1217                }
1218        }
1219
1220        if (!page_node)
1221                return NULL;
1222
1223        list_del(&page_node->list);
1224        DO_NUMA(page_node->nid = nid);
1225        rb_link_node(&page_node->node, parent, new);
1226        rb_insert_color(&page_node->node, root);
1227        get_page(page);
1228        return page;
1229
1230replace:
1231        if (page_node) {
1232                list_del(&page_node->list);
1233                DO_NUMA(page_node->nid = nid);
1234                rb_replace_node(&stable_node->node, &page_node->node, root);
1235                get_page(page);
1236        } else {
1237                rb_erase(&stable_node->node, root);
1238                page = NULL;
1239        }
1240        stable_node->head = &migrate_nodes;
1241        list_add(&stable_node->list, stable_node->head);
1242        return page;
1243}
1244
1245/*
1246 * stable_tree_insert - insert stable tree node pointing to new ksm page
1247 * into the stable tree.
1248 *
1249 * This function returns the stable tree node just allocated on success,
1250 * NULL otherwise.
1251 */
1252static struct stable_node *stable_tree_insert(struct page *kpage)
1253{
1254        int nid;
1255        unsigned long kpfn;
1256        struct rb_root *root;
1257        struct rb_node **new;
1258        struct rb_node *parent = NULL;
1259        struct stable_node *stable_node;
1260
1261        kpfn = page_to_pfn(kpage);
1262        nid = get_kpfn_nid(kpfn);
1263        root = root_stable_tree + nid;
1264        new = &root->rb_node;
1265
1266        while (*new) {
1267                struct page *tree_page;
1268                int ret;
1269
1270                cond_resched();
1271                stable_node = rb_entry(*new, struct stable_node, node);
1272                tree_page = get_ksm_page(stable_node, false);
1273                if (!tree_page)
1274                        return NULL;
1275
1276                ret = memcmp_pages(kpage, tree_page);
1277                put_page(tree_page);
1278
1279                parent = *new;
1280                if (ret < 0)
1281                        new = &parent->rb_left;
1282                else if (ret > 0)
1283                        new = &parent->rb_right;
1284                else {
1285                        /*
1286                         * It is not a bug that stable_tree_search() didn't
1287                         * find this node: because at that time our page was
1288                         * not yet write-protected, so may have changed since.
1289                         */
1290                        return NULL;
1291                }
1292        }
1293
1294        stable_node = alloc_stable_node();
1295        if (!stable_node)
1296                return NULL;
1297
1298        INIT_HLIST_HEAD(&stable_node->hlist);
1299        stable_node->kpfn = kpfn;
1300        set_page_stable_node(kpage, stable_node);
1301        DO_NUMA(stable_node->nid = nid);
1302        rb_link_node(&stable_node->node, parent, new);
1303        rb_insert_color(&stable_node->node, root);
1304
1305        return stable_node;
1306}
1307
1308/*
1309 * unstable_tree_search_insert - search for identical page,
1310 * else insert rmap_item into the unstable tree.
1311 *
1312 * This function searches for a page in the unstable tree identical to the
1313 * page currently being scanned; and if no identical page is found in the
1314 * tree, we insert rmap_item as a new object into the unstable tree.
1315 *
1316 * This function returns pointer to rmap_item found to be identical
1317 * to the currently scanned page, NULL otherwise.
1318 *
1319 * This function does both searching and inserting, because they share
1320 * the same walking algorithm in an rbtree.
1321 */
1322static
1323struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1324                                              struct page *page,
1325                                              struct page **tree_pagep)
1326{
1327        struct rb_node **new;
1328        struct rb_root *root;
1329        struct rb_node *parent = NULL;
1330        int nid;
1331
1332        nid = get_kpfn_nid(page_to_pfn(page));
1333        root = root_unstable_tree + nid;
1334        new = &root->rb_node;
1335
1336        while (*new) {
1337                struct rmap_item *tree_rmap_item;
1338                struct page *tree_page;
1339                int ret;
1340
1341                cond_resched();
1342                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1343                tree_page = get_mergeable_page(tree_rmap_item);
1344                if (IS_ERR_OR_NULL(tree_page))
1345                        return NULL;
1346
1347                /*
1348                 * Don't substitute a ksm page for a forked page.
1349                 */
1350                if (page == tree_page) {
1351                        put_page(tree_page);
1352                        return NULL;
1353                }
1354
1355                ret = memcmp_pages(page, tree_page);
1356
1357                parent = *new;
1358                if (ret < 0) {
1359                        put_page(tree_page);
1360                        new = &parent->rb_left;
1361                } else if (ret > 0) {
1362                        put_page(tree_page);
1363                        new = &parent->rb_right;
1364                } else if (!ksm_merge_across_nodes &&
1365                           page_to_nid(tree_page) != nid) {
1366                        /*
1367                         * If tree_page has been migrated to another NUMA node,
1368                         * it will be flushed out and put in the right unstable
1369                         * tree next time: only merge with it when across_nodes.
1370                         */
1371                        put_page(tree_page);
1372                        return NULL;
1373                } else {
1374                        *tree_pagep = tree_page;
1375                        return tree_rmap_item;
1376                }
1377        }
1378
1379        rmap_item->address |= UNSTABLE_FLAG;
1380        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1381        DO_NUMA(rmap_item->nid = nid);
1382        rb_link_node(&rmap_item->node, parent, new);
1383        rb_insert_color(&rmap_item->node, root);
1384
1385        ksm_pages_unshared++;
1386        return NULL;
1387}
1388
1389/*
1390 * stable_tree_append - add another rmap_item to the linked list of
1391 * rmap_items hanging off a given node of the stable tree, all sharing
1392 * the same ksm page.
1393 */
1394static void stable_tree_append(struct rmap_item *rmap_item,
1395                               struct stable_node *stable_node)
1396{
1397        rmap_item->head = stable_node;
1398        rmap_item->address |= STABLE_FLAG;
1399        hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1400
1401        if (rmap_item->hlist.next)
1402                ksm_pages_sharing++;
1403        else
1404                ksm_pages_shared++;
1405}
1406
1407/*
1408 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1409 * if not, compare checksum to previous and if it's the same, see if page can
1410 * be inserted into the unstable tree, or merged with a page already there and
1411 * both transferred to the stable tree.
1412 *
1413 * @page: the page that we are searching identical page to.
1414 * @rmap_item: the reverse mapping into the virtual address of this page
1415 */
1416static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1417{
1418        struct rmap_item *tree_rmap_item;
1419        struct page *tree_page = NULL;
1420        struct stable_node *stable_node;
1421        struct page *kpage;
1422        unsigned int checksum;
1423        int err;
1424
1425        stable_node = page_stable_node(page);
1426        if (stable_node) {
1427                if (stable_node->head != &migrate_nodes &&
1428                    get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1429                        rb_erase(&stable_node->node,
1430                                 root_stable_tree + NUMA(stable_node->nid));
1431                        stable_node->head = &migrate_nodes;
1432                        list_add(&stable_node->list, stable_node->head);
1433                }
1434                if (stable_node->head != &migrate_nodes &&
1435                    rmap_item->head == stable_node)
1436                        return;
1437        }
1438
1439        /* We first start with searching the page inside the stable tree */
1440        kpage = stable_tree_search(page);
1441        if (kpage == page && rmap_item->head == stable_node) {
1442                put_page(kpage);
1443                return;
1444        }
1445
1446        remove_rmap_item_from_tree(rmap_item);
1447
1448        if (kpage) {
1449                err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1450                if (!err) {
1451                        /*
1452                         * The page was successfully merged:
1453                         * add its rmap_item to the stable tree.
1454                         */
1455                        lock_page(kpage);
1456                        stable_tree_append(rmap_item, page_stable_node(kpage));
1457                        unlock_page(kpage);
1458                }
1459                put_page(kpage);
1460                return;
1461        }
1462
1463        /*
1464         * If the hash value of the page has changed from the last time
1465         * we calculated it, this page is changing frequently: therefore we
1466         * don't want to insert it in the unstable tree, and we don't want
1467         * to waste our time searching for something identical to it there.
1468         */
1469        checksum = calc_checksum(page);
1470        if (rmap_item->oldchecksum != checksum) {
1471                rmap_item->oldchecksum = checksum;
1472                return;
1473        }
1474
1475        tree_rmap_item =
1476                unstable_tree_search_insert(rmap_item, page, &tree_page);
1477        if (tree_rmap_item) {
1478                kpage = try_to_merge_two_pages(rmap_item, page,
1479                                                tree_rmap_item, tree_page);
1480                put_page(tree_page);
1481                if (kpage) {
1482                        /*
1483                         * The pages were successfully merged: insert new
1484                         * node in the stable tree and add both rmap_items.
1485                         */
1486                        lock_page(kpage);
1487                        stable_node = stable_tree_insert(kpage);
1488                        if (stable_node) {
1489                                stable_tree_append(tree_rmap_item, stable_node);
1490                                stable_tree_append(rmap_item, stable_node);
1491                        }
1492                        unlock_page(kpage);
1493
1494                        /*
1495                         * If we fail to insert the page into the stable tree,
1496                         * we will have 2 virtual addresses that are pointing
1497                         * to a ksm page left outside the stable tree,
1498                         * in which case we need to break_cow on both.
1499                         */
1500                        if (!stable_node) {
1501                                break_cow(tree_rmap_item);
1502                                break_cow(rmap_item);
1503                        }
1504                }
1505        }
1506}
1507
1508static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1509                                            struct rmap_item **rmap_list,
1510                                            unsigned long addr)
1511{
1512        struct rmap_item *rmap_item;
1513
1514        while (*rmap_list) {
1515                rmap_item = *rmap_list;
1516                if ((rmap_item->address & PAGE_MASK) == addr)
1517                        return rmap_item;
1518                if (rmap_item->address > addr)
1519                        break;
1520                *rmap_list = rmap_item->rmap_list;
1521                remove_rmap_item_from_tree(rmap_item);
1522                free_rmap_item(rmap_item);
1523        }
1524
1525        rmap_item = alloc_rmap_item();
1526        if (rmap_item) {
1527                /* It has already been zeroed */
1528                rmap_item->mm = mm_slot->mm;
1529                rmap_item->address = addr;
1530                rmap_item->rmap_list = *rmap_list;
1531                *rmap_list = rmap_item;
1532        }
1533        return rmap_item;
1534}
1535
1536static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1537{
1538        struct mm_struct *mm;
1539        struct mm_slot *slot;
1540        struct vm_area_struct *vma;
1541        struct rmap_item *rmap_item;
1542        int nid;
1543
1544        if (list_empty(&ksm_mm_head.mm_list))
1545                return NULL;
1546
1547        slot = ksm_scan.mm_slot;
1548        if (slot == &ksm_mm_head) {
1549                /*
1550                 * A number of pages can hang around indefinitely on per-cpu
1551                 * pagevecs, raised page count preventing write_protect_page
1552                 * from merging them.  Though it doesn't really matter much,
1553                 * it is puzzling to see some stuck in pages_volatile until
1554                 * other activity jostles them out, and they also prevented
1555                 * LTP's KSM test from succeeding deterministically; so drain
1556                 * them here (here rather than on entry to ksm_do_scan(),
1557                 * so we don't IPI too often when pages_to_scan is set low).
1558                 */
1559                lru_add_drain_all();
1560
1561                /*
1562                 * Whereas stale stable_nodes on the stable_tree itself
1563                 * get pruned in the regular course of stable_tree_search(),
1564                 * those moved out to the migrate_nodes list can accumulate:
1565                 * so prune them once before each full scan.
1566                 */
1567                if (!ksm_merge_across_nodes) {
1568                        struct stable_node *stable_node;
1569                        struct list_head *this, *next;
1570                        struct page *page;
1571
1572                        list_for_each_safe(this, next, &migrate_nodes) {
1573                                stable_node = list_entry(this,
1574                                                struct stable_node, list);
1575                                page = get_ksm_page(stable_node, false);
1576                                if (page)
1577                                        put_page(page);
1578                                cond_resched();
1579                        }
1580                }
1581
1582                for (nid = 0; nid < ksm_nr_node_ids; nid++)
1583                        root_unstable_tree[nid] = RB_ROOT;
1584
1585                spin_lock(&ksm_mmlist_lock);
1586                slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1587                ksm_scan.mm_slot = slot;
1588                spin_unlock(&ksm_mmlist_lock);
1589                /*
1590                 * Although we tested list_empty() above, a racing __ksm_exit
1591                 * of the last mm on the list may have removed it since then.
1592                 */
1593                if (slot == &ksm_mm_head)
1594                        return NULL;
1595next_mm:
1596                ksm_scan.address = 0;
1597                ksm_scan.rmap_list = &slot->rmap_list;
1598        }
1599
1600        mm = slot->mm;
1601        down_read(&mm->mmap_sem);
1602        if (ksm_test_exit(mm))
1603                vma = NULL;
1604        else
1605                vma = find_vma(mm, ksm_scan.address);
1606
1607        for (; vma; vma = vma->vm_next) {
1608                if (!(vma->vm_flags & VM_MERGEABLE))
1609                        continue;
1610                if (ksm_scan.address < vma->vm_start)
1611                        ksm_scan.address = vma->vm_start;
1612                if (!vma->anon_vma)
1613                        ksm_scan.address = vma->vm_end;
1614
1615                while (ksm_scan.address < vma->vm_end) {
1616                        if (ksm_test_exit(mm))
1617                                break;
1618                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1619                        if (IS_ERR_OR_NULL(*page)) {
1620                                ksm_scan.address += PAGE_SIZE;
1621                                cond_resched();
1622                                continue;
1623                        }
1624                        if (PageAnon(*page) ||
1625                            page_trans_compound_anon(*page)) {
1626                                flush_anon_page(vma, *page, ksm_scan.address);
1627                                flush_dcache_page(*page);
1628                                rmap_item = get_next_rmap_item(slot,
1629                                        ksm_scan.rmap_list, ksm_scan.address);
1630                                if (rmap_item) {
1631                                        ksm_scan.rmap_list =
1632                                                        &rmap_item->rmap_list;
1633                                        ksm_scan.address += PAGE_SIZE;
1634                                } else
1635                                        put_page(*page);
1636                                up_read(&mm->mmap_sem);
1637                                return rmap_item;
1638                        }
1639                        put_page(*page);
1640                        ksm_scan.address += PAGE_SIZE;
1641                        cond_resched();
1642                }
1643        }
1644
1645        if (ksm_test_exit(mm)) {
1646                ksm_scan.address = 0;
1647                ksm_scan.rmap_list = &slot->rmap_list;
1648        }
1649        /*
1650         * Nuke all the rmap_items that are above this current rmap:
1651         * because there were no VM_MERGEABLE vmas with such addresses.
1652         */
1653        remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1654
1655        spin_lock(&ksm_mmlist_lock);
1656        ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1657                                                struct mm_slot, mm_list);
1658        if (ksm_scan.address == 0) {
1659                /*
1660                 * We've completed a full scan of all vmas, holding mmap_sem
1661                 * throughout, and found no VM_MERGEABLE: so do the same as
1662                 * __ksm_exit does to remove this mm from all our lists now.
1663                 * This applies either when cleaning up after __ksm_exit
1664                 * (but beware: we can reach here even before __ksm_exit),
1665                 * or when all VM_MERGEABLE areas have been unmapped (and
1666                 * mmap_sem then protects against race with MADV_MERGEABLE).
1667                 */
1668                hash_del(&slot->link);
1669                list_del(&slot->mm_list);
1670                spin_unlock(&ksm_mmlist_lock);
1671
1672                free_mm_slot(slot);
1673                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1674                up_read(&mm->mmap_sem);
1675                mmdrop(mm);
1676        } else {
1677                spin_unlock(&ksm_mmlist_lock);
1678                up_read(&mm->mmap_sem);
1679        }
1680
1681        /* Repeat until we've completed scanning the whole list */
1682        slot = ksm_scan.mm_slot;
1683        if (slot != &ksm_mm_head)
1684                goto next_mm;
1685
1686        ksm_scan.seqnr++;
1687        return NULL;
1688}
1689
1690/**
1691 * ksm_do_scan  - the ksm scanner main worker function.
1692 * @scan_npages - number of pages we want to scan before we return.
1693 */
1694static void ksm_do_scan(unsigned int scan_npages)
1695{
1696        struct rmap_item *rmap_item;
1697        struct page *uninitialized_var(page);
1698
1699        while (scan_npages-- && likely(!freezing(current))) {
1700                cond_resched();
1701                rmap_item = scan_get_next_rmap_item(&page);
1702                if (!rmap_item)
1703                        return;
1704                cmp_and_merge_page(page, rmap_item);
1705                put_page(page);
1706        }
1707}
1708
1709static int ksmd_should_run(void)
1710{
1711        return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1712}
1713
1714static int ksm_scan_thread(void *nothing)
1715{
1716        set_freezable();
1717        set_user_nice(current, 5);
1718
1719        while (!kthread_should_stop()) {
1720                mutex_lock(&ksm_thread_mutex);
1721                wait_while_offlining();
1722                if (ksmd_should_run())
1723                        ksm_do_scan(ksm_thread_pages_to_scan);
1724                mutex_unlock(&ksm_thread_mutex);
1725
1726                try_to_freeze();
1727
1728                if (ksmd_should_run()) {
1729                        schedule_timeout_interruptible(
1730                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
1731                } else {
1732                        wait_event_freezable(ksm_thread_wait,
1733                                ksmd_should_run() || kthread_should_stop());
1734                }
1735        }
1736        return 0;
1737}
1738
1739int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1740                unsigned long end, int advice, unsigned long *vm_flags)
1741{
1742        struct mm_struct *mm = vma->vm_mm;
1743        int err;
1744
1745        switch (advice) {
1746        case MADV_MERGEABLE:
1747                /*
1748                 * Be somewhat over-protective for now!
1749                 */
1750                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1751                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1752                                 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
1753                        return 0;               /* just ignore the advice */
1754
1755#ifdef VM_SAO
1756                if (*vm_flags & VM_SAO)
1757                        return 0;
1758#endif
1759
1760                if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1761                        err = __ksm_enter(mm);
1762                        if (err)
1763                                return err;
1764                }
1765
1766                *vm_flags |= VM_MERGEABLE;
1767                break;
1768
1769        case MADV_UNMERGEABLE:
1770                if (!(*vm_flags & VM_MERGEABLE))
1771                        return 0;               /* just ignore the advice */
1772
1773                if (vma->anon_vma) {
1774                        err = unmerge_ksm_pages(vma, start, end);
1775                        if (err)
1776                                return err;
1777                }
1778
1779                *vm_flags &= ~VM_MERGEABLE;
1780                break;
1781        }
1782
1783        return 0;
1784}
1785
1786int __ksm_enter(struct mm_struct *mm)
1787{
1788        struct mm_slot *mm_slot;
1789        int needs_wakeup;
1790
1791        mm_slot = alloc_mm_slot();
1792        if (!mm_slot)
1793                return -ENOMEM;
1794
1795        /* Check ksm_run too?  Would need tighter locking */
1796        needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1797
1798        spin_lock(&ksm_mmlist_lock);
1799        insert_to_mm_slots_hash(mm, mm_slot);
1800        /*
1801         * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1802         * insert just behind the scanning cursor, to let the area settle
1803         * down a little; when fork is followed by immediate exec, we don't
1804         * want ksmd to waste time setting up and tearing down an rmap_list.
1805         *
1806         * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1807         * scanning cursor, otherwise KSM pages in newly forked mms will be
1808         * missed: then we might as well insert at the end of the list.
1809         */
1810        if (ksm_run & KSM_RUN_UNMERGE)
1811                list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1812        else
1813                list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1814        spin_unlock(&ksm_mmlist_lock);
1815
1816        set_bit(MMF_VM_MERGEABLE, &mm->flags);
1817        atomic_inc(&mm->mm_count);
1818
1819        if (needs_wakeup)
1820                wake_up_interruptible(&ksm_thread_wait);
1821
1822        return 0;
1823}
1824
1825void __ksm_exit(struct mm_struct *mm)
1826{
1827        struct mm_slot *mm_slot;
1828        int easy_to_free = 0;
1829
1830        /*
1831         * This process is exiting: if it's straightforward (as is the
1832         * case when ksmd was never running), free mm_slot immediately.
1833         * But if it's at the cursor or has rmap_items linked to it, use
1834         * mmap_sem to synchronize with any break_cows before pagetables
1835         * are freed, and leave the mm_slot on the list for ksmd to free.
1836         * Beware: ksm may already have noticed it exiting and freed the slot.
1837         */
1838
1839        spin_lock(&ksm_mmlist_lock);
1840        mm_slot = get_mm_slot(mm);
1841        if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1842                if (!mm_slot->rmap_list) {
1843                        hash_del(&mm_slot->link);
1844                        list_del(&mm_slot->mm_list);
1845                        easy_to_free = 1;
1846                } else {
1847                        list_move(&mm_slot->mm_list,
1848                                  &ksm_scan.mm_slot->mm_list);
1849                }
1850        }
1851        spin_unlock(&ksm_mmlist_lock);
1852
1853        if (easy_to_free) {
1854                free_mm_slot(mm_slot);
1855                clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1856                mmdrop(mm);
1857        } else if (mm_slot) {
1858                down_write(&mm->mmap_sem);
1859                up_write(&mm->mmap_sem);
1860        }
1861}
1862
1863struct page *ksm_might_need_to_copy(struct page *page,
1864                        struct vm_area_struct *vma, unsigned long address)
1865{
1866        struct anon_vma *anon_vma = page_anon_vma(page);
1867        struct page *new_page;
1868
1869        if (PageKsm(page)) {
1870                if (page_stable_node(page) &&
1871                    !(ksm_run & KSM_RUN_UNMERGE))
1872                        return page;    /* no need to copy it */
1873        } else if (!anon_vma) {
1874                return page;            /* no need to copy it */
1875        } else if (anon_vma->root == vma->anon_vma->root &&
1876                 page->index == linear_page_index(vma, address)) {
1877                return page;            /* still no need to copy it */
1878        }
1879        if (!PageUptodate(page))
1880                return page;            /* let do_swap_page report the error */
1881
1882        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1883        if (new_page) {
1884                copy_user_highpage(new_page, page, address, vma);
1885
1886                SetPageDirty(new_page);
1887                __SetPageUptodate(new_page);
1888                __set_page_locked(new_page);
1889        }
1890
1891        return new_page;
1892}
1893
1894int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1895                        unsigned long *vm_flags)
1896{
1897        struct stable_node *stable_node;
1898        struct rmap_item *rmap_item;
1899        unsigned int mapcount = page_mapcount(page);
1900        int referenced = 0;
1901        int search_new_forks = 0;
1902
1903        VM_BUG_ON(!PageKsm(page));
1904        VM_BUG_ON(!PageLocked(page));
1905
1906        stable_node = page_stable_node(page);
1907        if (!stable_node)
1908                return 0;
1909again:
1910        hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1911                struct anon_vma *anon_vma = rmap_item->anon_vma;
1912                struct anon_vma_chain *vmac;
1913                struct vm_area_struct *vma;
1914
1915                anon_vma_lock_read(anon_vma);
1916                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1917                                               0, ULONG_MAX) {
1918                        vma = vmac->vma;
1919                        if (rmap_item->address < vma->vm_start ||
1920                            rmap_item->address >= vma->vm_end)
1921                                continue;
1922                        /*
1923                         * Initially we examine only the vma which covers this
1924                         * rmap_item; but later, if there is still work to do,
1925                         * we examine covering vmas in other mms: in case they
1926                         * were forked from the original since ksmd passed.
1927                         */
1928                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1929                                continue;
1930
1931                        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1932                                continue;
1933
1934                        referenced += page_referenced_one(page, vma,
1935                                rmap_item->address, &mapcount, vm_flags);
1936                        if (!search_new_forks || !mapcount)
1937                                break;
1938                }
1939                anon_vma_unlock_read(anon_vma);
1940                if (!mapcount)
1941                        goto out;
1942        }
1943        if (!search_new_forks++)
1944                goto again;
1945out:
1946        return referenced;
1947}
1948
1949int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1950{
1951        struct stable_node *stable_node;
1952        struct rmap_item *rmap_item;
1953        int ret = SWAP_AGAIN;
1954        int search_new_forks = 0;
1955
1956        VM_BUG_ON(!PageKsm(page));
1957        VM_BUG_ON(!PageLocked(page));
1958
1959        stable_node = page_stable_node(page);
1960        if (!stable_node)
1961                return SWAP_FAIL;
1962again:
1963        hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1964                struct anon_vma *anon_vma = rmap_item->anon_vma;
1965                struct anon_vma_chain *vmac;
1966                struct vm_area_struct *vma;
1967
1968                anon_vma_lock_read(anon_vma);
1969                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1970                                               0, ULONG_MAX) {
1971                        vma = vmac->vma;
1972                        if (rmap_item->address < vma->vm_start ||
1973                            rmap_item->address >= vma->vm_end)
1974                                continue;
1975                        /*
1976                         * Initially we examine only the vma which covers this
1977                         * rmap_item; but later, if there is still work to do,
1978                         * we examine covering vmas in other mms: in case they
1979                         * were forked from the original since ksmd passed.
1980                         */
1981                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1982                                continue;
1983
1984                        ret = try_to_unmap_one(page, vma,
1985                                        rmap_item->address, flags);
1986                        if (ret != SWAP_AGAIN || !page_mapped(page)) {
1987                                anon_vma_unlock_read(anon_vma);
1988                                goto out;
1989                        }
1990                }
1991                anon_vma_unlock_read(anon_vma);
1992        }
1993        if (!search_new_forks++)
1994                goto again;
1995out:
1996        return ret;
1997}
1998
1999#ifdef CONFIG_MIGRATION
2000int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
2001                  struct vm_area_struct *, unsigned long, void *), void *arg)
2002{
2003        struct stable_node *stable_node;
2004        struct rmap_item *rmap_item;
2005        int ret = SWAP_AGAIN;
2006        int search_new_forks = 0;
2007
2008        VM_BUG_ON(!PageKsm(page));
2009        VM_BUG_ON(!PageLocked(page));
2010
2011        stable_node = page_stable_node(page);
2012        if (!stable_node)
2013                return ret;
2014again:
2015        hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2016                struct anon_vma *anon_vma = rmap_item->anon_vma;
2017                struct anon_vma_chain *vmac;
2018                struct vm_area_struct *vma;
2019
2020                anon_vma_lock_read(anon_vma);
2021                anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2022                                               0, ULONG_MAX) {
2023                        vma = vmac->vma;
2024                        if (rmap_item->address < vma->vm_start ||
2025                            rmap_item->address >= vma->vm_end)
2026                                continue;
2027                        /*
2028                         * Initially we examine only the vma which covers this
2029                         * rmap_item; but later, if there is still work to do,
2030                         * we examine covering vmas in other mms: in case they
2031                         * were forked from the original since ksmd passed.
2032                         */
2033                        if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2034                                continue;
2035
2036                        ret = rmap_one(page, vma, rmap_item->address, arg);
2037                        if (ret != SWAP_AGAIN) {
2038                                anon_vma_unlock_read(anon_vma);
2039                                goto out;
2040                        }
2041                }
2042                anon_vma_unlock_read(anon_vma);
2043        }
2044        if (!search_new_forks++)
2045                goto again;
2046out:
2047        return ret;
2048}
2049
2050void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2051{
2052        struct stable_node *stable_node;
2053
2054        VM_BUG_ON(!PageLocked(oldpage));
2055        VM_BUG_ON(!PageLocked(newpage));
2056        VM_BUG_ON(newpage->mapping != oldpage->mapping);
2057
2058        stable_node = page_stable_node(newpage);
2059        if (stable_node) {
2060                VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
2061                stable_node->kpfn = page_to_pfn(newpage);
2062                /*
2063                 * newpage->mapping was set in advance; now we need smp_wmb()
2064                 * to make sure that the new stable_node->kpfn is visible
2065                 * to get_ksm_page() before it can see that oldpage->mapping
2066                 * has gone stale (or that PageSwapCache has been cleared).
2067                 */
2068                smp_wmb();
2069                set_page_stable_node(oldpage, NULL);
2070        }
2071}
2072#endif /* CONFIG_MIGRATION */
2073
2074#ifdef CONFIG_MEMORY_HOTREMOVE
2075static int just_wait(void *word)
2076{
2077        schedule();
2078        return 0;
2079}
2080
2081static void wait_while_offlining(void)
2082{
2083        while (ksm_run & KSM_RUN_OFFLINE) {
2084                mutex_unlock(&ksm_thread_mutex);
2085                wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2086                                just_wait, TASK_UNINTERRUPTIBLE);
2087                mutex_lock(&ksm_thread_mutex);
2088        }
2089}
2090
2091static void ksm_check_stable_tree(unsigned long start_pfn,
2092                                  unsigned long end_pfn)
2093{
2094        struct stable_node *stable_node;
2095        struct list_head *this, *next;
2096        struct rb_node *node;
2097        int nid;
2098
2099        for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2100                node = rb_first(root_stable_tree + nid);
2101                while (node) {
2102                        stable_node = rb_entry(node, struct stable_node, node);
2103                        if (stable_node->kpfn >= start_pfn &&
2104                            stable_node->kpfn < end_pfn) {
2105                                /*
2106                                 * Don't get_ksm_page, page has already gone:
2107                                 * which is why we keep kpfn instead of page*
2108                                 */
2109                                remove_node_from_stable_tree(stable_node);
2110                                node = rb_first(root_stable_tree + nid);
2111                        } else
2112                                node = rb_next(node);
2113                        cond_resched();
2114                }
2115        }
2116        list_for_each_safe(this, next, &migrate_nodes) {
2117                stable_node = list_entry(this, struct stable_node, list);
2118                if (stable_node->kpfn >= start_pfn &&
2119                    stable_node->kpfn < end_pfn)
2120                        remove_node_from_stable_tree(stable_node);
2121                cond_resched();
2122        }
2123}
2124
2125static int ksm_memory_callback(struct notifier_block *self,
2126                               unsigned long action, void *arg)
2127{
2128        struct memory_notify *mn = arg;
2129
2130        switch (action) {
2131        case MEM_GOING_OFFLINE:
2132                /*
2133                 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2134                 * and remove_all_stable_nodes() while memory is going offline:
2135                 * it is unsafe for them to touch the stable tree at this time.
2136                 * But unmerge_ksm_pages(), rmap lookups and other entry points
2137                 * which do not need the ksm_thread_mutex are all safe.
2138                 */
2139                mutex_lock(&ksm_thread_mutex);
2140                ksm_run |= KSM_RUN_OFFLINE;
2141                mutex_unlock(&ksm_thread_mutex);
2142                break;
2143
2144        case MEM_OFFLINE:
2145                /*
2146                 * Most of the work is done by page migration; but there might
2147                 * be a few stable_nodes left over, still pointing to struct
2148                 * pages which have been offlined: prune those from the tree,
2149                 * otherwise get_ksm_page() might later try to access a
2150                 * non-existent struct page.
2151                 */
2152                ksm_check_stable_tree(mn->start_pfn,
2153                                      mn->start_pfn + mn->nr_pages);
2154                /* fallthrough */
2155
2156        case MEM_CANCEL_OFFLINE:
2157                mutex_lock(&ksm_thread_mutex);
2158                ksm_run &= ~KSM_RUN_OFFLINE;
2159                mutex_unlock(&ksm_thread_mutex);
2160
2161                smp_mb();       /* wake_up_bit advises this */
2162                wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2163                break;
2164        }
2165        return NOTIFY_OK;
2166}
2167#else
2168static void wait_while_offlining(void)
2169{
2170}
2171#endif /* CONFIG_MEMORY_HOTREMOVE */
2172
2173#ifdef CONFIG_SYSFS
2174/*
2175 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2176 */
2177
2178#define KSM_ATTR_RO(_name) \
2179        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2180#define KSM_ATTR(_name) \
2181        static struct kobj_attribute _name##_attr = \
2182                __ATTR(_name, 0644, _name##_show, _name##_store)
2183
2184static ssize_t sleep_millisecs_show(struct kobject *kobj,
2185                                    struct kobj_attribute *attr, char *buf)
2186{
2187        return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2188}
2189
2190static ssize_t sleep_millisecs_store(struct kobject *kobj,
2191                                     struct kobj_attribute *attr,
2192                                     const char *buf, size_t count)
2193{
2194        unsigned long msecs;
2195        int err;
2196
2197        err = strict_strtoul(buf, 10, &msecs);
2198        if (err || msecs > UINT_MAX)
2199                return -EINVAL;
2200
2201        ksm_thread_sleep_millisecs = msecs;
2202
2203        return count;
2204}
2205KSM_ATTR(sleep_millisecs);
2206
2207static ssize_t pages_to_scan_show(struct kobject *kobj,
2208                                  struct kobj_attribute *attr, char *buf)
2209{
2210        return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2211}
2212
2213static ssize_t pages_to_scan_store(struct kobject *kobj,
2214                                   struct kobj_attribute *attr,
2215                                   const char *buf, size_t count)
2216{
2217        int err;
2218        unsigned long nr_pages;
2219
2220        err = strict_strtoul(buf, 10, &nr_pages);
2221        if (err || nr_pages > UINT_MAX)
2222                return -EINVAL;
2223
2224        ksm_thread_pages_to_scan = nr_pages;
2225
2226        return count;
2227}
2228KSM_ATTR(pages_to_scan);
2229
2230static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2231                        char *buf)
2232{
2233        return sprintf(buf, "%lu\n", ksm_run);
2234}
2235
2236static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2237                         const char *buf, size_t count)
2238{
2239        int err;
2240        unsigned long flags;
2241
2242        err = strict_strtoul(buf, 10, &flags);
2243        if (err || flags > UINT_MAX)
2244                return -EINVAL;
2245        if (flags > KSM_RUN_UNMERGE)
2246                return -EINVAL;
2247
2248        /*
2249         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2250         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2251         * breaking COW to free the pages_shared (but leaves mm_slots
2252         * on the list for when ksmd may be set running again).
2253         */
2254
2255        mutex_lock(&ksm_thread_mutex);
2256        wait_while_offlining();
2257        if (ksm_run != flags) {
2258                ksm_run = flags;
2259                if (flags & KSM_RUN_UNMERGE) {
2260                        set_current_oom_origin();
2261                        err = unmerge_and_remove_all_rmap_items();
2262                        clear_current_oom_origin();
2263                        if (err) {
2264                                ksm_run = KSM_RUN_STOP;
2265                                count = err;
2266                        }
2267                }
2268        }
2269        mutex_unlock(&ksm_thread_mutex);
2270
2271        if (flags & KSM_RUN_MERGE)
2272                wake_up_interruptible(&ksm_thread_wait);
2273
2274        return count;
2275}
2276KSM_ATTR(run);
2277
2278#ifdef CONFIG_NUMA
2279static ssize_t merge_across_nodes_show(struct kobject *kobj,
2280                                struct kobj_attribute *attr, char *buf)
2281{
2282        return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2283}
2284
2285static ssize_t merge_across_nodes_store(struct kobject *kobj,
2286                                   struct kobj_attribute *attr,
2287                                   const char *buf, size_t count)
2288{
2289        int err;
2290        unsigned long knob;
2291
2292        err = kstrtoul(buf, 10, &knob);
2293        if (err)
2294                return err;
2295        if (knob > 1)
2296                return -EINVAL;
2297
2298        mutex_lock(&ksm_thread_mutex);
2299        wait_while_offlining();
2300        if (ksm_merge_across_nodes != knob) {
2301                if (ksm_pages_shared || remove_all_stable_nodes())
2302                        err = -EBUSY;
2303                else if (root_stable_tree == one_stable_tree) {
2304                        struct rb_root *buf;
2305                        /*
2306                         * This is the first time that we switch away from the
2307                         * default of merging across nodes: must now allocate
2308                         * a buffer to hold as many roots as may be needed.
2309                         * Allocate stable and unstable together:
2310                         * MAXSMP NODES_SHIFT 10 will use 16kB.
2311                         */
2312                        buf = kcalloc(nr_node_ids + nr_node_ids,
2313                                sizeof(*buf), GFP_KERNEL | __GFP_ZERO);
2314                        /* Let us assume that RB_ROOT is NULL is zero */
2315                        if (!buf)
2316                                err = -ENOMEM;
2317                        else {
2318                                root_stable_tree = buf;
2319                                root_unstable_tree = buf + nr_node_ids;
2320                                /* Stable tree is empty but not the unstable */
2321                                root_unstable_tree[0] = one_unstable_tree[0];
2322                        }
2323                }
2324                if (!err) {
2325                        ksm_merge_across_nodes = knob;
2326                        ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2327                }
2328        }
2329        mutex_unlock(&ksm_thread_mutex);
2330
2331        return err ? err : count;
2332}
2333KSM_ATTR(merge_across_nodes);
2334#endif
2335
2336static ssize_t pages_shared_show(struct kobject *kobj,
2337                                 struct kobj_attribute *attr, char *buf)
2338{
2339        return sprintf(buf, "%lu\n", ksm_pages_shared);
2340}
2341KSM_ATTR_RO(pages_shared);
2342
2343static ssize_t pages_sharing_show(struct kobject *kobj,
2344                                  struct kobj_attribute *attr, char *buf)
2345{
2346        return sprintf(buf, "%lu\n", ksm_pages_sharing);
2347}
2348KSM_ATTR_RO(pages_sharing);
2349
2350static ssize_t pages_unshared_show(struct kobject *kobj,
2351                                   struct kobj_attribute *attr, char *buf)
2352{
2353        return sprintf(buf, "%lu\n", ksm_pages_unshared);
2354}
2355KSM_ATTR_RO(pages_unshared);
2356
2357static ssize_t pages_volatile_show(struct kobject *kobj,
2358                                   struct kobj_attribute *attr, char *buf)
2359{
2360        long ksm_pages_volatile;
2361
2362        ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2363                                - ksm_pages_sharing - ksm_pages_unshared;
2364        /*
2365         * It was not worth any locking to calculate that statistic,
2366         * but it might therefore sometimes be negative: conceal that.
2367         */
2368        if (ksm_pages_volatile < 0)
2369                ksm_pages_volatile = 0;
2370        return sprintf(buf, "%ld\n", ksm_pages_volatile);
2371}
2372KSM_ATTR_RO(pages_volatile);
2373
2374static ssize_t full_scans_show(struct kobject *kobj,
2375                               struct kobj_attribute *attr, char *buf)
2376{
2377        return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2378}
2379KSM_ATTR_RO(full_scans);
2380
2381static struct attribute *ksm_attrs[] = {
2382        &sleep_millisecs_attr.attr,
2383        &pages_to_scan_attr.attr,
2384        &run_attr.attr,
2385        &pages_shared_attr.attr,
2386        &pages_sharing_attr.attr,
2387        &pages_unshared_attr.attr,
2388        &pages_volatile_attr.attr,
2389        &full_scans_attr.attr,
2390#ifdef CONFIG_NUMA
2391        &merge_across_nodes_attr.attr,
2392#endif
2393        NULL,
2394};
2395
2396static struct attribute_group ksm_attr_group = {
2397        .attrs = ksm_attrs,
2398        .name = "ksm",
2399};
2400#endif /* CONFIG_SYSFS */
2401
2402static int __init ksm_init(void)
2403{
2404        struct task_struct *ksm_thread;
2405        int err;
2406
2407        err = ksm_slab_init();
2408        if (err)
2409                goto out;
2410
2411        ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2412        if (IS_ERR(ksm_thread)) {
2413                printk(KERN_ERR "ksm: creating kthread failed\n");
2414                err = PTR_ERR(ksm_thread);
2415                goto out_free;
2416        }
2417
2418#ifdef CONFIG_SYSFS
2419        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2420        if (err) {
2421                printk(KERN_ERR "ksm: register sysfs failed\n");
2422                kthread_stop(ksm_thread);
2423                goto out_free;
2424        }
2425#else
2426        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2427
2428#endif /* CONFIG_SYSFS */
2429
2430#ifdef CONFIG_MEMORY_HOTREMOVE
2431        /* There is no significance to this priority 100 */
2432        hotplug_memory_notifier(ksm_memory_callback, 100);
2433#endif
2434        return 0;
2435
2436out_free:
2437        ksm_slab_free();
2438out:
2439        return err;
2440}
2441module_init(ksm_init)
2442
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