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1 /*
2 * Memory merging support.
3 *
4 * This code enables dynamic sharing of identical pages found in different
5 * memory areas, even if they are not shared by fork()
6 *
7 * Copyright (C) 2008-2009 Red Hat, Inc.
8 * Authors:
9 * Izik Eidus
10 * Andrea Arcangeli
11 * Chris Wright
12 * Hugh Dickins
13 *
14 * This work is licensed under the terms of the GNU GPL, version 2.
15 */
16
17 #include <linux/errno.h>
18 #include <linux/mm.h>
19 #include <linux/fs.h>
20 #include <linux/mman.h>
21 #include <linux/sched.h>
22 #include <linux/rwsem.h>
23 #include <linux/pagemap.h>
24 #include <linux/rmap.h>
25 #include <linux/spinlock.h>
26 #include <linux/jhash.h>
27 #include <linux/delay.h>
28 #include <linux/kthread.h>
29 #include <linux/wait.h>
30 #include <linux/slab.h>
31 #include <linux/rbtree.h>
32 #include <linux/memory.h>
33 #include <linux/mmu_notifier.h>
34 #include <linux/swap.h>
35 #include <linux/ksm.h>
36 #include <linux/hashtable.h>
37 #include <linux/freezer.h>
38 #include <linux/oom.h>
39 #include <linux/numa.h>
40
41 #include <asm/tlbflush.h>
42 #include "internal.h"
43
44 #ifdef CONFIG_NUMA
45 #define NUMA(x) (x)
46 #define DO_NUMA(x) do { (x); } while (0)
47 #else
48 #define NUMA(x) (0)
49 #define DO_NUMA(x) do { } while (0)
50 #endif
51
52 /*
53 * A few notes about the KSM scanning process,
54 * to make it easier to understand the data structures below:
55 *
56 * In order to reduce excessive scanning, KSM sorts the memory pages by their
57 * contents into a data structure that holds pointers to the pages' locations.
58 *
59 * Since the contents of the pages may change at any moment, KSM cannot just
60 * insert the pages into a normal sorted tree and expect it to find anything.
61 * Therefore KSM uses two data structures - the stable and the unstable tree.
62 *
63 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
64 * by their contents. Because each such page is write-protected, searching on
65 * this tree is fully assured to be working (except when pages are unmapped),
66 * and therefore this tree is called the stable tree.
67 *
68 * In addition to the stable tree, KSM uses a second data structure called the
69 * unstable tree: this tree holds pointers to pages which have been found to
70 * be "unchanged for a period of time". The unstable tree sorts these pages
71 * by their contents, but since they are not write-protected, KSM cannot rely
72 * upon the unstable tree to work correctly - the unstable tree is liable to
73 * be corrupted as its contents are modified, and so it is called unstable.
74 *
75 * KSM solves this problem by several techniques:
76 *
77 * 1) The unstable tree is flushed every time KSM completes scanning all
78 * memory areas, and then the tree is rebuilt again from the beginning.
79 * 2) KSM will only insert into the unstable tree, pages whose hash value
80 * has not changed since the previous scan of all memory areas.
81 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
82 * colors of the nodes and not on their contents, assuring that even when
83 * the tree gets "corrupted" it won't get out of balance, so scanning time
84 * remains the same (also, searching and inserting nodes in an rbtree uses
85 * the same algorithm, so we have no overhead when we flush and rebuild).
86 * 4) KSM never flushes the stable tree, which means that even if it were to
87 * take 10 attempts to find a page in the unstable tree, once it is found,
88 * it is secured in the stable tree. (When we scan a new page, we first
89 * compare it against the stable tree, and then against the unstable tree.)
90 *
91 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
92 * stable trees and multiple unstable trees: one of each for each NUMA node.
93 */
94
95 /**
96 * struct mm_slot - ksm information per mm that is being scanned
97 * @link: link to the mm_slots hash list
98 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
99 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
100 * @mm: the mm that this information is valid for
101 */
102 struct mm_slot {
103 struct hlist_node link;
104 struct list_head mm_list;
105 struct rmap_item *rmap_list;
106 struct mm_struct *mm;
107 };
108
109 /**
110 * struct ksm_scan - cursor for scanning
111 * @mm_slot: the current mm_slot we are scanning
112 * @address: the next address inside that to be scanned
113 * @rmap_list: link to the next rmap to be scanned in the rmap_list
114 * @seqnr: count of completed full scans (needed when removing unstable node)
115 *
116 * There is only the one ksm_scan instance of this cursor structure.
117 */
118 struct ksm_scan {
119 struct mm_slot *mm_slot;
120 unsigned long address;
121 struct rmap_item **rmap_list;
122 unsigned long seqnr;
123 };
124
125 /**
126 * struct stable_node - node of the stable rbtree
127 * @node: rb node of this ksm page in the stable tree
128 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129 * @list: linked into migrate_nodes, pending placement in the proper node tree
130 * @hlist: hlist head of rmap_items using this ksm page
131 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
132 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
133 */
134 struct stable_node {
135 union {
136 struct rb_node node; /* when node of stable tree */
137 struct { /* when listed for migration */
138 struct list_head *head;
139 struct list_head list;
140 };
141 };
142 struct hlist_head hlist;
143 unsigned long kpfn;
144 #ifdef CONFIG_NUMA
145 int nid;
146 #endif
147 };
148
149 /**
150 * struct rmap_item - reverse mapping item for virtual addresses
151 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
152 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
154 * @mm: the memory structure this rmap_item is pointing into
155 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
156 * @oldchecksum: previous checksum of the page at that virtual address
157 * @node: rb node of this rmap_item in the unstable tree
158 * @head: pointer to stable_node heading this list in the stable tree
159 * @hlist: link into hlist of rmap_items hanging off that stable_node
160 */
161 struct rmap_item {
162 struct rmap_item *rmap_list;
163 union {
164 struct anon_vma *anon_vma; /* when stable */
165 #ifdef CONFIG_NUMA
166 int nid; /* when node of unstable tree */
167 #endif
168 };
169 struct mm_struct *mm;
170 unsigned long address; /* + low bits used for flags below */
171 unsigned int oldchecksum; /* when unstable */
172 union {
173 struct rb_node node; /* when node of unstable tree */
174 struct { /* when listed from stable tree */
175 struct stable_node *head;
176 struct hlist_node hlist;
177 };
178 };
179 };
180
181 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
182 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
183 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
184
185 /* The stable and unstable tree heads */
186 static struct rb_root one_stable_tree[1] = { RB_ROOT };
187 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188 static struct rb_root *root_stable_tree = one_stable_tree;
189 static struct rb_root *root_unstable_tree = one_unstable_tree;
190
191 /* Recently migrated nodes of stable tree, pending proper placement */
192 static LIST_HEAD(migrate_nodes);
193
194 #define MM_SLOTS_HASH_BITS 10
195 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
196
197 static struct mm_slot ksm_mm_head = {
198 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
199 };
200 static struct ksm_scan ksm_scan = {
201 .mm_slot = &ksm_mm_head,
202 };
203
204 static struct kmem_cache *rmap_item_cache;
205 static struct kmem_cache *stable_node_cache;
206 static struct kmem_cache *mm_slot_cache;
207
208 /* The number of nodes in the stable tree */
209 static unsigned long ksm_pages_shared;
210
211 /* The number of page slots additionally sharing those nodes */
212 static unsigned long ksm_pages_sharing;
213
214 /* The number of nodes in the unstable tree */
215 static unsigned long ksm_pages_unshared;
216
217 /* The number of rmap_items in use: to calculate pages_volatile */
218 static unsigned long ksm_rmap_items;
219
220 /* Number of pages ksmd should scan in one batch */
221 static unsigned int ksm_thread_pages_to_scan = 100;
222
223 /* Milliseconds ksmd should sleep between batches */
224 static unsigned int ksm_thread_sleep_millisecs = 20;
225
226 #ifdef CONFIG_NUMA
227 /* Zeroed when merging across nodes is not allowed */
228 static unsigned int ksm_merge_across_nodes = 1;
229 static int ksm_nr_node_ids = 1;
230 #else
231 #define ksm_merge_across_nodes 1U
232 #define ksm_nr_node_ids 1
233 #endif
234
235 #define KSM_RUN_STOP 0
236 #define KSM_RUN_MERGE 1
237 #define KSM_RUN_UNMERGE 2
238 #define KSM_RUN_OFFLINE 4
239 static unsigned long ksm_run = KSM_RUN_STOP;
240 static void wait_while_offlining(void);
241
242 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243 static DEFINE_MUTEX(ksm_thread_mutex);
244 static DEFINE_SPINLOCK(ksm_mmlist_lock);
245
246 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247 sizeof(struct __struct), __alignof__(struct __struct),\
248 (__flags), NULL)
249
250 static int __init ksm_slab_init(void)
251 {
252 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
253 if (!rmap_item_cache)
254 goto out;
255
256 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257 if (!stable_node_cache)
258 goto out_free1;
259
260 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261 if (!mm_slot_cache)
262 goto out_free2;
263
264 return 0;
265
266 out_free2:
267 kmem_cache_destroy(stable_node_cache);
268 out_free1:
269 kmem_cache_destroy(rmap_item_cache);
270 out:
271 return -ENOMEM;
272 }
273
274 static void __init ksm_slab_free(void)
275 {
276 kmem_cache_destroy(mm_slot_cache);
277 kmem_cache_destroy(stable_node_cache);
278 kmem_cache_destroy(rmap_item_cache);
279 mm_slot_cache = NULL;
280 }
281
282 static inline struct rmap_item *alloc_rmap_item(void)
283 {
284 struct rmap_item *rmap_item;
285
286 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
287 if (rmap_item)
288 ksm_rmap_items++;
289 return rmap_item;
290 }
291
292 static inline void free_rmap_item(struct rmap_item *rmap_item)
293 {
294 ksm_rmap_items--;
295 rmap_item->mm = NULL; /* debug safety */
296 kmem_cache_free(rmap_item_cache, rmap_item);
297 }
298
299 static inline struct stable_node *alloc_stable_node(void)
300 {
301 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
302 }
303
304 static inline void free_stable_node(struct stable_node *stable_node)
305 {
306 kmem_cache_free(stable_node_cache, stable_node);
307 }
308
309 static inline struct mm_slot *alloc_mm_slot(void)
310 {
311 if (!mm_slot_cache) /* initialization failed */
312 return NULL;
313 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
314 }
315
316 static inline void free_mm_slot(struct mm_slot *mm_slot)
317 {
318 kmem_cache_free(mm_slot_cache, mm_slot);
319 }
320
321 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
322 {
323 struct mm_slot *slot;
324
325 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
326 if (slot->mm == mm)
327 return slot;
328
329 return NULL;
330 }
331
332 static void insert_to_mm_slots_hash(struct mm_struct *mm,
333 struct mm_slot *mm_slot)
334 {
335 mm_slot->mm = mm;
336 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
337 }
338
339 /*
340 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
341 * page tables after it has passed through ksm_exit() - which, if necessary,
342 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
343 * a special flag: they can just back out as soon as mm_users goes to zero.
344 * ksm_test_exit() is used throughout to make this test for exit: in some
345 * places for correctness, in some places just to avoid unnecessary work.
346 */
347 static inline bool ksm_test_exit(struct mm_struct *mm)
348 {
349 return atomic_read(&mm->mm_users) == 0;
350 }
351
352 /*
353 * We use break_ksm to break COW on a ksm page: it's a stripped down
354 *
355 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
356 * put_page(page);
357 *
358 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
359 * in case the application has unmapped and remapped mm,addr meanwhile.
360 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
361 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
362 */
363 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
364 {
365 struct page *page;
366 int ret = 0;
367
368 do {
369 cond_resched();
370 page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
371 if (IS_ERR_OR_NULL(page))
372 break;
373 if (PageKsm(page))
374 ret = handle_mm_fault(vma->vm_mm, vma, addr,
375 FAULT_FLAG_WRITE);
376 else
377 ret = VM_FAULT_WRITE;
378 put_page(page);
379 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
380 /*
381 * We must loop because handle_mm_fault() may back out if there's
382 * any difficulty e.g. if pte accessed bit gets updated concurrently.
383 *
384 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
385 * COW has been broken, even if the vma does not permit VM_WRITE;
386 * but note that a concurrent fault might break PageKsm for us.
387 *
388 * VM_FAULT_SIGBUS could occur if we race with truncation of the
389 * backing file, which also invalidates anonymous pages: that's
390 * okay, that truncation will have unmapped the PageKsm for us.
391 *
392 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
393 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
394 * current task has TIF_MEMDIE set, and will be OOM killed on return
395 * to user; and ksmd, having no mm, would never be chosen for that.
396 *
397 * But if the mm is in a limited mem_cgroup, then the fault may fail
398 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
399 * even ksmd can fail in this way - though it's usually breaking ksm
400 * just to undo a merge it made a moment before, so unlikely to oom.
401 *
402 * That's a pity: we might therefore have more kernel pages allocated
403 * than we're counting as nodes in the stable tree; but ksm_do_scan
404 * will retry to break_cow on each pass, so should recover the page
405 * in due course. The important thing is to not let VM_MERGEABLE
406 * be cleared while any such pages might remain in the area.
407 */
408 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
409 }
410
411 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
412 unsigned long addr)
413 {
414 struct vm_area_struct *vma;
415 if (ksm_test_exit(mm))
416 return NULL;
417 vma = find_vma(mm, addr);
418 if (!vma || vma->vm_start > addr)
419 return NULL;
420 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
421 return NULL;
422 return vma;
423 }
424
425 static void break_cow(struct rmap_item *rmap_item)
426 {
427 struct mm_struct *mm = rmap_item->mm;
428 unsigned long addr = rmap_item->address;
429 struct vm_area_struct *vma;
430
431 /*
432 * It is not an accident that whenever we want to break COW
433 * to undo, we also need to drop a reference to the anon_vma.
434 */
435 put_anon_vma(rmap_item->anon_vma);
436
437 down_read(&mm->mmap_sem);
438 vma = find_mergeable_vma(mm, addr);
439 if (vma)
440 break_ksm(vma, addr);
441 up_read(&mm->mmap_sem);
442 }
443
444 static struct page *page_trans_compound_anon(struct page *page)
445 {
446 if (PageTransCompound(page)) {
447 struct page *head = compound_head(page);
448 /*
449 * head may actually be splitted and freed from under
450 * us but it's ok here.
451 */
452 if (PageAnon(head))
453 return head;
454 }
455 return NULL;
456 }
457
458 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
459 {
460 struct mm_struct *mm = rmap_item->mm;
461 unsigned long addr = rmap_item->address;
462 struct vm_area_struct *vma;
463 struct page *page;
464
465 down_read(&mm->mmap_sem);
466 vma = find_mergeable_vma(mm, addr);
467 if (!vma)
468 goto out;
469
470 page = follow_page(vma, addr, FOLL_GET);
471 if (IS_ERR_OR_NULL(page))
472 goto out;
473 if (PageAnon(page) || page_trans_compound_anon(page)) {
474 flush_anon_page(vma, page, addr);
475 flush_dcache_page(page);
476 } else {
477 put_page(page);
478 out: page = NULL;
479 }
480 up_read(&mm->mmap_sem);
481 return page;
482 }
483
484 /*
485 * This helper is used for getting right index into array of tree roots.
486 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
487 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
488 * every node has its own stable and unstable tree.
489 */
490 static inline int get_kpfn_nid(unsigned long kpfn)
491 {
492 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
493 }
494
495 static void remove_node_from_stable_tree(struct stable_node *stable_node)
496 {
497 struct rmap_item *rmap_item;
498
499 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
500 if (rmap_item->hlist.next)
501 ksm_pages_sharing--;
502 else
503 ksm_pages_shared--;
504 put_anon_vma(rmap_item->anon_vma);
505 rmap_item->address &= PAGE_MASK;
506 cond_resched();
507 }
508
509 if (stable_node->head == &migrate_nodes)
510 list_del(&stable_node->list);
511 else
512 rb_erase(&stable_node->node,
513 root_stable_tree + NUMA(stable_node->nid));
514 free_stable_node(stable_node);
515 }
516
517 /*
518 * get_ksm_page: checks if the page indicated by the stable node
519 * is still its ksm page, despite having held no reference to it.
520 * In which case we can trust the content of the page, and it
521 * returns the gotten page; but if the page has now been zapped,
522 * remove the stale node from the stable tree and return NULL.
523 * But beware, the stable node's page might be being migrated.
524 *
525 * You would expect the stable_node to hold a reference to the ksm page.
526 * But if it increments the page's count, swapping out has to wait for
527 * ksmd to come around again before it can free the page, which may take
528 * seconds or even minutes: much too unresponsive. So instead we use a
529 * "keyhole reference": access to the ksm page from the stable node peeps
530 * out through its keyhole to see if that page still holds the right key,
531 * pointing back to this stable node. This relies on freeing a PageAnon
532 * page to reset its page->mapping to NULL, and relies on no other use of
533 * a page to put something that might look like our key in page->mapping.
534 * is on its way to being freed; but it is an anomaly to bear in mind.
535 */
536 static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
537 {
538 struct page *page;
539 void *expected_mapping;
540 unsigned long kpfn;
541
542 expected_mapping = (void *)stable_node +
543 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
544 again:
545 kpfn = READ_ONCE(stable_node->kpfn);
546 page = pfn_to_page(kpfn);
547
548 /*
549 * page is computed from kpfn, so on most architectures reading
550 * page->mapping is naturally ordered after reading node->kpfn,
551 * but on Alpha we need to be more careful.
552 */
553 smp_read_barrier_depends();
554 if (READ_ONCE(page->mapping) != expected_mapping)
555 goto stale;
556
557 /*
558 * We cannot do anything with the page while its refcount is 0.
559 * Usually 0 means free, or tail of a higher-order page: in which
560 * case this node is no longer referenced, and should be freed;
561 * however, it might mean that the page is under page_freeze_refs().
562 * The __remove_mapping() case is easy, again the node is now stale;
563 * but if page is swapcache in migrate_page_move_mapping(), it might
564 * still be our page, in which case it's essential to keep the node.
565 */
566 while (!get_page_unless_zero(page)) {
567 /*
568 * Another check for page->mapping != expected_mapping would
569 * work here too. We have chosen the !PageSwapCache test to
570 * optimize the common case, when the page is or is about to
571 * be freed: PageSwapCache is cleared (under spin_lock_irq)
572 * in the freeze_refs section of __remove_mapping(); but Anon
573 * page->mapping reset to NULL later, in free_pages_prepare().
574 */
575 if (!PageSwapCache(page))
576 goto stale;
577 cpu_relax();
578 }
579
580 if (READ_ONCE(page->mapping) != expected_mapping) {
581 put_page(page);
582 goto stale;
583 }
584
585 if (lock_it) {
586 lock_page(page);
587 if (READ_ONCE(page->mapping) != expected_mapping) {
588 unlock_page(page);
589 put_page(page);
590 goto stale;
591 }
592 }
593 return page;
594
595 stale:
596 /*
597 * We come here from above when page->mapping or !PageSwapCache
598 * suggests that the node is stale; but it might be under migration.
599 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
600 * before checking whether node->kpfn has been changed.
601 */
602 smp_rmb();
603 if (READ_ONCE(stable_node->kpfn) != kpfn)
604 goto again;
605 remove_node_from_stable_tree(stable_node);
606 return NULL;
607 }
608
609 /*
610 * Removing rmap_item from stable or unstable tree.
611 * This function will clean the information from the stable/unstable tree.
612 */
613 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
614 {
615 if (rmap_item->address & STABLE_FLAG) {
616 struct stable_node *stable_node;
617 struct page *page;
618
619 stable_node = rmap_item->head;
620 page = get_ksm_page(stable_node, true);
621 if (!page)
622 goto out;
623
624 hlist_del(&rmap_item->hlist);
625 unlock_page(page);
626 put_page(page);
627
628 if (stable_node->hlist.first)
629 ksm_pages_sharing--;
630 else
631 ksm_pages_shared--;
632
633 put_anon_vma(rmap_item->anon_vma);
634 rmap_item->address &= PAGE_MASK;
635
636 } else if (rmap_item->address & UNSTABLE_FLAG) {
637 unsigned char age;
638 /*
639 * Usually ksmd can and must skip the rb_erase, because
640 * root_unstable_tree was already reset to RB_ROOT.
641 * But be careful when an mm is exiting: do the rb_erase
642 * if this rmap_item was inserted by this scan, rather
643 * than left over from before.
644 */
645 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
646 BUG_ON(age > 1);
647 if (!age)
648 rb_erase(&rmap_item->node,
649 root_unstable_tree + NUMA(rmap_item->nid));
650 ksm_pages_unshared--;
651 rmap_item->address &= PAGE_MASK;
652 }
653 out:
654 cond_resched(); /* we're called from many long loops */
655 }
656
657 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
658 struct rmap_item **rmap_list)
659 {
660 while (*rmap_list) {
661 struct rmap_item *rmap_item = *rmap_list;
662 *rmap_list = rmap_item->rmap_list;
663 remove_rmap_item_from_tree(rmap_item);
664 free_rmap_item(rmap_item);
665 }
666 }
667
668 /*
669 * Though it's very tempting to unmerge rmap_items from stable tree rather
670 * than check every pte of a given vma, the locking doesn't quite work for
671 * that - an rmap_item is assigned to the stable tree after inserting ksm
672 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
673 * rmap_items from parent to child at fork time (so as not to waste time
674 * if exit comes before the next scan reaches it).
675 *
676 * Similarly, although we'd like to remove rmap_items (so updating counts
677 * and freeing memory) when unmerging an area, it's easier to leave that
678 * to the next pass of ksmd - consider, for example, how ksmd might be
679 * in cmp_and_merge_page on one of the rmap_items we would be removing.
680 */
681 static int unmerge_ksm_pages(struct vm_area_struct *vma,
682 unsigned long start, unsigned long end)
683 {
684 unsigned long addr;
685 int err = 0;
686
687 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
688 if (ksm_test_exit(vma->vm_mm))
689 break;
690 if (signal_pending(current))
691 err = -ERESTARTSYS;
692 else
693 err = break_ksm(vma, addr);
694 }
695 return err;
696 }
697
698 #ifdef CONFIG_SYSFS
699 /*
700 * Only called through the sysfs control interface:
701 */
702 static int remove_stable_node(struct stable_node *stable_node)
703 {
704 struct page *page;
705 int err;
706
707 page = get_ksm_page(stable_node, true);
708 if (!page) {
709 /*
710 * get_ksm_page did remove_node_from_stable_tree itself.
711 */
712 return 0;
713 }
714
715 if (WARN_ON_ONCE(page_mapped(page))) {
716 /*
717 * This should not happen: but if it does, just refuse to let
718 * merge_across_nodes be switched - there is no need to panic.
719 */
720 err = -EBUSY;
721 } else {
722 /*
723 * The stable node did not yet appear stale to get_ksm_page(),
724 * since that allows for an unmapped ksm page to be recognized
725 * right up until it is freed; but the node is safe to remove.
726 * This page might be in a pagevec waiting to be freed,
727 * or it might be PageSwapCache (perhaps under writeback),
728 * or it might have been removed from swapcache a moment ago.
729 */
730 set_page_stable_node(page, NULL);
731 remove_node_from_stable_tree(stable_node);
732 err = 0;
733 }
734
735 unlock_page(page);
736 put_page(page);
737 return err;
738 }
739
740 static int remove_all_stable_nodes(void)
741 {
742 struct stable_node *stable_node;
743 struct list_head *this, *next;
744 int nid;
745 int err = 0;
746
747 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
748 while (root_stable_tree[nid].rb_node) {
749 stable_node = rb_entry(root_stable_tree[nid].rb_node,
750 struct stable_node, node);
751 if (remove_stable_node(stable_node)) {
752 err = -EBUSY;
753 break; /* proceed to next nid */
754 }
755 cond_resched();
756 }
757 }
758 list_for_each_safe(this, next, &migrate_nodes) {
759 stable_node = list_entry(this, struct stable_node, list);
760 if (remove_stable_node(stable_node))
761 err = -EBUSY;
762 cond_resched();
763 }
764 return err;
765 }
766
767 static int unmerge_and_remove_all_rmap_items(void)
768 {
769 struct mm_slot *mm_slot;
770 struct mm_struct *mm;
771 struct vm_area_struct *vma;
772 int err = 0;
773
774 spin_lock(&ksm_mmlist_lock);
775 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
776 struct mm_slot, mm_list);
777 spin_unlock(&ksm_mmlist_lock);
778
779 for (mm_slot = ksm_scan.mm_slot;
780 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
781 mm = mm_slot->mm;
782 down_read(&mm->mmap_sem);
783 for (vma = mm->mmap; vma; vma = vma->vm_next) {
784 if (ksm_test_exit(mm))
785 break;
786 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
787 continue;
788 err = unmerge_ksm_pages(vma,
789 vma->vm_start, vma->vm_end);
790 if (err)
791 goto error;
792 }
793
794 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
795
796 spin_lock(&ksm_mmlist_lock);
797 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
798 struct mm_slot, mm_list);
799 if (ksm_test_exit(mm)) {
800 hash_del(&mm_slot->link);
801 list_del(&mm_slot->mm_list);
802 spin_unlock(&ksm_mmlist_lock);
803
804 free_mm_slot(mm_slot);
805 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
806 up_read(&mm->mmap_sem);
807 mmdrop(mm);
808 } else {
809 spin_unlock(&ksm_mmlist_lock);
810 up_read(&mm->mmap_sem);
811 }
812 }
813
814 /* Clean up stable nodes, but don't worry if some are still busy */
815 remove_all_stable_nodes();
816 ksm_scan.seqnr = 0;
817 return 0;
818
819 error:
820 up_read(&mm->mmap_sem);
821 spin_lock(&ksm_mmlist_lock);
822 ksm_scan.mm_slot = &ksm_mm_head;
823 spin_unlock(&ksm_mmlist_lock);
824 return err;
825 }
826 #endif /* CONFIG_SYSFS */
827
828 static u32 calc_checksum(struct page *page)
829 {
830 u32 checksum;
831 void *addr = kmap_atomic(page);
832 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
833 kunmap_atomic(addr);
834 return checksum;
835 }
836
837 static int memcmp_pages(struct page *page1, struct page *page2)
838 {
839 char *addr1, *addr2;
840 int ret;
841
842 addr1 = kmap_atomic(page1);
843 addr2 = kmap_atomic(page2);
844 ret = memcmp(addr1, addr2, PAGE_SIZE);
845 kunmap_atomic(addr2);
846 kunmap_atomic(addr1);
847 return ret;
848 }
849
850 static inline int pages_identical(struct page *page1, struct page *page2)
851 {
852 return !memcmp_pages(page1, page2);
853 }
854
855 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
856 pte_t *orig_pte)
857 {
858 struct mm_struct *mm = vma->vm_mm;
859 unsigned long addr;
860 pte_t *ptep;
861 spinlock_t *ptl;
862 int swapped;
863 int err = -EFAULT;
864 unsigned long mmun_start; /* For mmu_notifiers */
865 unsigned long mmun_end; /* For mmu_notifiers */
866
867 addr = page_address_in_vma(page, vma);
868 if (addr == -EFAULT)
869 goto out;
870
871 BUG_ON(PageTransCompound(page));
872
873 mmun_start = addr;
874 mmun_end = addr + PAGE_SIZE;
875 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
876
877 ptep = page_check_address(page, mm, addr, &ptl, 0);
878 if (!ptep)
879 goto out_mn;
880
881 if (pte_write(*ptep) || pte_dirty(*ptep)) {
882 pte_t entry;
883
884 swapped = PageSwapCache(page);
885 flush_cache_page(vma, addr, page_to_pfn(page));
886 /*
887 * Ok this is tricky, when get_user_pages_fast() run it doesn't
888 * take any lock, therefore the check that we are going to make
889 * with the pagecount against the mapcount is racey and
890 * O_DIRECT can happen right after the check.
891 * So we clear the pte and flush the tlb before the check
892 * this assure us that no O_DIRECT can happen after the check
893 * or in the middle of the check.
894 */
895 entry = ptep_clear_flush_notify(vma, addr, ptep);
896 /*
897 * Check that no O_DIRECT or similar I/O is in progress on the
898 * page
899 */
900 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
901 set_pte_at(mm, addr, ptep, entry);
902 goto out_unlock;
903 }
904 if (pte_dirty(entry))
905 set_page_dirty(page);
906 entry = pte_mkclean(pte_wrprotect(entry));
907 set_pte_at_notify(mm, addr, ptep, entry);
908 }
909 *orig_pte = *ptep;
910 err = 0;
911
912 out_unlock:
913 pte_unmap_unlock(ptep, ptl);
914 out_mn:
915 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
916 out:
917 return err;
918 }
919
920 /**
921 * replace_page - replace page in vma by new ksm page
922 * @vma: vma that holds the pte pointing to page
923 * @page: the page we are replacing by kpage
924 * @kpage: the ksm page we replace page by
925 * @orig_pte: the original value of the pte
926 *
927 * Returns 0 on success, -EFAULT on failure.
928 */
929 static int replace_page(struct vm_area_struct *vma, struct page *page,
930 struct page *kpage, pte_t orig_pte)
931 {
932 struct mm_struct *mm = vma->vm_mm;
933 pmd_t *pmd;
934 pte_t *ptep;
935 spinlock_t *ptl;
936 unsigned long addr;
937 int err = -EFAULT;
938 unsigned long mmun_start; /* For mmu_notifiers */
939 unsigned long mmun_end; /* For mmu_notifiers */
940
941 addr = page_address_in_vma(page, vma);
942 if (addr == -EFAULT)
943 goto out;
944
945 pmd = mm_find_pmd(mm, addr);
946 if (!pmd)
947 goto out;
948
949 mmun_start = addr;
950 mmun_end = addr + PAGE_SIZE;
951 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
952
953 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
954 if (!pte_same(*ptep, orig_pte)) {
955 pte_unmap_unlock(ptep, ptl);
956 goto out_mn;
957 }
958
959 get_page(kpage);
960 page_add_anon_rmap(kpage, vma, addr);
961
962 flush_cache_page(vma, addr, pte_pfn(*ptep));
963 ptep_clear_flush_notify(vma, addr, ptep);
964 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
965
966 page_remove_rmap(page);
967 if (!page_mapped(page))
968 try_to_free_swap(page);
969 put_page(page);
970
971 pte_unmap_unlock(ptep, ptl);
972 err = 0;
973 out_mn:
974 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
975 out:
976 return err;
977 }
978
979 static int page_trans_compound_anon_split(struct page *page)
980 {
981 int ret = 0;
982 struct page *transhuge_head = page_trans_compound_anon(page);
983 if (transhuge_head) {
984 /* Get the reference on the head to split it. */
985 if (get_page_unless_zero(transhuge_head)) {
986 /*
987 * Recheck we got the reference while the head
988 * was still anonymous.
989 */
990 if (PageAnon(transhuge_head))
991 ret = split_huge_page(transhuge_head);
992 else
993 /*
994 * Retry later if split_huge_page run
995 * from under us.
996 */
997 ret = 1;
998 put_page(transhuge_head);
999 } else
1000 /* Retry later if split_huge_page run from under us. */
1001 ret = 1;
1002 }
1003 return ret;
1004 }
1005
1006 /*
1007 * try_to_merge_one_page - take two pages and merge them into one
1008 * @vma: the vma that holds the pte pointing to page
1009 * @page: the PageAnon page that we want to replace with kpage
1010 * @kpage: the PageKsm page that we want to map instead of page,
1011 * or NULL the first time when we want to use page as kpage.
1012 *
1013 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1014 */
1015 static int try_to_merge_one_page(struct vm_area_struct *vma,
1016 struct page *page, struct page *kpage)
1017 {
1018 pte_t orig_pte = __pte(0);
1019 int err = -EFAULT;
1020
1021 if (page == kpage) /* ksm page forked */
1022 return 0;
1023
1024 if (!(vma->vm_flags & VM_MERGEABLE))
1025 goto out;
1026 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
1027 goto out;
1028 BUG_ON(PageTransCompound(page));
1029 if (!PageAnon(page))
1030 goto out;
1031
1032 /*
1033 * We need the page lock to read a stable PageSwapCache in
1034 * write_protect_page(). We use trylock_page() instead of
1035 * lock_page() because we don't want to wait here - we
1036 * prefer to continue scanning and merging different pages,
1037 * then come back to this page when it is unlocked.
1038 */
1039 if (!trylock_page(page))
1040 goto out;
1041 /*
1042 * If this anonymous page is mapped only here, its pte may need
1043 * to be write-protected. If it's mapped elsewhere, all of its
1044 * ptes are necessarily already write-protected. But in either
1045 * case, we need to lock and check page_count is not raised.
1046 */
1047 if (write_protect_page(vma, page, &orig_pte) == 0) {
1048 if (!kpage) {
1049 /*
1050 * While we hold page lock, upgrade page from
1051 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1052 * stable_tree_insert() will update stable_node.
1053 */
1054 set_page_stable_node(page, NULL);
1055 mark_page_accessed(page);
1056 err = 0;
1057 } else if (pages_identical(page, kpage))
1058 err = replace_page(vma, page, kpage, orig_pte);
1059 }
1060
1061 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1062 munlock_vma_page(page);
1063 if (!PageMlocked(kpage)) {
1064 unlock_page(page);
1065 lock_page(kpage);
1066 mlock_vma_page(kpage);
1067 page = kpage; /* for final unlock */
1068 }
1069 }
1070
1071 unlock_page(page);
1072 out:
1073 return err;
1074 }
1075
1076 /*
1077 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1078 * but no new kernel page is allocated: kpage must already be a ksm page.
1079 *
1080 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1081 */
1082 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1083 struct page *page, struct page *kpage)
1084 {
1085 struct mm_struct *mm = rmap_item->mm;
1086 struct vm_area_struct *vma;
1087 int err = -EFAULT;
1088
1089 down_read(&mm->mmap_sem);
1090 if (ksm_test_exit(mm))
1091 goto out;
1092 vma = find_vma(mm, rmap_item->address);
1093 if (!vma || vma->vm_start > rmap_item->address)
1094 goto out;
1095
1096 err = try_to_merge_one_page(vma, page, kpage);
1097 if (err)
1098 goto out;
1099
1100 /* Unstable nid is in union with stable anon_vma: remove first */
1101 remove_rmap_item_from_tree(rmap_item);
1102
1103 /* Must get reference to anon_vma while still holding mmap_sem */
1104 rmap_item->anon_vma = vma->anon_vma;
1105 get_anon_vma(vma->anon_vma);
1106 out:
1107 up_read(&mm->mmap_sem);
1108 return err;
1109 }
1110
1111 /*
1112 * try_to_merge_two_pages - take two identical pages and prepare them
1113 * to be merged into one page.
1114 *
1115 * This function returns the kpage if we successfully merged two identical
1116 * pages into one ksm page, NULL otherwise.
1117 *
1118 * Note that this function upgrades page to ksm page: if one of the pages
1119 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1120 */
1121 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1122 struct page *page,
1123 struct rmap_item *tree_rmap_item,
1124 struct page *tree_page)
1125 {
1126 int err;
1127
1128 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1129 if (!err) {
1130 err = try_to_merge_with_ksm_page(tree_rmap_item,
1131 tree_page, page);
1132 /*
1133 * If that fails, we have a ksm page with only one pte
1134 * pointing to it: so break it.
1135 */
1136 if (err)
1137 break_cow(rmap_item);
1138 }
1139 return err ? NULL : page;
1140 }
1141
1142 /*
1143 * stable_tree_search - search for page inside the stable tree
1144 *
1145 * This function checks if there is a page inside the stable tree
1146 * with identical content to the page that we are scanning right now.
1147 *
1148 * This function returns the stable tree node of identical content if found,
1149 * NULL otherwise.
1150 */
1151 static struct page *stable_tree_search(struct page *page)
1152 {
1153 int nid;
1154 struct rb_root *root;
1155 struct rb_node **new;
1156 struct rb_node *parent;
1157 struct stable_node *stable_node;
1158 struct stable_node *page_node;
1159
1160 page_node = page_stable_node(page);
1161 if (page_node && page_node->head != &migrate_nodes) {
1162 /* ksm page forked */
1163 get_page(page);
1164 return page;
1165 }
1166
1167 nid = get_kpfn_nid(page_to_pfn(page));
1168 root = root_stable_tree + nid;
1169 again:
1170 new = &root->rb_node;
1171 parent = NULL;
1172
1173 while (*new) {
1174 struct page *tree_page;
1175 int ret;
1176
1177 cond_resched();
1178 stable_node = rb_entry(*new, struct stable_node, node);
1179 tree_page = get_ksm_page(stable_node, false);
1180 if (!tree_page)
1181 return NULL;
1182
1183 ret = memcmp_pages(page, tree_page);
1184 put_page(tree_page);
1185
1186 parent = *new;
1187 if (ret < 0)
1188 new = &parent->rb_left;
1189 else if (ret > 0)
1190 new = &parent->rb_right;
1191 else {
1192 /*
1193 * Lock and unlock the stable_node's page (which
1194 * might already have been migrated) so that page
1195 * migration is sure to notice its raised count.
1196 * It would be more elegant to return stable_node
1197 * than kpage, but that involves more changes.
1198 */
1199 tree_page = get_ksm_page(stable_node, true);
1200 if (tree_page) {
1201 unlock_page(tree_page);
1202 if (get_kpfn_nid(stable_node->kpfn) !=
1203 NUMA(stable_node->nid)) {
1204 put_page(tree_page);
1205 goto replace;
1206 }
1207 return tree_page;
1208 }
1209 /*
1210 * There is now a place for page_node, but the tree may
1211 * have been rebalanced, so re-evaluate parent and new.
1212 */
1213 if (page_node)
1214 goto again;
1215 return NULL;
1216 }
1217 }
1218
1219 if (!page_node)
1220 return NULL;
1221
1222 list_del(&page_node->list);
1223 DO_NUMA(page_node->nid = nid);
1224 rb_link_node(&page_node->node, parent, new);
1225 rb_insert_color(&page_node->node, root);
1226 get_page(page);
1227 return page;
1228
1229 replace:
1230 if (page_node) {
1231 list_del(&page_node->list);
1232 DO_NUMA(page_node->nid = nid);
1233 rb_replace_node(&stable_node->node, &page_node->node, root);
1234 get_page(page);
1235 } else {
1236 rb_erase(&stable_node->node, root);
1237 page = NULL;
1238 }
1239 stable_node->head = &migrate_nodes;
1240 list_add(&stable_node->list, stable_node->head);
1241 return page;
1242 }
1243
1244 /*
1245 * stable_tree_insert - insert stable tree node pointing to new ksm page
1246 * into the stable tree.
1247 *
1248 * This function returns the stable tree node just allocated on success,
1249 * NULL otherwise.
1250 */
1251 static struct stable_node *stable_tree_insert(struct page *kpage)
1252 {
1253 int nid;
1254 unsigned long kpfn;
1255 struct rb_root *root;
1256 struct rb_node **new;
1257 struct rb_node *parent = NULL;
1258 struct stable_node *stable_node;
1259
1260 kpfn = page_to_pfn(kpage);
1261 nid = get_kpfn_nid(kpfn);
1262 root = root_stable_tree + nid;
1263 new = &root->rb_node;
1264
1265 while (*new) {
1266 struct page *tree_page;
1267 int ret;
1268
1269 cond_resched();
1270 stable_node = rb_entry(*new, struct stable_node, node);
1271 tree_page = get_ksm_page(stable_node, false);
1272 if (!tree_page)
1273 return NULL;
1274
1275 ret = memcmp_pages(kpage, tree_page);
1276 put_page(tree_page);
1277
1278 parent = *new;
1279 if (ret < 0)
1280 new = &parent->rb_left;
1281 else if (ret > 0)
1282 new = &parent->rb_right;
1283 else {
1284 /*
1285 * It is not a bug that stable_tree_search() didn't
1286 * find this node: because at that time our page was
1287 * not yet write-protected, so may have changed since.
1288 */
1289 return NULL;
1290 }
1291 }
1292
1293 stable_node = alloc_stable_node();
1294 if (!stable_node)
1295 return NULL;
1296
1297 INIT_HLIST_HEAD(&stable_node->hlist);
1298 stable_node->kpfn = kpfn;
1299 set_page_stable_node(kpage, stable_node);
1300 DO_NUMA(stable_node->nid = nid);
1301 rb_link_node(&stable_node->node, parent, new);
1302 rb_insert_color(&stable_node->node, root);
1303
1304 return stable_node;
1305 }
1306
1307 /*
1308 * unstable_tree_search_insert - search for identical page,
1309 * else insert rmap_item into the unstable tree.
1310 *
1311 * This function searches for a page in the unstable tree identical to the
1312 * page currently being scanned; and if no identical page is found in the
1313 * tree, we insert rmap_item as a new object into the unstable tree.
1314 *
1315 * This function returns pointer to rmap_item found to be identical
1316 * to the currently scanned page, NULL otherwise.
1317 *
1318 * This function does both searching and inserting, because they share
1319 * the same walking algorithm in an rbtree.
1320 */
1321 static
1322 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1323 struct page *page,
1324 struct page **tree_pagep)
1325 {
1326 struct rb_node **new;
1327 struct rb_root *root;
1328 struct rb_node *parent = NULL;
1329 int nid;
1330
1331 nid = get_kpfn_nid(page_to_pfn(page));
1332 root = root_unstable_tree + nid;
1333 new = &root->rb_node;
1334
1335 while (*new) {
1336 struct rmap_item *tree_rmap_item;
1337 struct page *tree_page;
1338 int ret;
1339
1340 cond_resched();
1341 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1342 tree_page = get_mergeable_page(tree_rmap_item);
1343 if (IS_ERR_OR_NULL(tree_page))
1344 return NULL;
1345
1346 /*
1347 * Don't substitute a ksm page for a forked page.
1348 */
1349 if (page == tree_page) {
1350 put_page(tree_page);
1351 return NULL;
1352 }
1353
1354 ret = memcmp_pages(page, tree_page);
1355
1356 parent = *new;
1357 if (ret < 0) {
1358 put_page(tree_page);
1359 new = &parent->rb_left;
1360 } else if (ret > 0) {
1361 put_page(tree_page);
1362 new = &parent->rb_right;
1363 } else if (!ksm_merge_across_nodes &&
1364 page_to_nid(tree_page) != nid) {
1365 /*
1366 * If tree_page has been migrated to another NUMA node,
1367 * it will be flushed out and put in the right unstable
1368 * tree next time: only merge with it when across_nodes.
1369 */
1370 put_page(tree_page);
1371 return NULL;
1372 } else {
1373 *tree_pagep = tree_page;
1374 return tree_rmap_item;
1375 }
1376 }
1377
1378 rmap_item->address |= UNSTABLE_FLAG;
1379 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1380 DO_NUMA(rmap_item->nid = nid);
1381 rb_link_node(&rmap_item->node, parent, new);
1382 rb_insert_color(&rmap_item->node, root);
1383
1384 ksm_pages_unshared++;
1385 return NULL;
1386 }
1387
1388 /*
1389 * stable_tree_append - add another rmap_item to the linked list of
1390 * rmap_items hanging off a given node of the stable tree, all sharing
1391 * the same ksm page.
1392 */
1393 static void stable_tree_append(struct rmap_item *rmap_item,
1394 struct stable_node *stable_node)
1395 {
1396 rmap_item->head = stable_node;
1397 rmap_item->address |= STABLE_FLAG;
1398 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1399
1400 if (rmap_item->hlist.next)
1401 ksm_pages_sharing++;
1402 else
1403 ksm_pages_shared++;
1404 }
1405
1406 /*
1407 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1408 * if not, compare checksum to previous and if it's the same, see if page can
1409 * be inserted into the unstable tree, or merged with a page already there and
1410 * both transferred to the stable tree.
1411 *
1412 * @page: the page that we are searching identical page to.
1413 * @rmap_item: the reverse mapping into the virtual address of this page
1414 */
1415 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1416 {
1417 struct rmap_item *tree_rmap_item;
1418 struct page *tree_page = NULL;
1419 struct stable_node *stable_node;
1420 struct page *kpage;
1421 unsigned int checksum;
1422 int err;
1423
1424 stable_node = page_stable_node(page);
1425 if (stable_node) {
1426 if (stable_node->head != &migrate_nodes &&
1427 get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1428 rb_erase(&stable_node->node,
1429 root_stable_tree + NUMA(stable_node->nid));
1430 stable_node->head = &migrate_nodes;
1431 list_add(&stable_node->list, stable_node->head);
1432 }
1433 if (stable_node->head != &migrate_nodes &&
1434 rmap_item->head == stable_node)
1435 return;
1436 }
1437
1438 /* We first start with searching the page inside the stable tree */
1439 kpage = stable_tree_search(page);
1440 if (kpage == page && rmap_item->head == stable_node) {
1441 put_page(kpage);
1442 return;
1443 }
1444
1445 remove_rmap_item_from_tree(rmap_item);
1446
1447 if (kpage) {
1448 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1449 if (!err) {
1450 /*
1451 * The page was successfully merged:
1452 * add its rmap_item to the stable tree.
1453 */
1454 lock_page(kpage);
1455 stable_tree_append(rmap_item, page_stable_node(kpage));
1456 unlock_page(kpage);
1457 }
1458 put_page(kpage);
1459 return;
1460 }
1461
1462 /*
1463 * If the hash value of the page has changed from the last time
1464 * we calculated it, this page is changing frequently: therefore we
1465 * don't want to insert it in the unstable tree, and we don't want
1466 * to waste our time searching for something identical to it there.
1467 */
1468 checksum = calc_checksum(page);
1469 if (rmap_item->oldchecksum != checksum) {
1470 rmap_item->oldchecksum = checksum;
1471 return;
1472 }
1473
1474 tree_rmap_item =
1475 unstable_tree_search_insert(rmap_item, page, &tree_page);
1476 if (tree_rmap_item) {
1477 kpage = try_to_merge_two_pages(rmap_item, page,
1478 tree_rmap_item, tree_page);
1479 put_page(tree_page);
1480 if (kpage) {
1481 /*
1482 * The pages were successfully merged: insert new
1483 * node in the stable tree and add both rmap_items.
1484 */
1485 lock_page(kpage);
1486 stable_node = stable_tree_insert(kpage);
1487 if (stable_node) {
1488 stable_tree_append(tree_rmap_item, stable_node);
1489 stable_tree_append(rmap_item, stable_node);
1490 }
1491 unlock_page(kpage);
1492
1493 /*
1494 * If we fail to insert the page into the stable tree,
1495 * we will have 2 virtual addresses that are pointing
1496 * to a ksm page left outside the stable tree,
1497 * in which case we need to break_cow on both.
1498 */
1499 if (!stable_node) {
1500 break_cow(tree_rmap_item);
1501 break_cow(rmap_item);
1502 }
1503 }
1504 }
1505 }
1506
1507 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1508 struct rmap_item **rmap_list,
1509 unsigned long addr)
1510 {
1511 struct rmap_item *rmap_item;
1512
1513 while (*rmap_list) {
1514 rmap_item = *rmap_list;
1515 if ((rmap_item->address & PAGE_MASK) == addr)
1516 return rmap_item;
1517 if (rmap_item->address > addr)
1518 break;
1519 *rmap_list = rmap_item->rmap_list;
1520 remove_rmap_item_from_tree(rmap_item);
1521 free_rmap_item(rmap_item);
1522 }
1523
1524 rmap_item = alloc_rmap_item();
1525 if (rmap_item) {
1526 /* It has already been zeroed */
1527 rmap_item->mm = mm_slot->mm;
1528 rmap_item->address = addr;
1529 rmap_item->rmap_list = *rmap_list;
1530 *rmap_list = rmap_item;
1531 }
1532 return rmap_item;
1533 }
1534
1535 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1536 {
1537 struct mm_struct *mm;
1538 struct mm_slot *slot;
1539 struct vm_area_struct *vma;
1540 struct rmap_item *rmap_item;
1541 int nid;
1542
1543 if (list_empty(&ksm_mm_head.mm_list))
1544 return NULL;
1545
1546 slot = ksm_scan.mm_slot;
1547 if (slot == &ksm_mm_head) {
1548 /*
1549 * A number of pages can hang around indefinitely on per-cpu
1550 * pagevecs, raised page count preventing write_protect_page
1551 * from merging them. Though it doesn't really matter much,
1552 * it is puzzling to see some stuck in pages_volatile until
1553 * other activity jostles them out, and they also prevented
1554 * LTP's KSM test from succeeding deterministically; so drain
1555 * them here (here rather than on entry to ksm_do_scan(),
1556 * so we don't IPI too often when pages_to_scan is set low).
1557 */
1558 lru_add_drain_all();
1559
1560 /*
1561 * Whereas stale stable_nodes on the stable_tree itself
1562 * get pruned in the regular course of stable_tree_search(),
1563 * those moved out to the migrate_nodes list can accumulate:
1564 * so prune them once before each full scan.
1565 */
1566 if (!ksm_merge_across_nodes) {
1567 struct stable_node *stable_node;
1568 struct list_head *this, *next;
1569 struct page *page;
1570
1571 list_for_each_safe(this, next, &migrate_nodes) {
1572 stable_node = list_entry(this,
1573 struct stable_node, list);
1574 page = get_ksm_page(stable_node, false);
1575 if (page)
1576 put_page(page);
1577 cond_resched();
1578 }
1579 }
1580
1581 for (nid = 0; nid < ksm_nr_node_ids; nid++)
1582 root_unstable_tree[nid] = RB_ROOT;
1583
1584 spin_lock(&ksm_mmlist_lock);
1585 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1586 ksm_scan.mm_slot = slot;
1587 spin_unlock(&ksm_mmlist_lock);
1588 /*
1589 * Although we tested list_empty() above, a racing __ksm_exit
1590 * of the last mm on the list may have removed it since then.
1591 */
1592 if (slot == &ksm_mm_head)
1593 return NULL;
1594 next_mm:
1595 ksm_scan.address = 0;
1596 ksm_scan.rmap_list = &slot->rmap_list;
1597 }
1598
1599 mm = slot->mm;
1600 down_read(&mm->mmap_sem);
1601 if (ksm_test_exit(mm))
1602 vma = NULL;
1603 else
1604 vma = find_vma(mm, ksm_scan.address);
1605
1606 for (; vma; vma = vma->vm_next) {
1607 if (!(vma->vm_flags & VM_MERGEABLE))
1608 continue;
1609 if (ksm_scan.address < vma->vm_start)
1610 ksm_scan.address = vma->vm_start;
1611 if (!vma->anon_vma)
1612 ksm_scan.address = vma->vm_end;
1613
1614 while (ksm_scan.address < vma->vm_end) {
1615 if (ksm_test_exit(mm))
1616 break;
1617 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1618 if (IS_ERR_OR_NULL(*page)) {
1619 ksm_scan.address += PAGE_SIZE;
1620 cond_resched();
1621 continue;
1622 }
1623 if (PageAnon(*page) ||
1624 page_trans_compound_anon(*page)) {
1625 flush_anon_page(vma, *page, ksm_scan.address);
1626 flush_dcache_page(*page);
1627 rmap_item = get_next_rmap_item(slot,
1628 ksm_scan.rmap_list, ksm_scan.address);
1629 if (rmap_item) {
1630 ksm_scan.rmap_list =
1631 &rmap_item->rmap_list;
1632 ksm_scan.address += PAGE_SIZE;
1633 } else
1634 put_page(*page);
1635 up_read(&mm->mmap_sem);
1636 return rmap_item;
1637 }
1638 put_page(*page);
1639 ksm_scan.address += PAGE_SIZE;
1640 cond_resched();
1641 }
1642 }
1643
1644 if (ksm_test_exit(mm)) {
1645 ksm_scan.address = 0;
1646 ksm_scan.rmap_list = &slot->rmap_list;
1647 }
1648 /*
1649 * Nuke all the rmap_items that are above this current rmap:
1650 * because there were no VM_MERGEABLE vmas with such addresses.
1651 */
1652 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1653
1654 spin_lock(&ksm_mmlist_lock);
1655 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1656 struct mm_slot, mm_list);
1657 if (ksm_scan.address == 0) {
1658 /*
1659 * We've completed a full scan of all vmas, holding mmap_sem
1660 * throughout, and found no VM_MERGEABLE: so do the same as
1661 * __ksm_exit does to remove this mm from all our lists now.
1662 * This applies either when cleaning up after __ksm_exit
1663 * (but beware: we can reach here even before __ksm_exit),
1664 * or when all VM_MERGEABLE areas have been unmapped (and
1665 * mmap_sem then protects against race with MADV_MERGEABLE).
1666 */
1667 hash_del(&slot->link);
1668 list_del(&slot->mm_list);
1669 spin_unlock(&ksm_mmlist_lock);
1670
1671 free_mm_slot(slot);
1672 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1673 up_read(&mm->mmap_sem);
1674 mmdrop(mm);
1675 } else {
1676 spin_unlock(&ksm_mmlist_lock);
1677 up_read(&mm->mmap_sem);
1678 }
1679
1680 /* Repeat until we've completed scanning the whole list */
1681 slot = ksm_scan.mm_slot;
1682 if (slot != &ksm_mm_head)
1683 goto next_mm;
1684
1685 ksm_scan.seqnr++;
1686 return NULL;
1687 }
1688
1689 /**
1690 * ksm_do_scan - the ksm scanner main worker function.
1691 * @scan_npages - number of pages we want to scan before we return.
1692 */
1693 static void ksm_do_scan(unsigned int scan_npages)
1694 {
1695 struct rmap_item *rmap_item;
1696 struct page *uninitialized_var(page);
1697
1698 while (scan_npages-- && likely(!freezing(current))) {
1699 cond_resched();
1700 rmap_item = scan_get_next_rmap_item(&page);
1701 if (!rmap_item)
1702 return;
1703 cmp_and_merge_page(page, rmap_item);
1704 put_page(page);
1705 }
1706 }
1707
1708 static int ksmd_should_run(void)
1709 {
1710 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1711 }
1712
1713 static int ksm_scan_thread(void *nothing)
1714 {
1715 set_freezable();
1716 set_user_nice(current, 5);
1717
1718 while (!kthread_should_stop()) {
1719 mutex_lock(&ksm_thread_mutex);
1720 wait_while_offlining();
1721 if (ksmd_should_run())
1722 ksm_do_scan(ksm_thread_pages_to_scan);
1723 mutex_unlock(&ksm_thread_mutex);
1724
1725 try_to_freeze();
1726
1727 if (ksmd_should_run()) {
1728 schedule_timeout_interruptible(
1729 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1730 } else {
1731 wait_event_freezable(ksm_thread_wait,
1732 ksmd_should_run() || kthread_should_stop());
1733 }
1734 }
1735 return 0;
1736 }
1737
1738 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1739 unsigned long end, int advice, unsigned long *vm_flags)
1740 {
1741 struct mm_struct *mm = vma->vm_mm;
1742 int err;
1743
1744 switch (advice) {
1745 case MADV_MERGEABLE:
1746 /*
1747 * Be somewhat over-protective for now!
1748 */
1749 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1750 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1751 VM_HUGETLB | VM_MIXEDMAP))
1752 return 0; /* just ignore the advice */
1753
1754 #ifdef VM_SAO
1755 if (*vm_flags & VM_SAO)
1756 return 0;
1757 #endif
1758
1759 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1760 err = __ksm_enter(mm);
1761 if (err)
1762 return err;
1763 }
1764
1765 *vm_flags |= VM_MERGEABLE;
1766 break;
1767
1768 case MADV_UNMERGEABLE:
1769 if (!(*vm_flags & VM_MERGEABLE))
1770 return 0; /* just ignore the advice */
1771
1772 if (vma->anon_vma) {
1773 err = unmerge_ksm_pages(vma, start, end);
1774 if (err)
1775 return err;
1776 }
1777
1778 *vm_flags &= ~VM_MERGEABLE;
1779 break;
1780 }
1781
1782 return 0;
1783 }
1784
1785 int __ksm_enter(struct mm_struct *mm)
1786 {
1787 struct mm_slot *mm_slot;
1788 int needs_wakeup;
1789
1790 mm_slot = alloc_mm_slot();
1791 if (!mm_slot)
1792 return -ENOMEM;
1793
1794 /* Check ksm_run too? Would need tighter locking */
1795 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1796
1797 spin_lock(&ksm_mmlist_lock);
1798 insert_to_mm_slots_hash(mm, mm_slot);
1799 /*
1800 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1801 * insert just behind the scanning cursor, to let the area settle
1802 * down a little; when fork is followed by immediate exec, we don't
1803 * want ksmd to waste time setting up and tearing down an rmap_list.
1804 *
1805 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1806 * scanning cursor, otherwise KSM pages in newly forked mms will be
1807 * missed: then we might as well insert at the end of the list.
1808 */
1809 if (ksm_run & KSM_RUN_UNMERGE)
1810 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1811 else
1812 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1813 spin_unlock(&ksm_mmlist_lock);
1814
1815 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1816 atomic_inc(&mm->mm_count);
1817
1818 if (needs_wakeup)
1819 wake_up_interruptible(&ksm_thread_wait);
1820
1821 return 0;
1822 }
1823
1824 void __ksm_exit(struct mm_struct *mm)
1825 {
1826 struct mm_slot *mm_slot;
1827 int easy_to_free = 0;
1828
1829 /*
1830 * This process is exiting: if it's straightforward (as is the
1831 * case when ksmd was never running), free mm_slot immediately.
1832 * But if it's at the cursor or has rmap_items linked to it, use
1833 * mmap_sem to synchronize with any break_cows before pagetables
1834 * are freed, and leave the mm_slot on the list for ksmd to free.
1835 * Beware: ksm may already have noticed it exiting and freed the slot.
1836 */
1837
1838 spin_lock(&ksm_mmlist_lock);
1839 mm_slot = get_mm_slot(mm);
1840 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1841 if (!mm_slot->rmap_list) {
1842 hash_del(&mm_slot->link);
1843 list_del(&mm_slot->mm_list);
1844 easy_to_free = 1;
1845 } else {
1846 list_move(&mm_slot->mm_list,
1847 &ksm_scan.mm_slot->mm_list);
1848 }
1849 }
1850 spin_unlock(&ksm_mmlist_lock);
1851
1852 if (easy_to_free) {
1853 free_mm_slot(mm_slot);
1854 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1855 mmdrop(mm);
1856 } else if (mm_slot) {
1857 down_write(&mm->mmap_sem);
1858 up_write(&mm->mmap_sem);
1859 }
1860 }
1861
1862 struct page *ksm_might_need_to_copy(struct page *page,
1863 struct vm_area_struct *vma, unsigned long address)
1864 {
1865 struct anon_vma *anon_vma = page_anon_vma(page);
1866 struct page *new_page;
1867
1868 if (PageKsm(page)) {
1869 if (page_stable_node(page) &&
1870 !(ksm_run & KSM_RUN_UNMERGE))
1871 return page; /* no need to copy it */
1872 } else if (!anon_vma) {
1873 return page; /* no need to copy it */
1874 } else if (anon_vma->root == vma->anon_vma->root &&
1875 page->index == linear_page_index(vma, address)) {
1876 return page; /* still no need to copy it */
1877 }
1878 if (!PageUptodate(page))
1879 return page; /* let do_swap_page report the error */
1880
1881 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1882 if (new_page) {
1883 copy_user_highpage(new_page, page, address, vma);
1884
1885 SetPageDirty(new_page);
1886 __SetPageUptodate(new_page);
1887 __set_page_locked(new_page);
1888 }
1889
1890 return new_page;
1891 }
1892
1893 int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
1894 {
1895 struct stable_node *stable_node;
1896 struct rmap_item *rmap_item;
1897 int ret = SWAP_AGAIN;
1898 int search_new_forks = 0;
1899
1900 VM_BUG_ON_PAGE(!PageKsm(page), page);
1901
1902 /*
1903 * Rely on the page lock to protect against concurrent modifications
1904 * to that page's node of the stable tree.
1905 */
1906 VM_BUG_ON_PAGE(!PageLocked(page), page);
1907
1908 stable_node = page_stable_node(page);
1909 if (!stable_node)
1910 return ret;
1911 again:
1912 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1913 struct anon_vma *anon_vma = rmap_item->anon_vma;
1914 struct anon_vma_chain *vmac;
1915 struct vm_area_struct *vma;
1916
1917 anon_vma_lock_read(anon_vma);
1918 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1919 0, ULONG_MAX) {
1920 vma = vmac->vma;
1921 if (rmap_item->address < vma->vm_start ||
1922 rmap_item->address >= vma->vm_end)
1923 continue;
1924 /*
1925 * Initially we examine only the vma which covers this
1926 * rmap_item; but later, if there is still work to do,
1927 * we examine covering vmas in other mms: in case they
1928 * were forked from the original since ksmd passed.
1929 */
1930 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1931 continue;
1932
1933 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1934 continue;
1935
1936 ret = rwc->rmap_one(page, vma,
1937 rmap_item->address, rwc->arg);
1938 if (ret != SWAP_AGAIN) {
1939 anon_vma_unlock_read(anon_vma);
1940 goto out;
1941 }
1942 if (rwc->done && rwc->done(page)) {
1943 anon_vma_unlock_read(anon_vma);
1944 goto out;
1945 }
1946 }
1947 anon_vma_unlock_read(anon_vma);
1948 }
1949 if (!search_new_forks++)
1950 goto again;
1951 out:
1952 return ret;
1953 }
1954
1955 #ifdef CONFIG_MIGRATION
1956 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1957 {
1958 struct stable_node *stable_node;
1959
1960 VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
1961 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1962 VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
1963
1964 stable_node = page_stable_node(newpage);
1965 if (stable_node) {
1966 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
1967 stable_node->kpfn = page_to_pfn(newpage);
1968 /*
1969 * newpage->mapping was set in advance; now we need smp_wmb()
1970 * to make sure that the new stable_node->kpfn is visible
1971 * to get_ksm_page() before it can see that oldpage->mapping
1972 * has gone stale (or that PageSwapCache has been cleared).
1973 */
1974 smp_wmb();
1975 set_page_stable_node(oldpage, NULL);
1976 }
1977 }
1978 #endif /* CONFIG_MIGRATION */
1979
1980 #ifdef CONFIG_MEMORY_HOTREMOVE
1981 static void wait_while_offlining(void)
1982 {
1983 while (ksm_run & KSM_RUN_OFFLINE) {
1984 mutex_unlock(&ksm_thread_mutex);
1985 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
1986 TASK_UNINTERRUPTIBLE);
1987 mutex_lock(&ksm_thread_mutex);
1988 }
1989 }
1990
1991 static void ksm_check_stable_tree(unsigned long start_pfn,
1992 unsigned long end_pfn)
1993 {
1994 struct stable_node *stable_node;
1995 struct list_head *this, *next;
1996 struct rb_node *node;
1997 int nid;
1998
1999 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2000 node = rb_first(root_stable_tree + nid);
2001 while (node) {
2002 stable_node = rb_entry(node, struct stable_node, node);
2003 if (stable_node->kpfn >= start_pfn &&
2004 stable_node->kpfn < end_pfn) {
2005 /*
2006 * Don't get_ksm_page, page has already gone:
2007 * which is why we keep kpfn instead of page*
2008 */
2009 remove_node_from_stable_tree(stable_node);
2010 node = rb_first(root_stable_tree + nid);
2011 } else
2012 node = rb_next(node);
2013 cond_resched();
2014 }
2015 }
2016 list_for_each_safe(this, next, &migrate_nodes) {
2017 stable_node = list_entry(this, struct stable_node, list);
2018 if (stable_node->kpfn >= start_pfn &&
2019 stable_node->kpfn < end_pfn)
2020 remove_node_from_stable_tree(stable_node);
2021 cond_resched();
2022 }
2023 }
2024
2025 static int ksm_memory_callback(struct notifier_block *self,
2026 unsigned long action, void *arg)
2027 {
2028 struct memory_notify *mn = arg;
2029
2030 switch (action) {
2031 case MEM_GOING_OFFLINE:
2032 /*
2033 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2034 * and remove_all_stable_nodes() while memory is going offline:
2035 * it is unsafe for them to touch the stable tree at this time.
2036 * But unmerge_ksm_pages(), rmap lookups and other entry points
2037 * which do not need the ksm_thread_mutex are all safe.
2038 */
2039 mutex_lock(&ksm_thread_mutex);
2040 ksm_run |= KSM_RUN_OFFLINE;
2041 mutex_unlock(&ksm_thread_mutex);
2042 break;
2043
2044 case MEM_OFFLINE:
2045 /*
2046 * Most of the work is done by page migration; but there might
2047 * be a few stable_nodes left over, still pointing to struct
2048 * pages which have been offlined: prune those from the tree,
2049 * otherwise get_ksm_page() might later try to access a
2050 * non-existent struct page.
2051 */
2052 ksm_check_stable_tree(mn->start_pfn,
2053 mn->start_pfn + mn->nr_pages);
2054 /* fallthrough */
2055
2056 case MEM_CANCEL_OFFLINE:
2057 mutex_lock(&ksm_thread_mutex);
2058 ksm_run &= ~KSM_RUN_OFFLINE;
2059 mutex_unlock(&ksm_thread_mutex);
2060
2061 smp_mb(); /* wake_up_bit advises this */
2062 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2063 break;
2064 }
2065 return NOTIFY_OK;
2066 }
2067 #else
2068 static void wait_while_offlining(void)
2069 {
2070 }
2071 #endif /* CONFIG_MEMORY_HOTREMOVE */
2072
2073 #ifdef CONFIG_SYSFS
2074 /*
2075 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2076 */
2077
2078 #define KSM_ATTR_RO(_name) \
2079 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2080 #define KSM_ATTR(_name) \
2081 static struct kobj_attribute _name##_attr = \
2082 __ATTR(_name, 0644, _name##_show, _name##_store)
2083
2084 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2085 struct kobj_attribute *attr, char *buf)
2086 {
2087 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2088 }
2089
2090 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2091 struct kobj_attribute *attr,
2092 const char *buf, size_t count)
2093 {
2094 unsigned long msecs;
2095 int err;
2096
2097 err = kstrtoul(buf, 10, &msecs);
2098 if (err || msecs > UINT_MAX)
2099 return -EINVAL;
2100
2101 ksm_thread_sleep_millisecs = msecs;
2102
2103 return count;
2104 }
2105 KSM_ATTR(sleep_millisecs);
2106
2107 static ssize_t pages_to_scan_show(struct kobject *kobj,
2108 struct kobj_attribute *attr, char *buf)
2109 {
2110 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2111 }
2112
2113 static ssize_t pages_to_scan_store(struct kobject *kobj,
2114 struct kobj_attribute *attr,
2115 const char *buf, size_t count)
2116 {
2117 int err;
2118 unsigned long nr_pages;
2119
2120 err = kstrtoul(buf, 10, &nr_pages);
2121 if (err || nr_pages > UINT_MAX)
2122 return -EINVAL;
2123
2124 ksm_thread_pages_to_scan = nr_pages;
2125
2126 return count;
2127 }
2128 KSM_ATTR(pages_to_scan);
2129
2130 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2131 char *buf)
2132 {
2133 return sprintf(buf, "%lu\n", ksm_run);
2134 }
2135
2136 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2137 const char *buf, size_t count)
2138 {
2139 int err;
2140 unsigned long flags;
2141
2142 err = kstrtoul(buf, 10, &flags);
2143 if (err || flags > UINT_MAX)
2144 return -EINVAL;
2145 if (flags > KSM_RUN_UNMERGE)
2146 return -EINVAL;
2147
2148 /*
2149 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2150 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2151 * breaking COW to free the pages_shared (but leaves mm_slots
2152 * on the list for when ksmd may be set running again).
2153 */
2154
2155 mutex_lock(&ksm_thread_mutex);
2156 wait_while_offlining();
2157 if (ksm_run != flags) {
2158 ksm_run = flags;
2159 if (flags & KSM_RUN_UNMERGE) {
2160 set_current_oom_origin();
2161 err = unmerge_and_remove_all_rmap_items();
2162 clear_current_oom_origin();
2163 if (err) {
2164 ksm_run = KSM_RUN_STOP;
2165 count = err;
2166 }
2167 }
2168 }
2169 mutex_unlock(&ksm_thread_mutex);
2170
2171 if (flags & KSM_RUN_MERGE)
2172 wake_up_interruptible(&ksm_thread_wait);
2173
2174 return count;
2175 }
2176 KSM_ATTR(run);
2177
2178 #ifdef CONFIG_NUMA
2179 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2180 struct kobj_attribute *attr, char *buf)
2181 {
2182 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2183 }
2184
2185 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2186 struct kobj_attribute *attr,
2187 const char *buf, size_t count)
2188 {
2189 int err;
2190 unsigned long knob;
2191
2192 err = kstrtoul(buf, 10, &knob);
2193 if (err)
2194 return err;
2195 if (knob > 1)
2196 return -EINVAL;
2197
2198 mutex_lock(&ksm_thread_mutex);
2199 wait_while_offlining();
2200 if (ksm_merge_across_nodes != knob) {
2201 if (ksm_pages_shared || remove_all_stable_nodes())
2202 err = -EBUSY;
2203 else if (root_stable_tree == one_stable_tree) {
2204 struct rb_root *buf;
2205 /*
2206 * This is the first time that we switch away from the
2207 * default of merging across nodes: must now allocate
2208 * a buffer to hold as many roots as may be needed.
2209 * Allocate stable and unstable together:
2210 * MAXSMP NODES_SHIFT 10 will use 16kB.
2211 */
2212 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2213 GFP_KERNEL);
2214 /* Let us assume that RB_ROOT is NULL is zero */
2215 if (!buf)
2216 err = -ENOMEM;
2217 else {
2218 root_stable_tree = buf;
2219 root_unstable_tree = buf + nr_node_ids;
2220 /* Stable tree is empty but not the unstable */
2221 root_unstable_tree[0] = one_unstable_tree[0];
2222 }
2223 }
2224 if (!err) {
2225 ksm_merge_across_nodes = knob;
2226 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2227 }
2228 }
2229 mutex_unlock(&ksm_thread_mutex);
2230
2231 return err ? err : count;
2232 }
2233 KSM_ATTR(merge_across_nodes);
2234 #endif
2235
2236 static ssize_t pages_shared_show(struct kobject *kobj,
2237 struct kobj_attribute *attr, char *buf)
2238 {
2239 return sprintf(buf, "%lu\n", ksm_pages_shared);
2240 }
2241 KSM_ATTR_RO(pages_shared);
2242
2243 static ssize_t pages_sharing_show(struct kobject *kobj,
2244 struct kobj_attribute *attr, char *buf)
2245 {
2246 return sprintf(buf, "%lu\n", ksm_pages_sharing);
2247 }
2248 KSM_ATTR_RO(pages_sharing);
2249
2250 static ssize_t pages_unshared_show(struct kobject *kobj,
2251 struct kobj_attribute *attr, char *buf)
2252 {
2253 return sprintf(buf, "%lu\n", ksm_pages_unshared);
2254 }
2255 KSM_ATTR_RO(pages_unshared);
2256
2257 static ssize_t pages_volatile_show(struct kobject *kobj,
2258 struct kobj_attribute *attr, char *buf)
2259 {
2260 long ksm_pages_volatile;
2261
2262 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2263 - ksm_pages_sharing - ksm_pages_unshared;
2264 /*
2265 * It was not worth any locking to calculate that statistic,
2266 * but it might therefore sometimes be negative: conceal that.
2267 */
2268 if (ksm_pages_volatile < 0)
2269 ksm_pages_volatile = 0;
2270 return sprintf(buf, "%ld\n", ksm_pages_volatile);
2271 }
2272 KSM_ATTR_RO(pages_volatile);
2273
2274 static ssize_t full_scans_show(struct kobject *kobj,
2275 struct kobj_attribute *attr, char *buf)
2276 {
2277 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2278 }
2279 KSM_ATTR_RO(full_scans);
2280
2281 static struct attribute *ksm_attrs[] = {
2282 &sleep_millisecs_attr.attr,
2283 &pages_to_scan_attr.attr,
2284 &run_attr.attr,
2285 &pages_shared_attr.attr,
2286 &pages_sharing_attr.attr,
2287 &pages_unshared_attr.attr,
2288 &pages_volatile_attr.attr,
2289 &full_scans_attr.attr,
2290 #ifdef CONFIG_NUMA
2291 &merge_across_nodes_attr.attr,
2292 #endif
2293 NULL,
2294 };
2295
2296 static struct attribute_group ksm_attr_group = {
2297 .attrs = ksm_attrs,
2298 .name = "ksm",
2299 };
2300 #endif /* CONFIG_SYSFS */
2301
2302 static int __init ksm_init(void)
2303 {
2304 struct task_struct *ksm_thread;
2305 int err;
2306
2307 err = ksm_slab_init();
2308 if (err)
2309 goto out;
2310
2311 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2312 if (IS_ERR(ksm_thread)) {
2313 pr_err("ksm: creating kthread failed\n");
2314 err = PTR_ERR(ksm_thread);
2315 goto out_free;
2316 }
2317
2318 #ifdef CONFIG_SYSFS
2319 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2320 if (err) {
2321 pr_err("ksm: register sysfs failed\n");
2322 kthread_stop(ksm_thread);
2323 goto out_free;
2324 }
2325 #else
2326 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2327
2328 #endif /* CONFIG_SYSFS */
2329
2330 #ifdef CONFIG_MEMORY_HOTREMOVE
2331 /* There is no significance to this priority 100 */
2332 hotplug_memory_notifier(ksm_memory_callback, 100);
2333 #endif
2334 return 0;
2335
2336 out_free:
2337 ksm_slab_free();
2338 out:
2339 return err;
2340 }
2341 subsys_initcall(ksm_init);