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