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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Memory merging support.
4 *
5 * This code enables dynamic sharing of identical pages found in different
6 * memory areas, even if they are not shared by fork()
7 *
8 * Copyright (C) 2008-2009 Red Hat, Inc.
9 * Authors:
10 * Izik Eidus
11 * Andrea Arcangeli
12 * Chris Wright
13 * Hugh Dickins
14 */
15
16#include <linux/errno.h>
17#include <linux/mm.h>
18#include <linux/fs.h>
19#include <linux/mman.h>
20#include <linux/sched.h>
21#include <linux/sched/mm.h>
22#include <linux/sched/coredump.h>
23#include <linux/rwsem.h>
24#include <linux/pagemap.h>
25#include <linux/rmap.h>
26#include <linux/spinlock.h>
27#include <linux/xxhash.h>
28#include <linux/delay.h>
29#include <linux/kthread.h>
30#include <linux/wait.h>
31#include <linux/slab.h>
32#include <linux/rbtree.h>
33#include <linux/memory.h>
34#include <linux/mmu_notifier.h>
35#include <linux/swap.h>
36#include <linux/ksm.h>
37#include <linux/hashtable.h>
38#include <linux/freezer.h>
39#include <linux/oom.h>
40#include <linux/numa.h>
41
42#include <asm/tlbflush.h>
43#include "internal.h"
44
45#ifdef CONFIG_NUMA
46#define NUMA(x) (x)
47#define DO_NUMA(x) do { (x); } while (0)
48#else
49#define NUMA(x) (0)
50#define DO_NUMA(x) do { } while (0)
51#endif
52
53/**
54 * DOC: Overview
55 *
56 * A few notes about the KSM scanning process,
57 * to make it easier to understand the data structures below:
58 *
59 * In order to reduce excessive scanning, KSM sorts the memory pages by their
60 * contents into a data structure that holds pointers to the pages' locations.
61 *
62 * Since the contents of the pages may change at any moment, KSM cannot just
63 * insert the pages into a normal sorted tree and expect it to find anything.
64 * Therefore KSM uses two data structures - the stable and the unstable tree.
65 *
66 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
67 * by their contents. Because each such page is write-protected, searching on
68 * this tree is fully assured to be working (except when pages are unmapped),
69 * and therefore this tree is called the stable tree.
70 *
71 * The stable tree node includes information required for reverse
72 * mapping from a KSM page to virtual addresses that map this page.
73 *
74 * In order to avoid large latencies of the rmap walks on KSM pages,
75 * KSM maintains two types of nodes in the stable tree:
76 *
77 * * the regular nodes that keep the reverse mapping structures in a
78 * linked list
79 * * the "chains" that link nodes ("dups") that represent the same
80 * write protected memory content, but each "dup" corresponds to a
81 * different KSM page copy of that content
82 *
83 * Internally, the regular nodes, "dups" and "chains" are represented
84 * using the same struct stable_node structure.
85 *
86 * In addition to the stable tree, KSM uses a second data structure called the
87 * unstable tree: this tree holds pointers to pages which have been found to
88 * be "unchanged for a period of time". The unstable tree sorts these pages
89 * by their contents, but since they are not write-protected, KSM cannot rely
90 * upon the unstable tree to work correctly - the unstable tree is liable to
91 * be corrupted as its contents are modified, and so it is called unstable.
92 *
93 * KSM solves this problem by several techniques:
94 *
95 * 1) The unstable tree is flushed every time KSM completes scanning all
96 * memory areas, and then the tree is rebuilt again from the beginning.
97 * 2) KSM will only insert into the unstable tree, pages whose hash value
98 * has not changed since the previous scan of all memory areas.
99 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
100 * colors of the nodes and not on their contents, assuring that even when
101 * the tree gets "corrupted" it won't get out of balance, so scanning time
102 * remains the same (also, searching and inserting nodes in an rbtree uses
103 * the same algorithm, so we have no overhead when we flush and rebuild).
104 * 4) KSM never flushes the stable tree, which means that even if it were to
105 * take 10 attempts to find a page in the unstable tree, once it is found,
106 * it is secured in the stable tree. (When we scan a new page, we first
107 * compare it against the stable tree, and then against the unstable tree.)
108 *
109 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
110 * stable trees and multiple unstable trees: one of each for each NUMA node.
111 */
112
113/**
114 * struct mm_slot - ksm information per mm that is being scanned
115 * @link: link to the mm_slots hash list
116 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
117 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
118 * @mm: the mm that this information is valid for
119 */
120struct mm_slot {
121 struct hlist_node link;
122 struct list_head mm_list;
123 struct rmap_item *rmap_list;
124 struct mm_struct *mm;
125};
126
127/**
128 * struct ksm_scan - cursor for scanning
129 * @mm_slot: the current mm_slot we are scanning
130 * @address: the next address inside that to be scanned
131 * @rmap_list: link to the next rmap to be scanned in the rmap_list
132 * @seqnr: count of completed full scans (needed when removing unstable node)
133 *
134 * There is only the one ksm_scan instance of this cursor structure.
135 */
136struct ksm_scan {
137 struct mm_slot *mm_slot;
138 unsigned long address;
139 struct rmap_item **rmap_list;
140 unsigned long seqnr;
141};
142
143/**
144 * struct stable_node - node of the stable rbtree
145 * @node: rb node of this ksm page in the stable tree
146 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
147 * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
148 * @list: linked into migrate_nodes, pending placement in the proper node tree
149 * @hlist: hlist head of rmap_items using this ksm page
150 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
151 * @chain_prune_time: time of the last full garbage collection
152 * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
153 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
154 */
155struct stable_node {
156 union {
157 struct rb_node node; /* when node of stable tree */
158 struct { /* when listed for migration */
159 struct list_head *head;
160 struct {
161 struct hlist_node hlist_dup;
162 struct list_head list;
163 };
164 };
165 };
166 struct hlist_head hlist;
167 union {
168 unsigned long kpfn;
169 unsigned long chain_prune_time;
170 };
171 /*
172 * STABLE_NODE_CHAIN can be any negative number in
173 * rmap_hlist_len negative range, but better not -1 to be able
174 * to reliably detect underflows.
175 */
176#define STABLE_NODE_CHAIN -1024
177 int rmap_hlist_len;
178#ifdef CONFIG_NUMA
179 int nid;
180#endif
181};
182
183/**
184 * struct rmap_item - reverse mapping item for virtual addresses
185 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
186 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
187 * @nid: NUMA node id of unstable tree in which linked (may not match page)
188 * @mm: the memory structure this rmap_item is pointing into
189 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
190 * @oldchecksum: previous checksum of the page at that virtual address
191 * @node: rb node of this rmap_item in the unstable tree
192 * @head: pointer to stable_node heading this list in the stable tree
193 * @hlist: link into hlist of rmap_items hanging off that stable_node
194 */
195struct rmap_item {
196 struct rmap_item *rmap_list;
197 union {
198 struct anon_vma *anon_vma; /* when stable */
199#ifdef CONFIG_NUMA
200 int nid; /* when node of unstable tree */
201#endif
202 };
203 struct mm_struct *mm;
204 unsigned long address; /* + low bits used for flags below */
205 unsigned int oldchecksum; /* when unstable */
206 union {
207 struct rb_node node; /* when node of unstable tree */
208 struct { /* when listed from stable tree */
209 struct stable_node *head;
210 struct hlist_node hlist;
211 };
212 };
213};
214
215#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
216#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
217#define STABLE_FLAG 0x200 /* is listed from the stable tree */
218
219/* The stable and unstable tree heads */
220static struct rb_root one_stable_tree[1] = { RB_ROOT };
221static struct rb_root one_unstable_tree[1] = { RB_ROOT };
222static struct rb_root *root_stable_tree = one_stable_tree;
223static struct rb_root *root_unstable_tree = one_unstable_tree;
224
225/* Recently migrated nodes of stable tree, pending proper placement */
226static LIST_HEAD(migrate_nodes);
227#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
228
229#define MM_SLOTS_HASH_BITS 10
230static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
231
232static struct mm_slot ksm_mm_head = {
233 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
234};
235static struct ksm_scan ksm_scan = {
236 .mm_slot = &ksm_mm_head,
237};
238
239static struct kmem_cache *rmap_item_cache;
240static struct kmem_cache *stable_node_cache;
241static struct kmem_cache *mm_slot_cache;
242
243/* The number of nodes in the stable tree */
244static unsigned long ksm_pages_shared;
245
246/* The number of page slots additionally sharing those nodes */
247static unsigned long ksm_pages_sharing;
248
249/* The number of nodes in the unstable tree */
250static unsigned long ksm_pages_unshared;
251
252/* The number of rmap_items in use: to calculate pages_volatile */
253static unsigned long ksm_rmap_items;
254
255/* The number of stable_node chains */
256static unsigned long ksm_stable_node_chains;
257
258/* The number of stable_node dups linked to the stable_node chains */
259static unsigned long ksm_stable_node_dups;
260
261/* Delay in pruning stale stable_node_dups in the stable_node_chains */
262static int ksm_stable_node_chains_prune_millisecs = 2000;
263
264/* Maximum number of page slots sharing a stable node */
265static int ksm_max_page_sharing = 256;
266
267/* Number of pages ksmd should scan in one batch */
268static unsigned int ksm_thread_pages_to_scan = 100;
269
270/* Milliseconds ksmd should sleep between batches */
271static unsigned int ksm_thread_sleep_millisecs = 20;
272
273/* Checksum of an empty (zeroed) page */
274static unsigned int zero_checksum __read_mostly;
275
276/* Whether to merge empty (zeroed) pages with actual zero pages */
277static bool ksm_use_zero_pages __read_mostly;
278
279#ifdef CONFIG_NUMA
280/* Zeroed when merging across nodes is not allowed */
281static unsigned int ksm_merge_across_nodes = 1;
282static int ksm_nr_node_ids = 1;
283#else
284#define ksm_merge_across_nodes 1U
285#define ksm_nr_node_ids 1
286#endif
287
288#define KSM_RUN_STOP 0
289#define KSM_RUN_MERGE 1
290#define KSM_RUN_UNMERGE 2
291#define KSM_RUN_OFFLINE 4
292static unsigned long ksm_run = KSM_RUN_STOP;
293static void wait_while_offlining(void);
294
295static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
296static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
297static DEFINE_MUTEX(ksm_thread_mutex);
298static DEFINE_SPINLOCK(ksm_mmlist_lock);
299
300#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
301 sizeof(struct __struct), __alignof__(struct __struct),\
302 (__flags), NULL)
303
304static int __init ksm_slab_init(void)
305{
306 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
307 if (!rmap_item_cache)
308 goto out;
309
310 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
311 if (!stable_node_cache)
312 goto out_free1;
313
314 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
315 if (!mm_slot_cache)
316 goto out_free2;
317
318 return 0;
319
320out_free2:
321 kmem_cache_destroy(stable_node_cache);
322out_free1:
323 kmem_cache_destroy(rmap_item_cache);
324out:
325 return -ENOMEM;
326}
327
328static void __init ksm_slab_free(void)
329{
330 kmem_cache_destroy(mm_slot_cache);
331 kmem_cache_destroy(stable_node_cache);
332 kmem_cache_destroy(rmap_item_cache);
333 mm_slot_cache = NULL;
334}
335
336static __always_inline bool is_stable_node_chain(struct stable_node *chain)
337{
338 return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
339}
340
341static __always_inline bool is_stable_node_dup(struct stable_node *dup)
342{
343 return dup->head == STABLE_NODE_DUP_HEAD;
344}
345
346static inline void stable_node_chain_add_dup(struct stable_node *dup,
347 struct stable_node *chain)
348{
349 VM_BUG_ON(is_stable_node_dup(dup));
350 dup->head = STABLE_NODE_DUP_HEAD;
351 VM_BUG_ON(!is_stable_node_chain(chain));
352 hlist_add_head(&dup->hlist_dup, &chain->hlist);
353 ksm_stable_node_dups++;
354}
355
356static inline void __stable_node_dup_del(struct stable_node *dup)
357{
358 VM_BUG_ON(!is_stable_node_dup(dup));
359 hlist_del(&dup->hlist_dup);
360 ksm_stable_node_dups--;
361}
362
363static inline void stable_node_dup_del(struct stable_node *dup)
364{
365 VM_BUG_ON(is_stable_node_chain(dup));
366 if (is_stable_node_dup(dup))
367 __stable_node_dup_del(dup);
368 else
369 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
370#ifdef CONFIG_DEBUG_VM
371 dup->head = NULL;
372#endif
373}
374
375static inline struct rmap_item *alloc_rmap_item(void)
376{
377 struct rmap_item *rmap_item;
378
379 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
380 __GFP_NORETRY | __GFP_NOWARN);
381 if (rmap_item)
382 ksm_rmap_items++;
383 return rmap_item;
384}
385
386static inline void free_rmap_item(struct rmap_item *rmap_item)
387{
388 ksm_rmap_items--;
389 rmap_item->mm = NULL; /* debug safety */
390 kmem_cache_free(rmap_item_cache, rmap_item);
391}
392
393static inline struct stable_node *alloc_stable_node(void)
394{
395 /*
396 * The allocation can take too long with GFP_KERNEL when memory is under
397 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
398 * grants access to memory reserves, helping to avoid this problem.
399 */
400 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
401}
402
403static inline void free_stable_node(struct stable_node *stable_node)
404{
405 VM_BUG_ON(stable_node->rmap_hlist_len &&
406 !is_stable_node_chain(stable_node));
407 kmem_cache_free(stable_node_cache, stable_node);
408}
409
410static inline struct mm_slot *alloc_mm_slot(void)
411{
412 if (!mm_slot_cache) /* initialization failed */
413 return NULL;
414 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
415}
416
417static inline void free_mm_slot(struct mm_slot *mm_slot)
418{
419 kmem_cache_free(mm_slot_cache, mm_slot);
420}
421
422static struct mm_slot *get_mm_slot(struct mm_struct *mm)
423{
424 struct mm_slot *slot;
425
426 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
427 if (slot->mm == mm)
428 return slot;
429
430 return NULL;
431}
432
433static void insert_to_mm_slots_hash(struct mm_struct *mm,
434 struct mm_slot *mm_slot)
435{
436 mm_slot->mm = mm;
437 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
438}
439
440/*
441 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
442 * page tables after it has passed through ksm_exit() - which, if necessary,
443 * takes mmap_lock briefly to serialize against them. ksm_exit() does not set
444 * a special flag: they can just back out as soon as mm_users goes to zero.
445 * ksm_test_exit() is used throughout to make this test for exit: in some
446 * places for correctness, in some places just to avoid unnecessary work.
447 */
448static inline bool ksm_test_exit(struct mm_struct *mm)
449{
450 return atomic_read(&mm->mm_users) == 0;
451}
452
453/*
454 * We use break_ksm to break COW on a ksm page: it's a stripped down
455 *
456 * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
457 * put_page(page);
458 *
459 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
460 * in case the application has unmapped and remapped mm,addr meanwhile.
461 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
462 * mmap of /dev/mem, where we would not want to touch it.
463 *
464 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
465 * of the process that owns 'vma'. We also do not want to enforce
466 * protection keys here anyway.
467 */
468static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
469{
470 struct page *page;
471 vm_fault_t ret = 0;
472
473 do {
474 cond_resched();
475 page = follow_page(vma, addr,
476 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
477 if (IS_ERR_OR_NULL(page))
478 break;
479 if (PageKsm(page))
480 ret = handle_mm_fault(vma, addr,
481 FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
482 NULL);
483 else
484 ret = VM_FAULT_WRITE;
485 put_page(page);
486 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
487 /*
488 * We must loop because handle_mm_fault() may back out if there's
489 * any difficulty e.g. if pte accessed bit gets updated concurrently.
490 *
491 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
492 * COW has been broken, even if the vma does not permit VM_WRITE;
493 * but note that a concurrent fault might break PageKsm for us.
494 *
495 * VM_FAULT_SIGBUS could occur if we race with truncation of the
496 * backing file, which also invalidates anonymous pages: that's
497 * okay, that truncation will have unmapped the PageKsm for us.
498 *
499 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
500 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
501 * current task has TIF_MEMDIE set, and will be OOM killed on return
502 * to user; and ksmd, having no mm, would never be chosen for that.
503 *
504 * But if the mm is in a limited mem_cgroup, then the fault may fail
505 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
506 * even ksmd can fail in this way - though it's usually breaking ksm
507 * just to undo a merge it made a moment before, so unlikely to oom.
508 *
509 * That's a pity: we might therefore have more kernel pages allocated
510 * than we're counting as nodes in the stable tree; but ksm_do_scan
511 * will retry to break_cow on each pass, so should recover the page
512 * in due course. The important thing is to not let VM_MERGEABLE
513 * be cleared while any such pages might remain in the area.
514 */
515 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
516}
517
518static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
519 unsigned long addr)
520{
521 struct vm_area_struct *vma;
522 if (ksm_test_exit(mm))
523 return NULL;
524 vma = vma_lookup(mm, addr);
525 if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
526 return NULL;
527 return vma;
528}
529
530static void break_cow(struct rmap_item *rmap_item)
531{
532 struct mm_struct *mm = rmap_item->mm;
533 unsigned long addr = rmap_item->address;
534 struct vm_area_struct *vma;
535
536 /*
537 * It is not an accident that whenever we want to break COW
538 * to undo, we also need to drop a reference to the anon_vma.
539 */
540 put_anon_vma(rmap_item->anon_vma);
541
542 mmap_read_lock(mm);
543 vma = find_mergeable_vma(mm, addr);
544 if (vma)
545 break_ksm(vma, addr);
546 mmap_read_unlock(mm);
547}
548
549static struct page *get_mergeable_page(struct rmap_item *rmap_item)
550{
551 struct mm_struct *mm = rmap_item->mm;
552 unsigned long addr = rmap_item->address;
553 struct vm_area_struct *vma;
554 struct page *page;
555
556 mmap_read_lock(mm);
557 vma = find_mergeable_vma(mm, addr);
558 if (!vma)
559 goto out;
560
561 page = follow_page(vma, addr, FOLL_GET);
562 if (IS_ERR_OR_NULL(page))
563 goto out;
564 if (PageAnon(page)) {
565 flush_anon_page(vma, page, addr);
566 flush_dcache_page(page);
567 } else {
568 put_page(page);
569out:
570 page = NULL;
571 }
572 mmap_read_unlock(mm);
573 return page;
574}
575
576/*
577 * This helper is used for getting right index into array of tree roots.
578 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
579 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
580 * every node has its own stable and unstable tree.
581 */
582static inline int get_kpfn_nid(unsigned long kpfn)
583{
584 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
585}
586
587static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
588 struct rb_root *root)
589{
590 struct stable_node *chain = alloc_stable_node();
591 VM_BUG_ON(is_stable_node_chain(dup));
592 if (likely(chain)) {
593 INIT_HLIST_HEAD(&chain->hlist);
594 chain->chain_prune_time = jiffies;
595 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
596#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
597 chain->nid = NUMA_NO_NODE; /* debug */
598#endif
599 ksm_stable_node_chains++;
600
601 /*
602 * Put the stable node chain in the first dimension of
603 * the stable tree and at the same time remove the old
604 * stable node.
605 */
606 rb_replace_node(&dup->node, &chain->node, root);
607
608 /*
609 * Move the old stable node to the second dimension
610 * queued in the hlist_dup. The invariant is that all
611 * dup stable_nodes in the chain->hlist point to pages
612 * that are write protected and have the exact same
613 * content.
614 */
615 stable_node_chain_add_dup(dup, chain);
616 }
617 return chain;
618}
619
620static inline void free_stable_node_chain(struct stable_node *chain,
621 struct rb_root *root)
622{
623 rb_erase(&chain->node, root);
624 free_stable_node(chain);
625 ksm_stable_node_chains--;
626}
627
628static void remove_node_from_stable_tree(struct stable_node *stable_node)
629{
630 struct rmap_item *rmap_item;
631
632 /* check it's not STABLE_NODE_CHAIN or negative */
633 BUG_ON(stable_node->rmap_hlist_len < 0);
634
635 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
636 if (rmap_item->hlist.next)
637 ksm_pages_sharing--;
638 else
639 ksm_pages_shared--;
640 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
641 stable_node->rmap_hlist_len--;
642 put_anon_vma(rmap_item->anon_vma);
643 rmap_item->address &= PAGE_MASK;
644 cond_resched();
645 }
646
647 /*
648 * We need the second aligned pointer of the migrate_nodes
649 * list_head to stay clear from the rb_parent_color union
650 * (aligned and different than any node) and also different
651 * from &migrate_nodes. This will verify that future list.h changes
652 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
653 */
654#if defined(GCC_VERSION) && GCC_VERSION >= 40903
655 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
656 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
657#endif
658
659 if (stable_node->head == &migrate_nodes)
660 list_del(&stable_node->list);
661 else
662 stable_node_dup_del(stable_node);
663 free_stable_node(stable_node);
664}
665
666enum get_ksm_page_flags {
667 GET_KSM_PAGE_NOLOCK,
668 GET_KSM_PAGE_LOCK,
669 GET_KSM_PAGE_TRYLOCK
670};
671
672/*
673 * get_ksm_page: checks if the page indicated by the stable node
674 * is still its ksm page, despite having held no reference to it.
675 * In which case we can trust the content of the page, and it
676 * returns the gotten page; but if the page has now been zapped,
677 * remove the stale node from the stable tree and return NULL.
678 * But beware, the stable node's page might be being migrated.
679 *
680 * You would expect the stable_node to hold a reference to the ksm page.
681 * But if it increments the page's count, swapping out has to wait for
682 * ksmd to come around again before it can free the page, which may take
683 * seconds or even minutes: much too unresponsive. So instead we use a
684 * "keyhole reference": access to the ksm page from the stable node peeps
685 * out through its keyhole to see if that page still holds the right key,
686 * pointing back to this stable node. This relies on freeing a PageAnon
687 * page to reset its page->mapping to NULL, and relies on no other use of
688 * a page to put something that might look like our key in page->mapping.
689 * is on its way to being freed; but it is an anomaly to bear in mind.
690 */
691static struct page *get_ksm_page(struct stable_node *stable_node,
692 enum get_ksm_page_flags flags)
693{
694 struct page *page;
695 void *expected_mapping;
696 unsigned long kpfn;
697
698 expected_mapping = (void *)((unsigned long)stable_node |
699 PAGE_MAPPING_KSM);
700again:
701 kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
702 page = pfn_to_page(kpfn);
703 if (READ_ONCE(page->mapping) != expected_mapping)
704 goto stale;
705
706 /*
707 * We cannot do anything with the page while its refcount is 0.
708 * Usually 0 means free, or tail of a higher-order page: in which
709 * case this node is no longer referenced, and should be freed;
710 * however, it might mean that the page is under page_ref_freeze().
711 * The __remove_mapping() case is easy, again the node is now stale;
712 * the same is in reuse_ksm_page() case; but if page is swapcache
713 * in migrate_page_move_mapping(), it might still be our page,
714 * in which case it's essential to keep the node.
715 */
716 while (!get_page_unless_zero(page)) {
717 /*
718 * Another check for page->mapping != expected_mapping would
719 * work here too. We have chosen the !PageSwapCache test to
720 * optimize the common case, when the page is or is about to
721 * be freed: PageSwapCache is cleared (under spin_lock_irq)
722 * in the ref_freeze section of __remove_mapping(); but Anon
723 * page->mapping reset to NULL later, in free_pages_prepare().
724 */
725 if (!PageSwapCache(page))
726 goto stale;
727 cpu_relax();
728 }
729
730 if (READ_ONCE(page->mapping) != expected_mapping) {
731 put_page(page);
732 goto stale;
733 }
734
735 if (flags == GET_KSM_PAGE_TRYLOCK) {
736 if (!trylock_page(page)) {
737 put_page(page);
738 return ERR_PTR(-EBUSY);
739 }
740 } else if (flags == GET_KSM_PAGE_LOCK)
741 lock_page(page);
742
743 if (flags != GET_KSM_PAGE_NOLOCK) {
744 if (READ_ONCE(page->mapping) != expected_mapping) {
745 unlock_page(page);
746 put_page(page);
747 goto stale;
748 }
749 }
750 return page;
751
752stale:
753 /*
754 * We come here from above when page->mapping or !PageSwapCache
755 * suggests that the node is stale; but it might be under migration.
756 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
757 * before checking whether node->kpfn has been changed.
758 */
759 smp_rmb();
760 if (READ_ONCE(stable_node->kpfn) != kpfn)
761 goto again;
762 remove_node_from_stable_tree(stable_node);
763 return NULL;
764}
765
766/*
767 * Removing rmap_item from stable or unstable tree.
768 * This function will clean the information from the stable/unstable tree.
769 */
770static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
771{
772 if (rmap_item->address & STABLE_FLAG) {
773 struct stable_node *stable_node;
774 struct page *page;
775
776 stable_node = rmap_item->head;
777 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
778 if (!page)
779 goto out;
780
781 hlist_del(&rmap_item->hlist);
782 unlock_page(page);
783 put_page(page);
784
785 if (!hlist_empty(&stable_node->hlist))
786 ksm_pages_sharing--;
787 else
788 ksm_pages_shared--;
789 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
790 stable_node->rmap_hlist_len--;
791
792 put_anon_vma(rmap_item->anon_vma);
793 rmap_item->head = NULL;
794 rmap_item->address &= PAGE_MASK;
795
796 } else if (rmap_item->address & UNSTABLE_FLAG) {
797 unsigned char age;
798 /*
799 * Usually ksmd can and must skip the rb_erase, because
800 * root_unstable_tree was already reset to RB_ROOT.
801 * But be careful when an mm is exiting: do the rb_erase
802 * if this rmap_item was inserted by this scan, rather
803 * than left over from before.
804 */
805 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
806 BUG_ON(age > 1);
807 if (!age)
808 rb_erase(&rmap_item->node,
809 root_unstable_tree + NUMA(rmap_item->nid));
810 ksm_pages_unshared--;
811 rmap_item->address &= PAGE_MASK;
812 }
813out:
814 cond_resched(); /* we're called from many long loops */
815}
816
817static void remove_trailing_rmap_items(struct rmap_item **rmap_list)
818{
819 while (*rmap_list) {
820 struct rmap_item *rmap_item = *rmap_list;
821 *rmap_list = rmap_item->rmap_list;
822 remove_rmap_item_from_tree(rmap_item);
823 free_rmap_item(rmap_item);
824 }
825}
826
827/*
828 * Though it's very tempting to unmerge rmap_items from stable tree rather
829 * than check every pte of a given vma, the locking doesn't quite work for
830 * that - an rmap_item is assigned to the stable tree after inserting ksm
831 * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
832 * rmap_items from parent to child at fork time (so as not to waste time
833 * if exit comes before the next scan reaches it).
834 *
835 * Similarly, although we'd like to remove rmap_items (so updating counts
836 * and freeing memory) when unmerging an area, it's easier to leave that
837 * to the next pass of ksmd - consider, for example, how ksmd might be
838 * in cmp_and_merge_page on one of the rmap_items we would be removing.
839 */
840static int unmerge_ksm_pages(struct vm_area_struct *vma,
841 unsigned long start, unsigned long end)
842{
843 unsigned long addr;
844 int err = 0;
845
846 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
847 if (ksm_test_exit(vma->vm_mm))
848 break;
849 if (signal_pending(current))
850 err = -ERESTARTSYS;
851 else
852 err = break_ksm(vma, addr);
853 }
854 return err;
855}
856
857static inline struct stable_node *page_stable_node(struct page *page)
858{
859 return PageKsm(page) ? page_rmapping(page) : NULL;
860}
861
862static inline void set_page_stable_node(struct page *page,
863 struct stable_node *stable_node)
864{
865 page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
866}
867
868#ifdef CONFIG_SYSFS
869/*
870 * Only called through the sysfs control interface:
871 */
872static int remove_stable_node(struct stable_node *stable_node)
873{
874 struct page *page;
875 int err;
876
877 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
878 if (!page) {
879 /*
880 * get_ksm_page did remove_node_from_stable_tree itself.
881 */
882 return 0;
883 }
884
885 /*
886 * Page could be still mapped if this races with __mmput() running in
887 * between ksm_exit() and exit_mmap(). Just refuse to let
888 * merge_across_nodes/max_page_sharing be switched.
889 */
890 err = -EBUSY;
891 if (!page_mapped(page)) {
892 /*
893 * The stable node did not yet appear stale to get_ksm_page(),
894 * since that allows for an unmapped ksm page to be recognized
895 * right up until it is freed; but the node is safe to remove.
896 * This page might be in a pagevec waiting to be freed,
897 * or it might be PageSwapCache (perhaps under writeback),
898 * or it might have been removed from swapcache a moment ago.
899 */
900 set_page_stable_node(page, NULL);
901 remove_node_from_stable_tree(stable_node);
902 err = 0;
903 }
904
905 unlock_page(page);
906 put_page(page);
907 return err;
908}
909
910static int remove_stable_node_chain(struct stable_node *stable_node,
911 struct rb_root *root)
912{
913 struct stable_node *dup;
914 struct hlist_node *hlist_safe;
915
916 if (!is_stable_node_chain(stable_node)) {
917 VM_BUG_ON(is_stable_node_dup(stable_node));
918 if (remove_stable_node(stable_node))
919 return true;
920 else
921 return false;
922 }
923
924 hlist_for_each_entry_safe(dup, hlist_safe,
925 &stable_node->hlist, hlist_dup) {
926 VM_BUG_ON(!is_stable_node_dup(dup));
927 if (remove_stable_node(dup))
928 return true;
929 }
930 BUG_ON(!hlist_empty(&stable_node->hlist));
931 free_stable_node_chain(stable_node, root);
932 return false;
933}
934
935static int remove_all_stable_nodes(void)
936{
937 struct stable_node *stable_node, *next;
938 int nid;
939 int err = 0;
940
941 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
942 while (root_stable_tree[nid].rb_node) {
943 stable_node = rb_entry(root_stable_tree[nid].rb_node,
944 struct stable_node, node);
945 if (remove_stable_node_chain(stable_node,
946 root_stable_tree + nid)) {
947 err = -EBUSY;
948 break; /* proceed to next nid */
949 }
950 cond_resched();
951 }
952 }
953 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
954 if (remove_stable_node(stable_node))
955 err = -EBUSY;
956 cond_resched();
957 }
958 return err;
959}
960
961static int unmerge_and_remove_all_rmap_items(void)
962{
963 struct mm_slot *mm_slot;
964 struct mm_struct *mm;
965 struct vm_area_struct *vma;
966 int err = 0;
967
968 spin_lock(&ksm_mmlist_lock);
969 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
970 struct mm_slot, mm_list);
971 spin_unlock(&ksm_mmlist_lock);
972
973 for (mm_slot = ksm_scan.mm_slot;
974 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
975 mm = mm_slot->mm;
976 mmap_read_lock(mm);
977 for (vma = mm->mmap; vma; vma = vma->vm_next) {
978 if (ksm_test_exit(mm))
979 break;
980 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
981 continue;
982 err = unmerge_ksm_pages(vma,
983 vma->vm_start, vma->vm_end);
984 if (err)
985 goto error;
986 }
987
988 remove_trailing_rmap_items(&mm_slot->rmap_list);
989 mmap_read_unlock(mm);
990
991 spin_lock(&ksm_mmlist_lock);
992 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
993 struct mm_slot, mm_list);
994 if (ksm_test_exit(mm)) {
995 hash_del(&mm_slot->link);
996 list_del(&mm_slot->mm_list);
997 spin_unlock(&ksm_mmlist_lock);
998
999 free_mm_slot(mm_slot);
1000 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1001 mmdrop(mm);
1002 } else
1003 spin_unlock(&ksm_mmlist_lock);
1004 }
1005
1006 /* Clean up stable nodes, but don't worry if some are still busy */
1007 remove_all_stable_nodes();
1008 ksm_scan.seqnr = 0;
1009 return 0;
1010
1011error:
1012 mmap_read_unlock(mm);
1013 spin_lock(&ksm_mmlist_lock);
1014 ksm_scan.mm_slot = &ksm_mm_head;
1015 spin_unlock(&ksm_mmlist_lock);
1016 return err;
1017}
1018#endif /* CONFIG_SYSFS */
1019
1020static u32 calc_checksum(struct page *page)
1021{
1022 u32 checksum;
1023 void *addr = kmap_atomic(page);
1024 checksum = xxhash(addr, PAGE_SIZE, 0);
1025 kunmap_atomic(addr);
1026 return checksum;
1027}
1028
1029static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1030 pte_t *orig_pte)
1031{
1032 struct mm_struct *mm = vma->vm_mm;
1033 struct page_vma_mapped_walk pvmw = {
1034 .page = page,
1035 .vma = vma,
1036 };
1037 int swapped;
1038 int err = -EFAULT;
1039 struct mmu_notifier_range range;
1040
1041 pvmw.address = page_address_in_vma(page, vma);
1042 if (pvmw.address == -EFAULT)
1043 goto out;
1044
1045 BUG_ON(PageTransCompound(page));
1046
1047 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1048 pvmw.address,
1049 pvmw.address + PAGE_SIZE);
1050 mmu_notifier_invalidate_range_start(&range);
1051
1052 if (!page_vma_mapped_walk(&pvmw))
1053 goto out_mn;
1054 if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1055 goto out_unlock;
1056
1057 if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1058 (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1059 mm_tlb_flush_pending(mm)) {
1060 pte_t entry;
1061
1062 swapped = PageSwapCache(page);
1063 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1064 /*
1065 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1066 * take any lock, therefore the check that we are going to make
1067 * with the pagecount against the mapcount is racy and
1068 * O_DIRECT can happen right after the check.
1069 * So we clear the pte and flush the tlb before the check
1070 * this assure us that no O_DIRECT can happen after the check
1071 * or in the middle of the check.
1072 *
1073 * No need to notify as we are downgrading page table to read
1074 * only not changing it to point to a new page.
1075 *
1076 * See Documentation/vm/mmu_notifier.rst
1077 */
1078 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1079 /*
1080 * Check that no O_DIRECT or similar I/O is in progress on the
1081 * page
1082 */
1083 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1084 set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1085 goto out_unlock;
1086 }
1087 if (pte_dirty(entry))
1088 set_page_dirty(page);
1089
1090 if (pte_protnone(entry))
1091 entry = pte_mkclean(pte_clear_savedwrite(entry));
1092 else
1093 entry = pte_mkclean(pte_wrprotect(entry));
1094 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1095 }
1096 *orig_pte = *pvmw.pte;
1097 err = 0;
1098
1099out_unlock:
1100 page_vma_mapped_walk_done(&pvmw);
1101out_mn:
1102 mmu_notifier_invalidate_range_end(&range);
1103out:
1104 return err;
1105}
1106
1107/**
1108 * replace_page - replace page in vma by new ksm page
1109 * @vma: vma that holds the pte pointing to page
1110 * @page: the page we are replacing by kpage
1111 * @kpage: the ksm page we replace page by
1112 * @orig_pte: the original value of the pte
1113 *
1114 * Returns 0 on success, -EFAULT on failure.
1115 */
1116static int replace_page(struct vm_area_struct *vma, struct page *page,
1117 struct page *kpage, pte_t orig_pte)
1118{
1119 struct mm_struct *mm = vma->vm_mm;
1120 pmd_t *pmd;
1121 pte_t *ptep;
1122 pte_t newpte;
1123 spinlock_t *ptl;
1124 unsigned long addr;
1125 int err = -EFAULT;
1126 struct mmu_notifier_range range;
1127
1128 addr = page_address_in_vma(page, vma);
1129 if (addr == -EFAULT)
1130 goto out;
1131
1132 pmd = mm_find_pmd(mm, addr);
1133 if (!pmd)
1134 goto out;
1135
1136 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1137 addr + PAGE_SIZE);
1138 mmu_notifier_invalidate_range_start(&range);
1139
1140 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1141 if (!pte_same(*ptep, orig_pte)) {
1142 pte_unmap_unlock(ptep, ptl);
1143 goto out_mn;
1144 }
1145
1146 /*
1147 * No need to check ksm_use_zero_pages here: we can only have a
1148 * zero_page here if ksm_use_zero_pages was enabled already.
1149 */
1150 if (!is_zero_pfn(page_to_pfn(kpage))) {
1151 get_page(kpage);
1152 page_add_anon_rmap(kpage, vma, addr, false);
1153 newpte = mk_pte(kpage, vma->vm_page_prot);
1154 } else {
1155 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1156 vma->vm_page_prot));
1157 /*
1158 * We're replacing an anonymous page with a zero page, which is
1159 * not anonymous. We need to do proper accounting otherwise we
1160 * will get wrong values in /proc, and a BUG message in dmesg
1161 * when tearing down the mm.
1162 */
1163 dec_mm_counter(mm, MM_ANONPAGES);
1164 }
1165
1166 flush_cache_page(vma, addr, pte_pfn(*ptep));
1167 /*
1168 * No need to notify as we are replacing a read only page with another
1169 * read only page with the same content.
1170 *
1171 * See Documentation/vm/mmu_notifier.rst
1172 */
1173 ptep_clear_flush(vma, addr, ptep);
1174 set_pte_at_notify(mm, addr, ptep, newpte);
1175
1176 page_remove_rmap(page, false);
1177 if (!page_mapped(page))
1178 try_to_free_swap(page);
1179 put_page(page);
1180
1181 pte_unmap_unlock(ptep, ptl);
1182 err = 0;
1183out_mn:
1184 mmu_notifier_invalidate_range_end(&range);
1185out:
1186 return err;
1187}
1188
1189/*
1190 * try_to_merge_one_page - take two pages and merge them into one
1191 * @vma: the vma that holds the pte pointing to page
1192 * @page: the PageAnon page that we want to replace with kpage
1193 * @kpage: the PageKsm page that we want to map instead of page,
1194 * or NULL the first time when we want to use page as kpage.
1195 *
1196 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1197 */
1198static int try_to_merge_one_page(struct vm_area_struct *vma,
1199 struct page *page, struct page *kpage)
1200{
1201 pte_t orig_pte = __pte(0);
1202 int err = -EFAULT;
1203
1204 if (page == kpage) /* ksm page forked */
1205 return 0;
1206
1207 if (!PageAnon(page))
1208 goto out;
1209
1210 /*
1211 * We need the page lock to read a stable PageSwapCache in
1212 * write_protect_page(). We use trylock_page() instead of
1213 * lock_page() because we don't want to wait here - we
1214 * prefer to continue scanning and merging different pages,
1215 * then come back to this page when it is unlocked.
1216 */
1217 if (!trylock_page(page))
1218 goto out;
1219
1220 if (PageTransCompound(page)) {
1221 if (split_huge_page(page))
1222 goto out_unlock;
1223 }
1224
1225 /*
1226 * If this anonymous page is mapped only here, its pte may need
1227 * to be write-protected. If it's mapped elsewhere, all of its
1228 * ptes are necessarily already write-protected. But in either
1229 * case, we need to lock and check page_count is not raised.
1230 */
1231 if (write_protect_page(vma, page, &orig_pte) == 0) {
1232 if (!kpage) {
1233 /*
1234 * While we hold page lock, upgrade page from
1235 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1236 * stable_tree_insert() will update stable_node.
1237 */
1238 set_page_stable_node(page, NULL);
1239 mark_page_accessed(page);
1240 /*
1241 * Page reclaim just frees a clean page with no dirty
1242 * ptes: make sure that the ksm page would be swapped.
1243 */
1244 if (!PageDirty(page))
1245 SetPageDirty(page);
1246 err = 0;
1247 } else if (pages_identical(page, kpage))
1248 err = replace_page(vma, page, kpage, orig_pte);
1249 }
1250
1251 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1252 munlock_vma_page(page);
1253 if (!PageMlocked(kpage)) {
1254 unlock_page(page);
1255 lock_page(kpage);
1256 mlock_vma_page(kpage);
1257 page = kpage; /* for final unlock */
1258 }
1259 }
1260
1261out_unlock:
1262 unlock_page(page);
1263out:
1264 return err;
1265}
1266
1267/*
1268 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1269 * but no new kernel page is allocated: kpage must already be a ksm page.
1270 *
1271 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1272 */
1273static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1274 struct page *page, struct page *kpage)
1275{
1276 struct mm_struct *mm = rmap_item->mm;
1277 struct vm_area_struct *vma;
1278 int err = -EFAULT;
1279
1280 mmap_read_lock(mm);
1281 vma = find_mergeable_vma(mm, rmap_item->address);
1282 if (!vma)
1283 goto out;
1284
1285 err = try_to_merge_one_page(vma, page, kpage);
1286 if (err)
1287 goto out;
1288
1289 /* Unstable nid is in union with stable anon_vma: remove first */
1290 remove_rmap_item_from_tree(rmap_item);
1291
1292 /* Must get reference to anon_vma while still holding mmap_lock */
1293 rmap_item->anon_vma = vma->anon_vma;
1294 get_anon_vma(vma->anon_vma);
1295out:
1296 mmap_read_unlock(mm);
1297 return err;
1298}
1299
1300/*
1301 * try_to_merge_two_pages - take two identical pages and prepare them
1302 * to be merged into one page.
1303 *
1304 * This function returns the kpage if we successfully merged two identical
1305 * pages into one ksm page, NULL otherwise.
1306 *
1307 * Note that this function upgrades page to ksm page: if one of the pages
1308 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1309 */
1310static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1311 struct page *page,
1312 struct rmap_item *tree_rmap_item,
1313 struct page *tree_page)
1314{
1315 int err;
1316
1317 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1318 if (!err) {
1319 err = try_to_merge_with_ksm_page(tree_rmap_item,
1320 tree_page, page);
1321 /*
1322 * If that fails, we have a ksm page with only one pte
1323 * pointing to it: so break it.
1324 */
1325 if (err)
1326 break_cow(rmap_item);
1327 }
1328 return err ? NULL : page;
1329}
1330
1331static __always_inline
1332bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1333{
1334 VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1335 /*
1336 * Check that at least one mapping still exists, otherwise
1337 * there's no much point to merge and share with this
1338 * stable_node, as the underlying tree_page of the other
1339 * sharer is going to be freed soon.
1340 */
1341 return stable_node->rmap_hlist_len &&
1342 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1343}
1344
1345static __always_inline
1346bool is_page_sharing_candidate(struct stable_node *stable_node)
1347{
1348 return __is_page_sharing_candidate(stable_node, 0);
1349}
1350
1351static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1352 struct stable_node **_stable_node,
1353 struct rb_root *root,
1354 bool prune_stale_stable_nodes)
1355{
1356 struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1357 struct hlist_node *hlist_safe;
1358 struct page *_tree_page, *tree_page = NULL;
1359 int nr = 0;
1360 int found_rmap_hlist_len;
1361
1362 if (!prune_stale_stable_nodes ||
1363 time_before(jiffies, stable_node->chain_prune_time +
1364 msecs_to_jiffies(
1365 ksm_stable_node_chains_prune_millisecs)))
1366 prune_stale_stable_nodes = false;
1367 else
1368 stable_node->chain_prune_time = jiffies;
1369
1370 hlist_for_each_entry_safe(dup, hlist_safe,
1371 &stable_node->hlist, hlist_dup) {
1372 cond_resched();
1373 /*
1374 * We must walk all stable_node_dup to prune the stale
1375 * stable nodes during lookup.
1376 *
1377 * get_ksm_page can drop the nodes from the
1378 * stable_node->hlist if they point to freed pages
1379 * (that's why we do a _safe walk). The "dup"
1380 * stable_node parameter itself will be freed from
1381 * under us if it returns NULL.
1382 */
1383 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1384 if (!_tree_page)
1385 continue;
1386 nr += 1;
1387 if (is_page_sharing_candidate(dup)) {
1388 if (!found ||
1389 dup->rmap_hlist_len > found_rmap_hlist_len) {
1390 if (found)
1391 put_page(tree_page);
1392 found = dup;
1393 found_rmap_hlist_len = found->rmap_hlist_len;
1394 tree_page = _tree_page;
1395
1396 /* skip put_page for found dup */
1397 if (!prune_stale_stable_nodes)
1398 break;
1399 continue;
1400 }
1401 }
1402 put_page(_tree_page);
1403 }
1404
1405 if (found) {
1406 /*
1407 * nr is counting all dups in the chain only if
1408 * prune_stale_stable_nodes is true, otherwise we may
1409 * break the loop at nr == 1 even if there are
1410 * multiple entries.
1411 */
1412 if (prune_stale_stable_nodes && nr == 1) {
1413 /*
1414 * If there's not just one entry it would
1415 * corrupt memory, better BUG_ON. In KSM
1416 * context with no lock held it's not even
1417 * fatal.
1418 */
1419 BUG_ON(stable_node->hlist.first->next);
1420
1421 /*
1422 * There's just one entry and it is below the
1423 * deduplication limit so drop the chain.
1424 */
1425 rb_replace_node(&stable_node->node, &found->node,
1426 root);
1427 free_stable_node(stable_node);
1428 ksm_stable_node_chains--;
1429 ksm_stable_node_dups--;
1430 /*
1431 * NOTE: the caller depends on the stable_node
1432 * to be equal to stable_node_dup if the chain
1433 * was collapsed.
1434 */
1435 *_stable_node = found;
1436 /*
1437 * Just for robustness, as stable_node is
1438 * otherwise left as a stable pointer, the
1439 * compiler shall optimize it away at build
1440 * time.
1441 */
1442 stable_node = NULL;
1443 } else if (stable_node->hlist.first != &found->hlist_dup &&
1444 __is_page_sharing_candidate(found, 1)) {
1445 /*
1446 * If the found stable_node dup can accept one
1447 * more future merge (in addition to the one
1448 * that is underway) and is not at the head of
1449 * the chain, put it there so next search will
1450 * be quicker in the !prune_stale_stable_nodes
1451 * case.
1452 *
1453 * NOTE: it would be inaccurate to use nr > 1
1454 * instead of checking the hlist.first pointer
1455 * directly, because in the
1456 * prune_stale_stable_nodes case "nr" isn't
1457 * the position of the found dup in the chain,
1458 * but the total number of dups in the chain.
1459 */
1460 hlist_del(&found->hlist_dup);
1461 hlist_add_head(&found->hlist_dup,
1462 &stable_node->hlist);
1463 }
1464 }
1465
1466 *_stable_node_dup = found;
1467 return tree_page;
1468}
1469
1470static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1471 struct rb_root *root)
1472{
1473 if (!is_stable_node_chain(stable_node))
1474 return stable_node;
1475 if (hlist_empty(&stable_node->hlist)) {
1476 free_stable_node_chain(stable_node, root);
1477 return NULL;
1478 }
1479 return hlist_entry(stable_node->hlist.first,
1480 typeof(*stable_node), hlist_dup);
1481}
1482
1483/*
1484 * Like for get_ksm_page, this function can free the *_stable_node and
1485 * *_stable_node_dup if the returned tree_page is NULL.
1486 *
1487 * It can also free and overwrite *_stable_node with the found
1488 * stable_node_dup if the chain is collapsed (in which case
1489 * *_stable_node will be equal to *_stable_node_dup like if the chain
1490 * never existed). It's up to the caller to verify tree_page is not
1491 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1492 *
1493 * *_stable_node_dup is really a second output parameter of this
1494 * function and will be overwritten in all cases, the caller doesn't
1495 * need to initialize it.
1496 */
1497static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1498 struct stable_node **_stable_node,
1499 struct rb_root *root,
1500 bool prune_stale_stable_nodes)
1501{
1502 struct stable_node *stable_node = *_stable_node;
1503 if (!is_stable_node_chain(stable_node)) {
1504 if (is_page_sharing_candidate(stable_node)) {
1505 *_stable_node_dup = stable_node;
1506 return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1507 }
1508 /*
1509 * _stable_node_dup set to NULL means the stable_node
1510 * reached the ksm_max_page_sharing limit.
1511 */
1512 *_stable_node_dup = NULL;
1513 return NULL;
1514 }
1515 return stable_node_dup(_stable_node_dup, _stable_node, root,
1516 prune_stale_stable_nodes);
1517}
1518
1519static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1520 struct stable_node **s_n,
1521 struct rb_root *root)
1522{
1523 return __stable_node_chain(s_n_d, s_n, root, true);
1524}
1525
1526static __always_inline struct page *chain(struct stable_node **s_n_d,
1527 struct stable_node *s_n,
1528 struct rb_root *root)
1529{
1530 struct stable_node *old_stable_node = s_n;
1531 struct page *tree_page;
1532
1533 tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1534 /* not pruning dups so s_n cannot have changed */
1535 VM_BUG_ON(s_n != old_stable_node);
1536 return tree_page;
1537}
1538
1539/*
1540 * stable_tree_search - search for page inside the stable tree
1541 *
1542 * This function checks if there is a page inside the stable tree
1543 * with identical content to the page that we are scanning right now.
1544 *
1545 * This function returns the stable tree node of identical content if found,
1546 * NULL otherwise.
1547 */
1548static struct page *stable_tree_search(struct page *page)
1549{
1550 int nid;
1551 struct rb_root *root;
1552 struct rb_node **new;
1553 struct rb_node *parent;
1554 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1555 struct stable_node *page_node;
1556
1557 page_node = page_stable_node(page);
1558 if (page_node && page_node->head != &migrate_nodes) {
1559 /* ksm page forked */
1560 get_page(page);
1561 return page;
1562 }
1563
1564 nid = get_kpfn_nid(page_to_pfn(page));
1565 root = root_stable_tree + nid;
1566again:
1567 new = &root->rb_node;
1568 parent = NULL;
1569
1570 while (*new) {
1571 struct page *tree_page;
1572 int ret;
1573
1574 cond_resched();
1575 stable_node = rb_entry(*new, struct stable_node, node);
1576 stable_node_any = NULL;
1577 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
1578 /*
1579 * NOTE: stable_node may have been freed by
1580 * chain_prune() if the returned stable_node_dup is
1581 * not NULL. stable_node_dup may have been inserted in
1582 * the rbtree instead as a regular stable_node (in
1583 * order to collapse the stable_node chain if a single
1584 * stable_node dup was found in it). In such case the
1585 * stable_node is overwritten by the calleee to point
1586 * to the stable_node_dup that was collapsed in the
1587 * stable rbtree and stable_node will be equal to
1588 * stable_node_dup like if the chain never existed.
1589 */
1590 if (!stable_node_dup) {
1591 /*
1592 * Either all stable_node dups were full in
1593 * this stable_node chain, or this chain was
1594 * empty and should be rb_erased.
1595 */
1596 stable_node_any = stable_node_dup_any(stable_node,
1597 root);
1598 if (!stable_node_any) {
1599 /* rb_erase just run */
1600 goto again;
1601 }
1602 /*
1603 * Take any of the stable_node dups page of
1604 * this stable_node chain to let the tree walk
1605 * continue. All KSM pages belonging to the
1606 * stable_node dups in a stable_node chain
1607 * have the same content and they're
1608 * write protected at all times. Any will work
1609 * fine to continue the walk.
1610 */
1611 tree_page = get_ksm_page(stable_node_any,
1612 GET_KSM_PAGE_NOLOCK);
1613 }
1614 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1615 if (!tree_page) {
1616 /*
1617 * If we walked over a stale stable_node,
1618 * get_ksm_page() will call rb_erase() and it
1619 * may rebalance the tree from under us. So
1620 * restart the search from scratch. Returning
1621 * NULL would be safe too, but we'd generate
1622 * false negative insertions just because some
1623 * stable_node was stale.
1624 */
1625 goto again;
1626 }
1627
1628 ret = memcmp_pages(page, tree_page);
1629 put_page(tree_page);
1630
1631 parent = *new;
1632 if (ret < 0)
1633 new = &parent->rb_left;
1634 else if (ret > 0)
1635 new = &parent->rb_right;
1636 else {
1637 if (page_node) {
1638 VM_BUG_ON(page_node->head != &migrate_nodes);
1639 /*
1640 * Test if the migrated page should be merged
1641 * into a stable node dup. If the mapcount is
1642 * 1 we can migrate it with another KSM page
1643 * without adding it to the chain.
1644 */
1645 if (page_mapcount(page) > 1)
1646 goto chain_append;
1647 }
1648
1649 if (!stable_node_dup) {
1650 /*
1651 * If the stable_node is a chain and
1652 * we got a payload match in memcmp
1653 * but we cannot merge the scanned
1654 * page in any of the existing
1655 * stable_node dups because they're
1656 * all full, we need to wait the
1657 * scanned page to find itself a match
1658 * in the unstable tree to create a
1659 * brand new KSM page to add later to
1660 * the dups of this stable_node.
1661 */
1662 return NULL;
1663 }
1664
1665 /*
1666 * Lock and unlock the stable_node's page (which
1667 * might already have been migrated) so that page
1668 * migration is sure to notice its raised count.
1669 * It would be more elegant to return stable_node
1670 * than kpage, but that involves more changes.
1671 */
1672 tree_page = get_ksm_page(stable_node_dup,
1673 GET_KSM_PAGE_TRYLOCK);
1674
1675 if (PTR_ERR(tree_page) == -EBUSY)
1676 return ERR_PTR(-EBUSY);
1677
1678 if (unlikely(!tree_page))
1679 /*
1680 * The tree may have been rebalanced,
1681 * so re-evaluate parent and new.
1682 */
1683 goto again;
1684 unlock_page(tree_page);
1685
1686 if (get_kpfn_nid(stable_node_dup->kpfn) !=
1687 NUMA(stable_node_dup->nid)) {
1688 put_page(tree_page);
1689 goto replace;
1690 }
1691 return tree_page;
1692 }
1693 }
1694
1695 if (!page_node)
1696 return NULL;
1697
1698 list_del(&page_node->list);
1699 DO_NUMA(page_node->nid = nid);
1700 rb_link_node(&page_node->node, parent, new);
1701 rb_insert_color(&page_node->node, root);
1702out:
1703 if (is_page_sharing_candidate(page_node)) {
1704 get_page(page);
1705 return page;
1706 } else
1707 return NULL;
1708
1709replace:
1710 /*
1711 * If stable_node was a chain and chain_prune collapsed it,
1712 * stable_node has been updated to be the new regular
1713 * stable_node. A collapse of the chain is indistinguishable
1714 * from the case there was no chain in the stable
1715 * rbtree. Otherwise stable_node is the chain and
1716 * stable_node_dup is the dup to replace.
1717 */
1718 if (stable_node_dup == stable_node) {
1719 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1720 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1721 /* there is no chain */
1722 if (page_node) {
1723 VM_BUG_ON(page_node->head != &migrate_nodes);
1724 list_del(&page_node->list);
1725 DO_NUMA(page_node->nid = nid);
1726 rb_replace_node(&stable_node_dup->node,
1727 &page_node->node,
1728 root);
1729 if (is_page_sharing_candidate(page_node))
1730 get_page(page);
1731 else
1732 page = NULL;
1733 } else {
1734 rb_erase(&stable_node_dup->node, root);
1735 page = NULL;
1736 }
1737 } else {
1738 VM_BUG_ON(!is_stable_node_chain(stable_node));
1739 __stable_node_dup_del(stable_node_dup);
1740 if (page_node) {
1741 VM_BUG_ON(page_node->head != &migrate_nodes);
1742 list_del(&page_node->list);
1743 DO_NUMA(page_node->nid = nid);
1744 stable_node_chain_add_dup(page_node, stable_node);
1745 if (is_page_sharing_candidate(page_node))
1746 get_page(page);
1747 else
1748 page = NULL;
1749 } else {
1750 page = NULL;
1751 }
1752 }
1753 stable_node_dup->head = &migrate_nodes;
1754 list_add(&stable_node_dup->list, stable_node_dup->head);
1755 return page;
1756
1757chain_append:
1758 /* stable_node_dup could be null if it reached the limit */
1759 if (!stable_node_dup)
1760 stable_node_dup = stable_node_any;
1761 /*
1762 * If stable_node was a chain and chain_prune collapsed it,
1763 * stable_node has been updated to be the new regular
1764 * stable_node. A collapse of the chain is indistinguishable
1765 * from the case there was no chain in the stable
1766 * rbtree. Otherwise stable_node is the chain and
1767 * stable_node_dup is the dup to replace.
1768 */
1769 if (stable_node_dup == stable_node) {
1770 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1771 /* chain is missing so create it */
1772 stable_node = alloc_stable_node_chain(stable_node_dup,
1773 root);
1774 if (!stable_node)
1775 return NULL;
1776 }
1777 /*
1778 * Add this stable_node dup that was
1779 * migrated to the stable_node chain
1780 * of the current nid for this page
1781 * content.
1782 */
1783 VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1784 VM_BUG_ON(page_node->head != &migrate_nodes);
1785 list_del(&page_node->list);
1786 DO_NUMA(page_node->nid = nid);
1787 stable_node_chain_add_dup(page_node, stable_node);
1788 goto out;
1789}
1790
1791/*
1792 * stable_tree_insert - insert stable tree node pointing to new ksm page
1793 * into the stable tree.
1794 *
1795 * This function returns the stable tree node just allocated on success,
1796 * NULL otherwise.
1797 */
1798static struct stable_node *stable_tree_insert(struct page *kpage)
1799{
1800 int nid;
1801 unsigned long kpfn;
1802 struct rb_root *root;
1803 struct rb_node **new;
1804 struct rb_node *parent;
1805 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1806 bool need_chain = false;
1807
1808 kpfn = page_to_pfn(kpage);
1809 nid = get_kpfn_nid(kpfn);
1810 root = root_stable_tree + nid;
1811again:
1812 parent = NULL;
1813 new = &root->rb_node;
1814
1815 while (*new) {
1816 struct page *tree_page;
1817 int ret;
1818
1819 cond_resched();
1820 stable_node = rb_entry(*new, struct stable_node, node);
1821 stable_node_any = NULL;
1822 tree_page = chain(&stable_node_dup, stable_node, root);
1823 if (!stable_node_dup) {
1824 /*
1825 * Either all stable_node dups were full in
1826 * this stable_node chain, or this chain was
1827 * empty and should be rb_erased.
1828 */
1829 stable_node_any = stable_node_dup_any(stable_node,
1830 root);
1831 if (!stable_node_any) {
1832 /* rb_erase just run */
1833 goto again;
1834 }
1835 /*
1836 * Take any of the stable_node dups page of
1837 * this stable_node chain to let the tree walk
1838 * continue. All KSM pages belonging to the
1839 * stable_node dups in a stable_node chain
1840 * have the same content and they're
1841 * write protected at all times. Any will work
1842 * fine to continue the walk.
1843 */
1844 tree_page = get_ksm_page(stable_node_any,
1845 GET_KSM_PAGE_NOLOCK);
1846 }
1847 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1848 if (!tree_page) {
1849 /*
1850 * If we walked over a stale stable_node,
1851 * get_ksm_page() will call rb_erase() and it
1852 * may rebalance the tree from under us. So
1853 * restart the search from scratch. Returning
1854 * NULL would be safe too, but we'd generate
1855 * false negative insertions just because some
1856 * stable_node was stale.
1857 */
1858 goto again;
1859 }
1860
1861 ret = memcmp_pages(kpage, tree_page);
1862 put_page(tree_page);
1863
1864 parent = *new;
1865 if (ret < 0)
1866 new = &parent->rb_left;
1867 else if (ret > 0)
1868 new = &parent->rb_right;
1869 else {
1870 need_chain = true;
1871 break;
1872 }
1873 }
1874
1875 stable_node_dup = alloc_stable_node();
1876 if (!stable_node_dup)
1877 return NULL;
1878
1879 INIT_HLIST_HEAD(&stable_node_dup->hlist);
1880 stable_node_dup->kpfn = kpfn;
1881 set_page_stable_node(kpage, stable_node_dup);
1882 stable_node_dup->rmap_hlist_len = 0;
1883 DO_NUMA(stable_node_dup->nid = nid);
1884 if (!need_chain) {
1885 rb_link_node(&stable_node_dup->node, parent, new);
1886 rb_insert_color(&stable_node_dup->node, root);
1887 } else {
1888 if (!is_stable_node_chain(stable_node)) {
1889 struct stable_node *orig = stable_node;
1890 /* chain is missing so create it */
1891 stable_node = alloc_stable_node_chain(orig, root);
1892 if (!stable_node) {
1893 free_stable_node(stable_node_dup);
1894 return NULL;
1895 }
1896 }
1897 stable_node_chain_add_dup(stable_node_dup, stable_node);
1898 }
1899
1900 return stable_node_dup;
1901}
1902
1903/*
1904 * unstable_tree_search_insert - search for identical page,
1905 * else insert rmap_item into the unstable tree.
1906 *
1907 * This function searches for a page in the unstable tree identical to the
1908 * page currently being scanned; and if no identical page is found in the
1909 * tree, we insert rmap_item as a new object into the unstable tree.
1910 *
1911 * This function returns pointer to rmap_item found to be identical
1912 * to the currently scanned page, NULL otherwise.
1913 *
1914 * This function does both searching and inserting, because they share
1915 * the same walking algorithm in an rbtree.
1916 */
1917static
1918struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1919 struct page *page,
1920 struct page **tree_pagep)
1921{
1922 struct rb_node **new;
1923 struct rb_root *root;
1924 struct rb_node *parent = NULL;
1925 int nid;
1926
1927 nid = get_kpfn_nid(page_to_pfn(page));
1928 root = root_unstable_tree + nid;
1929 new = &root->rb_node;
1930
1931 while (*new) {
1932 struct rmap_item *tree_rmap_item;
1933 struct page *tree_page;
1934 int ret;
1935
1936 cond_resched();
1937 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1938 tree_page = get_mergeable_page(tree_rmap_item);
1939 if (!tree_page)
1940 return NULL;
1941
1942 /*
1943 * Don't substitute a ksm page for a forked page.
1944 */
1945 if (page == tree_page) {
1946 put_page(tree_page);
1947 return NULL;
1948 }
1949
1950 ret = memcmp_pages(page, tree_page);
1951
1952 parent = *new;
1953 if (ret < 0) {
1954 put_page(tree_page);
1955 new = &parent->rb_left;
1956 } else if (ret > 0) {
1957 put_page(tree_page);
1958 new = &parent->rb_right;
1959 } else if (!ksm_merge_across_nodes &&
1960 page_to_nid(tree_page) != nid) {
1961 /*
1962 * If tree_page has been migrated to another NUMA node,
1963 * it will be flushed out and put in the right unstable
1964 * tree next time: only merge with it when across_nodes.
1965 */
1966 put_page(tree_page);
1967 return NULL;
1968 } else {
1969 *tree_pagep = tree_page;
1970 return tree_rmap_item;
1971 }
1972 }
1973
1974 rmap_item->address |= UNSTABLE_FLAG;
1975 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1976 DO_NUMA(rmap_item->nid = nid);
1977 rb_link_node(&rmap_item->node, parent, new);
1978 rb_insert_color(&rmap_item->node, root);
1979
1980 ksm_pages_unshared++;
1981 return NULL;
1982}
1983
1984/*
1985 * stable_tree_append - add another rmap_item to the linked list of
1986 * rmap_items hanging off a given node of the stable tree, all sharing
1987 * the same ksm page.
1988 */
1989static void stable_tree_append(struct rmap_item *rmap_item,
1990 struct stable_node *stable_node,
1991 bool max_page_sharing_bypass)
1992{
1993 /*
1994 * rmap won't find this mapping if we don't insert the
1995 * rmap_item in the right stable_node
1996 * duplicate. page_migration could break later if rmap breaks,
1997 * so we can as well crash here. We really need to check for
1998 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
1999 * for other negative values as an underflow if detected here
2000 * for the first time (and not when decreasing rmap_hlist_len)
2001 * would be sign of memory corruption in the stable_node.
2002 */
2003 BUG_ON(stable_node->rmap_hlist_len < 0);
2004
2005 stable_node->rmap_hlist_len++;
2006 if (!max_page_sharing_bypass)
2007 /* possibly non fatal but unexpected overflow, only warn */
2008 WARN_ON_ONCE(stable_node->rmap_hlist_len >
2009 ksm_max_page_sharing);
2010
2011 rmap_item->head = stable_node;
2012 rmap_item->address |= STABLE_FLAG;
2013 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2014
2015 if (rmap_item->hlist.next)
2016 ksm_pages_sharing++;
2017 else
2018 ksm_pages_shared++;
2019}
2020
2021/*
2022 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2023 * if not, compare checksum to previous and if it's the same, see if page can
2024 * be inserted into the unstable tree, or merged with a page already there and
2025 * both transferred to the stable tree.
2026 *
2027 * @page: the page that we are searching identical page to.
2028 * @rmap_item: the reverse mapping into the virtual address of this page
2029 */
2030static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2031{
2032 struct mm_struct *mm = rmap_item->mm;
2033 struct rmap_item *tree_rmap_item;
2034 struct page *tree_page = NULL;
2035 struct stable_node *stable_node;
2036 struct page *kpage;
2037 unsigned int checksum;
2038 int err;
2039 bool max_page_sharing_bypass = false;
2040
2041 stable_node = page_stable_node(page);
2042 if (stable_node) {
2043 if (stable_node->head != &migrate_nodes &&
2044 get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2045 NUMA(stable_node->nid)) {
2046 stable_node_dup_del(stable_node);
2047 stable_node->head = &migrate_nodes;
2048 list_add(&stable_node->list, stable_node->head);
2049 }
2050 if (stable_node->head != &migrate_nodes &&
2051 rmap_item->head == stable_node)
2052 return;
2053 /*
2054 * If it's a KSM fork, allow it to go over the sharing limit
2055 * without warnings.
2056 */
2057 if (!is_page_sharing_candidate(stable_node))
2058 max_page_sharing_bypass = true;
2059 }
2060
2061 /* We first start with searching the page inside the stable tree */
2062 kpage = stable_tree_search(page);
2063 if (kpage == page && rmap_item->head == stable_node) {
2064 put_page(kpage);
2065 return;
2066 }
2067
2068 remove_rmap_item_from_tree(rmap_item);
2069
2070 if (kpage) {
2071 if (PTR_ERR(kpage) == -EBUSY)
2072 return;
2073
2074 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2075 if (!err) {
2076 /*
2077 * The page was successfully merged:
2078 * add its rmap_item to the stable tree.
2079 */
2080 lock_page(kpage);
2081 stable_tree_append(rmap_item, page_stable_node(kpage),
2082 max_page_sharing_bypass);
2083 unlock_page(kpage);
2084 }
2085 put_page(kpage);
2086 return;
2087 }
2088
2089 /*
2090 * If the hash value of the page has changed from the last time
2091 * we calculated it, this page is changing frequently: therefore we
2092 * don't want to insert it in the unstable tree, and we don't want
2093 * to waste our time searching for something identical to it there.
2094 */
2095 checksum = calc_checksum(page);
2096 if (rmap_item->oldchecksum != checksum) {
2097 rmap_item->oldchecksum = checksum;
2098 return;
2099 }
2100
2101 /*
2102 * Same checksum as an empty page. We attempt to merge it with the
2103 * appropriate zero page if the user enabled this via sysfs.
2104 */
2105 if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2106 struct vm_area_struct *vma;
2107
2108 mmap_read_lock(mm);
2109 vma = find_mergeable_vma(mm, rmap_item->address);
2110 if (vma) {
2111 err = try_to_merge_one_page(vma, page,
2112 ZERO_PAGE(rmap_item->address));
2113 } else {
2114 /*
2115 * If the vma is out of date, we do not need to
2116 * continue.
2117 */
2118 err = 0;
2119 }
2120 mmap_read_unlock(mm);
2121 /*
2122 * In case of failure, the page was not really empty, so we
2123 * need to continue. Otherwise we're done.
2124 */
2125 if (!err)
2126 return;
2127 }
2128 tree_rmap_item =
2129 unstable_tree_search_insert(rmap_item, page, &tree_page);
2130 if (tree_rmap_item) {
2131 bool split;
2132
2133 kpage = try_to_merge_two_pages(rmap_item, page,
2134 tree_rmap_item, tree_page);
2135 /*
2136 * If both pages we tried to merge belong to the same compound
2137 * page, then we actually ended up increasing the reference
2138 * count of the same compound page twice, and split_huge_page
2139 * failed.
2140 * Here we set a flag if that happened, and we use it later to
2141 * try split_huge_page again. Since we call put_page right
2142 * afterwards, the reference count will be correct and
2143 * split_huge_page should succeed.
2144 */
2145 split = PageTransCompound(page)
2146 && compound_head(page) == compound_head(tree_page);
2147 put_page(tree_page);
2148 if (kpage) {
2149 /*
2150 * The pages were successfully merged: insert new
2151 * node in the stable tree and add both rmap_items.
2152 */
2153 lock_page(kpage);
2154 stable_node = stable_tree_insert(kpage);
2155 if (stable_node) {
2156 stable_tree_append(tree_rmap_item, stable_node,
2157 false);
2158 stable_tree_append(rmap_item, stable_node,
2159 false);
2160 }
2161 unlock_page(kpage);
2162
2163 /*
2164 * If we fail to insert the page into the stable tree,
2165 * we will have 2 virtual addresses that are pointing
2166 * to a ksm page left outside the stable tree,
2167 * in which case we need to break_cow on both.
2168 */
2169 if (!stable_node) {
2170 break_cow(tree_rmap_item);
2171 break_cow(rmap_item);
2172 }
2173 } else if (split) {
2174 /*
2175 * We are here if we tried to merge two pages and
2176 * failed because they both belonged to the same
2177 * compound page. We will split the page now, but no
2178 * merging will take place.
2179 * We do not want to add the cost of a full lock; if
2180 * the page is locked, it is better to skip it and
2181 * perhaps try again later.
2182 */
2183 if (!trylock_page(page))
2184 return;
2185 split_huge_page(page);
2186 unlock_page(page);
2187 }
2188 }
2189}
2190
2191static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2192 struct rmap_item **rmap_list,
2193 unsigned long addr)
2194{
2195 struct rmap_item *rmap_item;
2196
2197 while (*rmap_list) {
2198 rmap_item = *rmap_list;
2199 if ((rmap_item->address & PAGE_MASK) == addr)
2200 return rmap_item;
2201 if (rmap_item->address > addr)
2202 break;
2203 *rmap_list = rmap_item->rmap_list;
2204 remove_rmap_item_from_tree(rmap_item);
2205 free_rmap_item(rmap_item);
2206 }
2207
2208 rmap_item = alloc_rmap_item();
2209 if (rmap_item) {
2210 /* It has already been zeroed */
2211 rmap_item->mm = mm_slot->mm;
2212 rmap_item->address = addr;
2213 rmap_item->rmap_list = *rmap_list;
2214 *rmap_list = rmap_item;
2215 }
2216 return rmap_item;
2217}
2218
2219static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2220{
2221 struct mm_struct *mm;
2222 struct mm_slot *slot;
2223 struct vm_area_struct *vma;
2224 struct rmap_item *rmap_item;
2225 int nid;
2226
2227 if (list_empty(&ksm_mm_head.mm_list))
2228 return NULL;
2229
2230 slot = ksm_scan.mm_slot;
2231 if (slot == &ksm_mm_head) {
2232 /*
2233 * A number of pages can hang around indefinitely on per-cpu
2234 * pagevecs, raised page count preventing write_protect_page
2235 * from merging them. Though it doesn't really matter much,
2236 * it is puzzling to see some stuck in pages_volatile until
2237 * other activity jostles them out, and they also prevented
2238 * LTP's KSM test from succeeding deterministically; so drain
2239 * them here (here rather than on entry to ksm_do_scan(),
2240 * so we don't IPI too often when pages_to_scan is set low).
2241 */
2242 lru_add_drain_all();
2243
2244 /*
2245 * Whereas stale stable_nodes on the stable_tree itself
2246 * get pruned in the regular course of stable_tree_search(),
2247 * those moved out to the migrate_nodes list can accumulate:
2248 * so prune them once before each full scan.
2249 */
2250 if (!ksm_merge_across_nodes) {
2251 struct stable_node *stable_node, *next;
2252 struct page *page;
2253
2254 list_for_each_entry_safe(stable_node, next,
2255 &migrate_nodes, list) {
2256 page = get_ksm_page(stable_node,
2257 GET_KSM_PAGE_NOLOCK);
2258 if (page)
2259 put_page(page);
2260 cond_resched();
2261 }
2262 }
2263
2264 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2265 root_unstable_tree[nid] = RB_ROOT;
2266
2267 spin_lock(&ksm_mmlist_lock);
2268 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2269 ksm_scan.mm_slot = slot;
2270 spin_unlock(&ksm_mmlist_lock);
2271 /*
2272 * Although we tested list_empty() above, a racing __ksm_exit
2273 * of the last mm on the list may have removed it since then.
2274 */
2275 if (slot == &ksm_mm_head)
2276 return NULL;
2277next_mm:
2278 ksm_scan.address = 0;
2279 ksm_scan.rmap_list = &slot->rmap_list;
2280 }
2281
2282 mm = slot->mm;
2283 mmap_read_lock(mm);
2284 if (ksm_test_exit(mm))
2285 vma = NULL;
2286 else
2287 vma = find_vma(mm, ksm_scan.address);
2288
2289 for (; vma; vma = vma->vm_next) {
2290 if (!(vma->vm_flags & VM_MERGEABLE))
2291 continue;
2292 if (ksm_scan.address < vma->vm_start)
2293 ksm_scan.address = vma->vm_start;
2294 if (!vma->anon_vma)
2295 ksm_scan.address = vma->vm_end;
2296
2297 while (ksm_scan.address < vma->vm_end) {
2298 if (ksm_test_exit(mm))
2299 break;
2300 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
2301 if (IS_ERR_OR_NULL(*page)) {
2302 ksm_scan.address += PAGE_SIZE;
2303 cond_resched();
2304 continue;
2305 }
2306 if (PageAnon(*page)) {
2307 flush_anon_page(vma, *page, ksm_scan.address);
2308 flush_dcache_page(*page);
2309 rmap_item = get_next_rmap_item(slot,
2310 ksm_scan.rmap_list, ksm_scan.address);
2311 if (rmap_item) {
2312 ksm_scan.rmap_list =
2313 &rmap_item->rmap_list;
2314 ksm_scan.address += PAGE_SIZE;
2315 } else
2316 put_page(*page);
2317 mmap_read_unlock(mm);
2318 return rmap_item;
2319 }
2320 put_page(*page);
2321 ksm_scan.address += PAGE_SIZE;
2322 cond_resched();
2323 }
2324 }
2325
2326 if (ksm_test_exit(mm)) {
2327 ksm_scan.address = 0;
2328 ksm_scan.rmap_list = &slot->rmap_list;
2329 }
2330 /*
2331 * Nuke all the rmap_items that are above this current rmap:
2332 * because there were no VM_MERGEABLE vmas with such addresses.
2333 */
2334 remove_trailing_rmap_items(ksm_scan.rmap_list);
2335
2336 spin_lock(&ksm_mmlist_lock);
2337 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2338 struct mm_slot, mm_list);
2339 if (ksm_scan.address == 0) {
2340 /*
2341 * We've completed a full scan of all vmas, holding mmap_lock
2342 * throughout, and found no VM_MERGEABLE: so do the same as
2343 * __ksm_exit does to remove this mm from all our lists now.
2344 * This applies either when cleaning up after __ksm_exit
2345 * (but beware: we can reach here even before __ksm_exit),
2346 * or when all VM_MERGEABLE areas have been unmapped (and
2347 * mmap_lock then protects against race with MADV_MERGEABLE).
2348 */
2349 hash_del(&slot->link);
2350 list_del(&slot->mm_list);
2351 spin_unlock(&ksm_mmlist_lock);
2352
2353 free_mm_slot(slot);
2354 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2355 mmap_read_unlock(mm);
2356 mmdrop(mm);
2357 } else {
2358 mmap_read_unlock(mm);
2359 /*
2360 * mmap_read_unlock(mm) first because after
2361 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2362 * already have been freed under us by __ksm_exit()
2363 * because the "mm_slot" is still hashed and
2364 * ksm_scan.mm_slot doesn't point to it anymore.
2365 */
2366 spin_unlock(&ksm_mmlist_lock);
2367 }
2368
2369 /* Repeat until we've completed scanning the whole list */
2370 slot = ksm_scan.mm_slot;
2371 if (slot != &ksm_mm_head)
2372 goto next_mm;
2373
2374 ksm_scan.seqnr++;
2375 return NULL;
2376}
2377
2378/**
2379 * ksm_do_scan - the ksm scanner main worker function.
2380 * @scan_npages: number of pages we want to scan before we return.
2381 */
2382static void ksm_do_scan(unsigned int scan_npages)
2383{
2384 struct rmap_item *rmap_item;
2385 struct page *page;
2386
2387 while (scan_npages-- && likely(!freezing(current))) {
2388 cond_resched();
2389 rmap_item = scan_get_next_rmap_item(&page);
2390 if (!rmap_item)
2391 return;
2392 cmp_and_merge_page(page, rmap_item);
2393 put_page(page);
2394 }
2395}
2396
2397static int ksmd_should_run(void)
2398{
2399 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2400}
2401
2402static int ksm_scan_thread(void *nothing)
2403{
2404 unsigned int sleep_ms;
2405
2406 set_freezable();
2407 set_user_nice(current, 5);
2408
2409 while (!kthread_should_stop()) {
2410 mutex_lock(&ksm_thread_mutex);
2411 wait_while_offlining();
2412 if (ksmd_should_run())
2413 ksm_do_scan(ksm_thread_pages_to_scan);
2414 mutex_unlock(&ksm_thread_mutex);
2415
2416 try_to_freeze();
2417
2418 if (ksmd_should_run()) {
2419 sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2420 wait_event_interruptible_timeout(ksm_iter_wait,
2421 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2422 msecs_to_jiffies(sleep_ms));
2423 } else {
2424 wait_event_freezable(ksm_thread_wait,
2425 ksmd_should_run() || kthread_should_stop());
2426 }
2427 }
2428 return 0;
2429}
2430
2431int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2432 unsigned long end, int advice, unsigned long *vm_flags)
2433{
2434 struct mm_struct *mm = vma->vm_mm;
2435 int err;
2436
2437 switch (advice) {
2438 case MADV_MERGEABLE:
2439 /*
2440 * Be somewhat over-protective for now!
2441 */
2442 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
2443 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
2444 VM_HUGETLB | VM_MIXEDMAP))
2445 return 0; /* just ignore the advice */
2446
2447 if (vma_is_dax(vma))
2448 return 0;
2449
2450#ifdef VM_SAO
2451 if (*vm_flags & VM_SAO)
2452 return 0;
2453#endif
2454#ifdef VM_SPARC_ADI
2455 if (*vm_flags & VM_SPARC_ADI)
2456 return 0;
2457#endif
2458
2459 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2460 err = __ksm_enter(mm);
2461 if (err)
2462 return err;
2463 }
2464
2465 *vm_flags |= VM_MERGEABLE;
2466 break;
2467
2468 case MADV_UNMERGEABLE:
2469 if (!(*vm_flags & VM_MERGEABLE))
2470 return 0; /* just ignore the advice */
2471
2472 if (vma->anon_vma) {
2473 err = unmerge_ksm_pages(vma, start, end);
2474 if (err)
2475 return err;
2476 }
2477
2478 *vm_flags &= ~VM_MERGEABLE;
2479 break;
2480 }
2481
2482 return 0;
2483}
2484EXPORT_SYMBOL_GPL(ksm_madvise);
2485
2486int __ksm_enter(struct mm_struct *mm)
2487{
2488 struct mm_slot *mm_slot;
2489 int needs_wakeup;
2490
2491 mm_slot = alloc_mm_slot();
2492 if (!mm_slot)
2493 return -ENOMEM;
2494
2495 /* Check ksm_run too? Would need tighter locking */
2496 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2497
2498 spin_lock(&ksm_mmlist_lock);
2499 insert_to_mm_slots_hash(mm, mm_slot);
2500 /*
2501 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2502 * insert just behind the scanning cursor, to let the area settle
2503 * down a little; when fork is followed by immediate exec, we don't
2504 * want ksmd to waste time setting up and tearing down an rmap_list.
2505 *
2506 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2507 * scanning cursor, otherwise KSM pages in newly forked mms will be
2508 * missed: then we might as well insert at the end of the list.
2509 */
2510 if (ksm_run & KSM_RUN_UNMERGE)
2511 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2512 else
2513 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2514 spin_unlock(&ksm_mmlist_lock);
2515
2516 set_bit(MMF_VM_MERGEABLE, &mm->flags);
2517 mmgrab(mm);
2518
2519 if (needs_wakeup)
2520 wake_up_interruptible(&ksm_thread_wait);
2521
2522 return 0;
2523}
2524
2525void __ksm_exit(struct mm_struct *mm)
2526{
2527 struct mm_slot *mm_slot;
2528 int easy_to_free = 0;
2529
2530 /*
2531 * This process is exiting: if it's straightforward (as is the
2532 * case when ksmd was never running), free mm_slot immediately.
2533 * But if it's at the cursor or has rmap_items linked to it, use
2534 * mmap_lock to synchronize with any break_cows before pagetables
2535 * are freed, and leave the mm_slot on the list for ksmd to free.
2536 * Beware: ksm may already have noticed it exiting and freed the slot.
2537 */
2538
2539 spin_lock(&ksm_mmlist_lock);
2540 mm_slot = get_mm_slot(mm);
2541 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2542 if (!mm_slot->rmap_list) {
2543 hash_del(&mm_slot->link);
2544 list_del(&mm_slot->mm_list);
2545 easy_to_free = 1;
2546 } else {
2547 list_move(&mm_slot->mm_list,
2548 &ksm_scan.mm_slot->mm_list);
2549 }
2550 }
2551 spin_unlock(&ksm_mmlist_lock);
2552
2553 if (easy_to_free) {
2554 free_mm_slot(mm_slot);
2555 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2556 mmdrop(mm);
2557 } else if (mm_slot) {
2558 mmap_write_lock(mm);
2559 mmap_write_unlock(mm);
2560 }
2561}
2562
2563struct page *ksm_might_need_to_copy(struct page *page,
2564 struct vm_area_struct *vma, unsigned long address)
2565{
2566 struct anon_vma *anon_vma = page_anon_vma(page);
2567 struct page *new_page;
2568
2569 if (PageKsm(page)) {
2570 if (page_stable_node(page) &&
2571 !(ksm_run & KSM_RUN_UNMERGE))
2572 return page; /* no need to copy it */
2573 } else if (!anon_vma) {
2574 return page; /* no need to copy it */
2575 } else if (anon_vma->root == vma->anon_vma->root &&
2576 page->index == linear_page_index(vma, address)) {
2577 return page; /* still no need to copy it */
2578 }
2579 if (!PageUptodate(page))
2580 return page; /* let do_swap_page report the error */
2581
2582 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2583 if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) {
2584 put_page(new_page);
2585 new_page = NULL;
2586 }
2587 if (new_page) {
2588 copy_user_highpage(new_page, page, address, vma);
2589
2590 SetPageDirty(new_page);
2591 __SetPageUptodate(new_page);
2592 __SetPageLocked(new_page);
2593 }
2594
2595 return new_page;
2596}
2597
2598void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2599{
2600 struct stable_node *stable_node;
2601 struct rmap_item *rmap_item;
2602 int search_new_forks = 0;
2603
2604 VM_BUG_ON_PAGE(!PageKsm(page), page);
2605
2606 /*
2607 * Rely on the page lock to protect against concurrent modifications
2608 * to that page's node of the stable tree.
2609 */
2610 VM_BUG_ON_PAGE(!PageLocked(page), page);
2611
2612 stable_node = page_stable_node(page);
2613 if (!stable_node)
2614 return;
2615again:
2616 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2617 struct anon_vma *anon_vma = rmap_item->anon_vma;
2618 struct anon_vma_chain *vmac;
2619 struct vm_area_struct *vma;
2620
2621 cond_resched();
2622 anon_vma_lock_read(anon_vma);
2623 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2624 0, ULONG_MAX) {
2625 unsigned long addr;
2626
2627 cond_resched();
2628 vma = vmac->vma;
2629
2630 /* Ignore the stable/unstable/sqnr flags */
2631 addr = rmap_item->address & PAGE_MASK;
2632
2633 if (addr < vma->vm_start || addr >= vma->vm_end)
2634 continue;
2635 /*
2636 * Initially we examine only the vma which covers this
2637 * rmap_item; but later, if there is still work to do,
2638 * we examine covering vmas in other mms: in case they
2639 * were forked from the original since ksmd passed.
2640 */
2641 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2642 continue;
2643
2644 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2645 continue;
2646
2647 if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2648 anon_vma_unlock_read(anon_vma);
2649 return;
2650 }
2651 if (rwc->done && rwc->done(page)) {
2652 anon_vma_unlock_read(anon_vma);
2653 return;
2654 }
2655 }
2656 anon_vma_unlock_read(anon_vma);
2657 }
2658 if (!search_new_forks++)
2659 goto again;
2660}
2661
2662#ifdef CONFIG_MIGRATION
2663void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2664{
2665 struct stable_node *stable_node;
2666
2667 VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2668 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2669 VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2670
2671 stable_node = page_stable_node(newpage);
2672 if (stable_node) {
2673 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2674 stable_node->kpfn = page_to_pfn(newpage);
2675 /*
2676 * newpage->mapping was set in advance; now we need smp_wmb()
2677 * to make sure that the new stable_node->kpfn is visible
2678 * to get_ksm_page() before it can see that oldpage->mapping
2679 * has gone stale (or that PageSwapCache has been cleared).
2680 */
2681 smp_wmb();
2682 set_page_stable_node(oldpage, NULL);
2683 }
2684}
2685#endif /* CONFIG_MIGRATION */
2686
2687#ifdef CONFIG_MEMORY_HOTREMOVE
2688static void wait_while_offlining(void)
2689{
2690 while (ksm_run & KSM_RUN_OFFLINE) {
2691 mutex_unlock(&ksm_thread_mutex);
2692 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2693 TASK_UNINTERRUPTIBLE);
2694 mutex_lock(&ksm_thread_mutex);
2695 }
2696}
2697
2698static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2699 unsigned long start_pfn,
2700 unsigned long end_pfn)
2701{
2702 if (stable_node->kpfn >= start_pfn &&
2703 stable_node->kpfn < end_pfn) {
2704 /*
2705 * Don't get_ksm_page, page has already gone:
2706 * which is why we keep kpfn instead of page*
2707 */
2708 remove_node_from_stable_tree(stable_node);
2709 return true;
2710 }
2711 return false;
2712}
2713
2714static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2715 unsigned long start_pfn,
2716 unsigned long end_pfn,
2717 struct rb_root *root)
2718{
2719 struct stable_node *dup;
2720 struct hlist_node *hlist_safe;
2721
2722 if (!is_stable_node_chain(stable_node)) {
2723 VM_BUG_ON(is_stable_node_dup(stable_node));
2724 return stable_node_dup_remove_range(stable_node, start_pfn,
2725 end_pfn);
2726 }
2727
2728 hlist_for_each_entry_safe(dup, hlist_safe,
2729 &stable_node->hlist, hlist_dup) {
2730 VM_BUG_ON(!is_stable_node_dup(dup));
2731 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2732 }
2733 if (hlist_empty(&stable_node->hlist)) {
2734 free_stable_node_chain(stable_node, root);
2735 return true; /* notify caller that tree was rebalanced */
2736 } else
2737 return false;
2738}
2739
2740static void ksm_check_stable_tree(unsigned long start_pfn,
2741 unsigned long end_pfn)
2742{
2743 struct stable_node *stable_node, *next;
2744 struct rb_node *node;
2745 int nid;
2746
2747 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2748 node = rb_first(root_stable_tree + nid);
2749 while (node) {
2750 stable_node = rb_entry(node, struct stable_node, node);
2751 if (stable_node_chain_remove_range(stable_node,
2752 start_pfn, end_pfn,
2753 root_stable_tree +
2754 nid))
2755 node = rb_first(root_stable_tree + nid);
2756 else
2757 node = rb_next(node);
2758 cond_resched();
2759 }
2760 }
2761 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2762 if (stable_node->kpfn >= start_pfn &&
2763 stable_node->kpfn < end_pfn)
2764 remove_node_from_stable_tree(stable_node);
2765 cond_resched();
2766 }
2767}
2768
2769static int ksm_memory_callback(struct notifier_block *self,
2770 unsigned long action, void *arg)
2771{
2772 struct memory_notify *mn = arg;
2773
2774 switch (action) {
2775 case MEM_GOING_OFFLINE:
2776 /*
2777 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2778 * and remove_all_stable_nodes() while memory is going offline:
2779 * it is unsafe for them to touch the stable tree at this time.
2780 * But unmerge_ksm_pages(), rmap lookups and other entry points
2781 * which do not need the ksm_thread_mutex are all safe.
2782 */
2783 mutex_lock(&ksm_thread_mutex);
2784 ksm_run |= KSM_RUN_OFFLINE;
2785 mutex_unlock(&ksm_thread_mutex);
2786 break;
2787
2788 case MEM_OFFLINE:
2789 /*
2790 * Most of the work is done by page migration; but there might
2791 * be a few stable_nodes left over, still pointing to struct
2792 * pages which have been offlined: prune those from the tree,
2793 * otherwise get_ksm_page() might later try to access a
2794 * non-existent struct page.
2795 */
2796 ksm_check_stable_tree(mn->start_pfn,
2797 mn->start_pfn + mn->nr_pages);
2798 fallthrough;
2799 case MEM_CANCEL_OFFLINE:
2800 mutex_lock(&ksm_thread_mutex);
2801 ksm_run &= ~KSM_RUN_OFFLINE;
2802 mutex_unlock(&ksm_thread_mutex);
2803
2804 smp_mb(); /* wake_up_bit advises this */
2805 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2806 break;
2807 }
2808 return NOTIFY_OK;
2809}
2810#else
2811static void wait_while_offlining(void)
2812{
2813}
2814#endif /* CONFIG_MEMORY_HOTREMOVE */
2815
2816#ifdef CONFIG_SYSFS
2817/*
2818 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2819 */
2820
2821#define KSM_ATTR_RO(_name) \
2822 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2823#define KSM_ATTR(_name) \
2824 static struct kobj_attribute _name##_attr = \
2825 __ATTR(_name, 0644, _name##_show, _name##_store)
2826
2827static ssize_t sleep_millisecs_show(struct kobject *kobj,
2828 struct kobj_attribute *attr, char *buf)
2829{
2830 return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
2831}
2832
2833static ssize_t sleep_millisecs_store(struct kobject *kobj,
2834 struct kobj_attribute *attr,
2835 const char *buf, size_t count)
2836{
2837 unsigned int msecs;
2838 int err;
2839
2840 err = kstrtouint(buf, 10, &msecs);
2841 if (err)
2842 return -EINVAL;
2843
2844 ksm_thread_sleep_millisecs = msecs;
2845 wake_up_interruptible(&ksm_iter_wait);
2846
2847 return count;
2848}
2849KSM_ATTR(sleep_millisecs);
2850
2851static ssize_t pages_to_scan_show(struct kobject *kobj,
2852 struct kobj_attribute *attr, char *buf)
2853{
2854 return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
2855}
2856
2857static ssize_t pages_to_scan_store(struct kobject *kobj,
2858 struct kobj_attribute *attr,
2859 const char *buf, size_t count)
2860{
2861 unsigned int nr_pages;
2862 int err;
2863
2864 err = kstrtouint(buf, 10, &nr_pages);
2865 if (err)
2866 return -EINVAL;
2867
2868 ksm_thread_pages_to_scan = nr_pages;
2869
2870 return count;
2871}
2872KSM_ATTR(pages_to_scan);
2873
2874static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2875 char *buf)
2876{
2877 return sysfs_emit(buf, "%lu\n", ksm_run);
2878}
2879
2880static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2881 const char *buf, size_t count)
2882{
2883 unsigned int flags;
2884 int err;
2885
2886 err = kstrtouint(buf, 10, &flags);
2887 if (err)
2888 return -EINVAL;
2889 if (flags > KSM_RUN_UNMERGE)
2890 return -EINVAL;
2891
2892 /*
2893 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2894 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2895 * breaking COW to free the pages_shared (but leaves mm_slots
2896 * on the list for when ksmd may be set running again).
2897 */
2898
2899 mutex_lock(&ksm_thread_mutex);
2900 wait_while_offlining();
2901 if (ksm_run != flags) {
2902 ksm_run = flags;
2903 if (flags & KSM_RUN_UNMERGE) {
2904 set_current_oom_origin();
2905 err = unmerge_and_remove_all_rmap_items();
2906 clear_current_oom_origin();
2907 if (err) {
2908 ksm_run = KSM_RUN_STOP;
2909 count = err;
2910 }
2911 }
2912 }
2913 mutex_unlock(&ksm_thread_mutex);
2914
2915 if (flags & KSM_RUN_MERGE)
2916 wake_up_interruptible(&ksm_thread_wait);
2917
2918 return count;
2919}
2920KSM_ATTR(run);
2921
2922#ifdef CONFIG_NUMA
2923static ssize_t merge_across_nodes_show(struct kobject *kobj,
2924 struct kobj_attribute *attr, char *buf)
2925{
2926 return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
2927}
2928
2929static ssize_t merge_across_nodes_store(struct kobject *kobj,
2930 struct kobj_attribute *attr,
2931 const char *buf, size_t count)
2932{
2933 int err;
2934 unsigned long knob;
2935
2936 err = kstrtoul(buf, 10, &knob);
2937 if (err)
2938 return err;
2939 if (knob > 1)
2940 return -EINVAL;
2941
2942 mutex_lock(&ksm_thread_mutex);
2943 wait_while_offlining();
2944 if (ksm_merge_across_nodes != knob) {
2945 if (ksm_pages_shared || remove_all_stable_nodes())
2946 err = -EBUSY;
2947 else if (root_stable_tree == one_stable_tree) {
2948 struct rb_root *buf;
2949 /*
2950 * This is the first time that we switch away from the
2951 * default of merging across nodes: must now allocate
2952 * a buffer to hold as many roots as may be needed.
2953 * Allocate stable and unstable together:
2954 * MAXSMP NODES_SHIFT 10 will use 16kB.
2955 */
2956 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2957 GFP_KERNEL);
2958 /* Let us assume that RB_ROOT is NULL is zero */
2959 if (!buf)
2960 err = -ENOMEM;
2961 else {
2962 root_stable_tree = buf;
2963 root_unstable_tree = buf + nr_node_ids;
2964 /* Stable tree is empty but not the unstable */
2965 root_unstable_tree[0] = one_unstable_tree[0];
2966 }
2967 }
2968 if (!err) {
2969 ksm_merge_across_nodes = knob;
2970 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2971 }
2972 }
2973 mutex_unlock(&ksm_thread_mutex);
2974
2975 return err ? err : count;
2976}
2977KSM_ATTR(merge_across_nodes);
2978#endif
2979
2980static ssize_t use_zero_pages_show(struct kobject *kobj,
2981 struct kobj_attribute *attr, char *buf)
2982{
2983 return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
2984}
2985static ssize_t use_zero_pages_store(struct kobject *kobj,
2986 struct kobj_attribute *attr,
2987 const char *buf, size_t count)
2988{
2989 int err;
2990 bool value;
2991
2992 err = kstrtobool(buf, &value);
2993 if (err)
2994 return -EINVAL;
2995
2996 ksm_use_zero_pages = value;
2997
2998 return count;
2999}
3000KSM_ATTR(use_zero_pages);
3001
3002static ssize_t max_page_sharing_show(struct kobject *kobj,
3003 struct kobj_attribute *attr, char *buf)
3004{
3005 return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
3006}
3007
3008static ssize_t max_page_sharing_store(struct kobject *kobj,
3009 struct kobj_attribute *attr,
3010 const char *buf, size_t count)
3011{
3012 int err;
3013 int knob;
3014
3015 err = kstrtoint(buf, 10, &knob);
3016 if (err)
3017 return err;
3018 /*
3019 * When a KSM page is created it is shared by 2 mappings. This
3020 * being a signed comparison, it implicitly verifies it's not
3021 * negative.
3022 */
3023 if (knob < 2)
3024 return -EINVAL;
3025
3026 if (READ_ONCE(ksm_max_page_sharing) == knob)
3027 return count;
3028
3029 mutex_lock(&ksm_thread_mutex);
3030 wait_while_offlining();
3031 if (ksm_max_page_sharing != knob) {
3032 if (ksm_pages_shared || remove_all_stable_nodes())
3033 err = -EBUSY;
3034 else
3035 ksm_max_page_sharing = knob;
3036 }
3037 mutex_unlock(&ksm_thread_mutex);
3038
3039 return err ? err : count;
3040}
3041KSM_ATTR(max_page_sharing);
3042
3043static ssize_t pages_shared_show(struct kobject *kobj,
3044 struct kobj_attribute *attr, char *buf)
3045{
3046 return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
3047}
3048KSM_ATTR_RO(pages_shared);
3049
3050static ssize_t pages_sharing_show(struct kobject *kobj,
3051 struct kobj_attribute *attr, char *buf)
3052{
3053 return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
3054}
3055KSM_ATTR_RO(pages_sharing);
3056
3057static ssize_t pages_unshared_show(struct kobject *kobj,
3058 struct kobj_attribute *attr, char *buf)
3059{
3060 return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
3061}
3062KSM_ATTR_RO(pages_unshared);
3063
3064static ssize_t pages_volatile_show(struct kobject *kobj,
3065 struct kobj_attribute *attr, char *buf)
3066{
3067 long ksm_pages_volatile;
3068
3069 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3070 - ksm_pages_sharing - ksm_pages_unshared;
3071 /*
3072 * It was not worth any locking to calculate that statistic,
3073 * but it might therefore sometimes be negative: conceal that.
3074 */
3075 if (ksm_pages_volatile < 0)
3076 ksm_pages_volatile = 0;
3077 return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
3078}
3079KSM_ATTR_RO(pages_volatile);
3080
3081static ssize_t stable_node_dups_show(struct kobject *kobj,
3082 struct kobj_attribute *attr, char *buf)
3083{
3084 return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
3085}
3086KSM_ATTR_RO(stable_node_dups);
3087
3088static ssize_t stable_node_chains_show(struct kobject *kobj,
3089 struct kobj_attribute *attr, char *buf)
3090{
3091 return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
3092}
3093KSM_ATTR_RO(stable_node_chains);
3094
3095static ssize_t
3096stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3097 struct kobj_attribute *attr,
3098 char *buf)
3099{
3100 return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3101}
3102
3103static ssize_t
3104stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3105 struct kobj_attribute *attr,
3106 const char *buf, size_t count)
3107{
3108 unsigned long msecs;
3109 int err;
3110
3111 err = kstrtoul(buf, 10, &msecs);
3112 if (err || msecs > UINT_MAX)
3113 return -EINVAL;
3114
3115 ksm_stable_node_chains_prune_millisecs = msecs;
3116
3117 return count;
3118}
3119KSM_ATTR(stable_node_chains_prune_millisecs);
3120
3121static ssize_t full_scans_show(struct kobject *kobj,
3122 struct kobj_attribute *attr, char *buf)
3123{
3124 return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
3125}
3126KSM_ATTR_RO(full_scans);
3127
3128static struct attribute *ksm_attrs[] = {
3129 &sleep_millisecs_attr.attr,
3130 &pages_to_scan_attr.attr,
3131 &run_attr.attr,
3132 &pages_shared_attr.attr,
3133 &pages_sharing_attr.attr,
3134 &pages_unshared_attr.attr,
3135 &pages_volatile_attr.attr,
3136 &full_scans_attr.attr,
3137#ifdef CONFIG_NUMA
3138 &merge_across_nodes_attr.attr,
3139#endif
3140 &max_page_sharing_attr.attr,
3141 &stable_node_chains_attr.attr,
3142 &stable_node_dups_attr.attr,
3143 &stable_node_chains_prune_millisecs_attr.attr,
3144 &use_zero_pages_attr.attr,
3145 NULL,
3146};
3147
3148static const struct attribute_group ksm_attr_group = {
3149 .attrs = ksm_attrs,
3150 .name = "ksm",
3151};
3152#endif /* CONFIG_SYSFS */
3153
3154static int __init ksm_init(void)
3155{
3156 struct task_struct *ksm_thread;
3157 int err;
3158
3159 /* The correct value depends on page size and endianness */
3160 zero_checksum = calc_checksum(ZERO_PAGE(0));
3161 /* Default to false for backwards compatibility */
3162 ksm_use_zero_pages = false;
3163
3164 err = ksm_slab_init();
3165 if (err)
3166 goto out;
3167
3168 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3169 if (IS_ERR(ksm_thread)) {
3170 pr_err("ksm: creating kthread failed\n");
3171 err = PTR_ERR(ksm_thread);
3172 goto out_free;
3173 }
3174
3175#ifdef CONFIG_SYSFS
3176 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3177 if (err) {
3178 pr_err("ksm: register sysfs failed\n");
3179 kthread_stop(ksm_thread);
3180 goto out_free;
3181 }
3182#else
3183 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
3184
3185#endif /* CONFIG_SYSFS */
3186
3187#ifdef CONFIG_MEMORY_HOTREMOVE
3188 /* There is no significance to this priority 100 */
3189 hotplug_memory_notifier(ksm_memory_callback, 100);
3190#endif
3191 return 0;
3192
3193out_free:
3194 ksm_slab_free();
3195out:
3196 return err;
3197}
3198subsys_initcall(ksm_init);
1/*
2 * Memory merging support.
3 *
4 * This code enables dynamic sharing of identical pages found in different
5 * memory areas, even if they are not shared by fork()
6 *
7 * Copyright (C) 2008-2009 Red Hat, Inc.
8 * Authors:
9 * Izik Eidus
10 * Andrea Arcangeli
11 * Chris Wright
12 * Hugh Dickins
13 *
14 * This work is licensed under the terms of the GNU GPL, version 2.
15 */
16
17#include <linux/errno.h>
18#include <linux/mm.h>
19#include <linux/fs.h>
20#include <linux/mman.h>
21#include <linux/sched.h>
22#include <linux/rwsem.h>
23#include <linux/pagemap.h>
24#include <linux/rmap.h>
25#include <linux/spinlock.h>
26#include <linux/jhash.h>
27#include <linux/delay.h>
28#include <linux/kthread.h>
29#include <linux/wait.h>
30#include <linux/slab.h>
31#include <linux/rbtree.h>
32#include <linux/memory.h>
33#include <linux/mmu_notifier.h>
34#include <linux/swap.h>
35#include <linux/ksm.h>
36#include <linux/hash.h>
37#include <linux/freezer.h>
38#include <linux/oom.h>
39
40#include <asm/tlbflush.h>
41#include "internal.h"
42
43/*
44 * A few notes about the KSM scanning process,
45 * to make it easier to understand the data structures below:
46 *
47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
48 * contents into a data structure that holds pointers to the pages' locations.
49 *
50 * Since the contents of the pages may change at any moment, KSM cannot just
51 * insert the pages into a normal sorted tree and expect it to find anything.
52 * Therefore KSM uses two data structures - the stable and the unstable tree.
53 *
54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
55 * by their contents. Because each such page is write-protected, searching on
56 * this tree is fully assured to be working (except when pages are unmapped),
57 * and therefore this tree is called the stable tree.
58 *
59 * In addition to the stable tree, KSM uses a second data structure called the
60 * unstable tree: this tree holds pointers to pages which have been found to
61 * be "unchanged for a period of time". The unstable tree sorts these pages
62 * by their contents, but since they are not write-protected, KSM cannot rely
63 * upon the unstable tree to work correctly - the unstable tree is liable to
64 * be corrupted as its contents are modified, and so it is called unstable.
65 *
66 * KSM solves this problem by several techniques:
67 *
68 * 1) The unstable tree is flushed every time KSM completes scanning all
69 * memory areas, and then the tree is rebuilt again from the beginning.
70 * 2) KSM will only insert into the unstable tree, pages whose hash value
71 * has not changed since the previous scan of all memory areas.
72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
73 * colors of the nodes and not on their contents, assuring that even when
74 * the tree gets "corrupted" it won't get out of balance, so scanning time
75 * remains the same (also, searching and inserting nodes in an rbtree uses
76 * the same algorithm, so we have no overhead when we flush and rebuild).
77 * 4) KSM never flushes the stable tree, which means that even if it were to
78 * take 10 attempts to find a page in the unstable tree, once it is found,
79 * it is secured in the stable tree. (When we scan a new page, we first
80 * compare it against the stable tree, and then against the unstable tree.)
81 */
82
83/**
84 * struct mm_slot - ksm information per mm that is being scanned
85 * @link: link to the mm_slots hash list
86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
88 * @mm: the mm that this information is valid for
89 */
90struct mm_slot {
91 struct hlist_node link;
92 struct list_head mm_list;
93 struct rmap_item *rmap_list;
94 struct mm_struct *mm;
95};
96
97/**
98 * struct ksm_scan - cursor for scanning
99 * @mm_slot: the current mm_slot we are scanning
100 * @address: the next address inside that to be scanned
101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
102 * @seqnr: count of completed full scans (needed when removing unstable node)
103 *
104 * There is only the one ksm_scan instance of this cursor structure.
105 */
106struct ksm_scan {
107 struct mm_slot *mm_slot;
108 unsigned long address;
109 struct rmap_item **rmap_list;
110 unsigned long seqnr;
111};
112
113/**
114 * struct stable_node - node of the stable rbtree
115 * @node: rb node of this ksm page in the stable tree
116 * @hlist: hlist head of rmap_items using this ksm page
117 * @kpfn: page frame number of this ksm page
118 */
119struct stable_node {
120 struct rb_node node;
121 struct hlist_head hlist;
122 unsigned long kpfn;
123};
124
125/**
126 * struct rmap_item - reverse mapping item for virtual addresses
127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
129 * @mm: the memory structure this rmap_item is pointing into
130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
131 * @oldchecksum: previous checksum of the page at that virtual address
132 * @node: rb node of this rmap_item in the unstable tree
133 * @head: pointer to stable_node heading this list in the stable tree
134 * @hlist: link into hlist of rmap_items hanging off that stable_node
135 */
136struct rmap_item {
137 struct rmap_item *rmap_list;
138 struct anon_vma *anon_vma; /* when stable */
139 struct mm_struct *mm;
140 unsigned long address; /* + low bits used for flags below */
141 unsigned int oldchecksum; /* when unstable */
142 union {
143 struct rb_node node; /* when node of unstable tree */
144 struct { /* when listed from stable tree */
145 struct stable_node *head;
146 struct hlist_node hlist;
147 };
148 };
149};
150
151#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
152#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
153#define STABLE_FLAG 0x200 /* is listed from the stable tree */
154
155/* The stable and unstable tree heads */
156static struct rb_root root_stable_tree = RB_ROOT;
157static struct rb_root root_unstable_tree = RB_ROOT;
158
159#define MM_SLOTS_HASH_SHIFT 10
160#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
161static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
162
163static struct mm_slot ksm_mm_head = {
164 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
165};
166static struct ksm_scan ksm_scan = {
167 .mm_slot = &ksm_mm_head,
168};
169
170static struct kmem_cache *rmap_item_cache;
171static struct kmem_cache *stable_node_cache;
172static struct kmem_cache *mm_slot_cache;
173
174/* The number of nodes in the stable tree */
175static unsigned long ksm_pages_shared;
176
177/* The number of page slots additionally sharing those nodes */
178static unsigned long ksm_pages_sharing;
179
180/* The number of nodes in the unstable tree */
181static unsigned long ksm_pages_unshared;
182
183/* The number of rmap_items in use: to calculate pages_volatile */
184static unsigned long ksm_rmap_items;
185
186/* Number of pages ksmd should scan in one batch */
187static unsigned int ksm_thread_pages_to_scan = 100;
188
189/* Milliseconds ksmd should sleep between batches */
190static unsigned int ksm_thread_sleep_millisecs = 20;
191
192#define KSM_RUN_STOP 0
193#define KSM_RUN_MERGE 1
194#define KSM_RUN_UNMERGE 2
195static unsigned int ksm_run = KSM_RUN_STOP;
196
197static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
198static DEFINE_MUTEX(ksm_thread_mutex);
199static DEFINE_SPINLOCK(ksm_mmlist_lock);
200
201#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
202 sizeof(struct __struct), __alignof__(struct __struct),\
203 (__flags), NULL)
204
205static int __init ksm_slab_init(void)
206{
207 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
208 if (!rmap_item_cache)
209 goto out;
210
211 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
212 if (!stable_node_cache)
213 goto out_free1;
214
215 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
216 if (!mm_slot_cache)
217 goto out_free2;
218
219 return 0;
220
221out_free2:
222 kmem_cache_destroy(stable_node_cache);
223out_free1:
224 kmem_cache_destroy(rmap_item_cache);
225out:
226 return -ENOMEM;
227}
228
229static void __init ksm_slab_free(void)
230{
231 kmem_cache_destroy(mm_slot_cache);
232 kmem_cache_destroy(stable_node_cache);
233 kmem_cache_destroy(rmap_item_cache);
234 mm_slot_cache = NULL;
235}
236
237static inline struct rmap_item *alloc_rmap_item(void)
238{
239 struct rmap_item *rmap_item;
240
241 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
242 if (rmap_item)
243 ksm_rmap_items++;
244 return rmap_item;
245}
246
247static inline void free_rmap_item(struct rmap_item *rmap_item)
248{
249 ksm_rmap_items--;
250 rmap_item->mm = NULL; /* debug safety */
251 kmem_cache_free(rmap_item_cache, rmap_item);
252}
253
254static inline struct stable_node *alloc_stable_node(void)
255{
256 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
257}
258
259static inline void free_stable_node(struct stable_node *stable_node)
260{
261 kmem_cache_free(stable_node_cache, stable_node);
262}
263
264static inline struct mm_slot *alloc_mm_slot(void)
265{
266 if (!mm_slot_cache) /* initialization failed */
267 return NULL;
268 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
269}
270
271static inline void free_mm_slot(struct mm_slot *mm_slot)
272{
273 kmem_cache_free(mm_slot_cache, mm_slot);
274}
275
276static struct mm_slot *get_mm_slot(struct mm_struct *mm)
277{
278 struct mm_slot *mm_slot;
279 struct hlist_head *bucket;
280 struct hlist_node *node;
281
282 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
283 hlist_for_each_entry(mm_slot, node, bucket, link) {
284 if (mm == mm_slot->mm)
285 return mm_slot;
286 }
287 return NULL;
288}
289
290static void insert_to_mm_slots_hash(struct mm_struct *mm,
291 struct mm_slot *mm_slot)
292{
293 struct hlist_head *bucket;
294
295 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
296 mm_slot->mm = mm;
297 hlist_add_head(&mm_slot->link, bucket);
298}
299
300static inline int in_stable_tree(struct rmap_item *rmap_item)
301{
302 return rmap_item->address & STABLE_FLAG;
303}
304
305/*
306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
307 * page tables after it has passed through ksm_exit() - which, if necessary,
308 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
309 * a special flag: they can just back out as soon as mm_users goes to zero.
310 * ksm_test_exit() is used throughout to make this test for exit: in some
311 * places for correctness, in some places just to avoid unnecessary work.
312 */
313static inline bool ksm_test_exit(struct mm_struct *mm)
314{
315 return atomic_read(&mm->mm_users) == 0;
316}
317
318/*
319 * We use break_ksm to break COW on a ksm page: it's a stripped down
320 *
321 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
322 * put_page(page);
323 *
324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
325 * in case the application has unmapped and remapped mm,addr meanwhile.
326 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
328 */
329static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
330{
331 struct page *page;
332 int ret = 0;
333
334 do {
335 cond_resched();
336 page = follow_page(vma, addr, FOLL_GET);
337 if (IS_ERR_OR_NULL(page))
338 break;
339 if (PageKsm(page))
340 ret = handle_mm_fault(vma->vm_mm, vma, addr,
341 FAULT_FLAG_WRITE);
342 else
343 ret = VM_FAULT_WRITE;
344 put_page(page);
345 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
346 /*
347 * We must loop because handle_mm_fault() may back out if there's
348 * any difficulty e.g. if pte accessed bit gets updated concurrently.
349 *
350 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
351 * COW has been broken, even if the vma does not permit VM_WRITE;
352 * but note that a concurrent fault might break PageKsm for us.
353 *
354 * VM_FAULT_SIGBUS could occur if we race with truncation of the
355 * backing file, which also invalidates anonymous pages: that's
356 * okay, that truncation will have unmapped the PageKsm for us.
357 *
358 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
359 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
360 * current task has TIF_MEMDIE set, and will be OOM killed on return
361 * to user; and ksmd, having no mm, would never be chosen for that.
362 *
363 * But if the mm is in a limited mem_cgroup, then the fault may fail
364 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
365 * even ksmd can fail in this way - though it's usually breaking ksm
366 * just to undo a merge it made a moment before, so unlikely to oom.
367 *
368 * That's a pity: we might therefore have more kernel pages allocated
369 * than we're counting as nodes in the stable tree; but ksm_do_scan
370 * will retry to break_cow on each pass, so should recover the page
371 * in due course. The important thing is to not let VM_MERGEABLE
372 * be cleared while any such pages might remain in the area.
373 */
374 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
375}
376
377static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
378 unsigned long addr)
379{
380 struct vm_area_struct *vma;
381 if (ksm_test_exit(mm))
382 return NULL;
383 vma = find_vma(mm, addr);
384 if (!vma || vma->vm_start > addr)
385 return NULL;
386 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
387 return NULL;
388 return vma;
389}
390
391static void break_cow(struct rmap_item *rmap_item)
392{
393 struct mm_struct *mm = rmap_item->mm;
394 unsigned long addr = rmap_item->address;
395 struct vm_area_struct *vma;
396
397 /*
398 * It is not an accident that whenever we want to break COW
399 * to undo, we also need to drop a reference to the anon_vma.
400 */
401 put_anon_vma(rmap_item->anon_vma);
402
403 down_read(&mm->mmap_sem);
404 vma = find_mergeable_vma(mm, addr);
405 if (vma)
406 break_ksm(vma, addr);
407 up_read(&mm->mmap_sem);
408}
409
410static struct page *page_trans_compound_anon(struct page *page)
411{
412 if (PageTransCompound(page)) {
413 struct page *head = compound_trans_head(page);
414 /*
415 * head may actually be splitted and freed from under
416 * us but it's ok here.
417 */
418 if (PageAnon(head))
419 return head;
420 }
421 return NULL;
422}
423
424static struct page *get_mergeable_page(struct rmap_item *rmap_item)
425{
426 struct mm_struct *mm = rmap_item->mm;
427 unsigned long addr = rmap_item->address;
428 struct vm_area_struct *vma;
429 struct page *page;
430
431 down_read(&mm->mmap_sem);
432 vma = find_mergeable_vma(mm, addr);
433 if (!vma)
434 goto out;
435
436 page = follow_page(vma, addr, FOLL_GET);
437 if (IS_ERR_OR_NULL(page))
438 goto out;
439 if (PageAnon(page) || page_trans_compound_anon(page)) {
440 flush_anon_page(vma, page, addr);
441 flush_dcache_page(page);
442 } else {
443 put_page(page);
444out: page = NULL;
445 }
446 up_read(&mm->mmap_sem);
447 return page;
448}
449
450static void remove_node_from_stable_tree(struct stable_node *stable_node)
451{
452 struct rmap_item *rmap_item;
453 struct hlist_node *hlist;
454
455 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
456 if (rmap_item->hlist.next)
457 ksm_pages_sharing--;
458 else
459 ksm_pages_shared--;
460 put_anon_vma(rmap_item->anon_vma);
461 rmap_item->address &= PAGE_MASK;
462 cond_resched();
463 }
464
465 rb_erase(&stable_node->node, &root_stable_tree);
466 free_stable_node(stable_node);
467}
468
469/*
470 * get_ksm_page: checks if the page indicated by the stable node
471 * is still its ksm page, despite having held no reference to it.
472 * In which case we can trust the content of the page, and it
473 * returns the gotten page; but if the page has now been zapped,
474 * remove the stale node from the stable tree and return NULL.
475 *
476 * You would expect the stable_node to hold a reference to the ksm page.
477 * But if it increments the page's count, swapping out has to wait for
478 * ksmd to come around again before it can free the page, which may take
479 * seconds or even minutes: much too unresponsive. So instead we use a
480 * "keyhole reference": access to the ksm page from the stable node peeps
481 * out through its keyhole to see if that page still holds the right key,
482 * pointing back to this stable node. This relies on freeing a PageAnon
483 * page to reset its page->mapping to NULL, and relies on no other use of
484 * a page to put something that might look like our key in page->mapping.
485 *
486 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
487 * but this is different - made simpler by ksm_thread_mutex being held, but
488 * interesting for assuming that no other use of the struct page could ever
489 * put our expected_mapping into page->mapping (or a field of the union which
490 * coincides with page->mapping). The RCU calls are not for KSM at all, but
491 * to keep the page_count protocol described with page_cache_get_speculative.
492 *
493 * Note: it is possible that get_ksm_page() will return NULL one moment,
494 * then page the next, if the page is in between page_freeze_refs() and
495 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
496 * is on its way to being freed; but it is an anomaly to bear in mind.
497 */
498static struct page *get_ksm_page(struct stable_node *stable_node)
499{
500 struct page *page;
501 void *expected_mapping;
502
503 page = pfn_to_page(stable_node->kpfn);
504 expected_mapping = (void *)stable_node +
505 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
506 rcu_read_lock();
507 if (page->mapping != expected_mapping)
508 goto stale;
509 if (!get_page_unless_zero(page))
510 goto stale;
511 if (page->mapping != expected_mapping) {
512 put_page(page);
513 goto stale;
514 }
515 rcu_read_unlock();
516 return page;
517stale:
518 rcu_read_unlock();
519 remove_node_from_stable_tree(stable_node);
520 return NULL;
521}
522
523/*
524 * Removing rmap_item from stable or unstable tree.
525 * This function will clean the information from the stable/unstable tree.
526 */
527static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
528{
529 if (rmap_item->address & STABLE_FLAG) {
530 struct stable_node *stable_node;
531 struct page *page;
532
533 stable_node = rmap_item->head;
534 page = get_ksm_page(stable_node);
535 if (!page)
536 goto out;
537
538 lock_page(page);
539 hlist_del(&rmap_item->hlist);
540 unlock_page(page);
541 put_page(page);
542
543 if (stable_node->hlist.first)
544 ksm_pages_sharing--;
545 else
546 ksm_pages_shared--;
547
548 put_anon_vma(rmap_item->anon_vma);
549 rmap_item->address &= PAGE_MASK;
550
551 } else if (rmap_item->address & UNSTABLE_FLAG) {
552 unsigned char age;
553 /*
554 * Usually ksmd can and must skip the rb_erase, because
555 * root_unstable_tree was already reset to RB_ROOT.
556 * But be careful when an mm is exiting: do the rb_erase
557 * if this rmap_item was inserted by this scan, rather
558 * than left over from before.
559 */
560 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
561 BUG_ON(age > 1);
562 if (!age)
563 rb_erase(&rmap_item->node, &root_unstable_tree);
564
565 ksm_pages_unshared--;
566 rmap_item->address &= PAGE_MASK;
567 }
568out:
569 cond_resched(); /* we're called from many long loops */
570}
571
572static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
573 struct rmap_item **rmap_list)
574{
575 while (*rmap_list) {
576 struct rmap_item *rmap_item = *rmap_list;
577 *rmap_list = rmap_item->rmap_list;
578 remove_rmap_item_from_tree(rmap_item);
579 free_rmap_item(rmap_item);
580 }
581}
582
583/*
584 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
585 * than check every pte of a given vma, the locking doesn't quite work for
586 * that - an rmap_item is assigned to the stable tree after inserting ksm
587 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
588 * rmap_items from parent to child at fork time (so as not to waste time
589 * if exit comes before the next scan reaches it).
590 *
591 * Similarly, although we'd like to remove rmap_items (so updating counts
592 * and freeing memory) when unmerging an area, it's easier to leave that
593 * to the next pass of ksmd - consider, for example, how ksmd might be
594 * in cmp_and_merge_page on one of the rmap_items we would be removing.
595 */
596static int unmerge_ksm_pages(struct vm_area_struct *vma,
597 unsigned long start, unsigned long end)
598{
599 unsigned long addr;
600 int err = 0;
601
602 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
603 if (ksm_test_exit(vma->vm_mm))
604 break;
605 if (signal_pending(current))
606 err = -ERESTARTSYS;
607 else
608 err = break_ksm(vma, addr);
609 }
610 return err;
611}
612
613#ifdef CONFIG_SYSFS
614/*
615 * Only called through the sysfs control interface:
616 */
617static int unmerge_and_remove_all_rmap_items(void)
618{
619 struct mm_slot *mm_slot;
620 struct mm_struct *mm;
621 struct vm_area_struct *vma;
622 int err = 0;
623
624 spin_lock(&ksm_mmlist_lock);
625 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
626 struct mm_slot, mm_list);
627 spin_unlock(&ksm_mmlist_lock);
628
629 for (mm_slot = ksm_scan.mm_slot;
630 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
631 mm = mm_slot->mm;
632 down_read(&mm->mmap_sem);
633 for (vma = mm->mmap; vma; vma = vma->vm_next) {
634 if (ksm_test_exit(mm))
635 break;
636 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
637 continue;
638 err = unmerge_ksm_pages(vma,
639 vma->vm_start, vma->vm_end);
640 if (err)
641 goto error;
642 }
643
644 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
645
646 spin_lock(&ksm_mmlist_lock);
647 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
648 struct mm_slot, mm_list);
649 if (ksm_test_exit(mm)) {
650 hlist_del(&mm_slot->link);
651 list_del(&mm_slot->mm_list);
652 spin_unlock(&ksm_mmlist_lock);
653
654 free_mm_slot(mm_slot);
655 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
656 up_read(&mm->mmap_sem);
657 mmdrop(mm);
658 } else {
659 spin_unlock(&ksm_mmlist_lock);
660 up_read(&mm->mmap_sem);
661 }
662 }
663
664 ksm_scan.seqnr = 0;
665 return 0;
666
667error:
668 up_read(&mm->mmap_sem);
669 spin_lock(&ksm_mmlist_lock);
670 ksm_scan.mm_slot = &ksm_mm_head;
671 spin_unlock(&ksm_mmlist_lock);
672 return err;
673}
674#endif /* CONFIG_SYSFS */
675
676static u32 calc_checksum(struct page *page)
677{
678 u32 checksum;
679 void *addr = kmap_atomic(page);
680 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
681 kunmap_atomic(addr);
682 return checksum;
683}
684
685static int memcmp_pages(struct page *page1, struct page *page2)
686{
687 char *addr1, *addr2;
688 int ret;
689
690 addr1 = kmap_atomic(page1);
691 addr2 = kmap_atomic(page2);
692 ret = memcmp(addr1, addr2, PAGE_SIZE);
693 kunmap_atomic(addr2);
694 kunmap_atomic(addr1);
695 return ret;
696}
697
698static inline int pages_identical(struct page *page1, struct page *page2)
699{
700 return !memcmp_pages(page1, page2);
701}
702
703static int write_protect_page(struct vm_area_struct *vma, struct page *page,
704 pte_t *orig_pte)
705{
706 struct mm_struct *mm = vma->vm_mm;
707 unsigned long addr;
708 pte_t *ptep;
709 spinlock_t *ptl;
710 int swapped;
711 int err = -EFAULT;
712
713 addr = page_address_in_vma(page, vma);
714 if (addr == -EFAULT)
715 goto out;
716
717 BUG_ON(PageTransCompound(page));
718 ptep = page_check_address(page, mm, addr, &ptl, 0);
719 if (!ptep)
720 goto out;
721
722 if (pte_write(*ptep) || pte_dirty(*ptep)) {
723 pte_t entry;
724
725 swapped = PageSwapCache(page);
726 flush_cache_page(vma, addr, page_to_pfn(page));
727 /*
728 * Ok this is tricky, when get_user_pages_fast() run it doesn't
729 * take any lock, therefore the check that we are going to make
730 * with the pagecount against the mapcount is racey and
731 * O_DIRECT can happen right after the check.
732 * So we clear the pte and flush the tlb before the check
733 * this assure us that no O_DIRECT can happen after the check
734 * or in the middle of the check.
735 */
736 entry = ptep_clear_flush(vma, addr, ptep);
737 /*
738 * Check that no O_DIRECT or similar I/O is in progress on the
739 * page
740 */
741 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
742 set_pte_at(mm, addr, ptep, entry);
743 goto out_unlock;
744 }
745 if (pte_dirty(entry))
746 set_page_dirty(page);
747 entry = pte_mkclean(pte_wrprotect(entry));
748 set_pte_at_notify(mm, addr, ptep, entry);
749 }
750 *orig_pte = *ptep;
751 err = 0;
752
753out_unlock:
754 pte_unmap_unlock(ptep, ptl);
755out:
756 return err;
757}
758
759/**
760 * replace_page - replace page in vma by new ksm page
761 * @vma: vma that holds the pte pointing to page
762 * @page: the page we are replacing by kpage
763 * @kpage: the ksm page we replace page by
764 * @orig_pte: the original value of the pte
765 *
766 * Returns 0 on success, -EFAULT on failure.
767 */
768static int replace_page(struct vm_area_struct *vma, struct page *page,
769 struct page *kpage, pte_t orig_pte)
770{
771 struct mm_struct *mm = vma->vm_mm;
772 pgd_t *pgd;
773 pud_t *pud;
774 pmd_t *pmd;
775 pte_t *ptep;
776 spinlock_t *ptl;
777 unsigned long addr;
778 int err = -EFAULT;
779
780 addr = page_address_in_vma(page, vma);
781 if (addr == -EFAULT)
782 goto out;
783
784 pgd = pgd_offset(mm, addr);
785 if (!pgd_present(*pgd))
786 goto out;
787
788 pud = pud_offset(pgd, addr);
789 if (!pud_present(*pud))
790 goto out;
791
792 pmd = pmd_offset(pud, addr);
793 BUG_ON(pmd_trans_huge(*pmd));
794 if (!pmd_present(*pmd))
795 goto out;
796
797 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
798 if (!pte_same(*ptep, orig_pte)) {
799 pte_unmap_unlock(ptep, ptl);
800 goto out;
801 }
802
803 get_page(kpage);
804 page_add_anon_rmap(kpage, vma, addr);
805
806 flush_cache_page(vma, addr, pte_pfn(*ptep));
807 ptep_clear_flush(vma, addr, ptep);
808 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
809
810 page_remove_rmap(page);
811 if (!page_mapped(page))
812 try_to_free_swap(page);
813 put_page(page);
814
815 pte_unmap_unlock(ptep, ptl);
816 err = 0;
817out:
818 return err;
819}
820
821static int page_trans_compound_anon_split(struct page *page)
822{
823 int ret = 0;
824 struct page *transhuge_head = page_trans_compound_anon(page);
825 if (transhuge_head) {
826 /* Get the reference on the head to split it. */
827 if (get_page_unless_zero(transhuge_head)) {
828 /*
829 * Recheck we got the reference while the head
830 * was still anonymous.
831 */
832 if (PageAnon(transhuge_head))
833 ret = split_huge_page(transhuge_head);
834 else
835 /*
836 * Retry later if split_huge_page run
837 * from under us.
838 */
839 ret = 1;
840 put_page(transhuge_head);
841 } else
842 /* Retry later if split_huge_page run from under us. */
843 ret = 1;
844 }
845 return ret;
846}
847
848/*
849 * try_to_merge_one_page - take two pages and merge them into one
850 * @vma: the vma that holds the pte pointing to page
851 * @page: the PageAnon page that we want to replace with kpage
852 * @kpage: the PageKsm page that we want to map instead of page,
853 * or NULL the first time when we want to use page as kpage.
854 *
855 * This function returns 0 if the pages were merged, -EFAULT otherwise.
856 */
857static int try_to_merge_one_page(struct vm_area_struct *vma,
858 struct page *page, struct page *kpage)
859{
860 pte_t orig_pte = __pte(0);
861 int err = -EFAULT;
862
863 if (page == kpage) /* ksm page forked */
864 return 0;
865
866 if (!(vma->vm_flags & VM_MERGEABLE))
867 goto out;
868 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
869 goto out;
870 BUG_ON(PageTransCompound(page));
871 if (!PageAnon(page))
872 goto out;
873
874 /*
875 * We need the page lock to read a stable PageSwapCache in
876 * write_protect_page(). We use trylock_page() instead of
877 * lock_page() because we don't want to wait here - we
878 * prefer to continue scanning and merging different pages,
879 * then come back to this page when it is unlocked.
880 */
881 if (!trylock_page(page))
882 goto out;
883 /*
884 * If this anonymous page is mapped only here, its pte may need
885 * to be write-protected. If it's mapped elsewhere, all of its
886 * ptes are necessarily already write-protected. But in either
887 * case, we need to lock and check page_count is not raised.
888 */
889 if (write_protect_page(vma, page, &orig_pte) == 0) {
890 if (!kpage) {
891 /*
892 * While we hold page lock, upgrade page from
893 * PageAnon+anon_vma to PageKsm+NULL stable_node:
894 * stable_tree_insert() will update stable_node.
895 */
896 set_page_stable_node(page, NULL);
897 mark_page_accessed(page);
898 err = 0;
899 } else if (pages_identical(page, kpage))
900 err = replace_page(vma, page, kpage, orig_pte);
901 }
902
903 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
904 munlock_vma_page(page);
905 if (!PageMlocked(kpage)) {
906 unlock_page(page);
907 lock_page(kpage);
908 mlock_vma_page(kpage);
909 page = kpage; /* for final unlock */
910 }
911 }
912
913 unlock_page(page);
914out:
915 return err;
916}
917
918/*
919 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
920 * but no new kernel page is allocated: kpage must already be a ksm page.
921 *
922 * This function returns 0 if the pages were merged, -EFAULT otherwise.
923 */
924static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
925 struct page *page, struct page *kpage)
926{
927 struct mm_struct *mm = rmap_item->mm;
928 struct vm_area_struct *vma;
929 int err = -EFAULT;
930
931 down_read(&mm->mmap_sem);
932 if (ksm_test_exit(mm))
933 goto out;
934 vma = find_vma(mm, rmap_item->address);
935 if (!vma || vma->vm_start > rmap_item->address)
936 goto out;
937
938 err = try_to_merge_one_page(vma, page, kpage);
939 if (err)
940 goto out;
941
942 /* Must get reference to anon_vma while still holding mmap_sem */
943 rmap_item->anon_vma = vma->anon_vma;
944 get_anon_vma(vma->anon_vma);
945out:
946 up_read(&mm->mmap_sem);
947 return err;
948}
949
950/*
951 * try_to_merge_two_pages - take two identical pages and prepare them
952 * to be merged into one page.
953 *
954 * This function returns the kpage if we successfully merged two identical
955 * pages into one ksm page, NULL otherwise.
956 *
957 * Note that this function upgrades page to ksm page: if one of the pages
958 * is already a ksm page, try_to_merge_with_ksm_page should be used.
959 */
960static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
961 struct page *page,
962 struct rmap_item *tree_rmap_item,
963 struct page *tree_page)
964{
965 int err;
966
967 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
968 if (!err) {
969 err = try_to_merge_with_ksm_page(tree_rmap_item,
970 tree_page, page);
971 /*
972 * If that fails, we have a ksm page with only one pte
973 * pointing to it: so break it.
974 */
975 if (err)
976 break_cow(rmap_item);
977 }
978 return err ? NULL : page;
979}
980
981/*
982 * stable_tree_search - search for page inside the stable tree
983 *
984 * This function checks if there is a page inside the stable tree
985 * with identical content to the page that we are scanning right now.
986 *
987 * This function returns the stable tree node of identical content if found,
988 * NULL otherwise.
989 */
990static struct page *stable_tree_search(struct page *page)
991{
992 struct rb_node *node = root_stable_tree.rb_node;
993 struct stable_node *stable_node;
994
995 stable_node = page_stable_node(page);
996 if (stable_node) { /* ksm page forked */
997 get_page(page);
998 return page;
999 }
1000
1001 while (node) {
1002 struct page *tree_page;
1003 int ret;
1004
1005 cond_resched();
1006 stable_node = rb_entry(node, struct stable_node, node);
1007 tree_page = get_ksm_page(stable_node);
1008 if (!tree_page)
1009 return NULL;
1010
1011 ret = memcmp_pages(page, tree_page);
1012
1013 if (ret < 0) {
1014 put_page(tree_page);
1015 node = node->rb_left;
1016 } else if (ret > 0) {
1017 put_page(tree_page);
1018 node = node->rb_right;
1019 } else
1020 return tree_page;
1021 }
1022
1023 return NULL;
1024}
1025
1026/*
1027 * stable_tree_insert - insert rmap_item pointing to new ksm page
1028 * into the stable tree.
1029 *
1030 * This function returns the stable tree node just allocated on success,
1031 * NULL otherwise.
1032 */
1033static struct stable_node *stable_tree_insert(struct page *kpage)
1034{
1035 struct rb_node **new = &root_stable_tree.rb_node;
1036 struct rb_node *parent = NULL;
1037 struct stable_node *stable_node;
1038
1039 while (*new) {
1040 struct page *tree_page;
1041 int ret;
1042
1043 cond_resched();
1044 stable_node = rb_entry(*new, struct stable_node, node);
1045 tree_page = get_ksm_page(stable_node);
1046 if (!tree_page)
1047 return NULL;
1048
1049 ret = memcmp_pages(kpage, tree_page);
1050 put_page(tree_page);
1051
1052 parent = *new;
1053 if (ret < 0)
1054 new = &parent->rb_left;
1055 else if (ret > 0)
1056 new = &parent->rb_right;
1057 else {
1058 /*
1059 * It is not a bug that stable_tree_search() didn't
1060 * find this node: because at that time our page was
1061 * not yet write-protected, so may have changed since.
1062 */
1063 return NULL;
1064 }
1065 }
1066
1067 stable_node = alloc_stable_node();
1068 if (!stable_node)
1069 return NULL;
1070
1071 rb_link_node(&stable_node->node, parent, new);
1072 rb_insert_color(&stable_node->node, &root_stable_tree);
1073
1074 INIT_HLIST_HEAD(&stable_node->hlist);
1075
1076 stable_node->kpfn = page_to_pfn(kpage);
1077 set_page_stable_node(kpage, stable_node);
1078
1079 return stable_node;
1080}
1081
1082/*
1083 * unstable_tree_search_insert - search for identical page,
1084 * else insert rmap_item into the unstable tree.
1085 *
1086 * This function searches for a page in the unstable tree identical to the
1087 * page currently being scanned; and if no identical page is found in the
1088 * tree, we insert rmap_item as a new object into the unstable tree.
1089 *
1090 * This function returns pointer to rmap_item found to be identical
1091 * to the currently scanned page, NULL otherwise.
1092 *
1093 * This function does both searching and inserting, because they share
1094 * the same walking algorithm in an rbtree.
1095 */
1096static
1097struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1098 struct page *page,
1099 struct page **tree_pagep)
1100
1101{
1102 struct rb_node **new = &root_unstable_tree.rb_node;
1103 struct rb_node *parent = NULL;
1104
1105 while (*new) {
1106 struct rmap_item *tree_rmap_item;
1107 struct page *tree_page;
1108 int ret;
1109
1110 cond_resched();
1111 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1112 tree_page = get_mergeable_page(tree_rmap_item);
1113 if (IS_ERR_OR_NULL(tree_page))
1114 return NULL;
1115
1116 /*
1117 * Don't substitute a ksm page for a forked page.
1118 */
1119 if (page == tree_page) {
1120 put_page(tree_page);
1121 return NULL;
1122 }
1123
1124 ret = memcmp_pages(page, tree_page);
1125
1126 parent = *new;
1127 if (ret < 0) {
1128 put_page(tree_page);
1129 new = &parent->rb_left;
1130 } else if (ret > 0) {
1131 put_page(tree_page);
1132 new = &parent->rb_right;
1133 } else {
1134 *tree_pagep = tree_page;
1135 return tree_rmap_item;
1136 }
1137 }
1138
1139 rmap_item->address |= UNSTABLE_FLAG;
1140 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1141 rb_link_node(&rmap_item->node, parent, new);
1142 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1143
1144 ksm_pages_unshared++;
1145 return NULL;
1146}
1147
1148/*
1149 * stable_tree_append - add another rmap_item to the linked list of
1150 * rmap_items hanging off a given node of the stable tree, all sharing
1151 * the same ksm page.
1152 */
1153static void stable_tree_append(struct rmap_item *rmap_item,
1154 struct stable_node *stable_node)
1155{
1156 rmap_item->head = stable_node;
1157 rmap_item->address |= STABLE_FLAG;
1158 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1159
1160 if (rmap_item->hlist.next)
1161 ksm_pages_sharing++;
1162 else
1163 ksm_pages_shared++;
1164}
1165
1166/*
1167 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1168 * if not, compare checksum to previous and if it's the same, see if page can
1169 * be inserted into the unstable tree, or merged with a page already there and
1170 * both transferred to the stable tree.
1171 *
1172 * @page: the page that we are searching identical page to.
1173 * @rmap_item: the reverse mapping into the virtual address of this page
1174 */
1175static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1176{
1177 struct rmap_item *tree_rmap_item;
1178 struct page *tree_page = NULL;
1179 struct stable_node *stable_node;
1180 struct page *kpage;
1181 unsigned int checksum;
1182 int err;
1183
1184 remove_rmap_item_from_tree(rmap_item);
1185
1186 /* We first start with searching the page inside the stable tree */
1187 kpage = stable_tree_search(page);
1188 if (kpage) {
1189 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1190 if (!err) {
1191 /*
1192 * The page was successfully merged:
1193 * add its rmap_item to the stable tree.
1194 */
1195 lock_page(kpage);
1196 stable_tree_append(rmap_item, page_stable_node(kpage));
1197 unlock_page(kpage);
1198 }
1199 put_page(kpage);
1200 return;
1201 }
1202
1203 /*
1204 * If the hash value of the page has changed from the last time
1205 * we calculated it, this page is changing frequently: therefore we
1206 * don't want to insert it in the unstable tree, and we don't want
1207 * to waste our time searching for something identical to it there.
1208 */
1209 checksum = calc_checksum(page);
1210 if (rmap_item->oldchecksum != checksum) {
1211 rmap_item->oldchecksum = checksum;
1212 return;
1213 }
1214
1215 tree_rmap_item =
1216 unstable_tree_search_insert(rmap_item, page, &tree_page);
1217 if (tree_rmap_item) {
1218 kpage = try_to_merge_two_pages(rmap_item, page,
1219 tree_rmap_item, tree_page);
1220 put_page(tree_page);
1221 /*
1222 * As soon as we merge this page, we want to remove the
1223 * rmap_item of the page we have merged with from the unstable
1224 * tree, and insert it instead as new node in the stable tree.
1225 */
1226 if (kpage) {
1227 remove_rmap_item_from_tree(tree_rmap_item);
1228
1229 lock_page(kpage);
1230 stable_node = stable_tree_insert(kpage);
1231 if (stable_node) {
1232 stable_tree_append(tree_rmap_item, stable_node);
1233 stable_tree_append(rmap_item, stable_node);
1234 }
1235 unlock_page(kpage);
1236
1237 /*
1238 * If we fail to insert the page into the stable tree,
1239 * we will have 2 virtual addresses that are pointing
1240 * to a ksm page left outside the stable tree,
1241 * in which case we need to break_cow on both.
1242 */
1243 if (!stable_node) {
1244 break_cow(tree_rmap_item);
1245 break_cow(rmap_item);
1246 }
1247 }
1248 }
1249}
1250
1251static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1252 struct rmap_item **rmap_list,
1253 unsigned long addr)
1254{
1255 struct rmap_item *rmap_item;
1256
1257 while (*rmap_list) {
1258 rmap_item = *rmap_list;
1259 if ((rmap_item->address & PAGE_MASK) == addr)
1260 return rmap_item;
1261 if (rmap_item->address > addr)
1262 break;
1263 *rmap_list = rmap_item->rmap_list;
1264 remove_rmap_item_from_tree(rmap_item);
1265 free_rmap_item(rmap_item);
1266 }
1267
1268 rmap_item = alloc_rmap_item();
1269 if (rmap_item) {
1270 /* It has already been zeroed */
1271 rmap_item->mm = mm_slot->mm;
1272 rmap_item->address = addr;
1273 rmap_item->rmap_list = *rmap_list;
1274 *rmap_list = rmap_item;
1275 }
1276 return rmap_item;
1277}
1278
1279static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1280{
1281 struct mm_struct *mm;
1282 struct mm_slot *slot;
1283 struct vm_area_struct *vma;
1284 struct rmap_item *rmap_item;
1285
1286 if (list_empty(&ksm_mm_head.mm_list))
1287 return NULL;
1288
1289 slot = ksm_scan.mm_slot;
1290 if (slot == &ksm_mm_head) {
1291 /*
1292 * A number of pages can hang around indefinitely on per-cpu
1293 * pagevecs, raised page count preventing write_protect_page
1294 * from merging them. Though it doesn't really matter much,
1295 * it is puzzling to see some stuck in pages_volatile until
1296 * other activity jostles them out, and they also prevented
1297 * LTP's KSM test from succeeding deterministically; so drain
1298 * them here (here rather than on entry to ksm_do_scan(),
1299 * so we don't IPI too often when pages_to_scan is set low).
1300 */
1301 lru_add_drain_all();
1302
1303 root_unstable_tree = RB_ROOT;
1304
1305 spin_lock(&ksm_mmlist_lock);
1306 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1307 ksm_scan.mm_slot = slot;
1308 spin_unlock(&ksm_mmlist_lock);
1309 /*
1310 * Although we tested list_empty() above, a racing __ksm_exit
1311 * of the last mm on the list may have removed it since then.
1312 */
1313 if (slot == &ksm_mm_head)
1314 return NULL;
1315next_mm:
1316 ksm_scan.address = 0;
1317 ksm_scan.rmap_list = &slot->rmap_list;
1318 }
1319
1320 mm = slot->mm;
1321 down_read(&mm->mmap_sem);
1322 if (ksm_test_exit(mm))
1323 vma = NULL;
1324 else
1325 vma = find_vma(mm, ksm_scan.address);
1326
1327 for (; vma; vma = vma->vm_next) {
1328 if (!(vma->vm_flags & VM_MERGEABLE))
1329 continue;
1330 if (ksm_scan.address < vma->vm_start)
1331 ksm_scan.address = vma->vm_start;
1332 if (!vma->anon_vma)
1333 ksm_scan.address = vma->vm_end;
1334
1335 while (ksm_scan.address < vma->vm_end) {
1336 if (ksm_test_exit(mm))
1337 break;
1338 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1339 if (IS_ERR_OR_NULL(*page)) {
1340 ksm_scan.address += PAGE_SIZE;
1341 cond_resched();
1342 continue;
1343 }
1344 if (PageAnon(*page) ||
1345 page_trans_compound_anon(*page)) {
1346 flush_anon_page(vma, *page, ksm_scan.address);
1347 flush_dcache_page(*page);
1348 rmap_item = get_next_rmap_item(slot,
1349 ksm_scan.rmap_list, ksm_scan.address);
1350 if (rmap_item) {
1351 ksm_scan.rmap_list =
1352 &rmap_item->rmap_list;
1353 ksm_scan.address += PAGE_SIZE;
1354 } else
1355 put_page(*page);
1356 up_read(&mm->mmap_sem);
1357 return rmap_item;
1358 }
1359 put_page(*page);
1360 ksm_scan.address += PAGE_SIZE;
1361 cond_resched();
1362 }
1363 }
1364
1365 if (ksm_test_exit(mm)) {
1366 ksm_scan.address = 0;
1367 ksm_scan.rmap_list = &slot->rmap_list;
1368 }
1369 /*
1370 * Nuke all the rmap_items that are above this current rmap:
1371 * because there were no VM_MERGEABLE vmas with such addresses.
1372 */
1373 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1374
1375 spin_lock(&ksm_mmlist_lock);
1376 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1377 struct mm_slot, mm_list);
1378 if (ksm_scan.address == 0) {
1379 /*
1380 * We've completed a full scan of all vmas, holding mmap_sem
1381 * throughout, and found no VM_MERGEABLE: so do the same as
1382 * __ksm_exit does to remove this mm from all our lists now.
1383 * This applies either when cleaning up after __ksm_exit
1384 * (but beware: we can reach here even before __ksm_exit),
1385 * or when all VM_MERGEABLE areas have been unmapped (and
1386 * mmap_sem then protects against race with MADV_MERGEABLE).
1387 */
1388 hlist_del(&slot->link);
1389 list_del(&slot->mm_list);
1390 spin_unlock(&ksm_mmlist_lock);
1391
1392 free_mm_slot(slot);
1393 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1394 up_read(&mm->mmap_sem);
1395 mmdrop(mm);
1396 } else {
1397 spin_unlock(&ksm_mmlist_lock);
1398 up_read(&mm->mmap_sem);
1399 }
1400
1401 /* Repeat until we've completed scanning the whole list */
1402 slot = ksm_scan.mm_slot;
1403 if (slot != &ksm_mm_head)
1404 goto next_mm;
1405
1406 ksm_scan.seqnr++;
1407 return NULL;
1408}
1409
1410/**
1411 * ksm_do_scan - the ksm scanner main worker function.
1412 * @scan_npages - number of pages we want to scan before we return.
1413 */
1414static void ksm_do_scan(unsigned int scan_npages)
1415{
1416 struct rmap_item *rmap_item;
1417 struct page *uninitialized_var(page);
1418
1419 while (scan_npages-- && likely(!freezing(current))) {
1420 cond_resched();
1421 rmap_item = scan_get_next_rmap_item(&page);
1422 if (!rmap_item)
1423 return;
1424 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1425 cmp_and_merge_page(page, rmap_item);
1426 put_page(page);
1427 }
1428}
1429
1430static int ksmd_should_run(void)
1431{
1432 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1433}
1434
1435static int ksm_scan_thread(void *nothing)
1436{
1437 set_freezable();
1438 set_user_nice(current, 5);
1439
1440 while (!kthread_should_stop()) {
1441 mutex_lock(&ksm_thread_mutex);
1442 if (ksmd_should_run())
1443 ksm_do_scan(ksm_thread_pages_to_scan);
1444 mutex_unlock(&ksm_thread_mutex);
1445
1446 try_to_freeze();
1447
1448 if (ksmd_should_run()) {
1449 schedule_timeout_interruptible(
1450 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1451 } else {
1452 wait_event_freezable(ksm_thread_wait,
1453 ksmd_should_run() || kthread_should_stop());
1454 }
1455 }
1456 return 0;
1457}
1458
1459int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1460 unsigned long end, int advice, unsigned long *vm_flags)
1461{
1462 struct mm_struct *mm = vma->vm_mm;
1463 int err;
1464
1465 switch (advice) {
1466 case MADV_MERGEABLE:
1467 /*
1468 * Be somewhat over-protective for now!
1469 */
1470 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1471 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1472 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1473 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1474 return 0; /* just ignore the advice */
1475
1476 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1477 err = __ksm_enter(mm);
1478 if (err)
1479 return err;
1480 }
1481
1482 *vm_flags |= VM_MERGEABLE;
1483 break;
1484
1485 case MADV_UNMERGEABLE:
1486 if (!(*vm_flags & VM_MERGEABLE))
1487 return 0; /* just ignore the advice */
1488
1489 if (vma->anon_vma) {
1490 err = unmerge_ksm_pages(vma, start, end);
1491 if (err)
1492 return err;
1493 }
1494
1495 *vm_flags &= ~VM_MERGEABLE;
1496 break;
1497 }
1498
1499 return 0;
1500}
1501
1502int __ksm_enter(struct mm_struct *mm)
1503{
1504 struct mm_slot *mm_slot;
1505 int needs_wakeup;
1506
1507 mm_slot = alloc_mm_slot();
1508 if (!mm_slot)
1509 return -ENOMEM;
1510
1511 /* Check ksm_run too? Would need tighter locking */
1512 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1513
1514 spin_lock(&ksm_mmlist_lock);
1515 insert_to_mm_slots_hash(mm, mm_slot);
1516 /*
1517 * Insert just behind the scanning cursor, to let the area settle
1518 * down a little; when fork is followed by immediate exec, we don't
1519 * want ksmd to waste time setting up and tearing down an rmap_list.
1520 */
1521 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1522 spin_unlock(&ksm_mmlist_lock);
1523
1524 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1525 atomic_inc(&mm->mm_count);
1526
1527 if (needs_wakeup)
1528 wake_up_interruptible(&ksm_thread_wait);
1529
1530 return 0;
1531}
1532
1533void __ksm_exit(struct mm_struct *mm)
1534{
1535 struct mm_slot *mm_slot;
1536 int easy_to_free = 0;
1537
1538 /*
1539 * This process is exiting: if it's straightforward (as is the
1540 * case when ksmd was never running), free mm_slot immediately.
1541 * But if it's at the cursor or has rmap_items linked to it, use
1542 * mmap_sem to synchronize with any break_cows before pagetables
1543 * are freed, and leave the mm_slot on the list for ksmd to free.
1544 * Beware: ksm may already have noticed it exiting and freed the slot.
1545 */
1546
1547 spin_lock(&ksm_mmlist_lock);
1548 mm_slot = get_mm_slot(mm);
1549 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1550 if (!mm_slot->rmap_list) {
1551 hlist_del(&mm_slot->link);
1552 list_del(&mm_slot->mm_list);
1553 easy_to_free = 1;
1554 } else {
1555 list_move(&mm_slot->mm_list,
1556 &ksm_scan.mm_slot->mm_list);
1557 }
1558 }
1559 spin_unlock(&ksm_mmlist_lock);
1560
1561 if (easy_to_free) {
1562 free_mm_slot(mm_slot);
1563 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1564 mmdrop(mm);
1565 } else if (mm_slot) {
1566 down_write(&mm->mmap_sem);
1567 up_write(&mm->mmap_sem);
1568 }
1569}
1570
1571struct page *ksm_does_need_to_copy(struct page *page,
1572 struct vm_area_struct *vma, unsigned long address)
1573{
1574 struct page *new_page;
1575
1576 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1577 if (new_page) {
1578 copy_user_highpage(new_page, page, address, vma);
1579
1580 SetPageDirty(new_page);
1581 __SetPageUptodate(new_page);
1582 SetPageSwapBacked(new_page);
1583 __set_page_locked(new_page);
1584
1585 if (page_evictable(new_page, vma))
1586 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1587 else
1588 add_page_to_unevictable_list(new_page);
1589 }
1590
1591 return new_page;
1592}
1593
1594int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1595 unsigned long *vm_flags)
1596{
1597 struct stable_node *stable_node;
1598 struct rmap_item *rmap_item;
1599 struct hlist_node *hlist;
1600 unsigned int mapcount = page_mapcount(page);
1601 int referenced = 0;
1602 int search_new_forks = 0;
1603
1604 VM_BUG_ON(!PageKsm(page));
1605 VM_BUG_ON(!PageLocked(page));
1606
1607 stable_node = page_stable_node(page);
1608 if (!stable_node)
1609 return 0;
1610again:
1611 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1612 struct anon_vma *anon_vma = rmap_item->anon_vma;
1613 struct anon_vma_chain *vmac;
1614 struct vm_area_struct *vma;
1615
1616 anon_vma_lock(anon_vma);
1617 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1618 vma = vmac->vma;
1619 if (rmap_item->address < vma->vm_start ||
1620 rmap_item->address >= vma->vm_end)
1621 continue;
1622 /*
1623 * Initially we examine only the vma which covers this
1624 * rmap_item; but later, if there is still work to do,
1625 * we examine covering vmas in other mms: in case they
1626 * were forked from the original since ksmd passed.
1627 */
1628 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1629 continue;
1630
1631 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1632 continue;
1633
1634 referenced += page_referenced_one(page, vma,
1635 rmap_item->address, &mapcount, vm_flags);
1636 if (!search_new_forks || !mapcount)
1637 break;
1638 }
1639 anon_vma_unlock(anon_vma);
1640 if (!mapcount)
1641 goto out;
1642 }
1643 if (!search_new_forks++)
1644 goto again;
1645out:
1646 return referenced;
1647}
1648
1649int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1650{
1651 struct stable_node *stable_node;
1652 struct hlist_node *hlist;
1653 struct rmap_item *rmap_item;
1654 int ret = SWAP_AGAIN;
1655 int search_new_forks = 0;
1656
1657 VM_BUG_ON(!PageKsm(page));
1658 VM_BUG_ON(!PageLocked(page));
1659
1660 stable_node = page_stable_node(page);
1661 if (!stable_node)
1662 return SWAP_FAIL;
1663again:
1664 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1665 struct anon_vma *anon_vma = rmap_item->anon_vma;
1666 struct anon_vma_chain *vmac;
1667 struct vm_area_struct *vma;
1668
1669 anon_vma_lock(anon_vma);
1670 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1671 vma = vmac->vma;
1672 if (rmap_item->address < vma->vm_start ||
1673 rmap_item->address >= vma->vm_end)
1674 continue;
1675 /*
1676 * Initially we examine only the vma which covers this
1677 * rmap_item; but later, if there is still work to do,
1678 * we examine covering vmas in other mms: in case they
1679 * were forked from the original since ksmd passed.
1680 */
1681 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1682 continue;
1683
1684 ret = try_to_unmap_one(page, vma,
1685 rmap_item->address, flags);
1686 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1687 anon_vma_unlock(anon_vma);
1688 goto out;
1689 }
1690 }
1691 anon_vma_unlock(anon_vma);
1692 }
1693 if (!search_new_forks++)
1694 goto again;
1695out:
1696 return ret;
1697}
1698
1699#ifdef CONFIG_MIGRATION
1700int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1701 struct vm_area_struct *, unsigned long, void *), void *arg)
1702{
1703 struct stable_node *stable_node;
1704 struct hlist_node *hlist;
1705 struct rmap_item *rmap_item;
1706 int ret = SWAP_AGAIN;
1707 int search_new_forks = 0;
1708
1709 VM_BUG_ON(!PageKsm(page));
1710 VM_BUG_ON(!PageLocked(page));
1711
1712 stable_node = page_stable_node(page);
1713 if (!stable_node)
1714 return ret;
1715again:
1716 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1717 struct anon_vma *anon_vma = rmap_item->anon_vma;
1718 struct anon_vma_chain *vmac;
1719 struct vm_area_struct *vma;
1720
1721 anon_vma_lock(anon_vma);
1722 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1723 vma = vmac->vma;
1724 if (rmap_item->address < vma->vm_start ||
1725 rmap_item->address >= vma->vm_end)
1726 continue;
1727 /*
1728 * Initially we examine only the vma which covers this
1729 * rmap_item; but later, if there is still work to do,
1730 * we examine covering vmas in other mms: in case they
1731 * were forked from the original since ksmd passed.
1732 */
1733 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1734 continue;
1735
1736 ret = rmap_one(page, vma, rmap_item->address, arg);
1737 if (ret != SWAP_AGAIN) {
1738 anon_vma_unlock(anon_vma);
1739 goto out;
1740 }
1741 }
1742 anon_vma_unlock(anon_vma);
1743 }
1744 if (!search_new_forks++)
1745 goto again;
1746out:
1747 return ret;
1748}
1749
1750void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1751{
1752 struct stable_node *stable_node;
1753
1754 VM_BUG_ON(!PageLocked(oldpage));
1755 VM_BUG_ON(!PageLocked(newpage));
1756 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1757
1758 stable_node = page_stable_node(newpage);
1759 if (stable_node) {
1760 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1761 stable_node->kpfn = page_to_pfn(newpage);
1762 }
1763}
1764#endif /* CONFIG_MIGRATION */
1765
1766#ifdef CONFIG_MEMORY_HOTREMOVE
1767static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1768 unsigned long end_pfn)
1769{
1770 struct rb_node *node;
1771
1772 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1773 struct stable_node *stable_node;
1774
1775 stable_node = rb_entry(node, struct stable_node, node);
1776 if (stable_node->kpfn >= start_pfn &&
1777 stable_node->kpfn < end_pfn)
1778 return stable_node;
1779 }
1780 return NULL;
1781}
1782
1783static int ksm_memory_callback(struct notifier_block *self,
1784 unsigned long action, void *arg)
1785{
1786 struct memory_notify *mn = arg;
1787 struct stable_node *stable_node;
1788
1789 switch (action) {
1790 case MEM_GOING_OFFLINE:
1791 /*
1792 * Keep it very simple for now: just lock out ksmd and
1793 * MADV_UNMERGEABLE while any memory is going offline.
1794 * mutex_lock_nested() is necessary because lockdep was alarmed
1795 * that here we take ksm_thread_mutex inside notifier chain
1796 * mutex, and later take notifier chain mutex inside
1797 * ksm_thread_mutex to unlock it. But that's safe because both
1798 * are inside mem_hotplug_mutex.
1799 */
1800 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1801 break;
1802
1803 case MEM_OFFLINE:
1804 /*
1805 * Most of the work is done by page migration; but there might
1806 * be a few stable_nodes left over, still pointing to struct
1807 * pages which have been offlined: prune those from the tree.
1808 */
1809 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1810 mn->start_pfn + mn->nr_pages)) != NULL)
1811 remove_node_from_stable_tree(stable_node);
1812 /* fallthrough */
1813
1814 case MEM_CANCEL_OFFLINE:
1815 mutex_unlock(&ksm_thread_mutex);
1816 break;
1817 }
1818 return NOTIFY_OK;
1819}
1820#endif /* CONFIG_MEMORY_HOTREMOVE */
1821
1822#ifdef CONFIG_SYSFS
1823/*
1824 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1825 */
1826
1827#define KSM_ATTR_RO(_name) \
1828 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1829#define KSM_ATTR(_name) \
1830 static struct kobj_attribute _name##_attr = \
1831 __ATTR(_name, 0644, _name##_show, _name##_store)
1832
1833static ssize_t sleep_millisecs_show(struct kobject *kobj,
1834 struct kobj_attribute *attr, char *buf)
1835{
1836 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1837}
1838
1839static ssize_t sleep_millisecs_store(struct kobject *kobj,
1840 struct kobj_attribute *attr,
1841 const char *buf, size_t count)
1842{
1843 unsigned long msecs;
1844 int err;
1845
1846 err = strict_strtoul(buf, 10, &msecs);
1847 if (err || msecs > UINT_MAX)
1848 return -EINVAL;
1849
1850 ksm_thread_sleep_millisecs = msecs;
1851
1852 return count;
1853}
1854KSM_ATTR(sleep_millisecs);
1855
1856static ssize_t pages_to_scan_show(struct kobject *kobj,
1857 struct kobj_attribute *attr, char *buf)
1858{
1859 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1860}
1861
1862static ssize_t pages_to_scan_store(struct kobject *kobj,
1863 struct kobj_attribute *attr,
1864 const char *buf, size_t count)
1865{
1866 int err;
1867 unsigned long nr_pages;
1868
1869 err = strict_strtoul(buf, 10, &nr_pages);
1870 if (err || nr_pages > UINT_MAX)
1871 return -EINVAL;
1872
1873 ksm_thread_pages_to_scan = nr_pages;
1874
1875 return count;
1876}
1877KSM_ATTR(pages_to_scan);
1878
1879static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1880 char *buf)
1881{
1882 return sprintf(buf, "%u\n", ksm_run);
1883}
1884
1885static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1886 const char *buf, size_t count)
1887{
1888 int err;
1889 unsigned long flags;
1890
1891 err = strict_strtoul(buf, 10, &flags);
1892 if (err || flags > UINT_MAX)
1893 return -EINVAL;
1894 if (flags > KSM_RUN_UNMERGE)
1895 return -EINVAL;
1896
1897 /*
1898 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1899 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1900 * breaking COW to free the pages_shared (but leaves mm_slots
1901 * on the list for when ksmd may be set running again).
1902 */
1903
1904 mutex_lock(&ksm_thread_mutex);
1905 if (ksm_run != flags) {
1906 ksm_run = flags;
1907 if (flags & KSM_RUN_UNMERGE) {
1908 int oom_score_adj;
1909
1910 oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1911 err = unmerge_and_remove_all_rmap_items();
1912 compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1913 oom_score_adj);
1914 if (err) {
1915 ksm_run = KSM_RUN_STOP;
1916 count = err;
1917 }
1918 }
1919 }
1920 mutex_unlock(&ksm_thread_mutex);
1921
1922 if (flags & KSM_RUN_MERGE)
1923 wake_up_interruptible(&ksm_thread_wait);
1924
1925 return count;
1926}
1927KSM_ATTR(run);
1928
1929static ssize_t pages_shared_show(struct kobject *kobj,
1930 struct kobj_attribute *attr, char *buf)
1931{
1932 return sprintf(buf, "%lu\n", ksm_pages_shared);
1933}
1934KSM_ATTR_RO(pages_shared);
1935
1936static ssize_t pages_sharing_show(struct kobject *kobj,
1937 struct kobj_attribute *attr, char *buf)
1938{
1939 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1940}
1941KSM_ATTR_RO(pages_sharing);
1942
1943static ssize_t pages_unshared_show(struct kobject *kobj,
1944 struct kobj_attribute *attr, char *buf)
1945{
1946 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1947}
1948KSM_ATTR_RO(pages_unshared);
1949
1950static ssize_t pages_volatile_show(struct kobject *kobj,
1951 struct kobj_attribute *attr, char *buf)
1952{
1953 long ksm_pages_volatile;
1954
1955 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1956 - ksm_pages_sharing - ksm_pages_unshared;
1957 /*
1958 * It was not worth any locking to calculate that statistic,
1959 * but it might therefore sometimes be negative: conceal that.
1960 */
1961 if (ksm_pages_volatile < 0)
1962 ksm_pages_volatile = 0;
1963 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1964}
1965KSM_ATTR_RO(pages_volatile);
1966
1967static ssize_t full_scans_show(struct kobject *kobj,
1968 struct kobj_attribute *attr, char *buf)
1969{
1970 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1971}
1972KSM_ATTR_RO(full_scans);
1973
1974static struct attribute *ksm_attrs[] = {
1975 &sleep_millisecs_attr.attr,
1976 &pages_to_scan_attr.attr,
1977 &run_attr.attr,
1978 &pages_shared_attr.attr,
1979 &pages_sharing_attr.attr,
1980 &pages_unshared_attr.attr,
1981 &pages_volatile_attr.attr,
1982 &full_scans_attr.attr,
1983 NULL,
1984};
1985
1986static struct attribute_group ksm_attr_group = {
1987 .attrs = ksm_attrs,
1988 .name = "ksm",
1989};
1990#endif /* CONFIG_SYSFS */
1991
1992static int __init ksm_init(void)
1993{
1994 struct task_struct *ksm_thread;
1995 int err;
1996
1997 err = ksm_slab_init();
1998 if (err)
1999 goto out;
2000
2001 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2002 if (IS_ERR(ksm_thread)) {
2003 printk(KERN_ERR "ksm: creating kthread failed\n");
2004 err = PTR_ERR(ksm_thread);
2005 goto out_free;
2006 }
2007
2008#ifdef CONFIG_SYSFS
2009 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2010 if (err) {
2011 printk(KERN_ERR "ksm: register sysfs failed\n");
2012 kthread_stop(ksm_thread);
2013 goto out_free;
2014 }
2015#else
2016 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2017
2018#endif /* CONFIG_SYSFS */
2019
2020#ifdef CONFIG_MEMORY_HOTREMOVE
2021 /*
2022 * Choose a high priority since the callback takes ksm_thread_mutex:
2023 * later callbacks could only be taking locks which nest within that.
2024 */
2025 hotplug_memory_notifier(ksm_memory_callback, 100);
2026#endif
2027 return 0;
2028
2029out_free:
2030 ksm_slab_free();
2031out:
2032 return err;
2033}
2034module_init(ksm_init)