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