Loading...
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 :c:type:`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#define KSM_FLAG_MASK (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG)
219 /* to mask all the flags */
220
221/* The stable and unstable tree heads */
222static struct rb_root one_stable_tree[1] = { RB_ROOT };
223static struct rb_root one_unstable_tree[1] = { RB_ROOT };
224static struct rb_root *root_stable_tree = one_stable_tree;
225static struct rb_root *root_unstable_tree = one_unstable_tree;
226
227/* Recently migrated nodes of stable tree, pending proper placement */
228static LIST_HEAD(migrate_nodes);
229#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
230
231#define MM_SLOTS_HASH_BITS 10
232static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
233
234static struct mm_slot ksm_mm_head = {
235 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
236};
237static struct ksm_scan ksm_scan = {
238 .mm_slot = &ksm_mm_head,
239};
240
241static struct kmem_cache *rmap_item_cache;
242static struct kmem_cache *stable_node_cache;
243static struct kmem_cache *mm_slot_cache;
244
245/* The number of nodes in the stable tree */
246static unsigned long ksm_pages_shared;
247
248/* The number of page slots additionally sharing those nodes */
249static unsigned long ksm_pages_sharing;
250
251/* The number of nodes in the unstable tree */
252static unsigned long ksm_pages_unshared;
253
254/* The number of rmap_items in use: to calculate pages_volatile */
255static unsigned long ksm_rmap_items;
256
257/* The number of stable_node chains */
258static unsigned long ksm_stable_node_chains;
259
260/* The number of stable_node dups linked to the stable_node chains */
261static unsigned long ksm_stable_node_dups;
262
263/* Delay in pruning stale stable_node_dups in the stable_node_chains */
264static int ksm_stable_node_chains_prune_millisecs = 2000;
265
266/* Maximum number of page slots sharing a stable node */
267static int ksm_max_page_sharing = 256;
268
269/* Number of pages ksmd should scan in one batch */
270static unsigned int ksm_thread_pages_to_scan = 100;
271
272/* Milliseconds ksmd should sleep between batches */
273static unsigned int ksm_thread_sleep_millisecs = 20;
274
275/* Checksum of an empty (zeroed) page */
276static unsigned int zero_checksum __read_mostly;
277
278/* Whether to merge empty (zeroed) pages with actual zero pages */
279static bool ksm_use_zero_pages __read_mostly;
280
281#ifdef CONFIG_NUMA
282/* Zeroed when merging across nodes is not allowed */
283static unsigned int ksm_merge_across_nodes = 1;
284static int ksm_nr_node_ids = 1;
285#else
286#define ksm_merge_across_nodes 1U
287#define ksm_nr_node_ids 1
288#endif
289
290#define KSM_RUN_STOP 0
291#define KSM_RUN_MERGE 1
292#define KSM_RUN_UNMERGE 2
293#define KSM_RUN_OFFLINE 4
294static unsigned long ksm_run = KSM_RUN_STOP;
295static void wait_while_offlining(void);
296
297static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
298static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
299static DEFINE_MUTEX(ksm_thread_mutex);
300static DEFINE_SPINLOCK(ksm_mmlist_lock);
301
302#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
303 sizeof(struct __struct), __alignof__(struct __struct),\
304 (__flags), NULL)
305
306static int __init ksm_slab_init(void)
307{
308 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
309 if (!rmap_item_cache)
310 goto out;
311
312 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
313 if (!stable_node_cache)
314 goto out_free1;
315
316 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
317 if (!mm_slot_cache)
318 goto out_free2;
319
320 return 0;
321
322out_free2:
323 kmem_cache_destroy(stable_node_cache);
324out_free1:
325 kmem_cache_destroy(rmap_item_cache);
326out:
327 return -ENOMEM;
328}
329
330static void __init ksm_slab_free(void)
331{
332 kmem_cache_destroy(mm_slot_cache);
333 kmem_cache_destroy(stable_node_cache);
334 kmem_cache_destroy(rmap_item_cache);
335 mm_slot_cache = NULL;
336}
337
338static __always_inline bool is_stable_node_chain(struct stable_node *chain)
339{
340 return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
341}
342
343static __always_inline bool is_stable_node_dup(struct stable_node *dup)
344{
345 return dup->head == STABLE_NODE_DUP_HEAD;
346}
347
348static inline void stable_node_chain_add_dup(struct stable_node *dup,
349 struct stable_node *chain)
350{
351 VM_BUG_ON(is_stable_node_dup(dup));
352 dup->head = STABLE_NODE_DUP_HEAD;
353 VM_BUG_ON(!is_stable_node_chain(chain));
354 hlist_add_head(&dup->hlist_dup, &chain->hlist);
355 ksm_stable_node_dups++;
356}
357
358static inline void __stable_node_dup_del(struct stable_node *dup)
359{
360 VM_BUG_ON(!is_stable_node_dup(dup));
361 hlist_del(&dup->hlist_dup);
362 ksm_stable_node_dups--;
363}
364
365static inline void stable_node_dup_del(struct stable_node *dup)
366{
367 VM_BUG_ON(is_stable_node_chain(dup));
368 if (is_stable_node_dup(dup))
369 __stable_node_dup_del(dup);
370 else
371 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
372#ifdef CONFIG_DEBUG_VM
373 dup->head = NULL;
374#endif
375}
376
377static inline struct rmap_item *alloc_rmap_item(void)
378{
379 struct rmap_item *rmap_item;
380
381 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
382 __GFP_NORETRY | __GFP_NOWARN);
383 if (rmap_item)
384 ksm_rmap_items++;
385 return rmap_item;
386}
387
388static inline void free_rmap_item(struct rmap_item *rmap_item)
389{
390 ksm_rmap_items--;
391 rmap_item->mm = NULL; /* debug safety */
392 kmem_cache_free(rmap_item_cache, rmap_item);
393}
394
395static inline struct stable_node *alloc_stable_node(void)
396{
397 /*
398 * The allocation can take too long with GFP_KERNEL when memory is under
399 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
400 * grants access to memory reserves, helping to avoid this problem.
401 */
402 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
403}
404
405static inline void free_stable_node(struct stable_node *stable_node)
406{
407 VM_BUG_ON(stable_node->rmap_hlist_len &&
408 !is_stable_node_chain(stable_node));
409 kmem_cache_free(stable_node_cache, stable_node);
410}
411
412static inline struct mm_slot *alloc_mm_slot(void)
413{
414 if (!mm_slot_cache) /* initialization failed */
415 return NULL;
416 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
417}
418
419static inline void free_mm_slot(struct mm_slot *mm_slot)
420{
421 kmem_cache_free(mm_slot_cache, mm_slot);
422}
423
424static struct mm_slot *get_mm_slot(struct mm_struct *mm)
425{
426 struct mm_slot *slot;
427
428 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
429 if (slot->mm == mm)
430 return slot;
431
432 return NULL;
433}
434
435static void insert_to_mm_slots_hash(struct mm_struct *mm,
436 struct mm_slot *mm_slot)
437{
438 mm_slot->mm = mm;
439 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
440}
441
442/*
443 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
444 * page tables after it has passed through ksm_exit() - which, if necessary,
445 * takes mmap_lock briefly to serialize against them. ksm_exit() does not set
446 * a special flag: they can just back out as soon as mm_users goes to zero.
447 * ksm_test_exit() is used throughout to make this test for exit: in some
448 * places for correctness, in some places just to avoid unnecessary work.
449 */
450static inline bool ksm_test_exit(struct mm_struct *mm)
451{
452 return atomic_read(&mm->mm_users) == 0;
453}
454
455/*
456 * We use break_ksm to break COW on a ksm page: it's a stripped down
457 *
458 * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
459 * put_page(page);
460 *
461 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
462 * in case the application has unmapped and remapped mm,addr meanwhile.
463 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
464 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
465 *
466 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
467 * of the process that owns 'vma'. We also do not want to enforce
468 * protection keys here anyway.
469 */
470static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
471{
472 struct page *page;
473 vm_fault_t ret = 0;
474
475 do {
476 cond_resched();
477 page = follow_page(vma, addr,
478 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
479 if (IS_ERR_OR_NULL(page))
480 break;
481 if (PageKsm(page))
482 ret = handle_mm_fault(vma, addr,
483 FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
484 NULL);
485 else
486 ret = VM_FAULT_WRITE;
487 put_page(page);
488 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
489 /*
490 * We must loop because handle_mm_fault() may back out if there's
491 * any difficulty e.g. if pte accessed bit gets updated concurrently.
492 *
493 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
494 * COW has been broken, even if the vma does not permit VM_WRITE;
495 * but note that a concurrent fault might break PageKsm for us.
496 *
497 * VM_FAULT_SIGBUS could occur if we race with truncation of the
498 * backing file, which also invalidates anonymous pages: that's
499 * okay, that truncation will have unmapped the PageKsm for us.
500 *
501 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
502 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
503 * current task has TIF_MEMDIE set, and will be OOM killed on return
504 * to user; and ksmd, having no mm, would never be chosen for that.
505 *
506 * But if the mm is in a limited mem_cgroup, then the fault may fail
507 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
508 * even ksmd can fail in this way - though it's usually breaking ksm
509 * just to undo a merge it made a moment before, so unlikely to oom.
510 *
511 * That's a pity: we might therefore have more kernel pages allocated
512 * than we're counting as nodes in the stable tree; but ksm_do_scan
513 * will retry to break_cow on each pass, so should recover the page
514 * in due course. The important thing is to not let VM_MERGEABLE
515 * be cleared while any such pages might remain in the area.
516 */
517 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
518}
519
520static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
521 unsigned long addr)
522{
523 struct vm_area_struct *vma;
524 if (ksm_test_exit(mm))
525 return NULL;
526 vma = find_vma(mm, addr);
527 if (!vma || vma->vm_start > addr)
528 return NULL;
529 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
530 return NULL;
531 return vma;
532}
533
534static void break_cow(struct rmap_item *rmap_item)
535{
536 struct mm_struct *mm = rmap_item->mm;
537 unsigned long addr = rmap_item->address;
538 struct vm_area_struct *vma;
539
540 /*
541 * It is not an accident that whenever we want to break COW
542 * to undo, we also need to drop a reference to the anon_vma.
543 */
544 put_anon_vma(rmap_item->anon_vma);
545
546 mmap_read_lock(mm);
547 vma = find_mergeable_vma(mm, addr);
548 if (vma)
549 break_ksm(vma, addr);
550 mmap_read_unlock(mm);
551}
552
553static struct page *get_mergeable_page(struct rmap_item *rmap_item)
554{
555 struct mm_struct *mm = rmap_item->mm;
556 unsigned long addr = rmap_item->address;
557 struct vm_area_struct *vma;
558 struct page *page;
559
560 mmap_read_lock(mm);
561 vma = find_mergeable_vma(mm, addr);
562 if (!vma)
563 goto out;
564
565 page = follow_page(vma, addr, FOLL_GET);
566 if (IS_ERR_OR_NULL(page))
567 goto out;
568 if (PageAnon(page)) {
569 flush_anon_page(vma, page, addr);
570 flush_dcache_page(page);
571 } else {
572 put_page(page);
573out:
574 page = NULL;
575 }
576 mmap_read_unlock(mm);
577 return page;
578}
579
580/*
581 * This helper is used for getting right index into array of tree roots.
582 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
583 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
584 * every node has its own stable and unstable tree.
585 */
586static inline int get_kpfn_nid(unsigned long kpfn)
587{
588 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
589}
590
591static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
592 struct rb_root *root)
593{
594 struct stable_node *chain = alloc_stable_node();
595 VM_BUG_ON(is_stable_node_chain(dup));
596 if (likely(chain)) {
597 INIT_HLIST_HEAD(&chain->hlist);
598 chain->chain_prune_time = jiffies;
599 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
600#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
601 chain->nid = NUMA_NO_NODE; /* debug */
602#endif
603 ksm_stable_node_chains++;
604
605 /*
606 * Put the stable node chain in the first dimension of
607 * the stable tree and at the same time remove the old
608 * stable node.
609 */
610 rb_replace_node(&dup->node, &chain->node, root);
611
612 /*
613 * Move the old stable node to the second dimension
614 * queued in the hlist_dup. The invariant is that all
615 * dup stable_nodes in the chain->hlist point to pages
616 * that are write protected and have the exact same
617 * content.
618 */
619 stable_node_chain_add_dup(dup, chain);
620 }
621 return chain;
622}
623
624static inline void free_stable_node_chain(struct stable_node *chain,
625 struct rb_root *root)
626{
627 rb_erase(&chain->node, root);
628 free_stable_node(chain);
629 ksm_stable_node_chains--;
630}
631
632static void remove_node_from_stable_tree(struct stable_node *stable_node)
633{
634 struct rmap_item *rmap_item;
635
636 /* check it's not STABLE_NODE_CHAIN or negative */
637 BUG_ON(stable_node->rmap_hlist_len < 0);
638
639 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
640 if (rmap_item->hlist.next)
641 ksm_pages_sharing--;
642 else
643 ksm_pages_shared--;
644 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
645 stable_node->rmap_hlist_len--;
646 put_anon_vma(rmap_item->anon_vma);
647 rmap_item->address &= PAGE_MASK;
648 cond_resched();
649 }
650
651 /*
652 * We need the second aligned pointer of the migrate_nodes
653 * list_head to stay clear from the rb_parent_color union
654 * (aligned and different than any node) and also different
655 * from &migrate_nodes. This will verify that future list.h changes
656 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
657 */
658#if defined(GCC_VERSION) && GCC_VERSION >= 40903
659 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
660 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
661#endif
662
663 if (stable_node->head == &migrate_nodes)
664 list_del(&stable_node->list);
665 else
666 stable_node_dup_del(stable_node);
667 free_stable_node(stable_node);
668}
669
670enum get_ksm_page_flags {
671 GET_KSM_PAGE_NOLOCK,
672 GET_KSM_PAGE_LOCK,
673 GET_KSM_PAGE_TRYLOCK
674};
675
676/*
677 * get_ksm_page: checks if the page indicated by the stable node
678 * is still its ksm page, despite having held no reference to it.
679 * In which case we can trust the content of the page, and it
680 * returns the gotten page; but if the page has now been zapped,
681 * remove the stale node from the stable tree and return NULL.
682 * But beware, the stable node's page might be being migrated.
683 *
684 * You would expect the stable_node to hold a reference to the ksm page.
685 * But if it increments the page's count, swapping out has to wait for
686 * ksmd to come around again before it can free the page, which may take
687 * seconds or even minutes: much too unresponsive. So instead we use a
688 * "keyhole reference": access to the ksm page from the stable node peeps
689 * out through its keyhole to see if that page still holds the right key,
690 * pointing back to this stable node. This relies on freeing a PageAnon
691 * page to reset its page->mapping to NULL, and relies on no other use of
692 * a page to put something that might look like our key in page->mapping.
693 * is on its way to being freed; but it is an anomaly to bear in mind.
694 */
695static struct page *get_ksm_page(struct stable_node *stable_node,
696 enum get_ksm_page_flags flags)
697{
698 struct page *page;
699 void *expected_mapping;
700 unsigned long kpfn;
701
702 expected_mapping = (void *)((unsigned long)stable_node |
703 PAGE_MAPPING_KSM);
704again:
705 kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
706 page = pfn_to_page(kpfn);
707 if (READ_ONCE(page->mapping) != expected_mapping)
708 goto stale;
709
710 /*
711 * We cannot do anything with the page while its refcount is 0.
712 * Usually 0 means free, or tail of a higher-order page: in which
713 * case this node is no longer referenced, and should be freed;
714 * however, it might mean that the page is under page_ref_freeze().
715 * The __remove_mapping() case is easy, again the node is now stale;
716 * the same is in reuse_ksm_page() case; but if page is swapcache
717 * in migrate_page_move_mapping(), it might still be our page,
718 * in which case it's essential to keep the node.
719 */
720 while (!get_page_unless_zero(page)) {
721 /*
722 * Another check for page->mapping != expected_mapping would
723 * work here too. We have chosen the !PageSwapCache test to
724 * optimize the common case, when the page is or is about to
725 * be freed: PageSwapCache is cleared (under spin_lock_irq)
726 * in the ref_freeze section of __remove_mapping(); but Anon
727 * page->mapping reset to NULL later, in free_pages_prepare().
728 */
729 if (!PageSwapCache(page))
730 goto stale;
731 cpu_relax();
732 }
733
734 if (READ_ONCE(page->mapping) != expected_mapping) {
735 put_page(page);
736 goto stale;
737 }
738
739 if (flags == GET_KSM_PAGE_TRYLOCK) {
740 if (!trylock_page(page)) {
741 put_page(page);
742 return ERR_PTR(-EBUSY);
743 }
744 } else if (flags == GET_KSM_PAGE_LOCK)
745 lock_page(page);
746
747 if (flags != GET_KSM_PAGE_NOLOCK) {
748 if (READ_ONCE(page->mapping) != expected_mapping) {
749 unlock_page(page);
750 put_page(page);
751 goto stale;
752 }
753 }
754 return page;
755
756stale:
757 /*
758 * We come here from above when page->mapping or !PageSwapCache
759 * suggests that the node is stale; but it might be under migration.
760 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
761 * before checking whether node->kpfn has been changed.
762 */
763 smp_rmb();
764 if (READ_ONCE(stable_node->kpfn) != kpfn)
765 goto again;
766 remove_node_from_stable_tree(stable_node);
767 return NULL;
768}
769
770/*
771 * Removing rmap_item from stable or unstable tree.
772 * This function will clean the information from the stable/unstable tree.
773 */
774static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
775{
776 if (rmap_item->address & STABLE_FLAG) {
777 struct stable_node *stable_node;
778 struct page *page;
779
780 stable_node = rmap_item->head;
781 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
782 if (!page)
783 goto out;
784
785 hlist_del(&rmap_item->hlist);
786 unlock_page(page);
787 put_page(page);
788
789 if (!hlist_empty(&stable_node->hlist))
790 ksm_pages_sharing--;
791 else
792 ksm_pages_shared--;
793 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
794 stable_node->rmap_hlist_len--;
795
796 put_anon_vma(rmap_item->anon_vma);
797 rmap_item->address &= PAGE_MASK;
798
799 } else if (rmap_item->address & UNSTABLE_FLAG) {
800 unsigned char age;
801 /*
802 * Usually ksmd can and must skip the rb_erase, because
803 * root_unstable_tree was already reset to RB_ROOT.
804 * But be careful when an mm is exiting: do the rb_erase
805 * if this rmap_item was inserted by this scan, rather
806 * than left over from before.
807 */
808 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
809 BUG_ON(age > 1);
810 if (!age)
811 rb_erase(&rmap_item->node,
812 root_unstable_tree + NUMA(rmap_item->nid));
813 ksm_pages_unshared--;
814 rmap_item->address &= PAGE_MASK;
815 }
816out:
817 cond_resched(); /* we're called from many long loops */
818}
819
820static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
821 struct rmap_item **rmap_list)
822{
823 while (*rmap_list) {
824 struct rmap_item *rmap_item = *rmap_list;
825 *rmap_list = rmap_item->rmap_list;
826 remove_rmap_item_from_tree(rmap_item);
827 free_rmap_item(rmap_item);
828 }
829}
830
831/*
832 * Though it's very tempting to unmerge rmap_items from stable tree rather
833 * than check every pte of a given vma, the locking doesn't quite work for
834 * that - an rmap_item is assigned to the stable tree after inserting ksm
835 * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
836 * rmap_items from parent to child at fork time (so as not to waste time
837 * if exit comes before the next scan reaches it).
838 *
839 * Similarly, although we'd like to remove rmap_items (so updating counts
840 * and freeing memory) when unmerging an area, it's easier to leave that
841 * to the next pass of ksmd - consider, for example, how ksmd might be
842 * in cmp_and_merge_page on one of the rmap_items we would be removing.
843 */
844static int unmerge_ksm_pages(struct vm_area_struct *vma,
845 unsigned long start, unsigned long end)
846{
847 unsigned long addr;
848 int err = 0;
849
850 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
851 if (ksm_test_exit(vma->vm_mm))
852 break;
853 if (signal_pending(current))
854 err = -ERESTARTSYS;
855 else
856 err = break_ksm(vma, addr);
857 }
858 return err;
859}
860
861static inline struct stable_node *page_stable_node(struct page *page)
862{
863 return PageKsm(page) ? page_rmapping(page) : NULL;
864}
865
866static inline void set_page_stable_node(struct page *page,
867 struct stable_node *stable_node)
868{
869 page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
870}
871
872#ifdef CONFIG_SYSFS
873/*
874 * Only called through the sysfs control interface:
875 */
876static int remove_stable_node(struct stable_node *stable_node)
877{
878 struct page *page;
879 int err;
880
881 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
882 if (!page) {
883 /*
884 * get_ksm_page did remove_node_from_stable_tree itself.
885 */
886 return 0;
887 }
888
889 /*
890 * Page could be still mapped if this races with __mmput() running in
891 * between ksm_exit() and exit_mmap(). Just refuse to let
892 * merge_across_nodes/max_page_sharing be switched.
893 */
894 err = -EBUSY;
895 if (!page_mapped(page)) {
896 /*
897 * The stable node did not yet appear stale to get_ksm_page(),
898 * since that allows for an unmapped ksm page to be recognized
899 * right up until it is freed; but the node is safe to remove.
900 * This page might be in a pagevec waiting to be freed,
901 * or it might be PageSwapCache (perhaps under writeback),
902 * or it might have been removed from swapcache a moment ago.
903 */
904 set_page_stable_node(page, NULL);
905 remove_node_from_stable_tree(stable_node);
906 err = 0;
907 }
908
909 unlock_page(page);
910 put_page(page);
911 return err;
912}
913
914static int remove_stable_node_chain(struct stable_node *stable_node,
915 struct rb_root *root)
916{
917 struct stable_node *dup;
918 struct hlist_node *hlist_safe;
919
920 if (!is_stable_node_chain(stable_node)) {
921 VM_BUG_ON(is_stable_node_dup(stable_node));
922 if (remove_stable_node(stable_node))
923 return true;
924 else
925 return false;
926 }
927
928 hlist_for_each_entry_safe(dup, hlist_safe,
929 &stable_node->hlist, hlist_dup) {
930 VM_BUG_ON(!is_stable_node_dup(dup));
931 if (remove_stable_node(dup))
932 return true;
933 }
934 BUG_ON(!hlist_empty(&stable_node->hlist));
935 free_stable_node_chain(stable_node, root);
936 return false;
937}
938
939static int remove_all_stable_nodes(void)
940{
941 struct stable_node *stable_node, *next;
942 int nid;
943 int err = 0;
944
945 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
946 while (root_stable_tree[nid].rb_node) {
947 stable_node = rb_entry(root_stable_tree[nid].rb_node,
948 struct stable_node, node);
949 if (remove_stable_node_chain(stable_node,
950 root_stable_tree + nid)) {
951 err = -EBUSY;
952 break; /* proceed to next nid */
953 }
954 cond_resched();
955 }
956 }
957 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
958 if (remove_stable_node(stable_node))
959 err = -EBUSY;
960 cond_resched();
961 }
962 return err;
963}
964
965static int unmerge_and_remove_all_rmap_items(void)
966{
967 struct mm_slot *mm_slot;
968 struct mm_struct *mm;
969 struct vm_area_struct *vma;
970 int err = 0;
971
972 spin_lock(&ksm_mmlist_lock);
973 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
974 struct mm_slot, mm_list);
975 spin_unlock(&ksm_mmlist_lock);
976
977 for (mm_slot = ksm_scan.mm_slot;
978 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
979 mm = mm_slot->mm;
980 mmap_read_lock(mm);
981 for (vma = mm->mmap; vma; vma = vma->vm_next) {
982 if (ksm_test_exit(mm))
983 break;
984 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
985 continue;
986 err = unmerge_ksm_pages(vma,
987 vma->vm_start, vma->vm_end);
988 if (err)
989 goto error;
990 }
991
992 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
993 mmap_read_unlock(mm);
994
995 spin_lock(&ksm_mmlist_lock);
996 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
997 struct mm_slot, mm_list);
998 if (ksm_test_exit(mm)) {
999 hash_del(&mm_slot->link);
1000 list_del(&mm_slot->mm_list);
1001 spin_unlock(&ksm_mmlist_lock);
1002
1003 free_mm_slot(mm_slot);
1004 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1005 mmdrop(mm);
1006 } else
1007 spin_unlock(&ksm_mmlist_lock);
1008 }
1009
1010 /* Clean up stable nodes, but don't worry if some are still busy */
1011 remove_all_stable_nodes();
1012 ksm_scan.seqnr = 0;
1013 return 0;
1014
1015error:
1016 mmap_read_unlock(mm);
1017 spin_lock(&ksm_mmlist_lock);
1018 ksm_scan.mm_slot = &ksm_mm_head;
1019 spin_unlock(&ksm_mmlist_lock);
1020 return err;
1021}
1022#endif /* CONFIG_SYSFS */
1023
1024static u32 calc_checksum(struct page *page)
1025{
1026 u32 checksum;
1027 void *addr = kmap_atomic(page);
1028 checksum = xxhash(addr, PAGE_SIZE, 0);
1029 kunmap_atomic(addr);
1030 return checksum;
1031}
1032
1033static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1034 pte_t *orig_pte)
1035{
1036 struct mm_struct *mm = vma->vm_mm;
1037 struct page_vma_mapped_walk pvmw = {
1038 .page = page,
1039 .vma = vma,
1040 };
1041 int swapped;
1042 int err = -EFAULT;
1043 struct mmu_notifier_range range;
1044
1045 pvmw.address = page_address_in_vma(page, vma);
1046 if (pvmw.address == -EFAULT)
1047 goto out;
1048
1049 BUG_ON(PageTransCompound(page));
1050
1051 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1052 pvmw.address,
1053 pvmw.address + PAGE_SIZE);
1054 mmu_notifier_invalidate_range_start(&range);
1055
1056 if (!page_vma_mapped_walk(&pvmw))
1057 goto out_mn;
1058 if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1059 goto out_unlock;
1060
1061 if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1062 (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1063 mm_tlb_flush_pending(mm)) {
1064 pte_t entry;
1065
1066 swapped = PageSwapCache(page);
1067 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1068 /*
1069 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1070 * take any lock, therefore the check that we are going to make
1071 * with the pagecount against the mapcount is racey and
1072 * O_DIRECT can happen right after the check.
1073 * So we clear the pte and flush the tlb before the check
1074 * this assure us that no O_DIRECT can happen after the check
1075 * or in the middle of the check.
1076 *
1077 * No need to notify as we are downgrading page table to read
1078 * only not changing it to point to a new page.
1079 *
1080 * See Documentation/vm/mmu_notifier.rst
1081 */
1082 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1083 /*
1084 * Check that no O_DIRECT or similar I/O is in progress on the
1085 * page
1086 */
1087 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1088 set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1089 goto out_unlock;
1090 }
1091 if (pte_dirty(entry))
1092 set_page_dirty(page);
1093
1094 if (pte_protnone(entry))
1095 entry = pte_mkclean(pte_clear_savedwrite(entry));
1096 else
1097 entry = pte_mkclean(pte_wrprotect(entry));
1098 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1099 }
1100 *orig_pte = *pvmw.pte;
1101 err = 0;
1102
1103out_unlock:
1104 page_vma_mapped_walk_done(&pvmw);
1105out_mn:
1106 mmu_notifier_invalidate_range_end(&range);
1107out:
1108 return err;
1109}
1110
1111/**
1112 * replace_page - replace page in vma by new ksm page
1113 * @vma: vma that holds the pte pointing to page
1114 * @page: the page we are replacing by kpage
1115 * @kpage: the ksm page we replace page by
1116 * @orig_pte: the original value of the pte
1117 *
1118 * Returns 0 on success, -EFAULT on failure.
1119 */
1120static int replace_page(struct vm_area_struct *vma, struct page *page,
1121 struct page *kpage, pte_t orig_pte)
1122{
1123 struct mm_struct *mm = vma->vm_mm;
1124 pmd_t *pmd;
1125 pte_t *ptep;
1126 pte_t newpte;
1127 spinlock_t *ptl;
1128 unsigned long addr;
1129 int err = -EFAULT;
1130 struct mmu_notifier_range range;
1131
1132 addr = page_address_in_vma(page, vma);
1133 if (addr == -EFAULT)
1134 goto out;
1135
1136 pmd = mm_find_pmd(mm, addr);
1137 if (!pmd)
1138 goto out;
1139
1140 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1141 addr + PAGE_SIZE);
1142 mmu_notifier_invalidate_range_start(&range);
1143
1144 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1145 if (!pte_same(*ptep, orig_pte)) {
1146 pte_unmap_unlock(ptep, ptl);
1147 goto out_mn;
1148 }
1149
1150 /*
1151 * No need to check ksm_use_zero_pages here: we can only have a
1152 * zero_page here if ksm_use_zero_pages was enabled already.
1153 */
1154 if (!is_zero_pfn(page_to_pfn(kpage))) {
1155 get_page(kpage);
1156 page_add_anon_rmap(kpage, vma, addr, false);
1157 newpte = mk_pte(kpage, vma->vm_page_prot);
1158 } else {
1159 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1160 vma->vm_page_prot));
1161 /*
1162 * We're replacing an anonymous page with a zero page, which is
1163 * not anonymous. We need to do proper accounting otherwise we
1164 * will get wrong values in /proc, and a BUG message in dmesg
1165 * when tearing down the mm.
1166 */
1167 dec_mm_counter(mm, MM_ANONPAGES);
1168 }
1169
1170 flush_cache_page(vma, addr, pte_pfn(*ptep));
1171 /*
1172 * No need to notify as we are replacing a read only page with another
1173 * read only page with the same content.
1174 *
1175 * See Documentation/vm/mmu_notifier.rst
1176 */
1177 ptep_clear_flush(vma, addr, ptep);
1178 set_pte_at_notify(mm, addr, ptep, newpte);
1179
1180 page_remove_rmap(page, false);
1181 if (!page_mapped(page))
1182 try_to_free_swap(page);
1183 put_page(page);
1184
1185 pte_unmap_unlock(ptep, ptl);
1186 err = 0;
1187out_mn:
1188 mmu_notifier_invalidate_range_end(&range);
1189out:
1190 return err;
1191}
1192
1193/*
1194 * try_to_merge_one_page - take two pages and merge them into one
1195 * @vma: the vma that holds the pte pointing to page
1196 * @page: the PageAnon page that we want to replace with kpage
1197 * @kpage: the PageKsm page that we want to map instead of page,
1198 * or NULL the first time when we want to use page as kpage.
1199 *
1200 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1201 */
1202static int try_to_merge_one_page(struct vm_area_struct *vma,
1203 struct page *page, struct page *kpage)
1204{
1205 pte_t orig_pte = __pte(0);
1206 int err = -EFAULT;
1207
1208 if (page == kpage) /* ksm page forked */
1209 return 0;
1210
1211 if (!PageAnon(page))
1212 goto out;
1213
1214 /*
1215 * We need the page lock to read a stable PageSwapCache in
1216 * write_protect_page(). We use trylock_page() instead of
1217 * lock_page() because we don't want to wait here - we
1218 * prefer to continue scanning and merging different pages,
1219 * then come back to this page when it is unlocked.
1220 */
1221 if (!trylock_page(page))
1222 goto out;
1223
1224 if (PageTransCompound(page)) {
1225 if (split_huge_page(page))
1226 goto out_unlock;
1227 }
1228
1229 /*
1230 * If this anonymous page is mapped only here, its pte may need
1231 * to be write-protected. If it's mapped elsewhere, all of its
1232 * ptes are necessarily already write-protected. But in either
1233 * case, we need to lock and check page_count is not raised.
1234 */
1235 if (write_protect_page(vma, page, &orig_pte) == 0) {
1236 if (!kpage) {
1237 /*
1238 * While we hold page lock, upgrade page from
1239 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1240 * stable_tree_insert() will update stable_node.
1241 */
1242 set_page_stable_node(page, NULL);
1243 mark_page_accessed(page);
1244 /*
1245 * Page reclaim just frees a clean page with no dirty
1246 * ptes: make sure that the ksm page would be swapped.
1247 */
1248 if (!PageDirty(page))
1249 SetPageDirty(page);
1250 err = 0;
1251 } else if (pages_identical(page, kpage))
1252 err = replace_page(vma, page, kpage, orig_pte);
1253 }
1254
1255 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1256 munlock_vma_page(page);
1257 if (!PageMlocked(kpage)) {
1258 unlock_page(page);
1259 lock_page(kpage);
1260 mlock_vma_page(kpage);
1261 page = kpage; /* for final unlock */
1262 }
1263 }
1264
1265out_unlock:
1266 unlock_page(page);
1267out:
1268 return err;
1269}
1270
1271/*
1272 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1273 * but no new kernel page is allocated: kpage must already be a ksm page.
1274 *
1275 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1276 */
1277static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1278 struct page *page, struct page *kpage)
1279{
1280 struct mm_struct *mm = rmap_item->mm;
1281 struct vm_area_struct *vma;
1282 int err = -EFAULT;
1283
1284 mmap_read_lock(mm);
1285 vma = find_mergeable_vma(mm, rmap_item->address);
1286 if (!vma)
1287 goto out;
1288
1289 err = try_to_merge_one_page(vma, page, kpage);
1290 if (err)
1291 goto out;
1292
1293 /* Unstable nid is in union with stable anon_vma: remove first */
1294 remove_rmap_item_from_tree(rmap_item);
1295
1296 /* Must get reference to anon_vma while still holding mmap_lock */
1297 rmap_item->anon_vma = vma->anon_vma;
1298 get_anon_vma(vma->anon_vma);
1299out:
1300 mmap_read_unlock(mm);
1301 return err;
1302}
1303
1304/*
1305 * try_to_merge_two_pages - take two identical pages and prepare them
1306 * to be merged into one page.
1307 *
1308 * This function returns the kpage if we successfully merged two identical
1309 * pages into one ksm page, NULL otherwise.
1310 *
1311 * Note that this function upgrades page to ksm page: if one of the pages
1312 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1313 */
1314static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1315 struct page *page,
1316 struct rmap_item *tree_rmap_item,
1317 struct page *tree_page)
1318{
1319 int err;
1320
1321 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1322 if (!err) {
1323 err = try_to_merge_with_ksm_page(tree_rmap_item,
1324 tree_page, page);
1325 /*
1326 * If that fails, we have a ksm page with only one pte
1327 * pointing to it: so break it.
1328 */
1329 if (err)
1330 break_cow(rmap_item);
1331 }
1332 return err ? NULL : page;
1333}
1334
1335static __always_inline
1336bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1337{
1338 VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1339 /*
1340 * Check that at least one mapping still exists, otherwise
1341 * there's no much point to merge and share with this
1342 * stable_node, as the underlying tree_page of the other
1343 * sharer is going to be freed soon.
1344 */
1345 return stable_node->rmap_hlist_len &&
1346 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1347}
1348
1349static __always_inline
1350bool is_page_sharing_candidate(struct stable_node *stable_node)
1351{
1352 return __is_page_sharing_candidate(stable_node, 0);
1353}
1354
1355static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1356 struct stable_node **_stable_node,
1357 struct rb_root *root,
1358 bool prune_stale_stable_nodes)
1359{
1360 struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1361 struct hlist_node *hlist_safe;
1362 struct page *_tree_page, *tree_page = NULL;
1363 int nr = 0;
1364 int found_rmap_hlist_len;
1365
1366 if (!prune_stale_stable_nodes ||
1367 time_before(jiffies, stable_node->chain_prune_time +
1368 msecs_to_jiffies(
1369 ksm_stable_node_chains_prune_millisecs)))
1370 prune_stale_stable_nodes = false;
1371 else
1372 stable_node->chain_prune_time = jiffies;
1373
1374 hlist_for_each_entry_safe(dup, hlist_safe,
1375 &stable_node->hlist, hlist_dup) {
1376 cond_resched();
1377 /*
1378 * We must walk all stable_node_dup to prune the stale
1379 * stable nodes during lookup.
1380 *
1381 * get_ksm_page can drop the nodes from the
1382 * stable_node->hlist if they point to freed pages
1383 * (that's why we do a _safe walk). The "dup"
1384 * stable_node parameter itself will be freed from
1385 * under us if it returns NULL.
1386 */
1387 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1388 if (!_tree_page)
1389 continue;
1390 nr += 1;
1391 if (is_page_sharing_candidate(dup)) {
1392 if (!found ||
1393 dup->rmap_hlist_len > found_rmap_hlist_len) {
1394 if (found)
1395 put_page(tree_page);
1396 found = dup;
1397 found_rmap_hlist_len = found->rmap_hlist_len;
1398 tree_page = _tree_page;
1399
1400 /* skip put_page for found dup */
1401 if (!prune_stale_stable_nodes)
1402 break;
1403 continue;
1404 }
1405 }
1406 put_page(_tree_page);
1407 }
1408
1409 if (found) {
1410 /*
1411 * nr is counting all dups in the chain only if
1412 * prune_stale_stable_nodes is true, otherwise we may
1413 * break the loop at nr == 1 even if there are
1414 * multiple entries.
1415 */
1416 if (prune_stale_stable_nodes && nr == 1) {
1417 /*
1418 * If there's not just one entry it would
1419 * corrupt memory, better BUG_ON. In KSM
1420 * context with no lock held it's not even
1421 * fatal.
1422 */
1423 BUG_ON(stable_node->hlist.first->next);
1424
1425 /*
1426 * There's just one entry and it is below the
1427 * deduplication limit so drop the chain.
1428 */
1429 rb_replace_node(&stable_node->node, &found->node,
1430 root);
1431 free_stable_node(stable_node);
1432 ksm_stable_node_chains--;
1433 ksm_stable_node_dups--;
1434 /*
1435 * NOTE: the caller depends on the stable_node
1436 * to be equal to stable_node_dup if the chain
1437 * was collapsed.
1438 */
1439 *_stable_node = found;
1440 /*
1441 * Just for robustneess as stable_node is
1442 * otherwise left as a stable pointer, the
1443 * compiler shall optimize it away at build
1444 * time.
1445 */
1446 stable_node = NULL;
1447 } else if (stable_node->hlist.first != &found->hlist_dup &&
1448 __is_page_sharing_candidate(found, 1)) {
1449 /*
1450 * If the found stable_node dup can accept one
1451 * more future merge (in addition to the one
1452 * that is underway) and is not at the head of
1453 * the chain, put it there so next search will
1454 * be quicker in the !prune_stale_stable_nodes
1455 * case.
1456 *
1457 * NOTE: it would be inaccurate to use nr > 1
1458 * instead of checking the hlist.first pointer
1459 * directly, because in the
1460 * prune_stale_stable_nodes case "nr" isn't
1461 * the position of the found dup in the chain,
1462 * but the total number of dups in the chain.
1463 */
1464 hlist_del(&found->hlist_dup);
1465 hlist_add_head(&found->hlist_dup,
1466 &stable_node->hlist);
1467 }
1468 }
1469
1470 *_stable_node_dup = found;
1471 return tree_page;
1472}
1473
1474static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1475 struct rb_root *root)
1476{
1477 if (!is_stable_node_chain(stable_node))
1478 return stable_node;
1479 if (hlist_empty(&stable_node->hlist)) {
1480 free_stable_node_chain(stable_node, root);
1481 return NULL;
1482 }
1483 return hlist_entry(stable_node->hlist.first,
1484 typeof(*stable_node), hlist_dup);
1485}
1486
1487/*
1488 * Like for get_ksm_page, this function can free the *_stable_node and
1489 * *_stable_node_dup if the returned tree_page is NULL.
1490 *
1491 * It can also free and overwrite *_stable_node with the found
1492 * stable_node_dup if the chain is collapsed (in which case
1493 * *_stable_node will be equal to *_stable_node_dup like if the chain
1494 * never existed). It's up to the caller to verify tree_page is not
1495 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1496 *
1497 * *_stable_node_dup is really a second output parameter of this
1498 * function and will be overwritten in all cases, the caller doesn't
1499 * need to initialize it.
1500 */
1501static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1502 struct stable_node **_stable_node,
1503 struct rb_root *root,
1504 bool prune_stale_stable_nodes)
1505{
1506 struct stable_node *stable_node = *_stable_node;
1507 if (!is_stable_node_chain(stable_node)) {
1508 if (is_page_sharing_candidate(stable_node)) {
1509 *_stable_node_dup = stable_node;
1510 return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1511 }
1512 /*
1513 * _stable_node_dup set to NULL means the stable_node
1514 * reached the ksm_max_page_sharing limit.
1515 */
1516 *_stable_node_dup = NULL;
1517 return NULL;
1518 }
1519 return stable_node_dup(_stable_node_dup, _stable_node, root,
1520 prune_stale_stable_nodes);
1521}
1522
1523static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1524 struct stable_node **s_n,
1525 struct rb_root *root)
1526{
1527 return __stable_node_chain(s_n_d, s_n, root, true);
1528}
1529
1530static __always_inline struct page *chain(struct stable_node **s_n_d,
1531 struct stable_node *s_n,
1532 struct rb_root *root)
1533{
1534 struct stable_node *old_stable_node = s_n;
1535 struct page *tree_page;
1536
1537 tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1538 /* not pruning dups so s_n cannot have changed */
1539 VM_BUG_ON(s_n != old_stable_node);
1540 return tree_page;
1541}
1542
1543/*
1544 * stable_tree_search - search for page inside the stable tree
1545 *
1546 * This function checks if there is a page inside the stable tree
1547 * with identical content to the page that we are scanning right now.
1548 *
1549 * This function returns the stable tree node of identical content if found,
1550 * NULL otherwise.
1551 */
1552static struct page *stable_tree_search(struct page *page)
1553{
1554 int nid;
1555 struct rb_root *root;
1556 struct rb_node **new;
1557 struct rb_node *parent;
1558 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1559 struct stable_node *page_node;
1560
1561 page_node = page_stable_node(page);
1562 if (page_node && page_node->head != &migrate_nodes) {
1563 /* ksm page forked */
1564 get_page(page);
1565 return page;
1566 }
1567
1568 nid = get_kpfn_nid(page_to_pfn(page));
1569 root = root_stable_tree + nid;
1570again:
1571 new = &root->rb_node;
1572 parent = NULL;
1573
1574 while (*new) {
1575 struct page *tree_page;
1576 int ret;
1577
1578 cond_resched();
1579 stable_node = rb_entry(*new, struct stable_node, node);
1580 stable_node_any = NULL;
1581 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
1582 /*
1583 * NOTE: stable_node may have been freed by
1584 * chain_prune() if the returned stable_node_dup is
1585 * not NULL. stable_node_dup may have been inserted in
1586 * the rbtree instead as a regular stable_node (in
1587 * order to collapse the stable_node chain if a single
1588 * stable_node dup was found in it). In such case the
1589 * stable_node is overwritten by the calleee to point
1590 * to the stable_node_dup that was collapsed in the
1591 * stable rbtree and stable_node will be equal to
1592 * stable_node_dup like if the chain never existed.
1593 */
1594 if (!stable_node_dup) {
1595 /*
1596 * Either all stable_node dups were full in
1597 * this stable_node chain, or this chain was
1598 * empty and should be rb_erased.
1599 */
1600 stable_node_any = stable_node_dup_any(stable_node,
1601 root);
1602 if (!stable_node_any) {
1603 /* rb_erase just run */
1604 goto again;
1605 }
1606 /*
1607 * Take any of the stable_node dups page of
1608 * this stable_node chain to let the tree walk
1609 * continue. All KSM pages belonging to the
1610 * stable_node dups in a stable_node chain
1611 * have the same content and they're
1612 * write protected at all times. Any will work
1613 * fine to continue the walk.
1614 */
1615 tree_page = get_ksm_page(stable_node_any,
1616 GET_KSM_PAGE_NOLOCK);
1617 }
1618 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1619 if (!tree_page) {
1620 /*
1621 * If we walked over a stale stable_node,
1622 * get_ksm_page() will call rb_erase() and it
1623 * may rebalance the tree from under us. So
1624 * restart the search from scratch. Returning
1625 * NULL would be safe too, but we'd generate
1626 * false negative insertions just because some
1627 * stable_node was stale.
1628 */
1629 goto again;
1630 }
1631
1632 ret = memcmp_pages(page, tree_page);
1633 put_page(tree_page);
1634
1635 parent = *new;
1636 if (ret < 0)
1637 new = &parent->rb_left;
1638 else if (ret > 0)
1639 new = &parent->rb_right;
1640 else {
1641 if (page_node) {
1642 VM_BUG_ON(page_node->head != &migrate_nodes);
1643 /*
1644 * Test if the migrated page should be merged
1645 * into a stable node dup. If the mapcount is
1646 * 1 we can migrate it with another KSM page
1647 * without adding it to the chain.
1648 */
1649 if (page_mapcount(page) > 1)
1650 goto chain_append;
1651 }
1652
1653 if (!stable_node_dup) {
1654 /*
1655 * If the stable_node is a chain and
1656 * we got a payload match in memcmp
1657 * but we cannot merge the scanned
1658 * page in any of the existing
1659 * stable_node dups because they're
1660 * all full, we need to wait the
1661 * scanned page to find itself a match
1662 * in the unstable tree to create a
1663 * brand new KSM page to add later to
1664 * the dups of this stable_node.
1665 */
1666 return NULL;
1667 }
1668
1669 /*
1670 * Lock and unlock the stable_node's page (which
1671 * might already have been migrated) so that page
1672 * migration is sure to notice its raised count.
1673 * It would be more elegant to return stable_node
1674 * than kpage, but that involves more changes.
1675 */
1676 tree_page = get_ksm_page(stable_node_dup,
1677 GET_KSM_PAGE_TRYLOCK);
1678
1679 if (PTR_ERR(tree_page) == -EBUSY)
1680 return ERR_PTR(-EBUSY);
1681
1682 if (unlikely(!tree_page))
1683 /*
1684 * The tree may have been rebalanced,
1685 * so re-evaluate parent and new.
1686 */
1687 goto again;
1688 unlock_page(tree_page);
1689
1690 if (get_kpfn_nid(stable_node_dup->kpfn) !=
1691 NUMA(stable_node_dup->nid)) {
1692 put_page(tree_page);
1693 goto replace;
1694 }
1695 return tree_page;
1696 }
1697 }
1698
1699 if (!page_node)
1700 return NULL;
1701
1702 list_del(&page_node->list);
1703 DO_NUMA(page_node->nid = nid);
1704 rb_link_node(&page_node->node, parent, new);
1705 rb_insert_color(&page_node->node, root);
1706out:
1707 if (is_page_sharing_candidate(page_node)) {
1708 get_page(page);
1709 return page;
1710 } else
1711 return NULL;
1712
1713replace:
1714 /*
1715 * If stable_node was a chain and chain_prune collapsed it,
1716 * stable_node has been updated to be the new regular
1717 * stable_node. A collapse of the chain is indistinguishable
1718 * from the case there was no chain in the stable
1719 * rbtree. Otherwise stable_node is the chain and
1720 * stable_node_dup is the dup to replace.
1721 */
1722 if (stable_node_dup == stable_node) {
1723 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1724 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1725 /* there is no chain */
1726 if (page_node) {
1727 VM_BUG_ON(page_node->head != &migrate_nodes);
1728 list_del(&page_node->list);
1729 DO_NUMA(page_node->nid = nid);
1730 rb_replace_node(&stable_node_dup->node,
1731 &page_node->node,
1732 root);
1733 if (is_page_sharing_candidate(page_node))
1734 get_page(page);
1735 else
1736 page = NULL;
1737 } else {
1738 rb_erase(&stable_node_dup->node, root);
1739 page = NULL;
1740 }
1741 } else {
1742 VM_BUG_ON(!is_stable_node_chain(stable_node));
1743 __stable_node_dup_del(stable_node_dup);
1744 if (page_node) {
1745 VM_BUG_ON(page_node->head != &migrate_nodes);
1746 list_del(&page_node->list);
1747 DO_NUMA(page_node->nid = nid);
1748 stable_node_chain_add_dup(page_node, stable_node);
1749 if (is_page_sharing_candidate(page_node))
1750 get_page(page);
1751 else
1752 page = NULL;
1753 } else {
1754 page = NULL;
1755 }
1756 }
1757 stable_node_dup->head = &migrate_nodes;
1758 list_add(&stable_node_dup->list, stable_node_dup->head);
1759 return page;
1760
1761chain_append:
1762 /* stable_node_dup could be null if it reached the limit */
1763 if (!stable_node_dup)
1764 stable_node_dup = stable_node_any;
1765 /*
1766 * If stable_node was a chain and chain_prune collapsed it,
1767 * stable_node has been updated to be the new regular
1768 * stable_node. A collapse of the chain is indistinguishable
1769 * from the case there was no chain in the stable
1770 * rbtree. Otherwise stable_node is the chain and
1771 * stable_node_dup is the dup to replace.
1772 */
1773 if (stable_node_dup == stable_node) {
1774 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1775 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1776 /* chain is missing so create it */
1777 stable_node = alloc_stable_node_chain(stable_node_dup,
1778 root);
1779 if (!stable_node)
1780 return NULL;
1781 }
1782 /*
1783 * Add this stable_node dup that was
1784 * migrated to the stable_node chain
1785 * of the current nid for this page
1786 * content.
1787 */
1788 VM_BUG_ON(!is_stable_node_chain(stable_node));
1789 VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1790 VM_BUG_ON(page_node->head != &migrate_nodes);
1791 list_del(&page_node->list);
1792 DO_NUMA(page_node->nid = nid);
1793 stable_node_chain_add_dup(page_node, stable_node);
1794 goto out;
1795}
1796
1797/*
1798 * stable_tree_insert - insert stable tree node pointing to new ksm page
1799 * into the stable tree.
1800 *
1801 * This function returns the stable tree node just allocated on success,
1802 * NULL otherwise.
1803 */
1804static struct stable_node *stable_tree_insert(struct page *kpage)
1805{
1806 int nid;
1807 unsigned long kpfn;
1808 struct rb_root *root;
1809 struct rb_node **new;
1810 struct rb_node *parent;
1811 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1812 bool need_chain = false;
1813
1814 kpfn = page_to_pfn(kpage);
1815 nid = get_kpfn_nid(kpfn);
1816 root = root_stable_tree + nid;
1817again:
1818 parent = NULL;
1819 new = &root->rb_node;
1820
1821 while (*new) {
1822 struct page *tree_page;
1823 int ret;
1824
1825 cond_resched();
1826 stable_node = rb_entry(*new, struct stable_node, node);
1827 stable_node_any = NULL;
1828 tree_page = chain(&stable_node_dup, stable_node, root);
1829 if (!stable_node_dup) {
1830 /*
1831 * Either all stable_node dups were full in
1832 * this stable_node chain, or this chain was
1833 * empty and should be rb_erased.
1834 */
1835 stable_node_any = stable_node_dup_any(stable_node,
1836 root);
1837 if (!stable_node_any) {
1838 /* rb_erase just run */
1839 goto again;
1840 }
1841 /*
1842 * Take any of the stable_node dups page of
1843 * this stable_node chain to let the tree walk
1844 * continue. All KSM pages belonging to the
1845 * stable_node dups in a stable_node chain
1846 * have the same content and they're
1847 * write protected at all times. Any will work
1848 * fine to continue the walk.
1849 */
1850 tree_page = get_ksm_page(stable_node_any,
1851 GET_KSM_PAGE_NOLOCK);
1852 }
1853 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1854 if (!tree_page) {
1855 /*
1856 * If we walked over a stale stable_node,
1857 * get_ksm_page() will call rb_erase() and it
1858 * may rebalance the tree from under us. So
1859 * restart the search from scratch. Returning
1860 * NULL would be safe too, but we'd generate
1861 * false negative insertions just because some
1862 * stable_node was stale.
1863 */
1864 goto again;
1865 }
1866
1867 ret = memcmp_pages(kpage, tree_page);
1868 put_page(tree_page);
1869
1870 parent = *new;
1871 if (ret < 0)
1872 new = &parent->rb_left;
1873 else if (ret > 0)
1874 new = &parent->rb_right;
1875 else {
1876 need_chain = true;
1877 break;
1878 }
1879 }
1880
1881 stable_node_dup = alloc_stable_node();
1882 if (!stable_node_dup)
1883 return NULL;
1884
1885 INIT_HLIST_HEAD(&stable_node_dup->hlist);
1886 stable_node_dup->kpfn = kpfn;
1887 set_page_stable_node(kpage, stable_node_dup);
1888 stable_node_dup->rmap_hlist_len = 0;
1889 DO_NUMA(stable_node_dup->nid = nid);
1890 if (!need_chain) {
1891 rb_link_node(&stable_node_dup->node, parent, new);
1892 rb_insert_color(&stable_node_dup->node, root);
1893 } else {
1894 if (!is_stable_node_chain(stable_node)) {
1895 struct stable_node *orig = stable_node;
1896 /* chain is missing so create it */
1897 stable_node = alloc_stable_node_chain(orig, root);
1898 if (!stable_node) {
1899 free_stable_node(stable_node_dup);
1900 return NULL;
1901 }
1902 }
1903 stable_node_chain_add_dup(stable_node_dup, stable_node);
1904 }
1905
1906 return stable_node_dup;
1907}
1908
1909/*
1910 * unstable_tree_search_insert - search for identical page,
1911 * else insert rmap_item into the unstable tree.
1912 *
1913 * This function searches for a page in the unstable tree identical to the
1914 * page currently being scanned; and if no identical page is found in the
1915 * tree, we insert rmap_item as a new object into the unstable tree.
1916 *
1917 * This function returns pointer to rmap_item found to be identical
1918 * to the currently scanned page, NULL otherwise.
1919 *
1920 * This function does both searching and inserting, because they share
1921 * the same walking algorithm in an rbtree.
1922 */
1923static
1924struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1925 struct page *page,
1926 struct page **tree_pagep)
1927{
1928 struct rb_node **new;
1929 struct rb_root *root;
1930 struct rb_node *parent = NULL;
1931 int nid;
1932
1933 nid = get_kpfn_nid(page_to_pfn(page));
1934 root = root_unstable_tree + nid;
1935 new = &root->rb_node;
1936
1937 while (*new) {
1938 struct rmap_item *tree_rmap_item;
1939 struct page *tree_page;
1940 int ret;
1941
1942 cond_resched();
1943 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1944 tree_page = get_mergeable_page(tree_rmap_item);
1945 if (!tree_page)
1946 return NULL;
1947
1948 /*
1949 * Don't substitute a ksm page for a forked page.
1950 */
1951 if (page == tree_page) {
1952 put_page(tree_page);
1953 return NULL;
1954 }
1955
1956 ret = memcmp_pages(page, tree_page);
1957
1958 parent = *new;
1959 if (ret < 0) {
1960 put_page(tree_page);
1961 new = &parent->rb_left;
1962 } else if (ret > 0) {
1963 put_page(tree_page);
1964 new = &parent->rb_right;
1965 } else if (!ksm_merge_across_nodes &&
1966 page_to_nid(tree_page) != nid) {
1967 /*
1968 * If tree_page has been migrated to another NUMA node,
1969 * it will be flushed out and put in the right unstable
1970 * tree next time: only merge with it when across_nodes.
1971 */
1972 put_page(tree_page);
1973 return NULL;
1974 } else {
1975 *tree_pagep = tree_page;
1976 return tree_rmap_item;
1977 }
1978 }
1979
1980 rmap_item->address |= UNSTABLE_FLAG;
1981 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1982 DO_NUMA(rmap_item->nid = nid);
1983 rb_link_node(&rmap_item->node, parent, new);
1984 rb_insert_color(&rmap_item->node, root);
1985
1986 ksm_pages_unshared++;
1987 return NULL;
1988}
1989
1990/*
1991 * stable_tree_append - add another rmap_item to the linked list of
1992 * rmap_items hanging off a given node of the stable tree, all sharing
1993 * the same ksm page.
1994 */
1995static void stable_tree_append(struct rmap_item *rmap_item,
1996 struct stable_node *stable_node,
1997 bool max_page_sharing_bypass)
1998{
1999 /*
2000 * rmap won't find this mapping if we don't insert the
2001 * rmap_item in the right stable_node
2002 * duplicate. page_migration could break later if rmap breaks,
2003 * so we can as well crash here. We really need to check for
2004 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2005 * for other negative values as an underflow if detected here
2006 * for the first time (and not when decreasing rmap_hlist_len)
2007 * would be sign of memory corruption in the stable_node.
2008 */
2009 BUG_ON(stable_node->rmap_hlist_len < 0);
2010
2011 stable_node->rmap_hlist_len++;
2012 if (!max_page_sharing_bypass)
2013 /* possibly non fatal but unexpected overflow, only warn */
2014 WARN_ON_ONCE(stable_node->rmap_hlist_len >
2015 ksm_max_page_sharing);
2016
2017 rmap_item->head = stable_node;
2018 rmap_item->address |= STABLE_FLAG;
2019 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2020
2021 if (rmap_item->hlist.next)
2022 ksm_pages_sharing++;
2023 else
2024 ksm_pages_shared++;
2025}
2026
2027/*
2028 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2029 * if not, compare checksum to previous and if it's the same, see if page can
2030 * be inserted into the unstable tree, or merged with a page already there and
2031 * both transferred to the stable tree.
2032 *
2033 * @page: the page that we are searching identical page to.
2034 * @rmap_item: the reverse mapping into the virtual address of this page
2035 */
2036static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2037{
2038 struct mm_struct *mm = rmap_item->mm;
2039 struct rmap_item *tree_rmap_item;
2040 struct page *tree_page = NULL;
2041 struct stable_node *stable_node;
2042 struct page *kpage;
2043 unsigned int checksum;
2044 int err;
2045 bool max_page_sharing_bypass = false;
2046
2047 stable_node = page_stable_node(page);
2048 if (stable_node) {
2049 if (stable_node->head != &migrate_nodes &&
2050 get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2051 NUMA(stable_node->nid)) {
2052 stable_node_dup_del(stable_node);
2053 stable_node->head = &migrate_nodes;
2054 list_add(&stable_node->list, stable_node->head);
2055 }
2056 if (stable_node->head != &migrate_nodes &&
2057 rmap_item->head == stable_node)
2058 return;
2059 /*
2060 * If it's a KSM fork, allow it to go over the sharing limit
2061 * without warnings.
2062 */
2063 if (!is_page_sharing_candidate(stable_node))
2064 max_page_sharing_bypass = true;
2065 }
2066
2067 /* We first start with searching the page inside the stable tree */
2068 kpage = stable_tree_search(page);
2069 if (kpage == page && rmap_item->head == stable_node) {
2070 put_page(kpage);
2071 return;
2072 }
2073
2074 remove_rmap_item_from_tree(rmap_item);
2075
2076 if (kpage) {
2077 if (PTR_ERR(kpage) == -EBUSY)
2078 return;
2079
2080 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2081 if (!err) {
2082 /*
2083 * The page was successfully merged:
2084 * add its rmap_item to the stable tree.
2085 */
2086 lock_page(kpage);
2087 stable_tree_append(rmap_item, page_stable_node(kpage),
2088 max_page_sharing_bypass);
2089 unlock_page(kpage);
2090 }
2091 put_page(kpage);
2092 return;
2093 }
2094
2095 /*
2096 * If the hash value of the page has changed from the last time
2097 * we calculated it, this page is changing frequently: therefore we
2098 * don't want to insert it in the unstable tree, and we don't want
2099 * to waste our time searching for something identical to it there.
2100 */
2101 checksum = calc_checksum(page);
2102 if (rmap_item->oldchecksum != checksum) {
2103 rmap_item->oldchecksum = checksum;
2104 return;
2105 }
2106
2107 /*
2108 * Same checksum as an empty page. We attempt to merge it with the
2109 * appropriate zero page if the user enabled this via sysfs.
2110 */
2111 if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2112 struct vm_area_struct *vma;
2113
2114 mmap_read_lock(mm);
2115 vma = find_mergeable_vma(mm, rmap_item->address);
2116 if (vma) {
2117 err = try_to_merge_one_page(vma, page,
2118 ZERO_PAGE(rmap_item->address));
2119 } else {
2120 /*
2121 * If the vma is out of date, we do not need to
2122 * continue.
2123 */
2124 err = 0;
2125 }
2126 mmap_read_unlock(mm);
2127 /*
2128 * In case of failure, the page was not really empty, so we
2129 * need to continue. Otherwise we're done.
2130 */
2131 if (!err)
2132 return;
2133 }
2134 tree_rmap_item =
2135 unstable_tree_search_insert(rmap_item, page, &tree_page);
2136 if (tree_rmap_item) {
2137 bool split;
2138
2139 kpage = try_to_merge_two_pages(rmap_item, page,
2140 tree_rmap_item, tree_page);
2141 /*
2142 * If both pages we tried to merge belong to the same compound
2143 * page, then we actually ended up increasing the reference
2144 * count of the same compound page twice, and split_huge_page
2145 * failed.
2146 * Here we set a flag if that happened, and we use it later to
2147 * try split_huge_page again. Since we call put_page right
2148 * afterwards, the reference count will be correct and
2149 * split_huge_page should succeed.
2150 */
2151 split = PageTransCompound(page)
2152 && compound_head(page) == compound_head(tree_page);
2153 put_page(tree_page);
2154 if (kpage) {
2155 /*
2156 * The pages were successfully merged: insert new
2157 * node in the stable tree and add both rmap_items.
2158 */
2159 lock_page(kpage);
2160 stable_node = stable_tree_insert(kpage);
2161 if (stable_node) {
2162 stable_tree_append(tree_rmap_item, stable_node,
2163 false);
2164 stable_tree_append(rmap_item, stable_node,
2165 false);
2166 }
2167 unlock_page(kpage);
2168
2169 /*
2170 * If we fail to insert the page into the stable tree,
2171 * we will have 2 virtual addresses that are pointing
2172 * to a ksm page left outside the stable tree,
2173 * in which case we need to break_cow on both.
2174 */
2175 if (!stable_node) {
2176 break_cow(tree_rmap_item);
2177 break_cow(rmap_item);
2178 }
2179 } else if (split) {
2180 /*
2181 * We are here if we tried to merge two pages and
2182 * failed because they both belonged to the same
2183 * compound page. We will split the page now, but no
2184 * merging will take place.
2185 * We do not want to add the cost of a full lock; if
2186 * the page is locked, it is better to skip it and
2187 * perhaps try again later.
2188 */
2189 if (!trylock_page(page))
2190 return;
2191 split_huge_page(page);
2192 unlock_page(page);
2193 }
2194 }
2195}
2196
2197static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2198 struct rmap_item **rmap_list,
2199 unsigned long addr)
2200{
2201 struct rmap_item *rmap_item;
2202
2203 while (*rmap_list) {
2204 rmap_item = *rmap_list;
2205 if ((rmap_item->address & PAGE_MASK) == addr)
2206 return rmap_item;
2207 if (rmap_item->address > addr)
2208 break;
2209 *rmap_list = rmap_item->rmap_list;
2210 remove_rmap_item_from_tree(rmap_item);
2211 free_rmap_item(rmap_item);
2212 }
2213
2214 rmap_item = alloc_rmap_item();
2215 if (rmap_item) {
2216 /* It has already been zeroed */
2217 rmap_item->mm = mm_slot->mm;
2218 rmap_item->address = addr;
2219 rmap_item->rmap_list = *rmap_list;
2220 *rmap_list = rmap_item;
2221 }
2222 return rmap_item;
2223}
2224
2225static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2226{
2227 struct mm_struct *mm;
2228 struct mm_slot *slot;
2229 struct vm_area_struct *vma;
2230 struct rmap_item *rmap_item;
2231 int nid;
2232
2233 if (list_empty(&ksm_mm_head.mm_list))
2234 return NULL;
2235
2236 slot = ksm_scan.mm_slot;
2237 if (slot == &ksm_mm_head) {
2238 /*
2239 * A number of pages can hang around indefinitely on per-cpu
2240 * pagevecs, raised page count preventing write_protect_page
2241 * from merging them. Though it doesn't really matter much,
2242 * it is puzzling to see some stuck in pages_volatile until
2243 * other activity jostles them out, and they also prevented
2244 * LTP's KSM test from succeeding deterministically; so drain
2245 * them here (here rather than on entry to ksm_do_scan(),
2246 * so we don't IPI too often when pages_to_scan is set low).
2247 */
2248 lru_add_drain_all();
2249
2250 /*
2251 * Whereas stale stable_nodes on the stable_tree itself
2252 * get pruned in the regular course of stable_tree_search(),
2253 * those moved out to the migrate_nodes list can accumulate:
2254 * so prune them once before each full scan.
2255 */
2256 if (!ksm_merge_across_nodes) {
2257 struct stable_node *stable_node, *next;
2258 struct page *page;
2259
2260 list_for_each_entry_safe(stable_node, next,
2261 &migrate_nodes, list) {
2262 page = get_ksm_page(stable_node,
2263 GET_KSM_PAGE_NOLOCK);
2264 if (page)
2265 put_page(page);
2266 cond_resched();
2267 }
2268 }
2269
2270 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2271 root_unstable_tree[nid] = RB_ROOT;
2272
2273 spin_lock(&ksm_mmlist_lock);
2274 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2275 ksm_scan.mm_slot = slot;
2276 spin_unlock(&ksm_mmlist_lock);
2277 /*
2278 * Although we tested list_empty() above, a racing __ksm_exit
2279 * of the last mm on the list may have removed it since then.
2280 */
2281 if (slot == &ksm_mm_head)
2282 return NULL;
2283next_mm:
2284 ksm_scan.address = 0;
2285 ksm_scan.rmap_list = &slot->rmap_list;
2286 }
2287
2288 mm = slot->mm;
2289 mmap_read_lock(mm);
2290 if (ksm_test_exit(mm))
2291 vma = NULL;
2292 else
2293 vma = find_vma(mm, ksm_scan.address);
2294
2295 for (; vma; vma = vma->vm_next) {
2296 if (!(vma->vm_flags & VM_MERGEABLE))
2297 continue;
2298 if (ksm_scan.address < vma->vm_start)
2299 ksm_scan.address = vma->vm_start;
2300 if (!vma->anon_vma)
2301 ksm_scan.address = vma->vm_end;
2302
2303 while (ksm_scan.address < vma->vm_end) {
2304 if (ksm_test_exit(mm))
2305 break;
2306 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
2307 if (IS_ERR_OR_NULL(*page)) {
2308 ksm_scan.address += PAGE_SIZE;
2309 cond_resched();
2310 continue;
2311 }
2312 if (PageAnon(*page)) {
2313 flush_anon_page(vma, *page, ksm_scan.address);
2314 flush_dcache_page(*page);
2315 rmap_item = get_next_rmap_item(slot,
2316 ksm_scan.rmap_list, ksm_scan.address);
2317 if (rmap_item) {
2318 ksm_scan.rmap_list =
2319 &rmap_item->rmap_list;
2320 ksm_scan.address += PAGE_SIZE;
2321 } else
2322 put_page(*page);
2323 mmap_read_unlock(mm);
2324 return rmap_item;
2325 }
2326 put_page(*page);
2327 ksm_scan.address += PAGE_SIZE;
2328 cond_resched();
2329 }
2330 }
2331
2332 if (ksm_test_exit(mm)) {
2333 ksm_scan.address = 0;
2334 ksm_scan.rmap_list = &slot->rmap_list;
2335 }
2336 /*
2337 * Nuke all the rmap_items that are above this current rmap:
2338 * because there were no VM_MERGEABLE vmas with such addresses.
2339 */
2340 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
2341
2342 spin_lock(&ksm_mmlist_lock);
2343 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2344 struct mm_slot, mm_list);
2345 if (ksm_scan.address == 0) {
2346 /*
2347 * We've completed a full scan of all vmas, holding mmap_lock
2348 * throughout, and found no VM_MERGEABLE: so do the same as
2349 * __ksm_exit does to remove this mm from all our lists now.
2350 * This applies either when cleaning up after __ksm_exit
2351 * (but beware: we can reach here even before __ksm_exit),
2352 * or when all VM_MERGEABLE areas have been unmapped (and
2353 * mmap_lock then protects against race with MADV_MERGEABLE).
2354 */
2355 hash_del(&slot->link);
2356 list_del(&slot->mm_list);
2357 spin_unlock(&ksm_mmlist_lock);
2358
2359 free_mm_slot(slot);
2360 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2361 mmap_read_unlock(mm);
2362 mmdrop(mm);
2363 } else {
2364 mmap_read_unlock(mm);
2365 /*
2366 * mmap_read_unlock(mm) first because after
2367 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2368 * already have been freed under us by __ksm_exit()
2369 * because the "mm_slot" is still hashed and
2370 * ksm_scan.mm_slot doesn't point to it anymore.
2371 */
2372 spin_unlock(&ksm_mmlist_lock);
2373 }
2374
2375 /* Repeat until we've completed scanning the whole list */
2376 slot = ksm_scan.mm_slot;
2377 if (slot != &ksm_mm_head)
2378 goto next_mm;
2379
2380 ksm_scan.seqnr++;
2381 return NULL;
2382}
2383
2384/**
2385 * ksm_do_scan - the ksm scanner main worker function.
2386 * @scan_npages: number of pages we want to scan before we return.
2387 */
2388static void ksm_do_scan(unsigned int scan_npages)
2389{
2390 struct rmap_item *rmap_item;
2391 struct page *page;
2392
2393 while (scan_npages-- && likely(!freezing(current))) {
2394 cond_resched();
2395 rmap_item = scan_get_next_rmap_item(&page);
2396 if (!rmap_item)
2397 return;
2398 cmp_and_merge_page(page, rmap_item);
2399 put_page(page);
2400 }
2401}
2402
2403static int ksmd_should_run(void)
2404{
2405 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2406}
2407
2408static int ksm_scan_thread(void *nothing)
2409{
2410 unsigned int sleep_ms;
2411
2412 set_freezable();
2413 set_user_nice(current, 5);
2414
2415 while (!kthread_should_stop()) {
2416 mutex_lock(&ksm_thread_mutex);
2417 wait_while_offlining();
2418 if (ksmd_should_run())
2419 ksm_do_scan(ksm_thread_pages_to_scan);
2420 mutex_unlock(&ksm_thread_mutex);
2421
2422 try_to_freeze();
2423
2424 if (ksmd_should_run()) {
2425 sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2426 wait_event_interruptible_timeout(ksm_iter_wait,
2427 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2428 msecs_to_jiffies(sleep_ms));
2429 } else {
2430 wait_event_freezable(ksm_thread_wait,
2431 ksmd_should_run() || kthread_should_stop());
2432 }
2433 }
2434 return 0;
2435}
2436
2437int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2438 unsigned long end, int advice, unsigned long *vm_flags)
2439{
2440 struct mm_struct *mm = vma->vm_mm;
2441 int err;
2442
2443 switch (advice) {
2444 case MADV_MERGEABLE:
2445 /*
2446 * Be somewhat over-protective for now!
2447 */
2448 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
2449 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
2450 VM_HUGETLB | VM_MIXEDMAP))
2451 return 0; /* just ignore the advice */
2452
2453 if (vma_is_dax(vma))
2454 return 0;
2455
2456#ifdef VM_SAO
2457 if (*vm_flags & VM_SAO)
2458 return 0;
2459#endif
2460#ifdef VM_SPARC_ADI
2461 if (*vm_flags & VM_SPARC_ADI)
2462 return 0;
2463#endif
2464
2465 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2466 err = __ksm_enter(mm);
2467 if (err)
2468 return err;
2469 }
2470
2471 *vm_flags |= VM_MERGEABLE;
2472 break;
2473
2474 case MADV_UNMERGEABLE:
2475 if (!(*vm_flags & VM_MERGEABLE))
2476 return 0; /* just ignore the advice */
2477
2478 if (vma->anon_vma) {
2479 err = unmerge_ksm_pages(vma, start, end);
2480 if (err)
2481 return err;
2482 }
2483
2484 *vm_flags &= ~VM_MERGEABLE;
2485 break;
2486 }
2487
2488 return 0;
2489}
2490EXPORT_SYMBOL_GPL(ksm_madvise);
2491
2492int __ksm_enter(struct mm_struct *mm)
2493{
2494 struct mm_slot *mm_slot;
2495 int needs_wakeup;
2496
2497 mm_slot = alloc_mm_slot();
2498 if (!mm_slot)
2499 return -ENOMEM;
2500
2501 /* Check ksm_run too? Would need tighter locking */
2502 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2503
2504 spin_lock(&ksm_mmlist_lock);
2505 insert_to_mm_slots_hash(mm, mm_slot);
2506 /*
2507 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2508 * insert just behind the scanning cursor, to let the area settle
2509 * down a little; when fork is followed by immediate exec, we don't
2510 * want ksmd to waste time setting up and tearing down an rmap_list.
2511 *
2512 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2513 * scanning cursor, otherwise KSM pages in newly forked mms will be
2514 * missed: then we might as well insert at the end of the list.
2515 */
2516 if (ksm_run & KSM_RUN_UNMERGE)
2517 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2518 else
2519 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2520 spin_unlock(&ksm_mmlist_lock);
2521
2522 set_bit(MMF_VM_MERGEABLE, &mm->flags);
2523 mmgrab(mm);
2524
2525 if (needs_wakeup)
2526 wake_up_interruptible(&ksm_thread_wait);
2527
2528 return 0;
2529}
2530
2531void __ksm_exit(struct mm_struct *mm)
2532{
2533 struct mm_slot *mm_slot;
2534 int easy_to_free = 0;
2535
2536 /*
2537 * This process is exiting: if it's straightforward (as is the
2538 * case when ksmd was never running), free mm_slot immediately.
2539 * But if it's at the cursor or has rmap_items linked to it, use
2540 * mmap_lock to synchronize with any break_cows before pagetables
2541 * are freed, and leave the mm_slot on the list for ksmd to free.
2542 * Beware: ksm may already have noticed it exiting and freed the slot.
2543 */
2544
2545 spin_lock(&ksm_mmlist_lock);
2546 mm_slot = get_mm_slot(mm);
2547 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2548 if (!mm_slot->rmap_list) {
2549 hash_del(&mm_slot->link);
2550 list_del(&mm_slot->mm_list);
2551 easy_to_free = 1;
2552 } else {
2553 list_move(&mm_slot->mm_list,
2554 &ksm_scan.mm_slot->mm_list);
2555 }
2556 }
2557 spin_unlock(&ksm_mmlist_lock);
2558
2559 if (easy_to_free) {
2560 free_mm_slot(mm_slot);
2561 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2562 mmdrop(mm);
2563 } else if (mm_slot) {
2564 mmap_write_lock(mm);
2565 mmap_write_unlock(mm);
2566 }
2567}
2568
2569struct page *ksm_might_need_to_copy(struct page *page,
2570 struct vm_area_struct *vma, unsigned long address)
2571{
2572 struct anon_vma *anon_vma = page_anon_vma(page);
2573 struct page *new_page;
2574
2575 if (PageKsm(page)) {
2576 if (page_stable_node(page) &&
2577 !(ksm_run & KSM_RUN_UNMERGE))
2578 return page; /* no need to copy it */
2579 } else if (!anon_vma) {
2580 return page; /* no need to copy it */
2581 } else if (anon_vma->root == vma->anon_vma->root &&
2582 page->index == linear_page_index(vma, address)) {
2583 return page; /* still no need to copy it */
2584 }
2585 if (!PageUptodate(page))
2586 return page; /* let do_swap_page report the error */
2587
2588 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2589 if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) {
2590 put_page(new_page);
2591 new_page = NULL;
2592 }
2593 if (new_page) {
2594 copy_user_highpage(new_page, page, address, vma);
2595
2596 SetPageDirty(new_page);
2597 __SetPageUptodate(new_page);
2598 __SetPageLocked(new_page);
2599 }
2600
2601 return new_page;
2602}
2603
2604void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2605{
2606 struct stable_node *stable_node;
2607 struct rmap_item *rmap_item;
2608 int search_new_forks = 0;
2609
2610 VM_BUG_ON_PAGE(!PageKsm(page), page);
2611
2612 /*
2613 * Rely on the page lock to protect against concurrent modifications
2614 * to that page's node of the stable tree.
2615 */
2616 VM_BUG_ON_PAGE(!PageLocked(page), page);
2617
2618 stable_node = page_stable_node(page);
2619 if (!stable_node)
2620 return;
2621again:
2622 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2623 struct anon_vma *anon_vma = rmap_item->anon_vma;
2624 struct anon_vma_chain *vmac;
2625 struct vm_area_struct *vma;
2626
2627 cond_resched();
2628 anon_vma_lock_read(anon_vma);
2629 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2630 0, ULONG_MAX) {
2631 unsigned long addr;
2632
2633 cond_resched();
2634 vma = vmac->vma;
2635
2636 /* Ignore the stable/unstable/sqnr flags */
2637 addr = rmap_item->address & ~KSM_FLAG_MASK;
2638
2639 if (addr < vma->vm_start || addr >= vma->vm_end)
2640 continue;
2641 /*
2642 * Initially we examine only the vma which covers this
2643 * rmap_item; but later, if there is still work to do,
2644 * we examine covering vmas in other mms: in case they
2645 * were forked from the original since ksmd passed.
2646 */
2647 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2648 continue;
2649
2650 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2651 continue;
2652
2653 if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2654 anon_vma_unlock_read(anon_vma);
2655 return;
2656 }
2657 if (rwc->done && rwc->done(page)) {
2658 anon_vma_unlock_read(anon_vma);
2659 return;
2660 }
2661 }
2662 anon_vma_unlock_read(anon_vma);
2663 }
2664 if (!search_new_forks++)
2665 goto again;
2666}
2667
2668#ifdef CONFIG_MIGRATION
2669void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2670{
2671 struct stable_node *stable_node;
2672
2673 VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2674 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2675 VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2676
2677 stable_node = page_stable_node(newpage);
2678 if (stable_node) {
2679 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2680 stable_node->kpfn = page_to_pfn(newpage);
2681 /*
2682 * newpage->mapping was set in advance; now we need smp_wmb()
2683 * to make sure that the new stable_node->kpfn is visible
2684 * to get_ksm_page() before it can see that oldpage->mapping
2685 * has gone stale (or that PageSwapCache has been cleared).
2686 */
2687 smp_wmb();
2688 set_page_stable_node(oldpage, NULL);
2689 }
2690}
2691#endif /* CONFIG_MIGRATION */
2692
2693#ifdef CONFIG_MEMORY_HOTREMOVE
2694static void wait_while_offlining(void)
2695{
2696 while (ksm_run & KSM_RUN_OFFLINE) {
2697 mutex_unlock(&ksm_thread_mutex);
2698 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2699 TASK_UNINTERRUPTIBLE);
2700 mutex_lock(&ksm_thread_mutex);
2701 }
2702}
2703
2704static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2705 unsigned long start_pfn,
2706 unsigned long end_pfn)
2707{
2708 if (stable_node->kpfn >= start_pfn &&
2709 stable_node->kpfn < end_pfn) {
2710 /*
2711 * Don't get_ksm_page, page has already gone:
2712 * which is why we keep kpfn instead of page*
2713 */
2714 remove_node_from_stable_tree(stable_node);
2715 return true;
2716 }
2717 return false;
2718}
2719
2720static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2721 unsigned long start_pfn,
2722 unsigned long end_pfn,
2723 struct rb_root *root)
2724{
2725 struct stable_node *dup;
2726 struct hlist_node *hlist_safe;
2727
2728 if (!is_stable_node_chain(stable_node)) {
2729 VM_BUG_ON(is_stable_node_dup(stable_node));
2730 return stable_node_dup_remove_range(stable_node, start_pfn,
2731 end_pfn);
2732 }
2733
2734 hlist_for_each_entry_safe(dup, hlist_safe,
2735 &stable_node->hlist, hlist_dup) {
2736 VM_BUG_ON(!is_stable_node_dup(dup));
2737 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2738 }
2739 if (hlist_empty(&stable_node->hlist)) {
2740 free_stable_node_chain(stable_node, root);
2741 return true; /* notify caller that tree was rebalanced */
2742 } else
2743 return false;
2744}
2745
2746static void ksm_check_stable_tree(unsigned long start_pfn,
2747 unsigned long end_pfn)
2748{
2749 struct stable_node *stable_node, *next;
2750 struct rb_node *node;
2751 int nid;
2752
2753 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2754 node = rb_first(root_stable_tree + nid);
2755 while (node) {
2756 stable_node = rb_entry(node, struct stable_node, node);
2757 if (stable_node_chain_remove_range(stable_node,
2758 start_pfn, end_pfn,
2759 root_stable_tree +
2760 nid))
2761 node = rb_first(root_stable_tree + nid);
2762 else
2763 node = rb_next(node);
2764 cond_resched();
2765 }
2766 }
2767 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2768 if (stable_node->kpfn >= start_pfn &&
2769 stable_node->kpfn < end_pfn)
2770 remove_node_from_stable_tree(stable_node);
2771 cond_resched();
2772 }
2773}
2774
2775static int ksm_memory_callback(struct notifier_block *self,
2776 unsigned long action, void *arg)
2777{
2778 struct memory_notify *mn = arg;
2779
2780 switch (action) {
2781 case MEM_GOING_OFFLINE:
2782 /*
2783 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2784 * and remove_all_stable_nodes() while memory is going offline:
2785 * it is unsafe for them to touch the stable tree at this time.
2786 * But unmerge_ksm_pages(), rmap lookups and other entry points
2787 * which do not need the ksm_thread_mutex are all safe.
2788 */
2789 mutex_lock(&ksm_thread_mutex);
2790 ksm_run |= KSM_RUN_OFFLINE;
2791 mutex_unlock(&ksm_thread_mutex);
2792 break;
2793
2794 case MEM_OFFLINE:
2795 /*
2796 * Most of the work is done by page migration; but there might
2797 * be a few stable_nodes left over, still pointing to struct
2798 * pages which have been offlined: prune those from the tree,
2799 * otherwise get_ksm_page() might later try to access a
2800 * non-existent struct page.
2801 */
2802 ksm_check_stable_tree(mn->start_pfn,
2803 mn->start_pfn + mn->nr_pages);
2804 fallthrough;
2805 case MEM_CANCEL_OFFLINE:
2806 mutex_lock(&ksm_thread_mutex);
2807 ksm_run &= ~KSM_RUN_OFFLINE;
2808 mutex_unlock(&ksm_thread_mutex);
2809
2810 smp_mb(); /* wake_up_bit advises this */
2811 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2812 break;
2813 }
2814 return NOTIFY_OK;
2815}
2816#else
2817static void wait_while_offlining(void)
2818{
2819}
2820#endif /* CONFIG_MEMORY_HOTREMOVE */
2821
2822#ifdef CONFIG_SYSFS
2823/*
2824 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2825 */
2826
2827#define KSM_ATTR_RO(_name) \
2828 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2829#define KSM_ATTR(_name) \
2830 static struct kobj_attribute _name##_attr = \
2831 __ATTR(_name, 0644, _name##_show, _name##_store)
2832
2833static ssize_t sleep_millisecs_show(struct kobject *kobj,
2834 struct kobj_attribute *attr, char *buf)
2835{
2836 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2837}
2838
2839static ssize_t sleep_millisecs_store(struct kobject *kobj,
2840 struct kobj_attribute *attr,
2841 const char *buf, size_t count)
2842{
2843 unsigned long msecs;
2844 int err;
2845
2846 err = kstrtoul(buf, 10, &msecs);
2847 if (err || msecs > UINT_MAX)
2848 return -EINVAL;
2849
2850 ksm_thread_sleep_millisecs = msecs;
2851 wake_up_interruptible(&ksm_iter_wait);
2852
2853 return count;
2854}
2855KSM_ATTR(sleep_millisecs);
2856
2857static ssize_t pages_to_scan_show(struct kobject *kobj,
2858 struct kobj_attribute *attr, char *buf)
2859{
2860 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2861}
2862
2863static ssize_t pages_to_scan_store(struct kobject *kobj,
2864 struct kobj_attribute *attr,
2865 const char *buf, size_t count)
2866{
2867 int err;
2868 unsigned long nr_pages;
2869
2870 err = kstrtoul(buf, 10, &nr_pages);
2871 if (err || nr_pages > UINT_MAX)
2872 return -EINVAL;
2873
2874 ksm_thread_pages_to_scan = nr_pages;
2875
2876 return count;
2877}
2878KSM_ATTR(pages_to_scan);
2879
2880static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2881 char *buf)
2882{
2883 return sprintf(buf, "%lu\n", ksm_run);
2884}
2885
2886static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2887 const char *buf, size_t count)
2888{
2889 int err;
2890 unsigned long flags;
2891
2892 err = kstrtoul(buf, 10, &flags);
2893 if (err || flags > UINT_MAX)
2894 return -EINVAL;
2895 if (flags > KSM_RUN_UNMERGE)
2896 return -EINVAL;
2897
2898 /*
2899 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2900 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2901 * breaking COW to free the pages_shared (but leaves mm_slots
2902 * on the list for when ksmd may be set running again).
2903 */
2904
2905 mutex_lock(&ksm_thread_mutex);
2906 wait_while_offlining();
2907 if (ksm_run != flags) {
2908 ksm_run = flags;
2909 if (flags & KSM_RUN_UNMERGE) {
2910 set_current_oom_origin();
2911 err = unmerge_and_remove_all_rmap_items();
2912 clear_current_oom_origin();
2913 if (err) {
2914 ksm_run = KSM_RUN_STOP;
2915 count = err;
2916 }
2917 }
2918 }
2919 mutex_unlock(&ksm_thread_mutex);
2920
2921 if (flags & KSM_RUN_MERGE)
2922 wake_up_interruptible(&ksm_thread_wait);
2923
2924 return count;
2925}
2926KSM_ATTR(run);
2927
2928#ifdef CONFIG_NUMA
2929static ssize_t merge_across_nodes_show(struct kobject *kobj,
2930 struct kobj_attribute *attr, char *buf)
2931{
2932 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2933}
2934
2935static ssize_t merge_across_nodes_store(struct kobject *kobj,
2936 struct kobj_attribute *attr,
2937 const char *buf, size_t count)
2938{
2939 int err;
2940 unsigned long knob;
2941
2942 err = kstrtoul(buf, 10, &knob);
2943 if (err)
2944 return err;
2945 if (knob > 1)
2946 return -EINVAL;
2947
2948 mutex_lock(&ksm_thread_mutex);
2949 wait_while_offlining();
2950 if (ksm_merge_across_nodes != knob) {
2951 if (ksm_pages_shared || remove_all_stable_nodes())
2952 err = -EBUSY;
2953 else if (root_stable_tree == one_stable_tree) {
2954 struct rb_root *buf;
2955 /*
2956 * This is the first time that we switch away from the
2957 * default of merging across nodes: must now allocate
2958 * a buffer to hold as many roots as may be needed.
2959 * Allocate stable and unstable together:
2960 * MAXSMP NODES_SHIFT 10 will use 16kB.
2961 */
2962 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2963 GFP_KERNEL);
2964 /* Let us assume that RB_ROOT is NULL is zero */
2965 if (!buf)
2966 err = -ENOMEM;
2967 else {
2968 root_stable_tree = buf;
2969 root_unstable_tree = buf + nr_node_ids;
2970 /* Stable tree is empty but not the unstable */
2971 root_unstable_tree[0] = one_unstable_tree[0];
2972 }
2973 }
2974 if (!err) {
2975 ksm_merge_across_nodes = knob;
2976 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2977 }
2978 }
2979 mutex_unlock(&ksm_thread_mutex);
2980
2981 return err ? err : count;
2982}
2983KSM_ATTR(merge_across_nodes);
2984#endif
2985
2986static ssize_t use_zero_pages_show(struct kobject *kobj,
2987 struct kobj_attribute *attr, char *buf)
2988{
2989 return sprintf(buf, "%u\n", ksm_use_zero_pages);
2990}
2991static ssize_t use_zero_pages_store(struct kobject *kobj,
2992 struct kobj_attribute *attr,
2993 const char *buf, size_t count)
2994{
2995 int err;
2996 bool value;
2997
2998 err = kstrtobool(buf, &value);
2999 if (err)
3000 return -EINVAL;
3001
3002 ksm_use_zero_pages = value;
3003
3004 return count;
3005}
3006KSM_ATTR(use_zero_pages);
3007
3008static ssize_t max_page_sharing_show(struct kobject *kobj,
3009 struct kobj_attribute *attr, char *buf)
3010{
3011 return sprintf(buf, "%u\n", ksm_max_page_sharing);
3012}
3013
3014static ssize_t max_page_sharing_store(struct kobject *kobj,
3015 struct kobj_attribute *attr,
3016 const char *buf, size_t count)
3017{
3018 int err;
3019 int knob;
3020
3021 err = kstrtoint(buf, 10, &knob);
3022 if (err)
3023 return err;
3024 /*
3025 * When a KSM page is created it is shared by 2 mappings. This
3026 * being a signed comparison, it implicitly verifies it's not
3027 * negative.
3028 */
3029 if (knob < 2)
3030 return -EINVAL;
3031
3032 if (READ_ONCE(ksm_max_page_sharing) == knob)
3033 return count;
3034
3035 mutex_lock(&ksm_thread_mutex);
3036 wait_while_offlining();
3037 if (ksm_max_page_sharing != knob) {
3038 if (ksm_pages_shared || remove_all_stable_nodes())
3039 err = -EBUSY;
3040 else
3041 ksm_max_page_sharing = knob;
3042 }
3043 mutex_unlock(&ksm_thread_mutex);
3044
3045 return err ? err : count;
3046}
3047KSM_ATTR(max_page_sharing);
3048
3049static ssize_t pages_shared_show(struct kobject *kobj,
3050 struct kobj_attribute *attr, char *buf)
3051{
3052 return sprintf(buf, "%lu\n", ksm_pages_shared);
3053}
3054KSM_ATTR_RO(pages_shared);
3055
3056static ssize_t pages_sharing_show(struct kobject *kobj,
3057 struct kobj_attribute *attr, char *buf)
3058{
3059 return sprintf(buf, "%lu\n", ksm_pages_sharing);
3060}
3061KSM_ATTR_RO(pages_sharing);
3062
3063static ssize_t pages_unshared_show(struct kobject *kobj,
3064 struct kobj_attribute *attr, char *buf)
3065{
3066 return sprintf(buf, "%lu\n", ksm_pages_unshared);
3067}
3068KSM_ATTR_RO(pages_unshared);
3069
3070static ssize_t pages_volatile_show(struct kobject *kobj,
3071 struct kobj_attribute *attr, char *buf)
3072{
3073 long ksm_pages_volatile;
3074
3075 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3076 - ksm_pages_sharing - ksm_pages_unshared;
3077 /*
3078 * It was not worth any locking to calculate that statistic,
3079 * but it might therefore sometimes be negative: conceal that.
3080 */
3081 if (ksm_pages_volatile < 0)
3082 ksm_pages_volatile = 0;
3083 return sprintf(buf, "%ld\n", ksm_pages_volatile);
3084}
3085KSM_ATTR_RO(pages_volatile);
3086
3087static ssize_t stable_node_dups_show(struct kobject *kobj,
3088 struct kobj_attribute *attr, char *buf)
3089{
3090 return sprintf(buf, "%lu\n", ksm_stable_node_dups);
3091}
3092KSM_ATTR_RO(stable_node_dups);
3093
3094static ssize_t stable_node_chains_show(struct kobject *kobj,
3095 struct kobj_attribute *attr, char *buf)
3096{
3097 return sprintf(buf, "%lu\n", ksm_stable_node_chains);
3098}
3099KSM_ATTR_RO(stable_node_chains);
3100
3101static ssize_t
3102stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3103 struct kobj_attribute *attr,
3104 char *buf)
3105{
3106 return sprintf(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3107}
3108
3109static ssize_t
3110stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3111 struct kobj_attribute *attr,
3112 const char *buf, size_t count)
3113{
3114 unsigned long msecs;
3115 int err;
3116
3117 err = kstrtoul(buf, 10, &msecs);
3118 if (err || msecs > UINT_MAX)
3119 return -EINVAL;
3120
3121 ksm_stable_node_chains_prune_millisecs = msecs;
3122
3123 return count;
3124}
3125KSM_ATTR(stable_node_chains_prune_millisecs);
3126
3127static ssize_t full_scans_show(struct kobject *kobj,
3128 struct kobj_attribute *attr, char *buf)
3129{
3130 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
3131}
3132KSM_ATTR_RO(full_scans);
3133
3134static struct attribute *ksm_attrs[] = {
3135 &sleep_millisecs_attr.attr,
3136 &pages_to_scan_attr.attr,
3137 &run_attr.attr,
3138 &pages_shared_attr.attr,
3139 &pages_sharing_attr.attr,
3140 &pages_unshared_attr.attr,
3141 &pages_volatile_attr.attr,
3142 &full_scans_attr.attr,
3143#ifdef CONFIG_NUMA
3144 &merge_across_nodes_attr.attr,
3145#endif
3146 &max_page_sharing_attr.attr,
3147 &stable_node_chains_attr.attr,
3148 &stable_node_dups_attr.attr,
3149 &stable_node_chains_prune_millisecs_attr.attr,
3150 &use_zero_pages_attr.attr,
3151 NULL,
3152};
3153
3154static const struct attribute_group ksm_attr_group = {
3155 .attrs = ksm_attrs,
3156 .name = "ksm",
3157};
3158#endif /* CONFIG_SYSFS */
3159
3160static int __init ksm_init(void)
3161{
3162 struct task_struct *ksm_thread;
3163 int err;
3164
3165 /* The correct value depends on page size and endianness */
3166 zero_checksum = calc_checksum(ZERO_PAGE(0));
3167 /* Default to false for backwards compatibility */
3168 ksm_use_zero_pages = false;
3169
3170 err = ksm_slab_init();
3171 if (err)
3172 goto out;
3173
3174 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3175 if (IS_ERR(ksm_thread)) {
3176 pr_err("ksm: creating kthread failed\n");
3177 err = PTR_ERR(ksm_thread);
3178 goto out_free;
3179 }
3180
3181#ifdef CONFIG_SYSFS
3182 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3183 if (err) {
3184 pr_err("ksm: register sysfs failed\n");
3185 kthread_stop(ksm_thread);
3186 goto out_free;
3187 }
3188#else
3189 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
3190
3191#endif /* CONFIG_SYSFS */
3192
3193#ifdef CONFIG_MEMORY_HOTREMOVE
3194 /* There is no significance to this priority 100 */
3195 hotplug_memory_notifier(ksm_memory_callback, 100);
3196#endif
3197 return 0;
3198
3199out_free:
3200 ksm_slab_free();
3201out:
3202 return err;
3203}
3204subsys_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/hashtable.h>
37#include <linux/freezer.h>
38#include <linux/oom.h>
39#include <linux/numa.h>
40
41#include <asm/tlbflush.h>
42#include "internal.h"
43
44#ifdef CONFIG_NUMA
45#define NUMA(x) (x)
46#define DO_NUMA(x) do { (x); } while (0)
47#else
48#define NUMA(x) (0)
49#define DO_NUMA(x) do { } while (0)
50#endif
51
52/*
53 * A few notes about the KSM scanning process,
54 * to make it easier to understand the data structures below:
55 *
56 * In order to reduce excessive scanning, KSM sorts the memory pages by their
57 * contents into a data structure that holds pointers to the pages' locations.
58 *
59 * Since the contents of the pages may change at any moment, KSM cannot just
60 * insert the pages into a normal sorted tree and expect it to find anything.
61 * Therefore KSM uses two data structures - the stable and the unstable tree.
62 *
63 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
64 * by their contents. Because each such page is write-protected, searching on
65 * this tree is fully assured to be working (except when pages are unmapped),
66 * and therefore this tree is called the stable tree.
67 *
68 * In addition to the stable tree, KSM uses a second data structure called the
69 * unstable tree: this tree holds pointers to pages which have been found to
70 * be "unchanged for a period of time". The unstable tree sorts these pages
71 * by their contents, but since they are not write-protected, KSM cannot rely
72 * upon the unstable tree to work correctly - the unstable tree is liable to
73 * be corrupted as its contents are modified, and so it is called unstable.
74 *
75 * KSM solves this problem by several techniques:
76 *
77 * 1) The unstable tree is flushed every time KSM completes scanning all
78 * memory areas, and then the tree is rebuilt again from the beginning.
79 * 2) KSM will only insert into the unstable tree, pages whose hash value
80 * has not changed since the previous scan of all memory areas.
81 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
82 * colors of the nodes and not on their contents, assuring that even when
83 * the tree gets "corrupted" it won't get out of balance, so scanning time
84 * remains the same (also, searching and inserting nodes in an rbtree uses
85 * the same algorithm, so we have no overhead when we flush and rebuild).
86 * 4) KSM never flushes the stable tree, which means that even if it were to
87 * take 10 attempts to find a page in the unstable tree, once it is found,
88 * it is secured in the stable tree. (When we scan a new page, we first
89 * compare it against the stable tree, and then against the unstable tree.)
90 *
91 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
92 * stable trees and multiple unstable trees: one of each for each NUMA node.
93 */
94
95/**
96 * struct mm_slot - ksm information per mm that is being scanned
97 * @link: link to the mm_slots hash list
98 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
99 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
100 * @mm: the mm that this information is valid for
101 */
102struct mm_slot {
103 struct hlist_node link;
104 struct list_head mm_list;
105 struct rmap_item *rmap_list;
106 struct mm_struct *mm;
107};
108
109/**
110 * struct ksm_scan - cursor for scanning
111 * @mm_slot: the current mm_slot we are scanning
112 * @address: the next address inside that to be scanned
113 * @rmap_list: link to the next rmap to be scanned in the rmap_list
114 * @seqnr: count of completed full scans (needed when removing unstable node)
115 *
116 * There is only the one ksm_scan instance of this cursor structure.
117 */
118struct ksm_scan {
119 struct mm_slot *mm_slot;
120 unsigned long address;
121 struct rmap_item **rmap_list;
122 unsigned long seqnr;
123};
124
125/**
126 * struct stable_node - node of the stable rbtree
127 * @node: rb node of this ksm page in the stable tree
128 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129 * @list: linked into migrate_nodes, pending placement in the proper node tree
130 * @hlist: hlist head of rmap_items using this ksm page
131 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
132 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
133 */
134struct stable_node {
135 union {
136 struct rb_node node; /* when node of stable tree */
137 struct { /* when listed for migration */
138 struct list_head *head;
139 struct list_head list;
140 };
141 };
142 struct hlist_head hlist;
143 unsigned long kpfn;
144#ifdef CONFIG_NUMA
145 int nid;
146#endif
147};
148
149/**
150 * struct rmap_item - reverse mapping item for virtual addresses
151 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
152 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
154 * @mm: the memory structure this rmap_item is pointing into
155 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
156 * @oldchecksum: previous checksum of the page at that virtual address
157 * @node: rb node of this rmap_item in the unstable tree
158 * @head: pointer to stable_node heading this list in the stable tree
159 * @hlist: link into hlist of rmap_items hanging off that stable_node
160 */
161struct rmap_item {
162 struct rmap_item *rmap_list;
163 union {
164 struct anon_vma *anon_vma; /* when stable */
165#ifdef CONFIG_NUMA
166 int nid; /* when node of unstable tree */
167#endif
168 };
169 struct mm_struct *mm;
170 unsigned long address; /* + low bits used for flags below */
171 unsigned int oldchecksum; /* when unstable */
172 union {
173 struct rb_node node; /* when node of unstable tree */
174 struct { /* when listed from stable tree */
175 struct stable_node *head;
176 struct hlist_node hlist;
177 };
178 };
179};
180
181#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
182#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
183#define STABLE_FLAG 0x200 /* is listed from the stable tree */
184
185/* The stable and unstable tree heads */
186static struct rb_root one_stable_tree[1] = { RB_ROOT };
187static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188static struct rb_root *root_stable_tree = one_stable_tree;
189static struct rb_root *root_unstable_tree = one_unstable_tree;
190
191/* Recently migrated nodes of stable tree, pending proper placement */
192static LIST_HEAD(migrate_nodes);
193
194#define MM_SLOTS_HASH_BITS 10
195static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
196
197static struct mm_slot ksm_mm_head = {
198 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
199};
200static struct ksm_scan ksm_scan = {
201 .mm_slot = &ksm_mm_head,
202};
203
204static struct kmem_cache *rmap_item_cache;
205static struct kmem_cache *stable_node_cache;
206static struct kmem_cache *mm_slot_cache;
207
208/* The number of nodes in the stable tree */
209static unsigned long ksm_pages_shared;
210
211/* The number of page slots additionally sharing those nodes */
212static unsigned long ksm_pages_sharing;
213
214/* The number of nodes in the unstable tree */
215static unsigned long ksm_pages_unshared;
216
217/* The number of rmap_items in use: to calculate pages_volatile */
218static unsigned long ksm_rmap_items;
219
220/* Number of pages ksmd should scan in one batch */
221static unsigned int ksm_thread_pages_to_scan = 100;
222
223/* Milliseconds ksmd should sleep between batches */
224static unsigned int ksm_thread_sleep_millisecs = 20;
225
226#ifdef CONFIG_NUMA
227/* Zeroed when merging across nodes is not allowed */
228static unsigned int ksm_merge_across_nodes = 1;
229static int ksm_nr_node_ids = 1;
230#else
231#define ksm_merge_across_nodes 1U
232#define ksm_nr_node_ids 1
233#endif
234
235#define KSM_RUN_STOP 0
236#define KSM_RUN_MERGE 1
237#define KSM_RUN_UNMERGE 2
238#define KSM_RUN_OFFLINE 4
239static unsigned long ksm_run = KSM_RUN_STOP;
240static void wait_while_offlining(void);
241
242static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243static DEFINE_MUTEX(ksm_thread_mutex);
244static DEFINE_SPINLOCK(ksm_mmlist_lock);
245
246#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247 sizeof(struct __struct), __alignof__(struct __struct),\
248 (__flags), NULL)
249
250static int __init ksm_slab_init(void)
251{
252 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
253 if (!rmap_item_cache)
254 goto out;
255
256 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257 if (!stable_node_cache)
258 goto out_free1;
259
260 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261 if (!mm_slot_cache)
262 goto out_free2;
263
264 return 0;
265
266out_free2:
267 kmem_cache_destroy(stable_node_cache);
268out_free1:
269 kmem_cache_destroy(rmap_item_cache);
270out:
271 return -ENOMEM;
272}
273
274static void __init ksm_slab_free(void)
275{
276 kmem_cache_destroy(mm_slot_cache);
277 kmem_cache_destroy(stable_node_cache);
278 kmem_cache_destroy(rmap_item_cache);
279 mm_slot_cache = NULL;
280}
281
282static inline struct rmap_item *alloc_rmap_item(void)
283{
284 struct rmap_item *rmap_item;
285
286 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
287 __GFP_NORETRY | __GFP_NOWARN);
288 if (rmap_item)
289 ksm_rmap_items++;
290 return rmap_item;
291}
292
293static inline void free_rmap_item(struct rmap_item *rmap_item)
294{
295 ksm_rmap_items--;
296 rmap_item->mm = NULL; /* debug safety */
297 kmem_cache_free(rmap_item_cache, rmap_item);
298}
299
300static inline struct stable_node *alloc_stable_node(void)
301{
302 /*
303 * The allocation can take too long with GFP_KERNEL when memory is under
304 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
305 * grants access to memory reserves, helping to avoid this problem.
306 */
307 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
308}
309
310static inline void free_stable_node(struct stable_node *stable_node)
311{
312 kmem_cache_free(stable_node_cache, stable_node);
313}
314
315static inline struct mm_slot *alloc_mm_slot(void)
316{
317 if (!mm_slot_cache) /* initialization failed */
318 return NULL;
319 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
320}
321
322static inline void free_mm_slot(struct mm_slot *mm_slot)
323{
324 kmem_cache_free(mm_slot_cache, mm_slot);
325}
326
327static struct mm_slot *get_mm_slot(struct mm_struct *mm)
328{
329 struct mm_slot *slot;
330
331 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
332 if (slot->mm == mm)
333 return slot;
334
335 return NULL;
336}
337
338static void insert_to_mm_slots_hash(struct mm_struct *mm,
339 struct mm_slot *mm_slot)
340{
341 mm_slot->mm = mm;
342 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
343}
344
345/*
346 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
347 * page tables after it has passed through ksm_exit() - which, if necessary,
348 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
349 * a special flag: they can just back out as soon as mm_users goes to zero.
350 * ksm_test_exit() is used throughout to make this test for exit: in some
351 * places for correctness, in some places just to avoid unnecessary work.
352 */
353static inline bool ksm_test_exit(struct mm_struct *mm)
354{
355 return atomic_read(&mm->mm_users) == 0;
356}
357
358/*
359 * We use break_ksm to break COW on a ksm page: it's a stripped down
360 *
361 * if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1)
362 * put_page(page);
363 *
364 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
365 * in case the application has unmapped and remapped mm,addr meanwhile.
366 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
367 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
368 *
369 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
370 * of the process that owns 'vma'. We also do not want to enforce
371 * protection keys here anyway.
372 */
373static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
374{
375 struct page *page;
376 int ret = 0;
377
378 do {
379 cond_resched();
380 page = follow_page(vma, addr,
381 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
382 if (IS_ERR_OR_NULL(page))
383 break;
384 if (PageKsm(page))
385 ret = handle_mm_fault(vma, addr,
386 FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE);
387 else
388 ret = VM_FAULT_WRITE;
389 put_page(page);
390 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
391 /*
392 * We must loop because handle_mm_fault() may back out if there's
393 * any difficulty e.g. if pte accessed bit gets updated concurrently.
394 *
395 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
396 * COW has been broken, even if the vma does not permit VM_WRITE;
397 * but note that a concurrent fault might break PageKsm for us.
398 *
399 * VM_FAULT_SIGBUS could occur if we race with truncation of the
400 * backing file, which also invalidates anonymous pages: that's
401 * okay, that truncation will have unmapped the PageKsm for us.
402 *
403 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
404 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
405 * current task has TIF_MEMDIE set, and will be OOM killed on return
406 * to user; and ksmd, having no mm, would never be chosen for that.
407 *
408 * But if the mm is in a limited mem_cgroup, then the fault may fail
409 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
410 * even ksmd can fail in this way - though it's usually breaking ksm
411 * just to undo a merge it made a moment before, so unlikely to oom.
412 *
413 * That's a pity: we might therefore have more kernel pages allocated
414 * than we're counting as nodes in the stable tree; but ksm_do_scan
415 * will retry to break_cow on each pass, so should recover the page
416 * in due course. The important thing is to not let VM_MERGEABLE
417 * be cleared while any such pages might remain in the area.
418 */
419 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
420}
421
422static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
423 unsigned long addr)
424{
425 struct vm_area_struct *vma;
426 if (ksm_test_exit(mm))
427 return NULL;
428 vma = find_vma(mm, addr);
429 if (!vma || vma->vm_start > addr)
430 return NULL;
431 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
432 return NULL;
433 return vma;
434}
435
436static void break_cow(struct rmap_item *rmap_item)
437{
438 struct mm_struct *mm = rmap_item->mm;
439 unsigned long addr = rmap_item->address;
440 struct vm_area_struct *vma;
441
442 /*
443 * It is not an accident that whenever we want to break COW
444 * to undo, we also need to drop a reference to the anon_vma.
445 */
446 put_anon_vma(rmap_item->anon_vma);
447
448 down_read(&mm->mmap_sem);
449 vma = find_mergeable_vma(mm, addr);
450 if (vma)
451 break_ksm(vma, addr);
452 up_read(&mm->mmap_sem);
453}
454
455static struct page *get_mergeable_page(struct rmap_item *rmap_item)
456{
457 struct mm_struct *mm = rmap_item->mm;
458 unsigned long addr = rmap_item->address;
459 struct vm_area_struct *vma;
460 struct page *page;
461
462 down_read(&mm->mmap_sem);
463 vma = find_mergeable_vma(mm, addr);
464 if (!vma)
465 goto out;
466
467 page = follow_page(vma, addr, FOLL_GET);
468 if (IS_ERR_OR_NULL(page))
469 goto out;
470 if (PageAnon(page)) {
471 flush_anon_page(vma, page, addr);
472 flush_dcache_page(page);
473 } else {
474 put_page(page);
475out:
476 page = NULL;
477 }
478 up_read(&mm->mmap_sem);
479 return page;
480}
481
482/*
483 * This helper is used for getting right index into array of tree roots.
484 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
485 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
486 * every node has its own stable and unstable tree.
487 */
488static inline int get_kpfn_nid(unsigned long kpfn)
489{
490 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
491}
492
493static void remove_node_from_stable_tree(struct stable_node *stable_node)
494{
495 struct rmap_item *rmap_item;
496
497 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
498 if (rmap_item->hlist.next)
499 ksm_pages_sharing--;
500 else
501 ksm_pages_shared--;
502 put_anon_vma(rmap_item->anon_vma);
503 rmap_item->address &= PAGE_MASK;
504 cond_resched();
505 }
506
507 if (stable_node->head == &migrate_nodes)
508 list_del(&stable_node->list);
509 else
510 rb_erase(&stable_node->node,
511 root_stable_tree + NUMA(stable_node->nid));
512 free_stable_node(stable_node);
513}
514
515/*
516 * get_ksm_page: checks if the page indicated by the stable node
517 * is still its ksm page, despite having held no reference to it.
518 * In which case we can trust the content of the page, and it
519 * returns the gotten page; but if the page has now been zapped,
520 * remove the stale node from the stable tree and return NULL.
521 * But beware, the stable node's page might be being migrated.
522 *
523 * You would expect the stable_node to hold a reference to the ksm page.
524 * But if it increments the page's count, swapping out has to wait for
525 * ksmd to come around again before it can free the page, which may take
526 * seconds or even minutes: much too unresponsive. So instead we use a
527 * "keyhole reference": access to the ksm page from the stable node peeps
528 * out through its keyhole to see if that page still holds the right key,
529 * pointing back to this stable node. This relies on freeing a PageAnon
530 * page to reset its page->mapping to NULL, and relies on no other use of
531 * a page to put something that might look like our key in page->mapping.
532 * is on its way to being freed; but it is an anomaly to bear in mind.
533 */
534static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
535{
536 struct page *page;
537 void *expected_mapping;
538 unsigned long kpfn;
539
540 expected_mapping = (void *)((unsigned long)stable_node |
541 PAGE_MAPPING_KSM);
542again:
543 kpfn = READ_ONCE(stable_node->kpfn);
544 page = pfn_to_page(kpfn);
545
546 /*
547 * page is computed from kpfn, so on most architectures reading
548 * page->mapping is naturally ordered after reading node->kpfn,
549 * but on Alpha we need to be more careful.
550 */
551 smp_read_barrier_depends();
552 if (READ_ONCE(page->mapping) != expected_mapping)
553 goto stale;
554
555 /*
556 * We cannot do anything with the page while its refcount is 0.
557 * Usually 0 means free, or tail of a higher-order page: in which
558 * case this node is no longer referenced, and should be freed;
559 * however, it might mean that the page is under page_freeze_refs().
560 * The __remove_mapping() case is easy, again the node is now stale;
561 * but if page is swapcache in migrate_page_move_mapping(), it might
562 * still be our page, in which case it's essential to keep the node.
563 */
564 while (!get_page_unless_zero(page)) {
565 /*
566 * Another check for page->mapping != expected_mapping would
567 * work here too. We have chosen the !PageSwapCache test to
568 * optimize the common case, when the page is or is about to
569 * be freed: PageSwapCache is cleared (under spin_lock_irq)
570 * in the freeze_refs section of __remove_mapping(); but Anon
571 * page->mapping reset to NULL later, in free_pages_prepare().
572 */
573 if (!PageSwapCache(page))
574 goto stale;
575 cpu_relax();
576 }
577
578 if (READ_ONCE(page->mapping) != expected_mapping) {
579 put_page(page);
580 goto stale;
581 }
582
583 if (lock_it) {
584 lock_page(page);
585 if (READ_ONCE(page->mapping) != expected_mapping) {
586 unlock_page(page);
587 put_page(page);
588 goto stale;
589 }
590 }
591 return page;
592
593stale:
594 /*
595 * We come here from above when page->mapping or !PageSwapCache
596 * suggests that the node is stale; but it might be under migration.
597 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
598 * before checking whether node->kpfn has been changed.
599 */
600 smp_rmb();
601 if (READ_ONCE(stable_node->kpfn) != kpfn)
602 goto again;
603 remove_node_from_stable_tree(stable_node);
604 return NULL;
605}
606
607/*
608 * Removing rmap_item from stable or unstable tree.
609 * This function will clean the information from the stable/unstable tree.
610 */
611static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
612{
613 if (rmap_item->address & STABLE_FLAG) {
614 struct stable_node *stable_node;
615 struct page *page;
616
617 stable_node = rmap_item->head;
618 page = get_ksm_page(stable_node, true);
619 if (!page)
620 goto out;
621
622 hlist_del(&rmap_item->hlist);
623 unlock_page(page);
624 put_page(page);
625
626 if (!hlist_empty(&stable_node->hlist))
627 ksm_pages_sharing--;
628 else
629 ksm_pages_shared--;
630
631 put_anon_vma(rmap_item->anon_vma);
632 rmap_item->address &= PAGE_MASK;
633
634 } else if (rmap_item->address & UNSTABLE_FLAG) {
635 unsigned char age;
636 /*
637 * Usually ksmd can and must skip the rb_erase, because
638 * root_unstable_tree was already reset to RB_ROOT.
639 * But be careful when an mm is exiting: do the rb_erase
640 * if this rmap_item was inserted by this scan, rather
641 * than left over from before.
642 */
643 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
644 BUG_ON(age > 1);
645 if (!age)
646 rb_erase(&rmap_item->node,
647 root_unstable_tree + NUMA(rmap_item->nid));
648 ksm_pages_unshared--;
649 rmap_item->address &= PAGE_MASK;
650 }
651out:
652 cond_resched(); /* we're called from many long loops */
653}
654
655static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
656 struct rmap_item **rmap_list)
657{
658 while (*rmap_list) {
659 struct rmap_item *rmap_item = *rmap_list;
660 *rmap_list = rmap_item->rmap_list;
661 remove_rmap_item_from_tree(rmap_item);
662 free_rmap_item(rmap_item);
663 }
664}
665
666/*
667 * Though it's very tempting to unmerge rmap_items from stable tree rather
668 * than check every pte of a given vma, the locking doesn't quite work for
669 * that - an rmap_item is assigned to the stable tree after inserting ksm
670 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
671 * rmap_items from parent to child at fork time (so as not to waste time
672 * if exit comes before the next scan reaches it).
673 *
674 * Similarly, although we'd like to remove rmap_items (so updating counts
675 * and freeing memory) when unmerging an area, it's easier to leave that
676 * to the next pass of ksmd - consider, for example, how ksmd might be
677 * in cmp_and_merge_page on one of the rmap_items we would be removing.
678 */
679static int unmerge_ksm_pages(struct vm_area_struct *vma,
680 unsigned long start, unsigned long end)
681{
682 unsigned long addr;
683 int err = 0;
684
685 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
686 if (ksm_test_exit(vma->vm_mm))
687 break;
688 if (signal_pending(current))
689 err = -ERESTARTSYS;
690 else
691 err = break_ksm(vma, addr);
692 }
693 return err;
694}
695
696#ifdef CONFIG_SYSFS
697/*
698 * Only called through the sysfs control interface:
699 */
700static int remove_stable_node(struct stable_node *stable_node)
701{
702 struct page *page;
703 int err;
704
705 page = get_ksm_page(stable_node, true);
706 if (!page) {
707 /*
708 * get_ksm_page did remove_node_from_stable_tree itself.
709 */
710 return 0;
711 }
712
713 if (WARN_ON_ONCE(page_mapped(page))) {
714 /*
715 * This should not happen: but if it does, just refuse to let
716 * merge_across_nodes be switched - there is no need to panic.
717 */
718 err = -EBUSY;
719 } else {
720 /*
721 * The stable node did not yet appear stale to get_ksm_page(),
722 * since that allows for an unmapped ksm page to be recognized
723 * right up until it is freed; but the node is safe to remove.
724 * This page might be in a pagevec waiting to be freed,
725 * or it might be PageSwapCache (perhaps under writeback),
726 * or it might have been removed from swapcache a moment ago.
727 */
728 set_page_stable_node(page, NULL);
729 remove_node_from_stable_tree(stable_node);
730 err = 0;
731 }
732
733 unlock_page(page);
734 put_page(page);
735 return err;
736}
737
738static int remove_all_stable_nodes(void)
739{
740 struct stable_node *stable_node, *next;
741 int nid;
742 int err = 0;
743
744 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
745 while (root_stable_tree[nid].rb_node) {
746 stable_node = rb_entry(root_stable_tree[nid].rb_node,
747 struct stable_node, node);
748 if (remove_stable_node(stable_node)) {
749 err = -EBUSY;
750 break; /* proceed to next nid */
751 }
752 cond_resched();
753 }
754 }
755 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
756 if (remove_stable_node(stable_node))
757 err = -EBUSY;
758 cond_resched();
759 }
760 return err;
761}
762
763static int unmerge_and_remove_all_rmap_items(void)
764{
765 struct mm_slot *mm_slot;
766 struct mm_struct *mm;
767 struct vm_area_struct *vma;
768 int err = 0;
769
770 spin_lock(&ksm_mmlist_lock);
771 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
772 struct mm_slot, mm_list);
773 spin_unlock(&ksm_mmlist_lock);
774
775 for (mm_slot = ksm_scan.mm_slot;
776 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
777 mm = mm_slot->mm;
778 down_read(&mm->mmap_sem);
779 for (vma = mm->mmap; vma; vma = vma->vm_next) {
780 if (ksm_test_exit(mm))
781 break;
782 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
783 continue;
784 err = unmerge_ksm_pages(vma,
785 vma->vm_start, vma->vm_end);
786 if (err)
787 goto error;
788 }
789
790 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
791 up_read(&mm->mmap_sem);
792
793 spin_lock(&ksm_mmlist_lock);
794 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
795 struct mm_slot, mm_list);
796 if (ksm_test_exit(mm)) {
797 hash_del(&mm_slot->link);
798 list_del(&mm_slot->mm_list);
799 spin_unlock(&ksm_mmlist_lock);
800
801 free_mm_slot(mm_slot);
802 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
803 mmdrop(mm);
804 } else
805 spin_unlock(&ksm_mmlist_lock);
806 }
807
808 /* Clean up stable nodes, but don't worry if some are still busy */
809 remove_all_stable_nodes();
810 ksm_scan.seqnr = 0;
811 return 0;
812
813error:
814 up_read(&mm->mmap_sem);
815 spin_lock(&ksm_mmlist_lock);
816 ksm_scan.mm_slot = &ksm_mm_head;
817 spin_unlock(&ksm_mmlist_lock);
818 return err;
819}
820#endif /* CONFIG_SYSFS */
821
822static u32 calc_checksum(struct page *page)
823{
824 u32 checksum;
825 void *addr = kmap_atomic(page);
826 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
827 kunmap_atomic(addr);
828 return checksum;
829}
830
831static int memcmp_pages(struct page *page1, struct page *page2)
832{
833 char *addr1, *addr2;
834 int ret;
835
836 addr1 = kmap_atomic(page1);
837 addr2 = kmap_atomic(page2);
838 ret = memcmp(addr1, addr2, PAGE_SIZE);
839 kunmap_atomic(addr2);
840 kunmap_atomic(addr1);
841 return ret;
842}
843
844static inline int pages_identical(struct page *page1, struct page *page2)
845{
846 return !memcmp_pages(page1, page2);
847}
848
849static int write_protect_page(struct vm_area_struct *vma, struct page *page,
850 pte_t *orig_pte)
851{
852 struct mm_struct *mm = vma->vm_mm;
853 unsigned long addr;
854 pte_t *ptep;
855 spinlock_t *ptl;
856 int swapped;
857 int err = -EFAULT;
858 unsigned long mmun_start; /* For mmu_notifiers */
859 unsigned long mmun_end; /* For mmu_notifiers */
860
861 addr = page_address_in_vma(page, vma);
862 if (addr == -EFAULT)
863 goto out;
864
865 BUG_ON(PageTransCompound(page));
866
867 mmun_start = addr;
868 mmun_end = addr + PAGE_SIZE;
869 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
870
871 ptep = page_check_address(page, mm, addr, &ptl, 0);
872 if (!ptep)
873 goto out_mn;
874
875 if (pte_write(*ptep) || pte_dirty(*ptep)) {
876 pte_t entry;
877
878 swapped = PageSwapCache(page);
879 flush_cache_page(vma, addr, page_to_pfn(page));
880 /*
881 * Ok this is tricky, when get_user_pages_fast() run it doesn't
882 * take any lock, therefore the check that we are going to make
883 * with the pagecount against the mapcount is racey and
884 * O_DIRECT can happen right after the check.
885 * So we clear the pte and flush the tlb before the check
886 * this assure us that no O_DIRECT can happen after the check
887 * or in the middle of the check.
888 */
889 entry = ptep_clear_flush_notify(vma, addr, ptep);
890 /*
891 * Check that no O_DIRECT or similar I/O is in progress on the
892 * page
893 */
894 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
895 set_pte_at(mm, addr, ptep, entry);
896 goto out_unlock;
897 }
898 if (pte_dirty(entry))
899 set_page_dirty(page);
900 entry = pte_mkclean(pte_wrprotect(entry));
901 set_pte_at_notify(mm, addr, ptep, entry);
902 }
903 *orig_pte = *ptep;
904 err = 0;
905
906out_unlock:
907 pte_unmap_unlock(ptep, ptl);
908out_mn:
909 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
910out:
911 return err;
912}
913
914/**
915 * replace_page - replace page in vma by new ksm page
916 * @vma: vma that holds the pte pointing to page
917 * @page: the page we are replacing by kpage
918 * @kpage: the ksm page we replace page by
919 * @orig_pte: the original value of the pte
920 *
921 * Returns 0 on success, -EFAULT on failure.
922 */
923static int replace_page(struct vm_area_struct *vma, struct page *page,
924 struct page *kpage, pte_t orig_pte)
925{
926 struct mm_struct *mm = vma->vm_mm;
927 pmd_t *pmd;
928 pte_t *ptep;
929 spinlock_t *ptl;
930 unsigned long addr;
931 int err = -EFAULT;
932 unsigned long mmun_start; /* For mmu_notifiers */
933 unsigned long mmun_end; /* For mmu_notifiers */
934
935 addr = page_address_in_vma(page, vma);
936 if (addr == -EFAULT)
937 goto out;
938
939 pmd = mm_find_pmd(mm, addr);
940 if (!pmd)
941 goto out;
942
943 mmun_start = addr;
944 mmun_end = addr + PAGE_SIZE;
945 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
946
947 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
948 if (!pte_same(*ptep, orig_pte)) {
949 pte_unmap_unlock(ptep, ptl);
950 goto out_mn;
951 }
952
953 get_page(kpage);
954 page_add_anon_rmap(kpage, vma, addr, false);
955
956 flush_cache_page(vma, addr, pte_pfn(*ptep));
957 ptep_clear_flush_notify(vma, addr, ptep);
958 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
959
960 page_remove_rmap(page, false);
961 if (!page_mapped(page))
962 try_to_free_swap(page);
963 put_page(page);
964
965 pte_unmap_unlock(ptep, ptl);
966 err = 0;
967out_mn:
968 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
969out:
970 return err;
971}
972
973/*
974 * try_to_merge_one_page - take two pages and merge them into one
975 * @vma: the vma that holds the pte pointing to page
976 * @page: the PageAnon page that we want to replace with kpage
977 * @kpage: the PageKsm page that we want to map instead of page,
978 * or NULL the first time when we want to use page as kpage.
979 *
980 * This function returns 0 if the pages were merged, -EFAULT otherwise.
981 */
982static int try_to_merge_one_page(struct vm_area_struct *vma,
983 struct page *page, struct page *kpage)
984{
985 pte_t orig_pte = __pte(0);
986 int err = -EFAULT;
987
988 if (page == kpage) /* ksm page forked */
989 return 0;
990
991 if (!PageAnon(page))
992 goto out;
993
994 /*
995 * We need the page lock to read a stable PageSwapCache in
996 * write_protect_page(). We use trylock_page() instead of
997 * lock_page() because we don't want to wait here - we
998 * prefer to continue scanning and merging different pages,
999 * then come back to this page when it is unlocked.
1000 */
1001 if (!trylock_page(page))
1002 goto out;
1003
1004 if (PageTransCompound(page)) {
1005 err = split_huge_page(page);
1006 if (err)
1007 goto out_unlock;
1008 }
1009
1010 /*
1011 * If this anonymous page is mapped only here, its pte may need
1012 * to be write-protected. If it's mapped elsewhere, all of its
1013 * ptes are necessarily already write-protected. But in either
1014 * case, we need to lock and check page_count is not raised.
1015 */
1016 if (write_protect_page(vma, page, &orig_pte) == 0) {
1017 if (!kpage) {
1018 /*
1019 * While we hold page lock, upgrade page from
1020 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1021 * stable_tree_insert() will update stable_node.
1022 */
1023 set_page_stable_node(page, NULL);
1024 mark_page_accessed(page);
1025 /*
1026 * Page reclaim just frees a clean page with no dirty
1027 * ptes: make sure that the ksm page would be swapped.
1028 */
1029 if (!PageDirty(page))
1030 SetPageDirty(page);
1031 err = 0;
1032 } else if (pages_identical(page, kpage))
1033 err = replace_page(vma, page, kpage, orig_pte);
1034 }
1035
1036 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1037 munlock_vma_page(page);
1038 if (!PageMlocked(kpage)) {
1039 unlock_page(page);
1040 lock_page(kpage);
1041 mlock_vma_page(kpage);
1042 page = kpage; /* for final unlock */
1043 }
1044 }
1045
1046out_unlock:
1047 unlock_page(page);
1048out:
1049 return err;
1050}
1051
1052/*
1053 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1054 * but no new kernel page is allocated: kpage must already be a ksm page.
1055 *
1056 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1057 */
1058static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1059 struct page *page, struct page *kpage)
1060{
1061 struct mm_struct *mm = rmap_item->mm;
1062 struct vm_area_struct *vma;
1063 int err = -EFAULT;
1064
1065 down_read(&mm->mmap_sem);
1066 vma = find_mergeable_vma(mm, rmap_item->address);
1067 if (!vma)
1068 goto out;
1069
1070 err = try_to_merge_one_page(vma, page, kpage);
1071 if (err)
1072 goto out;
1073
1074 /* Unstable nid is in union with stable anon_vma: remove first */
1075 remove_rmap_item_from_tree(rmap_item);
1076
1077 /* Must get reference to anon_vma while still holding mmap_sem */
1078 rmap_item->anon_vma = vma->anon_vma;
1079 get_anon_vma(vma->anon_vma);
1080out:
1081 up_read(&mm->mmap_sem);
1082 return err;
1083}
1084
1085/*
1086 * try_to_merge_two_pages - take two identical pages and prepare them
1087 * to be merged into one page.
1088 *
1089 * This function returns the kpage if we successfully merged two identical
1090 * pages into one ksm page, NULL otherwise.
1091 *
1092 * Note that this function upgrades page to ksm page: if one of the pages
1093 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1094 */
1095static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1096 struct page *page,
1097 struct rmap_item *tree_rmap_item,
1098 struct page *tree_page)
1099{
1100 int err;
1101
1102 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1103 if (!err) {
1104 err = try_to_merge_with_ksm_page(tree_rmap_item,
1105 tree_page, page);
1106 /*
1107 * If that fails, we have a ksm page with only one pte
1108 * pointing to it: so break it.
1109 */
1110 if (err)
1111 break_cow(rmap_item);
1112 }
1113 return err ? NULL : page;
1114}
1115
1116/*
1117 * stable_tree_search - search for page inside the stable tree
1118 *
1119 * This function checks if there is a page inside the stable tree
1120 * with identical content to the page that we are scanning right now.
1121 *
1122 * This function returns the stable tree node of identical content if found,
1123 * NULL otherwise.
1124 */
1125static struct page *stable_tree_search(struct page *page)
1126{
1127 int nid;
1128 struct rb_root *root;
1129 struct rb_node **new;
1130 struct rb_node *parent;
1131 struct stable_node *stable_node;
1132 struct stable_node *page_node;
1133
1134 page_node = page_stable_node(page);
1135 if (page_node && page_node->head != &migrate_nodes) {
1136 /* ksm page forked */
1137 get_page(page);
1138 return page;
1139 }
1140
1141 nid = get_kpfn_nid(page_to_pfn(page));
1142 root = root_stable_tree + nid;
1143again:
1144 new = &root->rb_node;
1145 parent = NULL;
1146
1147 while (*new) {
1148 struct page *tree_page;
1149 int ret;
1150
1151 cond_resched();
1152 stable_node = rb_entry(*new, struct stable_node, node);
1153 tree_page = get_ksm_page(stable_node, false);
1154 if (!tree_page) {
1155 /*
1156 * If we walked over a stale stable_node,
1157 * get_ksm_page() will call rb_erase() and it
1158 * may rebalance the tree from under us. So
1159 * restart the search from scratch. Returning
1160 * NULL would be safe too, but we'd generate
1161 * false negative insertions just because some
1162 * stable_node was stale.
1163 */
1164 goto again;
1165 }
1166
1167 ret = memcmp_pages(page, tree_page);
1168 put_page(tree_page);
1169
1170 parent = *new;
1171 if (ret < 0)
1172 new = &parent->rb_left;
1173 else if (ret > 0)
1174 new = &parent->rb_right;
1175 else {
1176 /*
1177 * Lock and unlock the stable_node's page (which
1178 * might already have been migrated) so that page
1179 * migration is sure to notice its raised count.
1180 * It would be more elegant to return stable_node
1181 * than kpage, but that involves more changes.
1182 */
1183 tree_page = get_ksm_page(stable_node, true);
1184 if (tree_page) {
1185 unlock_page(tree_page);
1186 if (get_kpfn_nid(stable_node->kpfn) !=
1187 NUMA(stable_node->nid)) {
1188 put_page(tree_page);
1189 goto replace;
1190 }
1191 return tree_page;
1192 }
1193 /*
1194 * There is now a place for page_node, but the tree may
1195 * have been rebalanced, so re-evaluate parent and new.
1196 */
1197 if (page_node)
1198 goto again;
1199 return NULL;
1200 }
1201 }
1202
1203 if (!page_node)
1204 return NULL;
1205
1206 list_del(&page_node->list);
1207 DO_NUMA(page_node->nid = nid);
1208 rb_link_node(&page_node->node, parent, new);
1209 rb_insert_color(&page_node->node, root);
1210 get_page(page);
1211 return page;
1212
1213replace:
1214 if (page_node) {
1215 list_del(&page_node->list);
1216 DO_NUMA(page_node->nid = nid);
1217 rb_replace_node(&stable_node->node, &page_node->node, root);
1218 get_page(page);
1219 } else {
1220 rb_erase(&stable_node->node, root);
1221 page = NULL;
1222 }
1223 stable_node->head = &migrate_nodes;
1224 list_add(&stable_node->list, stable_node->head);
1225 return page;
1226}
1227
1228/*
1229 * stable_tree_insert - insert stable tree node pointing to new ksm page
1230 * into the stable tree.
1231 *
1232 * This function returns the stable tree node just allocated on success,
1233 * NULL otherwise.
1234 */
1235static struct stable_node *stable_tree_insert(struct page *kpage)
1236{
1237 int nid;
1238 unsigned long kpfn;
1239 struct rb_root *root;
1240 struct rb_node **new;
1241 struct rb_node *parent;
1242 struct stable_node *stable_node;
1243
1244 kpfn = page_to_pfn(kpage);
1245 nid = get_kpfn_nid(kpfn);
1246 root = root_stable_tree + nid;
1247again:
1248 parent = NULL;
1249 new = &root->rb_node;
1250
1251 while (*new) {
1252 struct page *tree_page;
1253 int ret;
1254
1255 cond_resched();
1256 stable_node = rb_entry(*new, struct stable_node, node);
1257 tree_page = get_ksm_page(stable_node, false);
1258 if (!tree_page) {
1259 /*
1260 * If we walked over a stale stable_node,
1261 * get_ksm_page() will call rb_erase() and it
1262 * may rebalance the tree from under us. So
1263 * restart the search from scratch. Returning
1264 * NULL would be safe too, but we'd generate
1265 * false negative insertions just because some
1266 * stable_node was stale.
1267 */
1268 goto again;
1269 }
1270
1271 ret = memcmp_pages(kpage, tree_page);
1272 put_page(tree_page);
1273
1274 parent = *new;
1275 if (ret < 0)
1276 new = &parent->rb_left;
1277 else if (ret > 0)
1278 new = &parent->rb_right;
1279 else {
1280 /*
1281 * It is not a bug that stable_tree_search() didn't
1282 * find this node: because at that time our page was
1283 * not yet write-protected, so may have changed since.
1284 */
1285 return NULL;
1286 }
1287 }
1288
1289 stable_node = alloc_stable_node();
1290 if (!stable_node)
1291 return NULL;
1292
1293 INIT_HLIST_HEAD(&stable_node->hlist);
1294 stable_node->kpfn = kpfn;
1295 set_page_stable_node(kpage, stable_node);
1296 DO_NUMA(stable_node->nid = nid);
1297 rb_link_node(&stable_node->node, parent, new);
1298 rb_insert_color(&stable_node->node, root);
1299
1300 return stable_node;
1301}
1302
1303/*
1304 * unstable_tree_search_insert - search for identical page,
1305 * else insert rmap_item into the unstable tree.
1306 *
1307 * This function searches for a page in the unstable tree identical to the
1308 * page currently being scanned; and if no identical page is found in the
1309 * tree, we insert rmap_item as a new object into the unstable tree.
1310 *
1311 * This function returns pointer to rmap_item found to be identical
1312 * to the currently scanned page, NULL otherwise.
1313 *
1314 * This function does both searching and inserting, because they share
1315 * the same walking algorithm in an rbtree.
1316 */
1317static
1318struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1319 struct page *page,
1320 struct page **tree_pagep)
1321{
1322 struct rb_node **new;
1323 struct rb_root *root;
1324 struct rb_node *parent = NULL;
1325 int nid;
1326
1327 nid = get_kpfn_nid(page_to_pfn(page));
1328 root = root_unstable_tree + nid;
1329 new = &root->rb_node;
1330
1331 while (*new) {
1332 struct rmap_item *tree_rmap_item;
1333 struct page *tree_page;
1334 int ret;
1335
1336 cond_resched();
1337 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1338 tree_page = get_mergeable_page(tree_rmap_item);
1339 if (!tree_page)
1340 return NULL;
1341
1342 /*
1343 * Don't substitute a ksm page for a forked page.
1344 */
1345 if (page == tree_page) {
1346 put_page(tree_page);
1347 return NULL;
1348 }
1349
1350 ret = memcmp_pages(page, tree_page);
1351
1352 parent = *new;
1353 if (ret < 0) {
1354 put_page(tree_page);
1355 new = &parent->rb_left;
1356 } else if (ret > 0) {
1357 put_page(tree_page);
1358 new = &parent->rb_right;
1359 } else if (!ksm_merge_across_nodes &&
1360 page_to_nid(tree_page) != nid) {
1361 /*
1362 * If tree_page has been migrated to another NUMA node,
1363 * it will be flushed out and put in the right unstable
1364 * tree next time: only merge with it when across_nodes.
1365 */
1366 put_page(tree_page);
1367 return NULL;
1368 } else {
1369 *tree_pagep = tree_page;
1370 return tree_rmap_item;
1371 }
1372 }
1373
1374 rmap_item->address |= UNSTABLE_FLAG;
1375 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1376 DO_NUMA(rmap_item->nid = nid);
1377 rb_link_node(&rmap_item->node, parent, new);
1378 rb_insert_color(&rmap_item->node, root);
1379
1380 ksm_pages_unshared++;
1381 return NULL;
1382}
1383
1384/*
1385 * stable_tree_append - add another rmap_item to the linked list of
1386 * rmap_items hanging off a given node of the stable tree, all sharing
1387 * the same ksm page.
1388 */
1389static void stable_tree_append(struct rmap_item *rmap_item,
1390 struct stable_node *stable_node)
1391{
1392 rmap_item->head = stable_node;
1393 rmap_item->address |= STABLE_FLAG;
1394 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1395
1396 if (rmap_item->hlist.next)
1397 ksm_pages_sharing++;
1398 else
1399 ksm_pages_shared++;
1400}
1401
1402/*
1403 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1404 * if not, compare checksum to previous and if it's the same, see if page can
1405 * be inserted into the unstable tree, or merged with a page already there and
1406 * both transferred to the stable tree.
1407 *
1408 * @page: the page that we are searching identical page to.
1409 * @rmap_item: the reverse mapping into the virtual address of this page
1410 */
1411static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1412{
1413 struct rmap_item *tree_rmap_item;
1414 struct page *tree_page = NULL;
1415 struct stable_node *stable_node;
1416 struct page *kpage;
1417 unsigned int checksum;
1418 int err;
1419
1420 stable_node = page_stable_node(page);
1421 if (stable_node) {
1422 if (stable_node->head != &migrate_nodes &&
1423 get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1424 rb_erase(&stable_node->node,
1425 root_stable_tree + NUMA(stable_node->nid));
1426 stable_node->head = &migrate_nodes;
1427 list_add(&stable_node->list, stable_node->head);
1428 }
1429 if (stable_node->head != &migrate_nodes &&
1430 rmap_item->head == stable_node)
1431 return;
1432 }
1433
1434 /* We first start with searching the page inside the stable tree */
1435 kpage = stable_tree_search(page);
1436 if (kpage == page && rmap_item->head == stable_node) {
1437 put_page(kpage);
1438 return;
1439 }
1440
1441 remove_rmap_item_from_tree(rmap_item);
1442
1443 if (kpage) {
1444 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1445 if (!err) {
1446 /*
1447 * The page was successfully merged:
1448 * add its rmap_item to the stable tree.
1449 */
1450 lock_page(kpage);
1451 stable_tree_append(rmap_item, page_stable_node(kpage));
1452 unlock_page(kpage);
1453 }
1454 put_page(kpage);
1455 return;
1456 }
1457
1458 /*
1459 * If the hash value of the page has changed from the last time
1460 * we calculated it, this page is changing frequently: therefore we
1461 * don't want to insert it in the unstable tree, and we don't want
1462 * to waste our time searching for something identical to it there.
1463 */
1464 checksum = calc_checksum(page);
1465 if (rmap_item->oldchecksum != checksum) {
1466 rmap_item->oldchecksum = checksum;
1467 return;
1468 }
1469
1470 tree_rmap_item =
1471 unstable_tree_search_insert(rmap_item, page, &tree_page);
1472 if (tree_rmap_item) {
1473 kpage = try_to_merge_two_pages(rmap_item, page,
1474 tree_rmap_item, tree_page);
1475 put_page(tree_page);
1476 if (kpage) {
1477 /*
1478 * The pages were successfully merged: insert new
1479 * node in the stable tree and add both rmap_items.
1480 */
1481 lock_page(kpage);
1482 stable_node = stable_tree_insert(kpage);
1483 if (stable_node) {
1484 stable_tree_append(tree_rmap_item, stable_node);
1485 stable_tree_append(rmap_item, stable_node);
1486 }
1487 unlock_page(kpage);
1488
1489 /*
1490 * If we fail to insert the page into the stable tree,
1491 * we will have 2 virtual addresses that are pointing
1492 * to a ksm page left outside the stable tree,
1493 * in which case we need to break_cow on both.
1494 */
1495 if (!stable_node) {
1496 break_cow(tree_rmap_item);
1497 break_cow(rmap_item);
1498 }
1499 }
1500 }
1501}
1502
1503static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1504 struct rmap_item **rmap_list,
1505 unsigned long addr)
1506{
1507 struct rmap_item *rmap_item;
1508
1509 while (*rmap_list) {
1510 rmap_item = *rmap_list;
1511 if ((rmap_item->address & PAGE_MASK) == addr)
1512 return rmap_item;
1513 if (rmap_item->address > addr)
1514 break;
1515 *rmap_list = rmap_item->rmap_list;
1516 remove_rmap_item_from_tree(rmap_item);
1517 free_rmap_item(rmap_item);
1518 }
1519
1520 rmap_item = alloc_rmap_item();
1521 if (rmap_item) {
1522 /* It has already been zeroed */
1523 rmap_item->mm = mm_slot->mm;
1524 rmap_item->address = addr;
1525 rmap_item->rmap_list = *rmap_list;
1526 *rmap_list = rmap_item;
1527 }
1528 return rmap_item;
1529}
1530
1531static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1532{
1533 struct mm_struct *mm;
1534 struct mm_slot *slot;
1535 struct vm_area_struct *vma;
1536 struct rmap_item *rmap_item;
1537 int nid;
1538
1539 if (list_empty(&ksm_mm_head.mm_list))
1540 return NULL;
1541
1542 slot = ksm_scan.mm_slot;
1543 if (slot == &ksm_mm_head) {
1544 /*
1545 * A number of pages can hang around indefinitely on per-cpu
1546 * pagevecs, raised page count preventing write_protect_page
1547 * from merging them. Though it doesn't really matter much,
1548 * it is puzzling to see some stuck in pages_volatile until
1549 * other activity jostles them out, and they also prevented
1550 * LTP's KSM test from succeeding deterministically; so drain
1551 * them here (here rather than on entry to ksm_do_scan(),
1552 * so we don't IPI too often when pages_to_scan is set low).
1553 */
1554 lru_add_drain_all();
1555
1556 /*
1557 * Whereas stale stable_nodes on the stable_tree itself
1558 * get pruned in the regular course of stable_tree_search(),
1559 * those moved out to the migrate_nodes list can accumulate:
1560 * so prune them once before each full scan.
1561 */
1562 if (!ksm_merge_across_nodes) {
1563 struct stable_node *stable_node, *next;
1564 struct page *page;
1565
1566 list_for_each_entry_safe(stable_node, next,
1567 &migrate_nodes, list) {
1568 page = get_ksm_page(stable_node, false);
1569 if (page)
1570 put_page(page);
1571 cond_resched();
1572 }
1573 }
1574
1575 for (nid = 0; nid < ksm_nr_node_ids; nid++)
1576 root_unstable_tree[nid] = RB_ROOT;
1577
1578 spin_lock(&ksm_mmlist_lock);
1579 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1580 ksm_scan.mm_slot = slot;
1581 spin_unlock(&ksm_mmlist_lock);
1582 /*
1583 * Although we tested list_empty() above, a racing __ksm_exit
1584 * of the last mm on the list may have removed it since then.
1585 */
1586 if (slot == &ksm_mm_head)
1587 return NULL;
1588next_mm:
1589 ksm_scan.address = 0;
1590 ksm_scan.rmap_list = &slot->rmap_list;
1591 }
1592
1593 mm = slot->mm;
1594 down_read(&mm->mmap_sem);
1595 if (ksm_test_exit(mm))
1596 vma = NULL;
1597 else
1598 vma = find_vma(mm, ksm_scan.address);
1599
1600 for (; vma; vma = vma->vm_next) {
1601 if (!(vma->vm_flags & VM_MERGEABLE))
1602 continue;
1603 if (ksm_scan.address < vma->vm_start)
1604 ksm_scan.address = vma->vm_start;
1605 if (!vma->anon_vma)
1606 ksm_scan.address = vma->vm_end;
1607
1608 while (ksm_scan.address < vma->vm_end) {
1609 if (ksm_test_exit(mm))
1610 break;
1611 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1612 if (IS_ERR_OR_NULL(*page)) {
1613 ksm_scan.address += PAGE_SIZE;
1614 cond_resched();
1615 continue;
1616 }
1617 if (PageAnon(*page)) {
1618 flush_anon_page(vma, *page, ksm_scan.address);
1619 flush_dcache_page(*page);
1620 rmap_item = get_next_rmap_item(slot,
1621 ksm_scan.rmap_list, ksm_scan.address);
1622 if (rmap_item) {
1623 ksm_scan.rmap_list =
1624 &rmap_item->rmap_list;
1625 ksm_scan.address += PAGE_SIZE;
1626 } else
1627 put_page(*page);
1628 up_read(&mm->mmap_sem);
1629 return rmap_item;
1630 }
1631 put_page(*page);
1632 ksm_scan.address += PAGE_SIZE;
1633 cond_resched();
1634 }
1635 }
1636
1637 if (ksm_test_exit(mm)) {
1638 ksm_scan.address = 0;
1639 ksm_scan.rmap_list = &slot->rmap_list;
1640 }
1641 /*
1642 * Nuke all the rmap_items that are above this current rmap:
1643 * because there were no VM_MERGEABLE vmas with such addresses.
1644 */
1645 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1646
1647 spin_lock(&ksm_mmlist_lock);
1648 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1649 struct mm_slot, mm_list);
1650 if (ksm_scan.address == 0) {
1651 /*
1652 * We've completed a full scan of all vmas, holding mmap_sem
1653 * throughout, and found no VM_MERGEABLE: so do the same as
1654 * __ksm_exit does to remove this mm from all our lists now.
1655 * This applies either when cleaning up after __ksm_exit
1656 * (but beware: we can reach here even before __ksm_exit),
1657 * or when all VM_MERGEABLE areas have been unmapped (and
1658 * mmap_sem then protects against race with MADV_MERGEABLE).
1659 */
1660 hash_del(&slot->link);
1661 list_del(&slot->mm_list);
1662 spin_unlock(&ksm_mmlist_lock);
1663
1664 free_mm_slot(slot);
1665 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1666 up_read(&mm->mmap_sem);
1667 mmdrop(mm);
1668 } else {
1669 up_read(&mm->mmap_sem);
1670 /*
1671 * up_read(&mm->mmap_sem) first because after
1672 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
1673 * already have been freed under us by __ksm_exit()
1674 * because the "mm_slot" is still hashed and
1675 * ksm_scan.mm_slot doesn't point to it anymore.
1676 */
1677 spin_unlock(&ksm_mmlist_lock);
1678 }
1679
1680 /* Repeat until we've completed scanning the whole list */
1681 slot = ksm_scan.mm_slot;
1682 if (slot != &ksm_mm_head)
1683 goto next_mm;
1684
1685 ksm_scan.seqnr++;
1686 return NULL;
1687}
1688
1689/**
1690 * ksm_do_scan - the ksm scanner main worker function.
1691 * @scan_npages - number of pages we want to scan before we return.
1692 */
1693static void ksm_do_scan(unsigned int scan_npages)
1694{
1695 struct rmap_item *rmap_item;
1696 struct page *uninitialized_var(page);
1697
1698 while (scan_npages-- && likely(!freezing(current))) {
1699 cond_resched();
1700 rmap_item = scan_get_next_rmap_item(&page);
1701 if (!rmap_item)
1702 return;
1703 cmp_and_merge_page(page, rmap_item);
1704 put_page(page);
1705 }
1706}
1707
1708static int ksmd_should_run(void)
1709{
1710 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1711}
1712
1713static int ksm_scan_thread(void *nothing)
1714{
1715 set_freezable();
1716 set_user_nice(current, 5);
1717
1718 while (!kthread_should_stop()) {
1719 mutex_lock(&ksm_thread_mutex);
1720 wait_while_offlining();
1721 if (ksmd_should_run())
1722 ksm_do_scan(ksm_thread_pages_to_scan);
1723 mutex_unlock(&ksm_thread_mutex);
1724
1725 try_to_freeze();
1726
1727 if (ksmd_should_run()) {
1728 schedule_timeout_interruptible(
1729 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1730 } else {
1731 wait_event_freezable(ksm_thread_wait,
1732 ksmd_should_run() || kthread_should_stop());
1733 }
1734 }
1735 return 0;
1736}
1737
1738int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1739 unsigned long end, int advice, unsigned long *vm_flags)
1740{
1741 struct mm_struct *mm = vma->vm_mm;
1742 int err;
1743
1744 switch (advice) {
1745 case MADV_MERGEABLE:
1746 /*
1747 * Be somewhat over-protective for now!
1748 */
1749 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1750 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1751 VM_HUGETLB | VM_MIXEDMAP))
1752 return 0; /* just ignore the advice */
1753
1754#ifdef VM_SAO
1755 if (*vm_flags & VM_SAO)
1756 return 0;
1757#endif
1758
1759 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1760 err = __ksm_enter(mm);
1761 if (err)
1762 return err;
1763 }
1764
1765 *vm_flags |= VM_MERGEABLE;
1766 break;
1767
1768 case MADV_UNMERGEABLE:
1769 if (!(*vm_flags & VM_MERGEABLE))
1770 return 0; /* just ignore the advice */
1771
1772 if (vma->anon_vma) {
1773 err = unmerge_ksm_pages(vma, start, end);
1774 if (err)
1775 return err;
1776 }
1777
1778 *vm_flags &= ~VM_MERGEABLE;
1779 break;
1780 }
1781
1782 return 0;
1783}
1784
1785int __ksm_enter(struct mm_struct *mm)
1786{
1787 struct mm_slot *mm_slot;
1788 int needs_wakeup;
1789
1790 mm_slot = alloc_mm_slot();
1791 if (!mm_slot)
1792 return -ENOMEM;
1793
1794 /* Check ksm_run too? Would need tighter locking */
1795 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1796
1797 spin_lock(&ksm_mmlist_lock);
1798 insert_to_mm_slots_hash(mm, mm_slot);
1799 /*
1800 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1801 * insert just behind the scanning cursor, to let the area settle
1802 * down a little; when fork is followed by immediate exec, we don't
1803 * want ksmd to waste time setting up and tearing down an rmap_list.
1804 *
1805 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1806 * scanning cursor, otherwise KSM pages in newly forked mms will be
1807 * missed: then we might as well insert at the end of the list.
1808 */
1809 if (ksm_run & KSM_RUN_UNMERGE)
1810 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1811 else
1812 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1813 spin_unlock(&ksm_mmlist_lock);
1814
1815 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1816 atomic_inc(&mm->mm_count);
1817
1818 if (needs_wakeup)
1819 wake_up_interruptible(&ksm_thread_wait);
1820
1821 return 0;
1822}
1823
1824void __ksm_exit(struct mm_struct *mm)
1825{
1826 struct mm_slot *mm_slot;
1827 int easy_to_free = 0;
1828
1829 /*
1830 * This process is exiting: if it's straightforward (as is the
1831 * case when ksmd was never running), free mm_slot immediately.
1832 * But if it's at the cursor or has rmap_items linked to it, use
1833 * mmap_sem to synchronize with any break_cows before pagetables
1834 * are freed, and leave the mm_slot on the list for ksmd to free.
1835 * Beware: ksm may already have noticed it exiting and freed the slot.
1836 */
1837
1838 spin_lock(&ksm_mmlist_lock);
1839 mm_slot = get_mm_slot(mm);
1840 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1841 if (!mm_slot->rmap_list) {
1842 hash_del(&mm_slot->link);
1843 list_del(&mm_slot->mm_list);
1844 easy_to_free = 1;
1845 } else {
1846 list_move(&mm_slot->mm_list,
1847 &ksm_scan.mm_slot->mm_list);
1848 }
1849 }
1850 spin_unlock(&ksm_mmlist_lock);
1851
1852 if (easy_to_free) {
1853 free_mm_slot(mm_slot);
1854 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1855 mmdrop(mm);
1856 } else if (mm_slot) {
1857 down_write(&mm->mmap_sem);
1858 up_write(&mm->mmap_sem);
1859 }
1860}
1861
1862struct page *ksm_might_need_to_copy(struct page *page,
1863 struct vm_area_struct *vma, unsigned long address)
1864{
1865 struct anon_vma *anon_vma = page_anon_vma(page);
1866 struct page *new_page;
1867
1868 if (PageKsm(page)) {
1869 if (page_stable_node(page) &&
1870 !(ksm_run & KSM_RUN_UNMERGE))
1871 return page; /* no need to copy it */
1872 } else if (!anon_vma) {
1873 return page; /* no need to copy it */
1874 } else if (anon_vma->root == vma->anon_vma->root &&
1875 page->index == linear_page_index(vma, address)) {
1876 return page; /* still no need to copy it */
1877 }
1878 if (!PageUptodate(page))
1879 return page; /* let do_swap_page report the error */
1880
1881 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1882 if (new_page) {
1883 copy_user_highpage(new_page, page, address, vma);
1884
1885 SetPageDirty(new_page);
1886 __SetPageUptodate(new_page);
1887 __SetPageLocked(new_page);
1888 }
1889
1890 return new_page;
1891}
1892
1893int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
1894{
1895 struct stable_node *stable_node;
1896 struct rmap_item *rmap_item;
1897 int ret = SWAP_AGAIN;
1898 int search_new_forks = 0;
1899
1900 VM_BUG_ON_PAGE(!PageKsm(page), page);
1901
1902 /*
1903 * Rely on the page lock to protect against concurrent modifications
1904 * to that page's node of the stable tree.
1905 */
1906 VM_BUG_ON_PAGE(!PageLocked(page), page);
1907
1908 stable_node = page_stable_node(page);
1909 if (!stable_node)
1910 return ret;
1911again:
1912 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1913 struct anon_vma *anon_vma = rmap_item->anon_vma;
1914 struct anon_vma_chain *vmac;
1915 struct vm_area_struct *vma;
1916
1917 cond_resched();
1918 anon_vma_lock_read(anon_vma);
1919 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1920 0, ULONG_MAX) {
1921 cond_resched();
1922 vma = vmac->vma;
1923 if (rmap_item->address < vma->vm_start ||
1924 rmap_item->address >= vma->vm_end)
1925 continue;
1926 /*
1927 * Initially we examine only the vma which covers this
1928 * rmap_item; but later, if there is still work to do,
1929 * we examine covering vmas in other mms: in case they
1930 * were forked from the original since ksmd passed.
1931 */
1932 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1933 continue;
1934
1935 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1936 continue;
1937
1938 ret = rwc->rmap_one(page, vma,
1939 rmap_item->address, rwc->arg);
1940 if (ret != SWAP_AGAIN) {
1941 anon_vma_unlock_read(anon_vma);
1942 goto out;
1943 }
1944 if (rwc->done && rwc->done(page)) {
1945 anon_vma_unlock_read(anon_vma);
1946 goto out;
1947 }
1948 }
1949 anon_vma_unlock_read(anon_vma);
1950 }
1951 if (!search_new_forks++)
1952 goto again;
1953out:
1954 return ret;
1955}
1956
1957#ifdef CONFIG_MIGRATION
1958void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1959{
1960 struct stable_node *stable_node;
1961
1962 VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
1963 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1964 VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
1965
1966 stable_node = page_stable_node(newpage);
1967 if (stable_node) {
1968 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
1969 stable_node->kpfn = page_to_pfn(newpage);
1970 /*
1971 * newpage->mapping was set in advance; now we need smp_wmb()
1972 * to make sure that the new stable_node->kpfn is visible
1973 * to get_ksm_page() before it can see that oldpage->mapping
1974 * has gone stale (or that PageSwapCache has been cleared).
1975 */
1976 smp_wmb();
1977 set_page_stable_node(oldpage, NULL);
1978 }
1979}
1980#endif /* CONFIG_MIGRATION */
1981
1982#ifdef CONFIG_MEMORY_HOTREMOVE
1983static void wait_while_offlining(void)
1984{
1985 while (ksm_run & KSM_RUN_OFFLINE) {
1986 mutex_unlock(&ksm_thread_mutex);
1987 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
1988 TASK_UNINTERRUPTIBLE);
1989 mutex_lock(&ksm_thread_mutex);
1990 }
1991}
1992
1993static void ksm_check_stable_tree(unsigned long start_pfn,
1994 unsigned long end_pfn)
1995{
1996 struct stable_node *stable_node, *next;
1997 struct rb_node *node;
1998 int nid;
1999
2000 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2001 node = rb_first(root_stable_tree + nid);
2002 while (node) {
2003 stable_node = rb_entry(node, struct stable_node, node);
2004 if (stable_node->kpfn >= start_pfn &&
2005 stable_node->kpfn < end_pfn) {
2006 /*
2007 * Don't get_ksm_page, page has already gone:
2008 * which is why we keep kpfn instead of page*
2009 */
2010 remove_node_from_stable_tree(stable_node);
2011 node = rb_first(root_stable_tree + nid);
2012 } else
2013 node = rb_next(node);
2014 cond_resched();
2015 }
2016 }
2017 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2018 if (stable_node->kpfn >= start_pfn &&
2019 stable_node->kpfn < end_pfn)
2020 remove_node_from_stable_tree(stable_node);
2021 cond_resched();
2022 }
2023}
2024
2025static int ksm_memory_callback(struct notifier_block *self,
2026 unsigned long action, void *arg)
2027{
2028 struct memory_notify *mn = arg;
2029
2030 switch (action) {
2031 case MEM_GOING_OFFLINE:
2032 /*
2033 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2034 * and remove_all_stable_nodes() while memory is going offline:
2035 * it is unsafe for them to touch the stable tree at this time.
2036 * But unmerge_ksm_pages(), rmap lookups and other entry points
2037 * which do not need the ksm_thread_mutex are all safe.
2038 */
2039 mutex_lock(&ksm_thread_mutex);
2040 ksm_run |= KSM_RUN_OFFLINE;
2041 mutex_unlock(&ksm_thread_mutex);
2042 break;
2043
2044 case MEM_OFFLINE:
2045 /*
2046 * Most of the work is done by page migration; but there might
2047 * be a few stable_nodes left over, still pointing to struct
2048 * pages which have been offlined: prune those from the tree,
2049 * otherwise get_ksm_page() might later try to access a
2050 * non-existent struct page.
2051 */
2052 ksm_check_stable_tree(mn->start_pfn,
2053 mn->start_pfn + mn->nr_pages);
2054 /* fallthrough */
2055
2056 case MEM_CANCEL_OFFLINE:
2057 mutex_lock(&ksm_thread_mutex);
2058 ksm_run &= ~KSM_RUN_OFFLINE;
2059 mutex_unlock(&ksm_thread_mutex);
2060
2061 smp_mb(); /* wake_up_bit advises this */
2062 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2063 break;
2064 }
2065 return NOTIFY_OK;
2066}
2067#else
2068static void wait_while_offlining(void)
2069{
2070}
2071#endif /* CONFIG_MEMORY_HOTREMOVE */
2072
2073#ifdef CONFIG_SYSFS
2074/*
2075 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2076 */
2077
2078#define KSM_ATTR_RO(_name) \
2079 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2080#define KSM_ATTR(_name) \
2081 static struct kobj_attribute _name##_attr = \
2082 __ATTR(_name, 0644, _name##_show, _name##_store)
2083
2084static ssize_t sleep_millisecs_show(struct kobject *kobj,
2085 struct kobj_attribute *attr, char *buf)
2086{
2087 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2088}
2089
2090static ssize_t sleep_millisecs_store(struct kobject *kobj,
2091 struct kobj_attribute *attr,
2092 const char *buf, size_t count)
2093{
2094 unsigned long msecs;
2095 int err;
2096
2097 err = kstrtoul(buf, 10, &msecs);
2098 if (err || msecs > UINT_MAX)
2099 return -EINVAL;
2100
2101 ksm_thread_sleep_millisecs = msecs;
2102
2103 return count;
2104}
2105KSM_ATTR(sleep_millisecs);
2106
2107static ssize_t pages_to_scan_show(struct kobject *kobj,
2108 struct kobj_attribute *attr, char *buf)
2109{
2110 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2111}
2112
2113static ssize_t pages_to_scan_store(struct kobject *kobj,
2114 struct kobj_attribute *attr,
2115 const char *buf, size_t count)
2116{
2117 int err;
2118 unsigned long nr_pages;
2119
2120 err = kstrtoul(buf, 10, &nr_pages);
2121 if (err || nr_pages > UINT_MAX)
2122 return -EINVAL;
2123
2124 ksm_thread_pages_to_scan = nr_pages;
2125
2126 return count;
2127}
2128KSM_ATTR(pages_to_scan);
2129
2130static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2131 char *buf)
2132{
2133 return sprintf(buf, "%lu\n", ksm_run);
2134}
2135
2136static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2137 const char *buf, size_t count)
2138{
2139 int err;
2140 unsigned long flags;
2141
2142 err = kstrtoul(buf, 10, &flags);
2143 if (err || flags > UINT_MAX)
2144 return -EINVAL;
2145 if (flags > KSM_RUN_UNMERGE)
2146 return -EINVAL;
2147
2148 /*
2149 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2150 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2151 * breaking COW to free the pages_shared (but leaves mm_slots
2152 * on the list for when ksmd may be set running again).
2153 */
2154
2155 mutex_lock(&ksm_thread_mutex);
2156 wait_while_offlining();
2157 if (ksm_run != flags) {
2158 ksm_run = flags;
2159 if (flags & KSM_RUN_UNMERGE) {
2160 set_current_oom_origin();
2161 err = unmerge_and_remove_all_rmap_items();
2162 clear_current_oom_origin();
2163 if (err) {
2164 ksm_run = KSM_RUN_STOP;
2165 count = err;
2166 }
2167 }
2168 }
2169 mutex_unlock(&ksm_thread_mutex);
2170
2171 if (flags & KSM_RUN_MERGE)
2172 wake_up_interruptible(&ksm_thread_wait);
2173
2174 return count;
2175}
2176KSM_ATTR(run);
2177
2178#ifdef CONFIG_NUMA
2179static ssize_t merge_across_nodes_show(struct kobject *kobj,
2180 struct kobj_attribute *attr, char *buf)
2181{
2182 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2183}
2184
2185static ssize_t merge_across_nodes_store(struct kobject *kobj,
2186 struct kobj_attribute *attr,
2187 const char *buf, size_t count)
2188{
2189 int err;
2190 unsigned long knob;
2191
2192 err = kstrtoul(buf, 10, &knob);
2193 if (err)
2194 return err;
2195 if (knob > 1)
2196 return -EINVAL;
2197
2198 mutex_lock(&ksm_thread_mutex);
2199 wait_while_offlining();
2200 if (ksm_merge_across_nodes != knob) {
2201 if (ksm_pages_shared || remove_all_stable_nodes())
2202 err = -EBUSY;
2203 else if (root_stable_tree == one_stable_tree) {
2204 struct rb_root *buf;
2205 /*
2206 * This is the first time that we switch away from the
2207 * default of merging across nodes: must now allocate
2208 * a buffer to hold as many roots as may be needed.
2209 * Allocate stable and unstable together:
2210 * MAXSMP NODES_SHIFT 10 will use 16kB.
2211 */
2212 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2213 GFP_KERNEL);
2214 /* Let us assume that RB_ROOT is NULL is zero */
2215 if (!buf)
2216 err = -ENOMEM;
2217 else {
2218 root_stable_tree = buf;
2219 root_unstable_tree = buf + nr_node_ids;
2220 /* Stable tree is empty but not the unstable */
2221 root_unstable_tree[0] = one_unstable_tree[0];
2222 }
2223 }
2224 if (!err) {
2225 ksm_merge_across_nodes = knob;
2226 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2227 }
2228 }
2229 mutex_unlock(&ksm_thread_mutex);
2230
2231 return err ? err : count;
2232}
2233KSM_ATTR(merge_across_nodes);
2234#endif
2235
2236static ssize_t pages_shared_show(struct kobject *kobj,
2237 struct kobj_attribute *attr, char *buf)
2238{
2239 return sprintf(buf, "%lu\n", ksm_pages_shared);
2240}
2241KSM_ATTR_RO(pages_shared);
2242
2243static ssize_t pages_sharing_show(struct kobject *kobj,
2244 struct kobj_attribute *attr, char *buf)
2245{
2246 return sprintf(buf, "%lu\n", ksm_pages_sharing);
2247}
2248KSM_ATTR_RO(pages_sharing);
2249
2250static ssize_t pages_unshared_show(struct kobject *kobj,
2251 struct kobj_attribute *attr, char *buf)
2252{
2253 return sprintf(buf, "%lu\n", ksm_pages_unshared);
2254}
2255KSM_ATTR_RO(pages_unshared);
2256
2257static ssize_t pages_volatile_show(struct kobject *kobj,
2258 struct kobj_attribute *attr, char *buf)
2259{
2260 long ksm_pages_volatile;
2261
2262 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2263 - ksm_pages_sharing - ksm_pages_unshared;
2264 /*
2265 * It was not worth any locking to calculate that statistic,
2266 * but it might therefore sometimes be negative: conceal that.
2267 */
2268 if (ksm_pages_volatile < 0)
2269 ksm_pages_volatile = 0;
2270 return sprintf(buf, "%ld\n", ksm_pages_volatile);
2271}
2272KSM_ATTR_RO(pages_volatile);
2273
2274static ssize_t full_scans_show(struct kobject *kobj,
2275 struct kobj_attribute *attr, char *buf)
2276{
2277 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2278}
2279KSM_ATTR_RO(full_scans);
2280
2281static struct attribute *ksm_attrs[] = {
2282 &sleep_millisecs_attr.attr,
2283 &pages_to_scan_attr.attr,
2284 &run_attr.attr,
2285 &pages_shared_attr.attr,
2286 &pages_sharing_attr.attr,
2287 &pages_unshared_attr.attr,
2288 &pages_volatile_attr.attr,
2289 &full_scans_attr.attr,
2290#ifdef CONFIG_NUMA
2291 &merge_across_nodes_attr.attr,
2292#endif
2293 NULL,
2294};
2295
2296static struct attribute_group ksm_attr_group = {
2297 .attrs = ksm_attrs,
2298 .name = "ksm",
2299};
2300#endif /* CONFIG_SYSFS */
2301
2302static int __init ksm_init(void)
2303{
2304 struct task_struct *ksm_thread;
2305 int err;
2306
2307 err = ksm_slab_init();
2308 if (err)
2309 goto out;
2310
2311 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2312 if (IS_ERR(ksm_thread)) {
2313 pr_err("ksm: creating kthread failed\n");
2314 err = PTR_ERR(ksm_thread);
2315 goto out_free;
2316 }
2317
2318#ifdef CONFIG_SYSFS
2319 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2320 if (err) {
2321 pr_err("ksm: register sysfs failed\n");
2322 kthread_stop(ksm_thread);
2323 goto out_free;
2324 }
2325#else
2326 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2327
2328#endif /* CONFIG_SYSFS */
2329
2330#ifdef CONFIG_MEMORY_HOTREMOVE
2331 /* There is no significance to this priority 100 */
2332 hotplug_memory_notifier(ksm_memory_callback, 100);
2333#endif
2334 return 0;
2335
2336out_free:
2337 ksm_slab_free();
2338out:
2339 return err;
2340}
2341subsys_initcall(ksm_init);