Root/mm/ksm.c

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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