sfc: Wrap __efx_rx_packet() with efx_rx_flush_packet()
[linux-2.6.git] / mm / ksm.c
blob85bfd4c1634629dc35a2f671c43cd3e2d8c818cc
1 /*
2 * Memory merging support.
4 * This code enables dynamic sharing of identical pages found in different
5 * memory areas, even if they are not shared by fork()
7 * Copyright (C) 2008-2009 Red Hat, Inc.
8 * Authors:
9 * Izik Eidus
10 * Andrea Arcangeli
11 * Chris Wright
12 * Hugh Dickins
14 * This work is licensed under the terms of the GNU GPL, version 2.
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>
41 #include <asm/tlbflush.h>
42 #include "internal.h"
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
53 * A few notes about the KSM scanning process,
54 * to make it easier to understand the data structures below:
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.
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.
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.
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.
75 * KSM solves this problem by several techniques:
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.)
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.
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
102 struct mm_slot {
103 struct hlist_node link;
104 struct list_head mm_list;
105 struct rmap_item *rmap_list;
106 struct mm_struct *mm;
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)
116 * There is only the one ksm_scan instance of this cursor structure.
118 struct ksm_scan {
119 struct mm_slot *mm_slot;
120 unsigned long address;
121 struct rmap_item **rmap_list;
122 unsigned long seqnr;
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)
134 struct stable_node {
135 union {
136 struct rb_node node; /* when node of stable tree */
137 struct { /* when listed for migration */
138 struct list_head *head;
139 struct list_head list;
142 struct hlist_head hlist;
143 unsigned long kpfn;
144 #ifdef CONFIG_NUMA
145 int nid;
146 #endif
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
161 struct rmap_item {
162 struct rmap_item *rmap_list;
163 union {
164 struct anon_vma *anon_vma; /* when stable */
165 #ifdef CONFIG_NUMA
166 int nid; /* when node of unstable tree */
167 #endif
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;
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 */
185 /* The stable and unstable tree heads */
186 static struct rb_root one_stable_tree[1] = { RB_ROOT };
187 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188 static struct rb_root *root_stable_tree = one_stable_tree;
189 static struct rb_root *root_unstable_tree = one_unstable_tree;
191 /* Recently migrated nodes of stable tree, pending proper placement */
192 static LIST_HEAD(migrate_nodes);
194 #define MM_SLOTS_HASH_BITS 10
195 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
197 static struct mm_slot ksm_mm_head = {
198 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
200 static struct ksm_scan ksm_scan = {
201 .mm_slot = &ksm_mm_head,
204 static struct kmem_cache *rmap_item_cache;
205 static struct kmem_cache *stable_node_cache;
206 static struct kmem_cache *mm_slot_cache;
208 /* The number of nodes in the stable tree */
209 static unsigned long ksm_pages_shared;
211 /* The number of page slots additionally sharing those nodes */
212 static unsigned long ksm_pages_sharing;
214 /* The number of nodes in the unstable tree */
215 static unsigned long ksm_pages_unshared;
217 /* The number of rmap_items in use: to calculate pages_volatile */
218 static unsigned long ksm_rmap_items;
220 /* Number of pages ksmd should scan in one batch */
221 static unsigned int ksm_thread_pages_to_scan = 100;
223 /* Milliseconds ksmd should sleep between batches */
224 static unsigned int ksm_thread_sleep_millisecs = 20;
226 #ifdef CONFIG_NUMA
227 /* Zeroed when merging across nodes is not allowed */
228 static unsigned int ksm_merge_across_nodes = 1;
229 static int ksm_nr_node_ids = 1;
230 #else
231 #define ksm_merge_across_nodes 1U
232 #define ksm_nr_node_ids 1
233 #endif
235 #define KSM_RUN_STOP 0
236 #define KSM_RUN_MERGE 1
237 #define KSM_RUN_UNMERGE 2
238 #define KSM_RUN_OFFLINE 4
239 static unsigned long ksm_run = KSM_RUN_STOP;
240 static void wait_while_offlining(void);
242 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243 static DEFINE_MUTEX(ksm_thread_mutex);
244 static DEFINE_SPINLOCK(ksm_mmlist_lock);
246 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247 sizeof(struct __struct), __alignof__(struct __struct),\
248 (__flags), NULL)
250 static int __init ksm_slab_init(void)
252 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
253 if (!rmap_item_cache)
254 goto out;
256 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257 if (!stable_node_cache)
258 goto out_free1;
260 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261 if (!mm_slot_cache)
262 goto out_free2;
264 return 0;
266 out_free2:
267 kmem_cache_destroy(stable_node_cache);
268 out_free1:
269 kmem_cache_destroy(rmap_item_cache);
270 out:
271 return -ENOMEM;
274 static void __init ksm_slab_free(void)
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;
282 static inline struct rmap_item *alloc_rmap_item(void)
284 struct rmap_item *rmap_item;
286 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
287 if (rmap_item)
288 ksm_rmap_items++;
289 return rmap_item;
292 static inline void free_rmap_item(struct rmap_item *rmap_item)
294 ksm_rmap_items--;
295 rmap_item->mm = NULL; /* debug safety */
296 kmem_cache_free(rmap_item_cache, rmap_item);
299 static inline struct stable_node *alloc_stable_node(void)
301 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
304 static inline void free_stable_node(struct stable_node *stable_node)
306 kmem_cache_free(stable_node_cache, stable_node);
309 static inline struct mm_slot *alloc_mm_slot(void)
311 if (!mm_slot_cache) /* initialization failed */
312 return NULL;
313 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
316 static inline void free_mm_slot(struct mm_slot *mm_slot)
318 kmem_cache_free(mm_slot_cache, mm_slot);
321 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
323 struct mm_slot *slot;
325 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
326 if (slot->mm == mm)
327 return slot;
329 return NULL;
332 static void insert_to_mm_slots_hash(struct mm_struct *mm,
333 struct mm_slot *mm_slot)
335 mm_slot->mm = mm;
336 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
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.
347 static inline bool ksm_test_exit(struct mm_struct *mm)
349 return atomic_read(&mm->mm_users) == 0;
353 * We use break_ksm to break COW on a ksm page: it's a stripped down
355 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
356 * put_page(page);
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.
363 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
365 struct page *page;
366 int ret = 0;
368 do {
369 cond_resched();
370 page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
371 if (IS_ERR_OR_NULL(page))
372 break;
373 if (PageKsm(page))
374 ret = handle_mm_fault(vma->vm_mm, vma, addr,
375 FAULT_FLAG_WRITE);
376 else
377 ret = VM_FAULT_WRITE;
378 put_page(page);
379 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
381 * We must loop because handle_mm_fault() may back out if there's
382 * any difficulty e.g. if pte accessed bit gets updated concurrently.
384 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
385 * COW has been broken, even if the vma does not permit VM_WRITE;
386 * but note that a concurrent fault might break PageKsm for us.
388 * VM_FAULT_SIGBUS could occur if we race with truncation of the
389 * backing file, which also invalidates anonymous pages: that's
390 * okay, that truncation will have unmapped the PageKsm for us.
392 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
393 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
394 * current task has TIF_MEMDIE set, and will be OOM killed on return
395 * to user; and ksmd, having no mm, would never be chosen for that.
397 * But if the mm is in a limited mem_cgroup, then the fault may fail
398 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
399 * even ksmd can fail in this way - though it's usually breaking ksm
400 * just to undo a merge it made a moment before, so unlikely to oom.
402 * That's a pity: we might therefore have more kernel pages allocated
403 * than we're counting as nodes in the stable tree; but ksm_do_scan
404 * will retry to break_cow on each pass, so should recover the page
405 * in due course. The important thing is to not let VM_MERGEABLE
406 * be cleared while any such pages might remain in the area.
408 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
411 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
412 unsigned long addr)
414 struct vm_area_struct *vma;
415 if (ksm_test_exit(mm))
416 return NULL;
417 vma = find_vma(mm, addr);
418 if (!vma || vma->vm_start > addr)
419 return NULL;
420 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
421 return NULL;
422 return vma;
425 static void break_cow(struct rmap_item *rmap_item)
427 struct mm_struct *mm = rmap_item->mm;
428 unsigned long addr = rmap_item->address;
429 struct vm_area_struct *vma;
432 * It is not an accident that whenever we want to break COW
433 * to undo, we also need to drop a reference to the anon_vma.
435 put_anon_vma(rmap_item->anon_vma);
437 down_read(&mm->mmap_sem);
438 vma = find_mergeable_vma(mm, addr);
439 if (vma)
440 break_ksm(vma, addr);
441 up_read(&mm->mmap_sem);
444 static struct page *page_trans_compound_anon(struct page *page)
446 if (PageTransCompound(page)) {
447 struct page *head = compound_trans_head(page);
449 * head may actually be splitted and freed from under
450 * us but it's ok here.
452 if (PageAnon(head))
453 return head;
455 return NULL;
458 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
460 struct mm_struct *mm = rmap_item->mm;
461 unsigned long addr = rmap_item->address;
462 struct vm_area_struct *vma;
463 struct page *page;
465 down_read(&mm->mmap_sem);
466 vma = find_mergeable_vma(mm, addr);
467 if (!vma)
468 goto out;
470 page = follow_page(vma, addr, FOLL_GET);
471 if (IS_ERR_OR_NULL(page))
472 goto out;
473 if (PageAnon(page) || page_trans_compound_anon(page)) {
474 flush_anon_page(vma, page, addr);
475 flush_dcache_page(page);
476 } else {
477 put_page(page);
478 out: page = NULL;
480 up_read(&mm->mmap_sem);
481 return page;
485 * This helper is used for getting right index into array of tree roots.
486 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
487 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
488 * every node has its own stable and unstable tree.
490 static inline int get_kpfn_nid(unsigned long kpfn)
492 return ksm_merge_across_nodes ? 0 : pfn_to_nid(kpfn);
495 static void remove_node_from_stable_tree(struct stable_node *stable_node)
497 struct rmap_item *rmap_item;
499 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
500 if (rmap_item->hlist.next)
501 ksm_pages_sharing--;
502 else
503 ksm_pages_shared--;
504 put_anon_vma(rmap_item->anon_vma);
505 rmap_item->address &= PAGE_MASK;
506 cond_resched();
509 if (stable_node->head == &migrate_nodes)
510 list_del(&stable_node->list);
511 else
512 rb_erase(&stable_node->node,
513 root_stable_tree + NUMA(stable_node->nid));
514 free_stable_node(stable_node);
518 * get_ksm_page: checks if the page indicated by the stable node
519 * is still its ksm page, despite having held no reference to it.
520 * In which case we can trust the content of the page, and it
521 * returns the gotten page; but if the page has now been zapped,
522 * remove the stale node from the stable tree and return NULL.
523 * But beware, the stable node's page might be being migrated.
525 * You would expect the stable_node to hold a reference to the ksm page.
526 * But if it increments the page's count, swapping out has to wait for
527 * ksmd to come around again before it can free the page, which may take
528 * seconds or even minutes: much too unresponsive. So instead we use a
529 * "keyhole reference": access to the ksm page from the stable node peeps
530 * out through its keyhole to see if that page still holds the right key,
531 * pointing back to this stable node. This relies on freeing a PageAnon
532 * page to reset its page->mapping to NULL, and relies on no other use of
533 * a page to put something that might look like our key in page->mapping.
534 * is on its way to being freed; but it is an anomaly to bear in mind.
536 static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
538 struct page *page;
539 void *expected_mapping;
540 unsigned long kpfn;
542 expected_mapping = (void *)stable_node +
543 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
544 again:
545 kpfn = ACCESS_ONCE(stable_node->kpfn);
546 page = pfn_to_page(kpfn);
549 * page is computed from kpfn, so on most architectures reading
550 * page->mapping is naturally ordered after reading node->kpfn,
551 * but on Alpha we need to be more careful.
553 smp_read_barrier_depends();
554 if (ACCESS_ONCE(page->mapping) != expected_mapping)
555 goto stale;
558 * We cannot do anything with the page while its refcount is 0.
559 * Usually 0 means free, or tail of a higher-order page: in which
560 * case this node is no longer referenced, and should be freed;
561 * however, it might mean that the page is under page_freeze_refs().
562 * The __remove_mapping() case is easy, again the node is now stale;
563 * but if page is swapcache in migrate_page_move_mapping(), it might
564 * still be our page, in which case it's essential to keep the node.
566 while (!get_page_unless_zero(page)) {
568 * Another check for page->mapping != expected_mapping would
569 * work here too. We have chosen the !PageSwapCache test to
570 * optimize the common case, when the page is or is about to
571 * be freed: PageSwapCache is cleared (under spin_lock_irq)
572 * in the freeze_refs section of __remove_mapping(); but Anon
573 * page->mapping reset to NULL later, in free_pages_prepare().
575 if (!PageSwapCache(page))
576 goto stale;
577 cpu_relax();
580 if (ACCESS_ONCE(page->mapping) != expected_mapping) {
581 put_page(page);
582 goto stale;
585 if (lock_it) {
586 lock_page(page);
587 if (ACCESS_ONCE(page->mapping) != expected_mapping) {
588 unlock_page(page);
589 put_page(page);
590 goto stale;
593 return page;
595 stale:
597 * We come here from above when page->mapping or !PageSwapCache
598 * suggests that the node is stale; but it might be under migration.
599 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
600 * before checking whether node->kpfn has been changed.
602 smp_rmb();
603 if (ACCESS_ONCE(stable_node->kpfn) != kpfn)
604 goto again;
605 remove_node_from_stable_tree(stable_node);
606 return NULL;
610 * Removing rmap_item from stable or unstable tree.
611 * This function will clean the information from the stable/unstable tree.
613 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
615 if (rmap_item->address & STABLE_FLAG) {
616 struct stable_node *stable_node;
617 struct page *page;
619 stable_node = rmap_item->head;
620 page = get_ksm_page(stable_node, true);
621 if (!page)
622 goto out;
624 hlist_del(&rmap_item->hlist);
625 unlock_page(page);
626 put_page(page);
628 if (stable_node->hlist.first)
629 ksm_pages_sharing--;
630 else
631 ksm_pages_shared--;
633 put_anon_vma(rmap_item->anon_vma);
634 rmap_item->address &= PAGE_MASK;
636 } else if (rmap_item->address & UNSTABLE_FLAG) {
637 unsigned char age;
639 * Usually ksmd can and must skip the rb_erase, because
640 * root_unstable_tree was already reset to RB_ROOT.
641 * But be careful when an mm is exiting: do the rb_erase
642 * if this rmap_item was inserted by this scan, rather
643 * than left over from before.
645 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
646 BUG_ON(age > 1);
647 if (!age)
648 rb_erase(&rmap_item->node,
649 root_unstable_tree + NUMA(rmap_item->nid));
650 ksm_pages_unshared--;
651 rmap_item->address &= PAGE_MASK;
653 out:
654 cond_resched(); /* we're called from many long loops */
657 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
658 struct rmap_item **rmap_list)
660 while (*rmap_list) {
661 struct rmap_item *rmap_item = *rmap_list;
662 *rmap_list = rmap_item->rmap_list;
663 remove_rmap_item_from_tree(rmap_item);
664 free_rmap_item(rmap_item);
669 * Though it's very tempting to unmerge rmap_items from stable tree rather
670 * than check every pte of a given vma, the locking doesn't quite work for
671 * that - an rmap_item is assigned to the stable tree after inserting ksm
672 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
673 * rmap_items from parent to child at fork time (so as not to waste time
674 * if exit comes before the next scan reaches it).
676 * Similarly, although we'd like to remove rmap_items (so updating counts
677 * and freeing memory) when unmerging an area, it's easier to leave that
678 * to the next pass of ksmd - consider, for example, how ksmd might be
679 * in cmp_and_merge_page on one of the rmap_items we would be removing.
681 static int unmerge_ksm_pages(struct vm_area_struct *vma,
682 unsigned long start, unsigned long end)
684 unsigned long addr;
685 int err = 0;
687 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
688 if (ksm_test_exit(vma->vm_mm))
689 break;
690 if (signal_pending(current))
691 err = -ERESTARTSYS;
692 else
693 err = break_ksm(vma, addr);
695 return err;
698 #ifdef CONFIG_SYSFS
700 * Only called through the sysfs control interface:
702 static int remove_stable_node(struct stable_node *stable_node)
704 struct page *page;
705 int err;
707 page = get_ksm_page(stable_node, true);
708 if (!page) {
710 * get_ksm_page did remove_node_from_stable_tree itself.
712 return 0;
715 if (WARN_ON_ONCE(page_mapped(page))) {
717 * This should not happen: but if it does, just refuse to let
718 * merge_across_nodes be switched - there is no need to panic.
720 err = -EBUSY;
721 } else {
723 * The stable node did not yet appear stale to get_ksm_page(),
724 * since that allows for an unmapped ksm page to be recognized
725 * right up until it is freed; but the node is safe to remove.
726 * This page might be in a pagevec waiting to be freed,
727 * or it might be PageSwapCache (perhaps under writeback),
728 * or it might have been removed from swapcache a moment ago.
730 set_page_stable_node(page, NULL);
731 remove_node_from_stable_tree(stable_node);
732 err = 0;
735 unlock_page(page);
736 put_page(page);
737 return err;
740 static int remove_all_stable_nodes(void)
742 struct stable_node *stable_node;
743 struct list_head *this, *next;
744 int nid;
745 int err = 0;
747 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
748 while (root_stable_tree[nid].rb_node) {
749 stable_node = rb_entry(root_stable_tree[nid].rb_node,
750 struct stable_node, node);
751 if (remove_stable_node(stable_node)) {
752 err = -EBUSY;
753 break; /* proceed to next nid */
755 cond_resched();
758 list_for_each_safe(this, next, &migrate_nodes) {
759 stable_node = list_entry(this, struct stable_node, list);
760 if (remove_stable_node(stable_node))
761 err = -EBUSY;
762 cond_resched();
764 return err;
767 static int unmerge_and_remove_all_rmap_items(void)
769 struct mm_slot *mm_slot;
770 struct mm_struct *mm;
771 struct vm_area_struct *vma;
772 int err = 0;
774 spin_lock(&ksm_mmlist_lock);
775 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
776 struct mm_slot, mm_list);
777 spin_unlock(&ksm_mmlist_lock);
779 for (mm_slot = ksm_scan.mm_slot;
780 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
781 mm = mm_slot->mm;
782 down_read(&mm->mmap_sem);
783 for (vma = mm->mmap; vma; vma = vma->vm_next) {
784 if (ksm_test_exit(mm))
785 break;
786 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
787 continue;
788 err = unmerge_ksm_pages(vma,
789 vma->vm_start, vma->vm_end);
790 if (err)
791 goto error;
794 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
796 spin_lock(&ksm_mmlist_lock);
797 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
798 struct mm_slot, mm_list);
799 if (ksm_test_exit(mm)) {
800 hash_del(&mm_slot->link);
801 list_del(&mm_slot->mm_list);
802 spin_unlock(&ksm_mmlist_lock);
804 free_mm_slot(mm_slot);
805 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
806 up_read(&mm->mmap_sem);
807 mmdrop(mm);
808 } else {
809 spin_unlock(&ksm_mmlist_lock);
810 up_read(&mm->mmap_sem);
814 /* Clean up stable nodes, but don't worry if some are still busy */
815 remove_all_stable_nodes();
816 ksm_scan.seqnr = 0;
817 return 0;
819 error:
820 up_read(&mm->mmap_sem);
821 spin_lock(&ksm_mmlist_lock);
822 ksm_scan.mm_slot = &ksm_mm_head;
823 spin_unlock(&ksm_mmlist_lock);
824 return err;
826 #endif /* CONFIG_SYSFS */
828 static u32 calc_checksum(struct page *page)
830 u32 checksum;
831 void *addr = kmap_atomic(page);
832 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
833 kunmap_atomic(addr);
834 return checksum;
837 static int memcmp_pages(struct page *page1, struct page *page2)
839 char *addr1, *addr2;
840 int ret;
842 addr1 = kmap_atomic(page1);
843 addr2 = kmap_atomic(page2);
844 ret = memcmp(addr1, addr2, PAGE_SIZE);
845 kunmap_atomic(addr2);
846 kunmap_atomic(addr1);
847 return ret;
850 static inline int pages_identical(struct page *page1, struct page *page2)
852 return !memcmp_pages(page1, page2);
855 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
856 pte_t *orig_pte)
858 struct mm_struct *mm = vma->vm_mm;
859 unsigned long addr;
860 pte_t *ptep;
861 spinlock_t *ptl;
862 int swapped;
863 int err = -EFAULT;
864 unsigned long mmun_start; /* For mmu_notifiers */
865 unsigned long mmun_end; /* For mmu_notifiers */
867 addr = page_address_in_vma(page, vma);
868 if (addr == -EFAULT)
869 goto out;
871 BUG_ON(PageTransCompound(page));
873 mmun_start = addr;
874 mmun_end = addr + PAGE_SIZE;
875 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
877 ptep = page_check_address(page, mm, addr, &ptl, 0);
878 if (!ptep)
879 goto out_mn;
881 if (pte_write(*ptep) || pte_dirty(*ptep)) {
882 pte_t entry;
884 swapped = PageSwapCache(page);
885 flush_cache_page(vma, addr, page_to_pfn(page));
887 * Ok this is tricky, when get_user_pages_fast() run it doesn't
888 * take any lock, therefore the check that we are going to make
889 * with the pagecount against the mapcount is racey and
890 * O_DIRECT can happen right after the check.
891 * So we clear the pte and flush the tlb before the check
892 * this assure us that no O_DIRECT can happen after the check
893 * or in the middle of the check.
895 entry = ptep_clear_flush(vma, addr, ptep);
897 * Check that no O_DIRECT or similar I/O is in progress on the
898 * page
900 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
901 set_pte_at(mm, addr, ptep, entry);
902 goto out_unlock;
904 if (pte_dirty(entry))
905 set_page_dirty(page);
906 entry = pte_mkclean(pte_wrprotect(entry));
907 set_pte_at_notify(mm, addr, ptep, entry);
909 *orig_pte = *ptep;
910 err = 0;
912 out_unlock:
913 pte_unmap_unlock(ptep, ptl);
914 out_mn:
915 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
916 out:
917 return err;
921 * replace_page - replace page in vma by new ksm page
922 * @vma: vma that holds the pte pointing to page
923 * @page: the page we are replacing by kpage
924 * @kpage: the ksm page we replace page by
925 * @orig_pte: the original value of the pte
927 * Returns 0 on success, -EFAULT on failure.
929 static int replace_page(struct vm_area_struct *vma, struct page *page,
930 struct page *kpage, pte_t orig_pte)
932 struct mm_struct *mm = vma->vm_mm;
933 pmd_t *pmd;
934 pte_t *ptep;
935 spinlock_t *ptl;
936 unsigned long addr;
937 int err = -EFAULT;
938 unsigned long mmun_start; /* For mmu_notifiers */
939 unsigned long mmun_end; /* For mmu_notifiers */
941 addr = page_address_in_vma(page, vma);
942 if (addr == -EFAULT)
943 goto out;
945 pmd = mm_find_pmd(mm, addr);
946 if (!pmd)
947 goto out;
948 BUG_ON(pmd_trans_huge(*pmd));
950 mmun_start = addr;
951 mmun_end = addr + PAGE_SIZE;
952 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
954 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
955 if (!pte_same(*ptep, orig_pte)) {
956 pte_unmap_unlock(ptep, ptl);
957 goto out_mn;
960 get_page(kpage);
961 page_add_anon_rmap(kpage, vma, addr);
963 flush_cache_page(vma, addr, pte_pfn(*ptep));
964 ptep_clear_flush(vma, addr, ptep);
965 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
967 page_remove_rmap(page);
968 if (!page_mapped(page))
969 try_to_free_swap(page);
970 put_page(page);
972 pte_unmap_unlock(ptep, ptl);
973 err = 0;
974 out_mn:
975 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
976 out:
977 return err;
980 static int page_trans_compound_anon_split(struct page *page)
982 int ret = 0;
983 struct page *transhuge_head = page_trans_compound_anon(page);
984 if (transhuge_head) {
985 /* Get the reference on the head to split it. */
986 if (get_page_unless_zero(transhuge_head)) {
988 * Recheck we got the reference while the head
989 * was still anonymous.
991 if (PageAnon(transhuge_head))
992 ret = split_huge_page(transhuge_head);
993 else
995 * Retry later if split_huge_page run
996 * from under us.
998 ret = 1;
999 put_page(transhuge_head);
1000 } else
1001 /* Retry later if split_huge_page run from under us. */
1002 ret = 1;
1004 return ret;
1008 * try_to_merge_one_page - take two pages and merge them into one
1009 * @vma: the vma that holds the pte pointing to page
1010 * @page: the PageAnon page that we want to replace with kpage
1011 * @kpage: the PageKsm page that we want to map instead of page,
1012 * or NULL the first time when we want to use page as kpage.
1014 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1016 static int try_to_merge_one_page(struct vm_area_struct *vma,
1017 struct page *page, struct page *kpage)
1019 pte_t orig_pte = __pte(0);
1020 int err = -EFAULT;
1022 if (page == kpage) /* ksm page forked */
1023 return 0;
1025 if (!(vma->vm_flags & VM_MERGEABLE))
1026 goto out;
1027 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
1028 goto out;
1029 BUG_ON(PageTransCompound(page));
1030 if (!PageAnon(page))
1031 goto out;
1034 * We need the page lock to read a stable PageSwapCache in
1035 * write_protect_page(). We use trylock_page() instead of
1036 * lock_page() because we don't want to wait here - we
1037 * prefer to continue scanning and merging different pages,
1038 * then come back to this page when it is unlocked.
1040 if (!trylock_page(page))
1041 goto out;
1043 * If this anonymous page is mapped only here, its pte may need
1044 * to be write-protected. If it's mapped elsewhere, all of its
1045 * ptes are necessarily already write-protected. But in either
1046 * case, we need to lock and check page_count is not raised.
1048 if (write_protect_page(vma, page, &orig_pte) == 0) {
1049 if (!kpage) {
1051 * While we hold page lock, upgrade page from
1052 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1053 * stable_tree_insert() will update stable_node.
1055 set_page_stable_node(page, NULL);
1056 mark_page_accessed(page);
1057 err = 0;
1058 } else if (pages_identical(page, kpage))
1059 err = replace_page(vma, page, kpage, orig_pte);
1062 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1063 munlock_vma_page(page);
1064 if (!PageMlocked(kpage)) {
1065 unlock_page(page);
1066 lock_page(kpage);
1067 mlock_vma_page(kpage);
1068 page = kpage; /* for final unlock */
1072 unlock_page(page);
1073 out:
1074 return err;
1078 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1079 * but no new kernel page is allocated: kpage must already be a ksm page.
1081 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1083 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1084 struct page *page, struct page *kpage)
1086 struct mm_struct *mm = rmap_item->mm;
1087 struct vm_area_struct *vma;
1088 int err = -EFAULT;
1090 down_read(&mm->mmap_sem);
1091 if (ksm_test_exit(mm))
1092 goto out;
1093 vma = find_vma(mm, rmap_item->address);
1094 if (!vma || vma->vm_start > rmap_item->address)
1095 goto out;
1097 err = try_to_merge_one_page(vma, page, kpage);
1098 if (err)
1099 goto out;
1101 /* Unstable nid is in union with stable anon_vma: remove first */
1102 remove_rmap_item_from_tree(rmap_item);
1104 /* Must get reference to anon_vma while still holding mmap_sem */
1105 rmap_item->anon_vma = vma->anon_vma;
1106 get_anon_vma(vma->anon_vma);
1107 out:
1108 up_read(&mm->mmap_sem);
1109 return err;
1113 * try_to_merge_two_pages - take two identical pages and prepare them
1114 * to be merged into one page.
1116 * This function returns the kpage if we successfully merged two identical
1117 * pages into one ksm page, NULL otherwise.
1119 * Note that this function upgrades page to ksm page: if one of the pages
1120 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1122 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1123 struct page *page,
1124 struct rmap_item *tree_rmap_item,
1125 struct page *tree_page)
1127 int err;
1129 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1130 if (!err) {
1131 err = try_to_merge_with_ksm_page(tree_rmap_item,
1132 tree_page, page);
1134 * If that fails, we have a ksm page with only one pte
1135 * pointing to it: so break it.
1137 if (err)
1138 break_cow(rmap_item);
1140 return err ? NULL : page;
1144 * stable_tree_search - search for page inside the stable tree
1146 * This function checks if there is a page inside the stable tree
1147 * with identical content to the page that we are scanning right now.
1149 * This function returns the stable tree node of identical content if found,
1150 * NULL otherwise.
1152 static struct page *stable_tree_search(struct page *page)
1154 int nid;
1155 struct rb_root *root;
1156 struct rb_node **new;
1157 struct rb_node *parent;
1158 struct stable_node *stable_node;
1159 struct stable_node *page_node;
1161 page_node = page_stable_node(page);
1162 if (page_node && page_node->head != &migrate_nodes) {
1163 /* ksm page forked */
1164 get_page(page);
1165 return page;
1168 nid = get_kpfn_nid(page_to_pfn(page));
1169 root = root_stable_tree + nid;
1170 again:
1171 new = &root->rb_node;
1172 parent = NULL;
1174 while (*new) {
1175 struct page *tree_page;
1176 int ret;
1178 cond_resched();
1179 stable_node = rb_entry(*new, struct stable_node, node);
1180 tree_page = get_ksm_page(stable_node, false);
1181 if (!tree_page)
1182 return NULL;
1184 ret = memcmp_pages(page, tree_page);
1185 put_page(tree_page);
1187 parent = *new;
1188 if (ret < 0)
1189 new = &parent->rb_left;
1190 else if (ret > 0)
1191 new = &parent->rb_right;
1192 else {
1194 * Lock and unlock the stable_node's page (which
1195 * might already have been migrated) so that page
1196 * migration is sure to notice its raised count.
1197 * It would be more elegant to return stable_node
1198 * than kpage, but that involves more changes.
1200 tree_page = get_ksm_page(stable_node, true);
1201 if (tree_page) {
1202 unlock_page(tree_page);
1203 if (get_kpfn_nid(stable_node->kpfn) !=
1204 NUMA(stable_node->nid)) {
1205 put_page(tree_page);
1206 goto replace;
1208 return tree_page;
1211 * There is now a place for page_node, but the tree may
1212 * have been rebalanced, so re-evaluate parent and new.
1214 if (page_node)
1215 goto again;
1216 return NULL;
1220 if (!page_node)
1221 return NULL;
1223 list_del(&page_node->list);
1224 DO_NUMA(page_node->nid = nid);
1225 rb_link_node(&page_node->node, parent, new);
1226 rb_insert_color(&page_node->node, root);
1227 get_page(page);
1228 return page;
1230 replace:
1231 if (page_node) {
1232 list_del(&page_node->list);
1233 DO_NUMA(page_node->nid = nid);
1234 rb_replace_node(&stable_node->node, &page_node->node, root);
1235 get_page(page);
1236 } else {
1237 rb_erase(&stable_node->node, root);
1238 page = NULL;
1240 stable_node->head = &migrate_nodes;
1241 list_add(&stable_node->list, stable_node->head);
1242 return page;
1246 * stable_tree_insert - insert stable tree node pointing to new ksm page
1247 * into the stable tree.
1249 * This function returns the stable tree node just allocated on success,
1250 * NULL otherwise.
1252 static struct stable_node *stable_tree_insert(struct page *kpage)
1254 int nid;
1255 unsigned long kpfn;
1256 struct rb_root *root;
1257 struct rb_node **new;
1258 struct rb_node *parent = NULL;
1259 struct stable_node *stable_node;
1261 kpfn = page_to_pfn(kpage);
1262 nid = get_kpfn_nid(kpfn);
1263 root = root_stable_tree + nid;
1264 new = &root->rb_node;
1266 while (*new) {
1267 struct page *tree_page;
1268 int ret;
1270 cond_resched();
1271 stable_node = rb_entry(*new, struct stable_node, node);
1272 tree_page = get_ksm_page(stable_node, false);
1273 if (!tree_page)
1274 return NULL;
1276 ret = memcmp_pages(kpage, tree_page);
1277 put_page(tree_page);
1279 parent = *new;
1280 if (ret < 0)
1281 new = &parent->rb_left;
1282 else if (ret > 0)
1283 new = &parent->rb_right;
1284 else {
1286 * It is not a bug that stable_tree_search() didn't
1287 * find this node: because at that time our page was
1288 * not yet write-protected, so may have changed since.
1290 return NULL;
1294 stable_node = alloc_stable_node();
1295 if (!stable_node)
1296 return NULL;
1298 INIT_HLIST_HEAD(&stable_node->hlist);
1299 stable_node->kpfn = kpfn;
1300 set_page_stable_node(kpage, stable_node);
1301 DO_NUMA(stable_node->nid = nid);
1302 rb_link_node(&stable_node->node, parent, new);
1303 rb_insert_color(&stable_node->node, root);
1305 return stable_node;
1309 * unstable_tree_search_insert - search for identical page,
1310 * else insert rmap_item into the unstable tree.
1312 * This function searches for a page in the unstable tree identical to the
1313 * page currently being scanned; and if no identical page is found in the
1314 * tree, we insert rmap_item as a new object into the unstable tree.
1316 * This function returns pointer to rmap_item found to be identical
1317 * to the currently scanned page, NULL otherwise.
1319 * This function does both searching and inserting, because they share
1320 * the same walking algorithm in an rbtree.
1322 static
1323 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1324 struct page *page,
1325 struct page **tree_pagep)
1327 struct rb_node **new;
1328 struct rb_root *root;
1329 struct rb_node *parent = NULL;
1330 int nid;
1332 nid = get_kpfn_nid(page_to_pfn(page));
1333 root = root_unstable_tree + nid;
1334 new = &root->rb_node;
1336 while (*new) {
1337 struct rmap_item *tree_rmap_item;
1338 struct page *tree_page;
1339 int ret;
1341 cond_resched();
1342 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1343 tree_page = get_mergeable_page(tree_rmap_item);
1344 if (IS_ERR_OR_NULL(tree_page))
1345 return NULL;
1348 * Don't substitute a ksm page for a forked page.
1350 if (page == tree_page) {
1351 put_page(tree_page);
1352 return NULL;
1355 ret = memcmp_pages(page, tree_page);
1357 parent = *new;
1358 if (ret < 0) {
1359 put_page(tree_page);
1360 new = &parent->rb_left;
1361 } else if (ret > 0) {
1362 put_page(tree_page);
1363 new = &parent->rb_right;
1364 } else if (!ksm_merge_across_nodes &&
1365 page_to_nid(tree_page) != nid) {
1367 * If tree_page has been migrated to another NUMA node,
1368 * it will be flushed out and put in the right unstable
1369 * tree next time: only merge with it when across_nodes.
1371 put_page(tree_page);
1372 return NULL;
1373 } else {
1374 *tree_pagep = tree_page;
1375 return tree_rmap_item;
1379 rmap_item->address |= UNSTABLE_FLAG;
1380 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1381 DO_NUMA(rmap_item->nid = nid);
1382 rb_link_node(&rmap_item->node, parent, new);
1383 rb_insert_color(&rmap_item->node, root);
1385 ksm_pages_unshared++;
1386 return NULL;
1390 * stable_tree_append - add another rmap_item to the linked list of
1391 * rmap_items hanging off a given node of the stable tree, all sharing
1392 * the same ksm page.
1394 static void stable_tree_append(struct rmap_item *rmap_item,
1395 struct stable_node *stable_node)
1397 rmap_item->head = stable_node;
1398 rmap_item->address |= STABLE_FLAG;
1399 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1401 if (rmap_item->hlist.next)
1402 ksm_pages_sharing++;
1403 else
1404 ksm_pages_shared++;
1408 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1409 * if not, compare checksum to previous and if it's the same, see if page can
1410 * be inserted into the unstable tree, or merged with a page already there and
1411 * both transferred to the stable tree.
1413 * @page: the page that we are searching identical page to.
1414 * @rmap_item: the reverse mapping into the virtual address of this page
1416 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1418 struct rmap_item *tree_rmap_item;
1419 struct page *tree_page = NULL;
1420 struct stable_node *stable_node;
1421 struct page *kpage;
1422 unsigned int checksum;
1423 int err;
1425 stable_node = page_stable_node(page);
1426 if (stable_node) {
1427 if (stable_node->head != &migrate_nodes &&
1428 get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1429 rb_erase(&stable_node->node,
1430 root_stable_tree + NUMA(stable_node->nid));
1431 stable_node->head = &migrate_nodes;
1432 list_add(&stable_node->list, stable_node->head);
1434 if (stable_node->head != &migrate_nodes &&
1435 rmap_item->head == stable_node)
1436 return;
1439 /* We first start with searching the page inside the stable tree */
1440 kpage = stable_tree_search(page);
1441 if (kpage == page && rmap_item->head == stable_node) {
1442 put_page(kpage);
1443 return;
1446 remove_rmap_item_from_tree(rmap_item);
1448 if (kpage) {
1449 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1450 if (!err) {
1452 * The page was successfully merged:
1453 * add its rmap_item to the stable tree.
1455 lock_page(kpage);
1456 stable_tree_append(rmap_item, page_stable_node(kpage));
1457 unlock_page(kpage);
1459 put_page(kpage);
1460 return;
1464 * If the hash value of the page has changed from the last time
1465 * we calculated it, this page is changing frequently: therefore we
1466 * don't want to insert it in the unstable tree, and we don't want
1467 * to waste our time searching for something identical to it there.
1469 checksum = calc_checksum(page);
1470 if (rmap_item->oldchecksum != checksum) {
1471 rmap_item->oldchecksum = checksum;
1472 return;
1475 tree_rmap_item =
1476 unstable_tree_search_insert(rmap_item, page, &tree_page);
1477 if (tree_rmap_item) {
1478 kpage = try_to_merge_two_pages(rmap_item, page,
1479 tree_rmap_item, tree_page);
1480 put_page(tree_page);
1481 if (kpage) {
1483 * The pages were successfully merged: insert new
1484 * node in the stable tree and add both rmap_items.
1486 lock_page(kpage);
1487 stable_node = stable_tree_insert(kpage);
1488 if (stable_node) {
1489 stable_tree_append(tree_rmap_item, stable_node);
1490 stable_tree_append(rmap_item, stable_node);
1492 unlock_page(kpage);
1495 * If we fail to insert the page into the stable tree,
1496 * we will have 2 virtual addresses that are pointing
1497 * to a ksm page left outside the stable tree,
1498 * in which case we need to break_cow on both.
1500 if (!stable_node) {
1501 break_cow(tree_rmap_item);
1502 break_cow(rmap_item);
1508 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1509 struct rmap_item **rmap_list,
1510 unsigned long addr)
1512 struct rmap_item *rmap_item;
1514 while (*rmap_list) {
1515 rmap_item = *rmap_list;
1516 if ((rmap_item->address & PAGE_MASK) == addr)
1517 return rmap_item;
1518 if (rmap_item->address > addr)
1519 break;
1520 *rmap_list = rmap_item->rmap_list;
1521 remove_rmap_item_from_tree(rmap_item);
1522 free_rmap_item(rmap_item);
1525 rmap_item = alloc_rmap_item();
1526 if (rmap_item) {
1527 /* It has already been zeroed */
1528 rmap_item->mm = mm_slot->mm;
1529 rmap_item->address = addr;
1530 rmap_item->rmap_list = *rmap_list;
1531 *rmap_list = rmap_item;
1533 return rmap_item;
1536 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1538 struct mm_struct *mm;
1539 struct mm_slot *slot;
1540 struct vm_area_struct *vma;
1541 struct rmap_item *rmap_item;
1542 int nid;
1544 if (list_empty(&ksm_mm_head.mm_list))
1545 return NULL;
1547 slot = ksm_scan.mm_slot;
1548 if (slot == &ksm_mm_head) {
1550 * A number of pages can hang around indefinitely on per-cpu
1551 * pagevecs, raised page count preventing write_protect_page
1552 * from merging them. Though it doesn't really matter much,
1553 * it is puzzling to see some stuck in pages_volatile until
1554 * other activity jostles them out, and they also prevented
1555 * LTP's KSM test from succeeding deterministically; so drain
1556 * them here (here rather than on entry to ksm_do_scan(),
1557 * so we don't IPI too often when pages_to_scan is set low).
1559 lru_add_drain_all();
1562 * Whereas stale stable_nodes on the stable_tree itself
1563 * get pruned in the regular course of stable_tree_search(),
1564 * those moved out to the migrate_nodes list can accumulate:
1565 * so prune them once before each full scan.
1567 if (!ksm_merge_across_nodes) {
1568 struct stable_node *stable_node;
1569 struct list_head *this, *next;
1570 struct page *page;
1572 list_for_each_safe(this, next, &migrate_nodes) {
1573 stable_node = list_entry(this,
1574 struct stable_node, list);
1575 page = get_ksm_page(stable_node, false);
1576 if (page)
1577 put_page(page);
1578 cond_resched();
1582 for (nid = 0; nid < ksm_nr_node_ids; nid++)
1583 root_unstable_tree[nid] = RB_ROOT;
1585 spin_lock(&ksm_mmlist_lock);
1586 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1587 ksm_scan.mm_slot = slot;
1588 spin_unlock(&ksm_mmlist_lock);
1590 * Although we tested list_empty() above, a racing __ksm_exit
1591 * of the last mm on the list may have removed it since then.
1593 if (slot == &ksm_mm_head)
1594 return NULL;
1595 next_mm:
1596 ksm_scan.address = 0;
1597 ksm_scan.rmap_list = &slot->rmap_list;
1600 mm = slot->mm;
1601 down_read(&mm->mmap_sem);
1602 if (ksm_test_exit(mm))
1603 vma = NULL;
1604 else
1605 vma = find_vma(mm, ksm_scan.address);
1607 for (; vma; vma = vma->vm_next) {
1608 if (!(vma->vm_flags & VM_MERGEABLE))
1609 continue;
1610 if (ksm_scan.address < vma->vm_start)
1611 ksm_scan.address = vma->vm_start;
1612 if (!vma->anon_vma)
1613 ksm_scan.address = vma->vm_end;
1615 while (ksm_scan.address < vma->vm_end) {
1616 if (ksm_test_exit(mm))
1617 break;
1618 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1619 if (IS_ERR_OR_NULL(*page)) {
1620 ksm_scan.address += PAGE_SIZE;
1621 cond_resched();
1622 continue;
1624 if (PageAnon(*page) ||
1625 page_trans_compound_anon(*page)) {
1626 flush_anon_page(vma, *page, ksm_scan.address);
1627 flush_dcache_page(*page);
1628 rmap_item = get_next_rmap_item(slot,
1629 ksm_scan.rmap_list, ksm_scan.address);
1630 if (rmap_item) {
1631 ksm_scan.rmap_list =
1632 &rmap_item->rmap_list;
1633 ksm_scan.address += PAGE_SIZE;
1634 } else
1635 put_page(*page);
1636 up_read(&mm->mmap_sem);
1637 return rmap_item;
1639 put_page(*page);
1640 ksm_scan.address += PAGE_SIZE;
1641 cond_resched();
1645 if (ksm_test_exit(mm)) {
1646 ksm_scan.address = 0;
1647 ksm_scan.rmap_list = &slot->rmap_list;
1650 * Nuke all the rmap_items that are above this current rmap:
1651 * because there were no VM_MERGEABLE vmas with such addresses.
1653 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1655 spin_lock(&ksm_mmlist_lock);
1656 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1657 struct mm_slot, mm_list);
1658 if (ksm_scan.address == 0) {
1660 * We've completed a full scan of all vmas, holding mmap_sem
1661 * throughout, and found no VM_MERGEABLE: so do the same as
1662 * __ksm_exit does to remove this mm from all our lists now.
1663 * This applies either when cleaning up after __ksm_exit
1664 * (but beware: we can reach here even before __ksm_exit),
1665 * or when all VM_MERGEABLE areas have been unmapped (and
1666 * mmap_sem then protects against race with MADV_MERGEABLE).
1668 hash_del(&slot->link);
1669 list_del(&slot->mm_list);
1670 spin_unlock(&ksm_mmlist_lock);
1672 free_mm_slot(slot);
1673 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1674 up_read(&mm->mmap_sem);
1675 mmdrop(mm);
1676 } else {
1677 spin_unlock(&ksm_mmlist_lock);
1678 up_read(&mm->mmap_sem);
1681 /* Repeat until we've completed scanning the whole list */
1682 slot = ksm_scan.mm_slot;
1683 if (slot != &ksm_mm_head)
1684 goto next_mm;
1686 ksm_scan.seqnr++;
1687 return NULL;
1691 * ksm_do_scan - the ksm scanner main worker function.
1692 * @scan_npages - number of pages we want to scan before we return.
1694 static void ksm_do_scan(unsigned int scan_npages)
1696 struct rmap_item *rmap_item;
1697 struct page *uninitialized_var(page);
1699 while (scan_npages-- && likely(!freezing(current))) {
1700 cond_resched();
1701 rmap_item = scan_get_next_rmap_item(&page);
1702 if (!rmap_item)
1703 return;
1704 cmp_and_merge_page(page, rmap_item);
1705 put_page(page);
1709 static int ksmd_should_run(void)
1711 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1714 static int ksm_scan_thread(void *nothing)
1716 set_freezable();
1717 set_user_nice(current, 5);
1719 while (!kthread_should_stop()) {
1720 mutex_lock(&ksm_thread_mutex);
1721 wait_while_offlining();
1722 if (ksmd_should_run())
1723 ksm_do_scan(ksm_thread_pages_to_scan);
1724 mutex_unlock(&ksm_thread_mutex);
1726 try_to_freeze();
1728 if (ksmd_should_run()) {
1729 schedule_timeout_interruptible(
1730 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1731 } else {
1732 wait_event_freezable(ksm_thread_wait,
1733 ksmd_should_run() || kthread_should_stop());
1736 return 0;
1739 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1740 unsigned long end, int advice, unsigned long *vm_flags)
1742 struct mm_struct *mm = vma->vm_mm;
1743 int err;
1745 switch (advice) {
1746 case MADV_MERGEABLE:
1748 * Be somewhat over-protective for now!
1750 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1751 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1752 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
1753 return 0; /* just ignore the advice */
1755 #ifdef VM_SAO
1756 if (*vm_flags & VM_SAO)
1757 return 0;
1758 #endif
1760 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1761 err = __ksm_enter(mm);
1762 if (err)
1763 return err;
1766 *vm_flags |= VM_MERGEABLE;
1767 break;
1769 case MADV_UNMERGEABLE:
1770 if (!(*vm_flags & VM_MERGEABLE))
1771 return 0; /* just ignore the advice */
1773 if (vma->anon_vma) {
1774 err = unmerge_ksm_pages(vma, start, end);
1775 if (err)
1776 return err;
1779 *vm_flags &= ~VM_MERGEABLE;
1780 break;
1783 return 0;
1786 int __ksm_enter(struct mm_struct *mm)
1788 struct mm_slot *mm_slot;
1789 int needs_wakeup;
1791 mm_slot = alloc_mm_slot();
1792 if (!mm_slot)
1793 return -ENOMEM;
1795 /* Check ksm_run too? Would need tighter locking */
1796 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1798 spin_lock(&ksm_mmlist_lock);
1799 insert_to_mm_slots_hash(mm, mm_slot);
1801 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1802 * insert just behind the scanning cursor, to let the area settle
1803 * down a little; when fork is followed by immediate exec, we don't
1804 * want ksmd to waste time setting up and tearing down an rmap_list.
1806 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1807 * scanning cursor, otherwise KSM pages in newly forked mms will be
1808 * missed: then we might as well insert at the end of the list.
1810 if (ksm_run & KSM_RUN_UNMERGE)
1811 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1812 else
1813 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1814 spin_unlock(&ksm_mmlist_lock);
1816 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1817 atomic_inc(&mm->mm_count);
1819 if (needs_wakeup)
1820 wake_up_interruptible(&ksm_thread_wait);
1822 return 0;
1825 void __ksm_exit(struct mm_struct *mm)
1827 struct mm_slot *mm_slot;
1828 int easy_to_free = 0;
1831 * This process is exiting: if it's straightforward (as is the
1832 * case when ksmd was never running), free mm_slot immediately.
1833 * But if it's at the cursor or has rmap_items linked to it, use
1834 * mmap_sem to synchronize with any break_cows before pagetables
1835 * are freed, and leave the mm_slot on the list for ksmd to free.
1836 * Beware: ksm may already have noticed it exiting and freed the slot.
1839 spin_lock(&ksm_mmlist_lock);
1840 mm_slot = get_mm_slot(mm);
1841 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1842 if (!mm_slot->rmap_list) {
1843 hash_del(&mm_slot->link);
1844 list_del(&mm_slot->mm_list);
1845 easy_to_free = 1;
1846 } else {
1847 list_move(&mm_slot->mm_list,
1848 &ksm_scan.mm_slot->mm_list);
1851 spin_unlock(&ksm_mmlist_lock);
1853 if (easy_to_free) {
1854 free_mm_slot(mm_slot);
1855 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1856 mmdrop(mm);
1857 } else if (mm_slot) {
1858 down_write(&mm->mmap_sem);
1859 up_write(&mm->mmap_sem);
1863 struct page *ksm_might_need_to_copy(struct page *page,
1864 struct vm_area_struct *vma, unsigned long address)
1866 struct anon_vma *anon_vma = page_anon_vma(page);
1867 struct page *new_page;
1869 if (PageKsm(page)) {
1870 if (page_stable_node(page) &&
1871 !(ksm_run & KSM_RUN_UNMERGE))
1872 return page; /* no need to copy it */
1873 } else if (!anon_vma) {
1874 return page; /* no need to copy it */
1875 } else if (anon_vma->root == vma->anon_vma->root &&
1876 page->index == linear_page_index(vma, address)) {
1877 return page; /* still no need to copy it */
1879 if (!PageUptodate(page))
1880 return page; /* let do_swap_page report the error */
1882 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1883 if (new_page) {
1884 copy_user_highpage(new_page, page, address, vma);
1886 SetPageDirty(new_page);
1887 __SetPageUptodate(new_page);
1888 __set_page_locked(new_page);
1891 return new_page;
1894 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1895 unsigned long *vm_flags)
1897 struct stable_node *stable_node;
1898 struct rmap_item *rmap_item;
1899 unsigned int mapcount = page_mapcount(page);
1900 int referenced = 0;
1901 int search_new_forks = 0;
1903 VM_BUG_ON(!PageKsm(page));
1904 VM_BUG_ON(!PageLocked(page));
1906 stable_node = page_stable_node(page);
1907 if (!stable_node)
1908 return 0;
1909 again:
1910 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1911 struct anon_vma *anon_vma = rmap_item->anon_vma;
1912 struct anon_vma_chain *vmac;
1913 struct vm_area_struct *vma;
1915 anon_vma_lock_read(anon_vma);
1916 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1917 0, ULONG_MAX) {
1918 vma = vmac->vma;
1919 if (rmap_item->address < vma->vm_start ||
1920 rmap_item->address >= vma->vm_end)
1921 continue;
1923 * Initially we examine only the vma which covers this
1924 * rmap_item; but later, if there is still work to do,
1925 * we examine covering vmas in other mms: in case they
1926 * were forked from the original since ksmd passed.
1928 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1929 continue;
1931 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1932 continue;
1934 referenced += page_referenced_one(page, vma,
1935 rmap_item->address, &mapcount, vm_flags);
1936 if (!search_new_forks || !mapcount)
1937 break;
1939 anon_vma_unlock_read(anon_vma);
1940 if (!mapcount)
1941 goto out;
1943 if (!search_new_forks++)
1944 goto again;
1945 out:
1946 return referenced;
1949 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1951 struct stable_node *stable_node;
1952 struct rmap_item *rmap_item;
1953 int ret = SWAP_AGAIN;
1954 int search_new_forks = 0;
1956 VM_BUG_ON(!PageKsm(page));
1957 VM_BUG_ON(!PageLocked(page));
1959 stable_node = page_stable_node(page);
1960 if (!stable_node)
1961 return SWAP_FAIL;
1962 again:
1963 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1964 struct anon_vma *anon_vma = rmap_item->anon_vma;
1965 struct anon_vma_chain *vmac;
1966 struct vm_area_struct *vma;
1968 anon_vma_lock_read(anon_vma);
1969 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1970 0, ULONG_MAX) {
1971 vma = vmac->vma;
1972 if (rmap_item->address < vma->vm_start ||
1973 rmap_item->address >= vma->vm_end)
1974 continue;
1976 * Initially we examine only the vma which covers this
1977 * rmap_item; but later, if there is still work to do,
1978 * we examine covering vmas in other mms: in case they
1979 * were forked from the original since ksmd passed.
1981 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1982 continue;
1984 ret = try_to_unmap_one(page, vma,
1985 rmap_item->address, flags);
1986 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1987 anon_vma_unlock_read(anon_vma);
1988 goto out;
1991 anon_vma_unlock_read(anon_vma);
1993 if (!search_new_forks++)
1994 goto again;
1995 out:
1996 return ret;
1999 #ifdef CONFIG_MIGRATION
2000 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
2001 struct vm_area_struct *, unsigned long, void *), void *arg)
2003 struct stable_node *stable_node;
2004 struct rmap_item *rmap_item;
2005 int ret = SWAP_AGAIN;
2006 int search_new_forks = 0;
2008 VM_BUG_ON(!PageKsm(page));
2009 VM_BUG_ON(!PageLocked(page));
2011 stable_node = page_stable_node(page);
2012 if (!stable_node)
2013 return ret;
2014 again:
2015 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2016 struct anon_vma *anon_vma = rmap_item->anon_vma;
2017 struct anon_vma_chain *vmac;
2018 struct vm_area_struct *vma;
2020 anon_vma_lock_read(anon_vma);
2021 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2022 0, ULONG_MAX) {
2023 vma = vmac->vma;
2024 if (rmap_item->address < vma->vm_start ||
2025 rmap_item->address >= vma->vm_end)
2026 continue;
2028 * Initially we examine only the vma which covers this
2029 * rmap_item; but later, if there is still work to do,
2030 * we examine covering vmas in other mms: in case they
2031 * were forked from the original since ksmd passed.
2033 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2034 continue;
2036 ret = rmap_one(page, vma, rmap_item->address, arg);
2037 if (ret != SWAP_AGAIN) {
2038 anon_vma_unlock_read(anon_vma);
2039 goto out;
2042 anon_vma_unlock_read(anon_vma);
2044 if (!search_new_forks++)
2045 goto again;
2046 out:
2047 return ret;
2050 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2052 struct stable_node *stable_node;
2054 VM_BUG_ON(!PageLocked(oldpage));
2055 VM_BUG_ON(!PageLocked(newpage));
2056 VM_BUG_ON(newpage->mapping != oldpage->mapping);
2058 stable_node = page_stable_node(newpage);
2059 if (stable_node) {
2060 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
2061 stable_node->kpfn = page_to_pfn(newpage);
2063 * newpage->mapping was set in advance; now we need smp_wmb()
2064 * to make sure that the new stable_node->kpfn is visible
2065 * to get_ksm_page() before it can see that oldpage->mapping
2066 * has gone stale (or that PageSwapCache has been cleared).
2068 smp_wmb();
2069 set_page_stable_node(oldpage, NULL);
2072 #endif /* CONFIG_MIGRATION */
2074 #ifdef CONFIG_MEMORY_HOTREMOVE
2075 static int just_wait(void *word)
2077 schedule();
2078 return 0;
2081 static void wait_while_offlining(void)
2083 while (ksm_run & KSM_RUN_OFFLINE) {
2084 mutex_unlock(&ksm_thread_mutex);
2085 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2086 just_wait, TASK_UNINTERRUPTIBLE);
2087 mutex_lock(&ksm_thread_mutex);
2091 static void ksm_check_stable_tree(unsigned long start_pfn,
2092 unsigned long end_pfn)
2094 struct stable_node *stable_node;
2095 struct list_head *this, *next;
2096 struct rb_node *node;
2097 int nid;
2099 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2100 node = rb_first(root_stable_tree + nid);
2101 while (node) {
2102 stable_node = rb_entry(node, struct stable_node, node);
2103 if (stable_node->kpfn >= start_pfn &&
2104 stable_node->kpfn < end_pfn) {
2106 * Don't get_ksm_page, page has already gone:
2107 * which is why we keep kpfn instead of page*
2109 remove_node_from_stable_tree(stable_node);
2110 node = rb_first(root_stable_tree + nid);
2111 } else
2112 node = rb_next(node);
2113 cond_resched();
2116 list_for_each_safe(this, next, &migrate_nodes) {
2117 stable_node = list_entry(this, struct stable_node, list);
2118 if (stable_node->kpfn >= start_pfn &&
2119 stable_node->kpfn < end_pfn)
2120 remove_node_from_stable_tree(stable_node);
2121 cond_resched();
2125 static int ksm_memory_callback(struct notifier_block *self,
2126 unsigned long action, void *arg)
2128 struct memory_notify *mn = arg;
2130 switch (action) {
2131 case MEM_GOING_OFFLINE:
2133 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2134 * and remove_all_stable_nodes() while memory is going offline:
2135 * it is unsafe for them to touch the stable tree at this time.
2136 * But unmerge_ksm_pages(), rmap lookups and other entry points
2137 * which do not need the ksm_thread_mutex are all safe.
2139 mutex_lock(&ksm_thread_mutex);
2140 ksm_run |= KSM_RUN_OFFLINE;
2141 mutex_unlock(&ksm_thread_mutex);
2142 break;
2144 case MEM_OFFLINE:
2146 * Most of the work is done by page migration; but there might
2147 * be a few stable_nodes left over, still pointing to struct
2148 * pages which have been offlined: prune those from the tree,
2149 * otherwise get_ksm_page() might later try to access a
2150 * non-existent struct page.
2152 ksm_check_stable_tree(mn->start_pfn,
2153 mn->start_pfn + mn->nr_pages);
2154 /* fallthrough */
2156 case MEM_CANCEL_OFFLINE:
2157 mutex_lock(&ksm_thread_mutex);
2158 ksm_run &= ~KSM_RUN_OFFLINE;
2159 mutex_unlock(&ksm_thread_mutex);
2161 smp_mb(); /* wake_up_bit advises this */
2162 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2163 break;
2165 return NOTIFY_OK;
2167 #else
2168 static void wait_while_offlining(void)
2171 #endif /* CONFIG_MEMORY_HOTREMOVE */
2173 #ifdef CONFIG_SYSFS
2175 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2178 #define KSM_ATTR_RO(_name) \
2179 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2180 #define KSM_ATTR(_name) \
2181 static struct kobj_attribute _name##_attr = \
2182 __ATTR(_name, 0644, _name##_show, _name##_store)
2184 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2185 struct kobj_attribute *attr, char *buf)
2187 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2190 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2191 struct kobj_attribute *attr,
2192 const char *buf, size_t count)
2194 unsigned long msecs;
2195 int err;
2197 err = strict_strtoul(buf, 10, &msecs);
2198 if (err || msecs > UINT_MAX)
2199 return -EINVAL;
2201 ksm_thread_sleep_millisecs = msecs;
2203 return count;
2205 KSM_ATTR(sleep_millisecs);
2207 static ssize_t pages_to_scan_show(struct kobject *kobj,
2208 struct kobj_attribute *attr, char *buf)
2210 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2213 static ssize_t pages_to_scan_store(struct kobject *kobj,
2214 struct kobj_attribute *attr,
2215 const char *buf, size_t count)
2217 int err;
2218 unsigned long nr_pages;
2220 err = strict_strtoul(buf, 10, &nr_pages);
2221 if (err || nr_pages > UINT_MAX)
2222 return -EINVAL;
2224 ksm_thread_pages_to_scan = nr_pages;
2226 return count;
2228 KSM_ATTR(pages_to_scan);
2230 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2231 char *buf)
2233 return sprintf(buf, "%lu\n", ksm_run);
2236 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2237 const char *buf, size_t count)
2239 int err;
2240 unsigned long flags;
2242 err = strict_strtoul(buf, 10, &flags);
2243 if (err || flags > UINT_MAX)
2244 return -EINVAL;
2245 if (flags > KSM_RUN_UNMERGE)
2246 return -EINVAL;
2249 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2250 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2251 * breaking COW to free the pages_shared (but leaves mm_slots
2252 * on the list for when ksmd may be set running again).
2255 mutex_lock(&ksm_thread_mutex);
2256 wait_while_offlining();
2257 if (ksm_run != flags) {
2258 ksm_run = flags;
2259 if (flags & KSM_RUN_UNMERGE) {
2260 set_current_oom_origin();
2261 err = unmerge_and_remove_all_rmap_items();
2262 clear_current_oom_origin();
2263 if (err) {
2264 ksm_run = KSM_RUN_STOP;
2265 count = err;
2269 mutex_unlock(&ksm_thread_mutex);
2271 if (flags & KSM_RUN_MERGE)
2272 wake_up_interruptible(&ksm_thread_wait);
2274 return count;
2276 KSM_ATTR(run);
2278 #ifdef CONFIG_NUMA
2279 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2280 struct kobj_attribute *attr, char *buf)
2282 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2285 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2286 struct kobj_attribute *attr,
2287 const char *buf, size_t count)
2289 int err;
2290 unsigned long knob;
2292 err = kstrtoul(buf, 10, &knob);
2293 if (err)
2294 return err;
2295 if (knob > 1)
2296 return -EINVAL;
2298 mutex_lock(&ksm_thread_mutex);
2299 wait_while_offlining();
2300 if (ksm_merge_across_nodes != knob) {
2301 if (ksm_pages_shared || remove_all_stable_nodes())
2302 err = -EBUSY;
2303 else if (root_stable_tree == one_stable_tree) {
2304 struct rb_root *buf;
2306 * This is the first time that we switch away from the
2307 * default of merging across nodes: must now allocate
2308 * a buffer to hold as many roots as may be needed.
2309 * Allocate stable and unstable together:
2310 * MAXSMP NODES_SHIFT 10 will use 16kB.
2312 buf = kcalloc(nr_node_ids + nr_node_ids,
2313 sizeof(*buf), GFP_KERNEL | __GFP_ZERO);
2314 /* Let us assume that RB_ROOT is NULL is zero */
2315 if (!buf)
2316 err = -ENOMEM;
2317 else {
2318 root_stable_tree = buf;
2319 root_unstable_tree = buf + nr_node_ids;
2320 /* Stable tree is empty but not the unstable */
2321 root_unstable_tree[0] = one_unstable_tree[0];
2324 if (!err) {
2325 ksm_merge_across_nodes = knob;
2326 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2329 mutex_unlock(&ksm_thread_mutex);
2331 return err ? err : count;
2333 KSM_ATTR(merge_across_nodes);
2334 #endif
2336 static ssize_t pages_shared_show(struct kobject *kobj,
2337 struct kobj_attribute *attr, char *buf)
2339 return sprintf(buf, "%lu\n", ksm_pages_shared);
2341 KSM_ATTR_RO(pages_shared);
2343 static ssize_t pages_sharing_show(struct kobject *kobj,
2344 struct kobj_attribute *attr, char *buf)
2346 return sprintf(buf, "%lu\n", ksm_pages_sharing);
2348 KSM_ATTR_RO(pages_sharing);
2350 static ssize_t pages_unshared_show(struct kobject *kobj,
2351 struct kobj_attribute *attr, char *buf)
2353 return sprintf(buf, "%lu\n", ksm_pages_unshared);
2355 KSM_ATTR_RO(pages_unshared);
2357 static ssize_t pages_volatile_show(struct kobject *kobj,
2358 struct kobj_attribute *attr, char *buf)
2360 long ksm_pages_volatile;
2362 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2363 - ksm_pages_sharing - ksm_pages_unshared;
2365 * It was not worth any locking to calculate that statistic,
2366 * but it might therefore sometimes be negative: conceal that.
2368 if (ksm_pages_volatile < 0)
2369 ksm_pages_volatile = 0;
2370 return sprintf(buf, "%ld\n", ksm_pages_volatile);
2372 KSM_ATTR_RO(pages_volatile);
2374 static ssize_t full_scans_show(struct kobject *kobj,
2375 struct kobj_attribute *attr, char *buf)
2377 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2379 KSM_ATTR_RO(full_scans);
2381 static struct attribute *ksm_attrs[] = {
2382 &sleep_millisecs_attr.attr,
2383 &pages_to_scan_attr.attr,
2384 &run_attr.attr,
2385 &pages_shared_attr.attr,
2386 &pages_sharing_attr.attr,
2387 &pages_unshared_attr.attr,
2388 &pages_volatile_attr.attr,
2389 &full_scans_attr.attr,
2390 #ifdef CONFIG_NUMA
2391 &merge_across_nodes_attr.attr,
2392 #endif
2393 NULL,
2396 static struct attribute_group ksm_attr_group = {
2397 .attrs = ksm_attrs,
2398 .name = "ksm",
2400 #endif /* CONFIG_SYSFS */
2402 static int __init ksm_init(void)
2404 struct task_struct *ksm_thread;
2405 int err;
2407 err = ksm_slab_init();
2408 if (err)
2409 goto out;
2411 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2412 if (IS_ERR(ksm_thread)) {
2413 printk(KERN_ERR "ksm: creating kthread failed\n");
2414 err = PTR_ERR(ksm_thread);
2415 goto out_free;
2418 #ifdef CONFIG_SYSFS
2419 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2420 if (err) {
2421 printk(KERN_ERR "ksm: register sysfs failed\n");
2422 kthread_stop(ksm_thread);
2423 goto out_free;
2425 #else
2426 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2428 #endif /* CONFIG_SYSFS */
2430 #ifdef CONFIG_MEMORY_HOTREMOVE
2431 /* There is no significance to this priority 100 */
2432 hotplug_memory_notifier(ksm_memory_callback, 100);
2433 #endif
2434 return 0;
2436 out_free:
2437 ksm_slab_free();
2438 out:
2439 return err;
2441 module_init(ksm_init)