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.
14 * This work is licensed under the terms of the GNU GPL, version 2.
17 #include <linux/errno.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>
46 #define DO_NUMA(x) do { (x); } while (0)
49 #define DO_NUMA(x) do { } while (0)
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.)
93 * struct mm_slot - ksm information per mm that is being scanned
94 * @link: link to the mm_slots hash list
95 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
96 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
97 * @mm: the mm that this information is valid for
100 struct hlist_node link
;
101 struct list_head mm_list
;
102 struct rmap_item
*rmap_list
;
103 struct mm_struct
*mm
;
107 * struct ksm_scan - cursor for scanning
108 * @mm_slot: the current mm_slot we are scanning
109 * @address: the next address inside that to be scanned
110 * @rmap_list: link to the next rmap to be scanned in the rmap_list
111 * @seqnr: count of completed full scans (needed when removing unstable node)
113 * There is only the one ksm_scan instance of this cursor structure.
116 struct mm_slot
*mm_slot
;
117 unsigned long address
;
118 struct rmap_item
**rmap_list
;
123 * struct stable_node - node of the stable rbtree
124 * @node: rb node of this ksm page in the stable tree
125 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
126 * @list: linked into migrate_nodes, pending placement in the proper node tree
127 * @hlist: hlist head of rmap_items using this ksm page
128 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
129 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
133 struct rb_node node
; /* when node of stable tree */
134 struct { /* when listed for migration */
135 struct list_head
*head
;
136 struct list_head list
;
139 struct hlist_head hlist
;
147 * struct rmap_item - reverse mapping item for virtual addresses
148 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
149 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
150 * @mm: the memory structure this rmap_item is pointing into
151 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
152 * @oldchecksum: previous checksum of the page at that virtual address
153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
154 * @node: rb node of this rmap_item in the unstable tree
155 * @head: pointer to stable_node heading this list in the stable tree
156 * @hlist: link into hlist of rmap_items hanging off that stable_node
159 struct rmap_item
*rmap_list
;
160 struct anon_vma
*anon_vma
; /* when stable */
161 struct mm_struct
*mm
;
162 unsigned long address
; /* + low bits used for flags below */
163 unsigned int oldchecksum
; /* when unstable */
168 struct rb_node node
; /* when node of unstable tree */
169 struct { /* when listed from stable tree */
170 struct stable_node
*head
;
171 struct hlist_node hlist
;
176 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
177 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
178 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
180 /* The stable and unstable tree heads */
181 static struct rb_root root_unstable_tree
[MAX_NUMNODES
];
182 static struct rb_root root_stable_tree
[MAX_NUMNODES
];
184 /* Recently migrated nodes of stable tree, pending proper placement */
185 static LIST_HEAD(migrate_nodes
);
187 #define MM_SLOTS_HASH_BITS 10
188 static DEFINE_HASHTABLE(mm_slots_hash
, MM_SLOTS_HASH_BITS
);
190 static struct mm_slot ksm_mm_head
= {
191 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
193 static struct ksm_scan ksm_scan
= {
194 .mm_slot
= &ksm_mm_head
,
197 static struct kmem_cache
*rmap_item_cache
;
198 static struct kmem_cache
*stable_node_cache
;
199 static struct kmem_cache
*mm_slot_cache
;
201 /* The number of nodes in the stable tree */
202 static unsigned long ksm_pages_shared
;
204 /* The number of page slots additionally sharing those nodes */
205 static unsigned long ksm_pages_sharing
;
207 /* The number of nodes in the unstable tree */
208 static unsigned long ksm_pages_unshared
;
210 /* The number of rmap_items in use: to calculate pages_volatile */
211 static unsigned long ksm_rmap_items
;
213 /* Number of pages ksmd should scan in one batch */
214 static unsigned int ksm_thread_pages_to_scan
= 100;
216 /* Milliseconds ksmd should sleep between batches */
217 static unsigned int ksm_thread_sleep_millisecs
= 20;
220 /* Zeroed when merging across nodes is not allowed */
221 static unsigned int ksm_merge_across_nodes
= 1;
223 #define ksm_merge_across_nodes 1U
226 #define KSM_RUN_STOP 0
227 #define KSM_RUN_MERGE 1
228 #define KSM_RUN_UNMERGE 2
229 #define KSM_RUN_OFFLINE 4
230 static unsigned long ksm_run
= KSM_RUN_STOP
;
231 static void wait_while_offlining(void);
233 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
234 static DEFINE_MUTEX(ksm_thread_mutex
);
235 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
237 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
238 sizeof(struct __struct), __alignof__(struct __struct),\
241 static int __init
ksm_slab_init(void)
243 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
244 if (!rmap_item_cache
)
247 stable_node_cache
= KSM_KMEM_CACHE(stable_node
, 0);
248 if (!stable_node_cache
)
251 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
258 kmem_cache_destroy(stable_node_cache
);
260 kmem_cache_destroy(rmap_item_cache
);
265 static void __init
ksm_slab_free(void)
267 kmem_cache_destroy(mm_slot_cache
);
268 kmem_cache_destroy(stable_node_cache
);
269 kmem_cache_destroy(rmap_item_cache
);
270 mm_slot_cache
= NULL
;
273 static inline struct rmap_item
*alloc_rmap_item(void)
275 struct rmap_item
*rmap_item
;
277 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
);
283 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
286 rmap_item
->mm
= NULL
; /* debug safety */
287 kmem_cache_free(rmap_item_cache
, rmap_item
);
290 static inline struct stable_node
*alloc_stable_node(void)
292 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
);
295 static inline void free_stable_node(struct stable_node
*stable_node
)
297 kmem_cache_free(stable_node_cache
, stable_node
);
300 static inline struct mm_slot
*alloc_mm_slot(void)
302 if (!mm_slot_cache
) /* initialization failed */
304 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
307 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
309 kmem_cache_free(mm_slot_cache
, mm_slot
);
312 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
314 struct hlist_node
*node
;
315 struct mm_slot
*slot
;
317 hash_for_each_possible(mm_slots_hash
, slot
, node
, link
, (unsigned long)mm
)
324 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
325 struct mm_slot
*mm_slot
)
328 hash_add(mm_slots_hash
, &mm_slot
->link
, (unsigned long)mm
);
332 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
333 * page tables after it has passed through ksm_exit() - which, if necessary,
334 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
335 * a special flag: they can just back out as soon as mm_users goes to zero.
336 * ksm_test_exit() is used throughout to make this test for exit: in some
337 * places for correctness, in some places just to avoid unnecessary work.
339 static inline bool ksm_test_exit(struct mm_struct
*mm
)
341 return atomic_read(&mm
->mm_users
) == 0;
345 * We use break_ksm to break COW on a ksm page: it's a stripped down
347 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
350 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
351 * in case the application has unmapped and remapped mm,addr meanwhile.
352 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
353 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
355 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
362 page
= follow_page(vma
, addr
, FOLL_GET
);
363 if (IS_ERR_OR_NULL(page
))
366 ret
= handle_mm_fault(vma
->vm_mm
, vma
, addr
,
369 ret
= VM_FAULT_WRITE
;
371 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_OOM
)));
373 * We must loop because handle_mm_fault() may back out if there's
374 * any difficulty e.g. if pte accessed bit gets updated concurrently.
376 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
377 * COW has been broken, even if the vma does not permit VM_WRITE;
378 * but note that a concurrent fault might break PageKsm for us.
380 * VM_FAULT_SIGBUS could occur if we race with truncation of the
381 * backing file, which also invalidates anonymous pages: that's
382 * okay, that truncation will have unmapped the PageKsm for us.
384 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
385 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
386 * current task has TIF_MEMDIE set, and will be OOM killed on return
387 * to user; and ksmd, having no mm, would never be chosen for that.
389 * But if the mm is in a limited mem_cgroup, then the fault may fail
390 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
391 * even ksmd can fail in this way - though it's usually breaking ksm
392 * just to undo a merge it made a moment before, so unlikely to oom.
394 * That's a pity: we might therefore have more kernel pages allocated
395 * than we're counting as nodes in the stable tree; but ksm_do_scan
396 * will retry to break_cow on each pass, so should recover the page
397 * in due course. The important thing is to not let VM_MERGEABLE
398 * be cleared while any such pages might remain in the area.
400 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
403 static struct vm_area_struct
*find_mergeable_vma(struct mm_struct
*mm
,
406 struct vm_area_struct
*vma
;
407 if (ksm_test_exit(mm
))
409 vma
= find_vma(mm
, addr
);
410 if (!vma
|| vma
->vm_start
> addr
)
412 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
417 static void break_cow(struct rmap_item
*rmap_item
)
419 struct mm_struct
*mm
= rmap_item
->mm
;
420 unsigned long addr
= rmap_item
->address
;
421 struct vm_area_struct
*vma
;
424 * It is not an accident that whenever we want to break COW
425 * to undo, we also need to drop a reference to the anon_vma.
427 put_anon_vma(rmap_item
->anon_vma
);
429 down_read(&mm
->mmap_sem
);
430 vma
= find_mergeable_vma(mm
, addr
);
432 break_ksm(vma
, addr
);
433 up_read(&mm
->mmap_sem
);
436 static struct page
*page_trans_compound_anon(struct page
*page
)
438 if (PageTransCompound(page
)) {
439 struct page
*head
= compound_trans_head(page
);
441 * head may actually be splitted and freed from under
442 * us but it's ok here.
450 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
452 struct mm_struct
*mm
= rmap_item
->mm
;
453 unsigned long addr
= rmap_item
->address
;
454 struct vm_area_struct
*vma
;
457 down_read(&mm
->mmap_sem
);
458 vma
= find_mergeable_vma(mm
, addr
);
462 page
= follow_page(vma
, addr
, FOLL_GET
);
463 if (IS_ERR_OR_NULL(page
))
465 if (PageAnon(page
) || page_trans_compound_anon(page
)) {
466 flush_anon_page(vma
, page
, addr
);
467 flush_dcache_page(page
);
472 up_read(&mm
->mmap_sem
);
477 * This helper is used for getting right index into array of tree roots.
478 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
479 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
480 * every node has its own stable and unstable tree.
482 static inline int get_kpfn_nid(unsigned long kpfn
)
484 return ksm_merge_across_nodes
? 0 : pfn_to_nid(kpfn
);
487 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
489 struct rmap_item
*rmap_item
;
490 struct hlist_node
*hlist
;
492 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
493 if (rmap_item
->hlist
.next
)
497 put_anon_vma(rmap_item
->anon_vma
);
498 rmap_item
->address
&= PAGE_MASK
;
502 if (stable_node
->head
== &migrate_nodes
)
503 list_del(&stable_node
->list
);
505 rb_erase(&stable_node
->node
,
506 &root_stable_tree
[NUMA(stable_node
->nid
)]);
507 free_stable_node(stable_node
);
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.
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.
529 static struct page
*get_ksm_page(struct stable_node
*stable_node
, bool locked
)
532 void *expected_mapping
;
535 expected_mapping
= (void *)stable_node
+
536 (PAGE_MAPPING_ANON
| PAGE_MAPPING_KSM
);
538 kpfn
= ACCESS_ONCE(stable_node
->kpfn
);
539 page
= pfn_to_page(kpfn
);
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.
546 smp_read_barrier_depends();
547 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
)
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.
559 while (!get_page_unless_zero(page
)) {
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().
568 if (!PageSwapCache(page
))
573 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
580 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
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.
596 if (ACCESS_ONCE(stable_node
->kpfn
) != kpfn
)
598 remove_node_from_stable_tree(stable_node
);
603 * Removing rmap_item from stable or unstable tree.
604 * This function will clean the information from the stable/unstable tree.
606 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
608 if (rmap_item
->address
& STABLE_FLAG
) {
609 struct stable_node
*stable_node
;
612 stable_node
= rmap_item
->head
;
613 page
= get_ksm_page(stable_node
, true);
617 hlist_del(&rmap_item
->hlist
);
621 if (stable_node
->hlist
.first
)
626 put_anon_vma(rmap_item
->anon_vma
);
627 rmap_item
->address
&= PAGE_MASK
;
629 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
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.
638 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
641 rb_erase(&rmap_item
->node
,
642 &root_unstable_tree
[NUMA(rmap_item
->nid
)]);
643 ksm_pages_unshared
--;
644 rmap_item
->address
&= PAGE_MASK
;
647 cond_resched(); /* we're called from many long loops */
650 static void remove_trailing_rmap_items(struct mm_slot
*mm_slot
,
651 struct rmap_item
**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
);
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).
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.
674 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
675 unsigned long start
, unsigned long end
)
680 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
681 if (ksm_test_exit(vma
->vm_mm
))
683 if (signal_pending(current
))
686 err
= break_ksm(vma
, addr
);
693 * Only called through the sysfs control interface:
695 static int remove_stable_node(struct stable_node
*stable_node
)
700 page
= get_ksm_page(stable_node
, true);
703 * get_ksm_page did remove_node_from_stable_tree itself.
708 if (WARN_ON_ONCE(page_mapped(page
)))
712 * This page might be in a pagevec waiting to be freed,
713 * or it might be PageSwapCache (perhaps under writeback),
714 * or it might have been removed from swapcache a moment ago.
716 set_page_stable_node(page
, NULL
);
717 remove_node_from_stable_tree(stable_node
);
726 static int remove_all_stable_nodes(void)
728 struct stable_node
*stable_node
;
729 struct list_head
*this, *next
;
733 for (nid
= 0; nid
< nr_node_ids
; nid
++) {
734 while (root_stable_tree
[nid
].rb_node
) {
735 stable_node
= rb_entry(root_stable_tree
[nid
].rb_node
,
736 struct stable_node
, node
);
737 if (remove_stable_node(stable_node
)) {
739 break; /* proceed to next nid */
744 list_for_each_safe(this, next
, &migrate_nodes
) {
745 stable_node
= list_entry(this, struct stable_node
, list
);
746 if (remove_stable_node(stable_node
))
753 static int unmerge_and_remove_all_rmap_items(void)
755 struct mm_slot
*mm_slot
;
756 struct mm_struct
*mm
;
757 struct vm_area_struct
*vma
;
760 spin_lock(&ksm_mmlist_lock
);
761 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
762 struct mm_slot
, mm_list
);
763 spin_unlock(&ksm_mmlist_lock
);
765 for (mm_slot
= ksm_scan
.mm_slot
;
766 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
768 down_read(&mm
->mmap_sem
);
769 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
770 if (ksm_test_exit(mm
))
772 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
774 err
= unmerge_ksm_pages(vma
,
775 vma
->vm_start
, vma
->vm_end
);
780 remove_trailing_rmap_items(mm_slot
, &mm_slot
->rmap_list
);
782 spin_lock(&ksm_mmlist_lock
);
783 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
784 struct mm_slot
, mm_list
);
785 if (ksm_test_exit(mm
)) {
786 hash_del(&mm_slot
->link
);
787 list_del(&mm_slot
->mm_list
);
788 spin_unlock(&ksm_mmlist_lock
);
790 free_mm_slot(mm_slot
);
791 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
792 up_read(&mm
->mmap_sem
);
795 spin_unlock(&ksm_mmlist_lock
);
796 up_read(&mm
->mmap_sem
);
800 /* Clean up stable nodes, but don't worry if some are still busy */
801 remove_all_stable_nodes();
806 up_read(&mm
->mmap_sem
);
807 spin_lock(&ksm_mmlist_lock
);
808 ksm_scan
.mm_slot
= &ksm_mm_head
;
809 spin_unlock(&ksm_mmlist_lock
);
812 #endif /* CONFIG_SYSFS */
814 static u32
calc_checksum(struct page
*page
)
817 void *addr
= kmap_atomic(page
);
818 checksum
= jhash2(addr
, PAGE_SIZE
/ 4, 17);
823 static int memcmp_pages(struct page
*page1
, struct page
*page2
)
828 addr1
= kmap_atomic(page1
);
829 addr2
= kmap_atomic(page2
);
830 ret
= memcmp(addr1
, addr2
, PAGE_SIZE
);
831 kunmap_atomic(addr2
);
832 kunmap_atomic(addr1
);
836 static inline int pages_identical(struct page
*page1
, struct page
*page2
)
838 return !memcmp_pages(page1
, page2
);
841 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
844 struct mm_struct
*mm
= vma
->vm_mm
;
850 unsigned long mmun_start
; /* For mmu_notifiers */
851 unsigned long mmun_end
; /* For mmu_notifiers */
853 addr
= page_address_in_vma(page
, vma
);
857 BUG_ON(PageTransCompound(page
));
860 mmun_end
= addr
+ PAGE_SIZE
;
861 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
863 ptep
= page_check_address(page
, mm
, addr
, &ptl
, 0);
867 if (pte_write(*ptep
) || pte_dirty(*ptep
)) {
870 swapped
= PageSwapCache(page
);
871 flush_cache_page(vma
, addr
, page_to_pfn(page
));
873 * Ok this is tricky, when get_user_pages_fast() run it doesn't
874 * take any lock, therefore the check that we are going to make
875 * with the pagecount against the mapcount is racey and
876 * O_DIRECT can happen right after the check.
877 * So we clear the pte and flush the tlb before the check
878 * this assure us that no O_DIRECT can happen after the check
879 * or in the middle of the check.
881 entry
= ptep_clear_flush(vma
, addr
, ptep
);
883 * Check that no O_DIRECT or similar I/O is in progress on the
886 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
887 set_pte_at(mm
, addr
, ptep
, entry
);
890 if (pte_dirty(entry
))
891 set_page_dirty(page
);
892 entry
= pte_mkclean(pte_wrprotect(entry
));
893 set_pte_at_notify(mm
, addr
, ptep
, entry
);
899 pte_unmap_unlock(ptep
, ptl
);
901 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
907 * replace_page - replace page in vma by new ksm page
908 * @vma: vma that holds the pte pointing to page
909 * @page: the page we are replacing by kpage
910 * @kpage: the ksm page we replace page by
911 * @orig_pte: the original value of the pte
913 * Returns 0 on success, -EFAULT on failure.
915 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
916 struct page
*kpage
, pte_t orig_pte
)
918 struct mm_struct
*mm
= vma
->vm_mm
;
924 unsigned long mmun_start
; /* For mmu_notifiers */
925 unsigned long mmun_end
; /* For mmu_notifiers */
927 addr
= page_address_in_vma(page
, vma
);
931 pmd
= mm_find_pmd(mm
, addr
);
934 BUG_ON(pmd_trans_huge(*pmd
));
937 mmun_end
= addr
+ PAGE_SIZE
;
938 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
940 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
941 if (!pte_same(*ptep
, orig_pte
)) {
942 pte_unmap_unlock(ptep
, ptl
);
947 page_add_anon_rmap(kpage
, vma
, addr
);
949 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
950 ptep_clear_flush(vma
, addr
, ptep
);
951 set_pte_at_notify(mm
, addr
, ptep
, mk_pte(kpage
, vma
->vm_page_prot
));
953 page_remove_rmap(page
);
954 if (!page_mapped(page
))
955 try_to_free_swap(page
);
958 pte_unmap_unlock(ptep
, ptl
);
961 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
966 static int page_trans_compound_anon_split(struct page
*page
)
969 struct page
*transhuge_head
= page_trans_compound_anon(page
);
970 if (transhuge_head
) {
971 /* Get the reference on the head to split it. */
972 if (get_page_unless_zero(transhuge_head
)) {
974 * Recheck we got the reference while the head
975 * was still anonymous.
977 if (PageAnon(transhuge_head
))
978 ret
= split_huge_page(transhuge_head
);
981 * Retry later if split_huge_page run
985 put_page(transhuge_head
);
987 /* Retry later if split_huge_page run from under us. */
994 * try_to_merge_one_page - take two pages and merge them into one
995 * @vma: the vma that holds the pte pointing to page
996 * @page: the PageAnon page that we want to replace with kpage
997 * @kpage: the PageKsm page that we want to map instead of page,
998 * or NULL the first time when we want to use page as kpage.
1000 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1002 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
1003 struct page
*page
, struct page
*kpage
)
1005 pte_t orig_pte
= __pte(0);
1008 if (page
== kpage
) /* ksm page forked */
1011 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1013 if (PageTransCompound(page
) && page_trans_compound_anon_split(page
))
1015 BUG_ON(PageTransCompound(page
));
1016 if (!PageAnon(page
))
1020 * We need the page lock to read a stable PageSwapCache in
1021 * write_protect_page(). We use trylock_page() instead of
1022 * lock_page() because we don't want to wait here - we
1023 * prefer to continue scanning and merging different pages,
1024 * then come back to this page when it is unlocked.
1026 if (!trylock_page(page
))
1029 * If this anonymous page is mapped only here, its pte may need
1030 * to be write-protected. If it's mapped elsewhere, all of its
1031 * ptes are necessarily already write-protected. But in either
1032 * case, we need to lock and check page_count is not raised.
1034 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
1037 * While we hold page lock, upgrade page from
1038 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1039 * stable_tree_insert() will update stable_node.
1041 set_page_stable_node(page
, NULL
);
1042 mark_page_accessed(page
);
1044 } else if (pages_identical(page
, kpage
))
1045 err
= replace_page(vma
, page
, kpage
, orig_pte
);
1048 if ((vma
->vm_flags
& VM_LOCKED
) && kpage
&& !err
) {
1049 munlock_vma_page(page
);
1050 if (!PageMlocked(kpage
)) {
1053 mlock_vma_page(kpage
);
1054 page
= kpage
; /* for final unlock */
1064 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1065 * but no new kernel page is allocated: kpage must already be a ksm page.
1067 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1069 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
1070 struct page
*page
, struct page
*kpage
)
1072 struct mm_struct
*mm
= rmap_item
->mm
;
1073 struct vm_area_struct
*vma
;
1076 down_read(&mm
->mmap_sem
);
1077 if (ksm_test_exit(mm
))
1079 vma
= find_vma(mm
, rmap_item
->address
);
1080 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
1083 err
= try_to_merge_one_page(vma
, page
, kpage
);
1087 /* Must get reference to anon_vma while still holding mmap_sem */
1088 rmap_item
->anon_vma
= vma
->anon_vma
;
1089 get_anon_vma(vma
->anon_vma
);
1091 up_read(&mm
->mmap_sem
);
1096 * try_to_merge_two_pages - take two identical pages and prepare them
1097 * to be merged into one page.
1099 * This function returns the kpage if we successfully merged two identical
1100 * pages into one ksm page, NULL otherwise.
1102 * Note that this function upgrades page to ksm page: if one of the pages
1103 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1105 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
1107 struct rmap_item
*tree_rmap_item
,
1108 struct page
*tree_page
)
1112 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
1114 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
1117 * If that fails, we have a ksm page with only one pte
1118 * pointing to it: so break it.
1121 break_cow(rmap_item
);
1123 return err
? NULL
: page
;
1127 * stable_tree_search - search for page inside the stable tree
1129 * This function checks if there is a page inside the stable tree
1130 * with identical content to the page that we are scanning right now.
1132 * This function returns the stable tree node of identical content if found,
1135 static struct page
*stable_tree_search(struct page
*page
)
1138 struct rb_node
**new;
1139 struct rb_node
*parent
;
1140 struct stable_node
*stable_node
;
1141 struct stable_node
*page_node
;
1143 page_node
= page_stable_node(page
);
1144 if (page_node
&& page_node
->head
!= &migrate_nodes
) {
1145 /* ksm page forked */
1150 nid
= get_kpfn_nid(page_to_pfn(page
));
1152 new = &root_stable_tree
[nid
].rb_node
;
1156 struct page
*tree_page
;
1160 stable_node
= rb_entry(*new, struct stable_node
, node
);
1161 tree_page
= get_ksm_page(stable_node
, false);
1165 ret
= memcmp_pages(page
, tree_page
);
1166 put_page(tree_page
);
1170 new = &parent
->rb_left
;
1172 new = &parent
->rb_right
;
1175 * Lock and unlock the stable_node's page (which
1176 * might already have been migrated) so that page
1177 * migration is sure to notice its raised count.
1178 * It would be more elegant to return stable_node
1179 * than kpage, but that involves more changes.
1181 tree_page
= get_ksm_page(stable_node
, true);
1183 unlock_page(tree_page
);
1184 if (get_kpfn_nid(stable_node
->kpfn
) !=
1185 NUMA(stable_node
->nid
)) {
1186 put_page(tree_page
);
1192 * There is now a place for page_node, but the tree may
1193 * have been rebalanced, so re-evaluate parent and new.
1204 list_del(&page_node
->list
);
1205 DO_NUMA(page_node
->nid
= nid
);
1206 rb_link_node(&page_node
->node
, parent
, new);
1207 rb_insert_color(&page_node
->node
, &root_stable_tree
[nid
]);
1213 list_del(&page_node
->list
);
1214 DO_NUMA(page_node
->nid
= nid
);
1215 rb_replace_node(&stable_node
->node
,
1216 &page_node
->node
, &root_stable_tree
[nid
]);
1219 rb_erase(&stable_node
->node
, &root_stable_tree
[nid
]);
1222 stable_node
->head
= &migrate_nodes
;
1223 list_add(&stable_node
->list
, stable_node
->head
);
1228 * stable_tree_insert - insert stable tree node pointing to new ksm page
1229 * into the stable tree.
1231 * This function returns the stable tree node just allocated on success,
1234 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1238 struct rb_node
**new;
1239 struct rb_node
*parent
= NULL
;
1240 struct stable_node
*stable_node
;
1242 kpfn
= page_to_pfn(kpage
);
1243 nid
= get_kpfn_nid(kpfn
);
1244 new = &root_stable_tree
[nid
].rb_node
;
1247 struct page
*tree_page
;
1251 stable_node
= rb_entry(*new, struct stable_node
, node
);
1252 tree_page
= get_ksm_page(stable_node
, false);
1256 ret
= memcmp_pages(kpage
, tree_page
);
1257 put_page(tree_page
);
1261 new = &parent
->rb_left
;
1263 new = &parent
->rb_right
;
1266 * It is not a bug that stable_tree_search() didn't
1267 * find this node: because at that time our page was
1268 * not yet write-protected, so may have changed since.
1274 stable_node
= alloc_stable_node();
1278 INIT_HLIST_HEAD(&stable_node
->hlist
);
1279 stable_node
->kpfn
= kpfn
;
1280 set_page_stable_node(kpage
, stable_node
);
1281 DO_NUMA(stable_node
->nid
= nid
);
1282 rb_link_node(&stable_node
->node
, parent
, new);
1283 rb_insert_color(&stable_node
->node
, &root_stable_tree
[nid
]);
1289 * unstable_tree_search_insert - search for identical page,
1290 * else insert rmap_item into the unstable tree.
1292 * This function searches for a page in the unstable tree identical to the
1293 * page currently being scanned; and if no identical page is found in the
1294 * tree, we insert rmap_item as a new object into the unstable tree.
1296 * This function returns pointer to rmap_item found to be identical
1297 * to the currently scanned page, NULL otherwise.
1299 * This function does both searching and inserting, because they share
1300 * the same walking algorithm in an rbtree.
1303 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1305 struct page
**tree_pagep
)
1307 struct rb_node
**new;
1308 struct rb_root
*root
;
1309 struct rb_node
*parent
= NULL
;
1312 nid
= get_kpfn_nid(page_to_pfn(page
));
1313 root
= &root_unstable_tree
[nid
];
1314 new = &root
->rb_node
;
1317 struct rmap_item
*tree_rmap_item
;
1318 struct page
*tree_page
;
1322 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1323 tree_page
= get_mergeable_page(tree_rmap_item
);
1324 if (IS_ERR_OR_NULL(tree_page
))
1328 * Don't substitute a ksm page for a forked page.
1330 if (page
== tree_page
) {
1331 put_page(tree_page
);
1336 * If tree_page has been migrated to another NUMA node, it
1337 * will be flushed out and put into the right unstable tree
1338 * next time: only merge with it if merge_across_nodes.
1340 if (!ksm_merge_across_nodes
&& page_to_nid(tree_page
) != nid
) {
1341 put_page(tree_page
);
1345 ret
= memcmp_pages(page
, tree_page
);
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
;
1355 *tree_pagep
= tree_page
;
1356 return tree_rmap_item
;
1360 rmap_item
->address
|= UNSTABLE_FLAG
;
1361 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1362 DO_NUMA(rmap_item
->nid
= nid
);
1363 rb_link_node(&rmap_item
->node
, parent
, new);
1364 rb_insert_color(&rmap_item
->node
, root
);
1366 ksm_pages_unshared
++;
1371 * stable_tree_append - add another rmap_item to the linked list of
1372 * rmap_items hanging off a given node of the stable tree, all sharing
1373 * the same ksm page.
1375 static void stable_tree_append(struct rmap_item
*rmap_item
,
1376 struct stable_node
*stable_node
)
1378 rmap_item
->head
= stable_node
;
1379 rmap_item
->address
|= STABLE_FLAG
;
1380 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
1382 if (rmap_item
->hlist
.next
)
1383 ksm_pages_sharing
++;
1389 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1390 * if not, compare checksum to previous and if it's the same, see if page can
1391 * be inserted into the unstable tree, or merged with a page already there and
1392 * both transferred to the stable tree.
1394 * @page: the page that we are searching identical page to.
1395 * @rmap_item: the reverse mapping into the virtual address of this page
1397 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
1399 struct rmap_item
*tree_rmap_item
;
1400 struct page
*tree_page
= NULL
;
1401 struct stable_node
*stable_node
;
1403 unsigned int checksum
;
1406 stable_node
= page_stable_node(page
);
1408 if (stable_node
->head
!= &migrate_nodes
&&
1409 get_kpfn_nid(stable_node
->kpfn
) != NUMA(stable_node
->nid
)) {
1410 rb_erase(&stable_node
->node
,
1411 &root_stable_tree
[NUMA(stable_node
->nid
)]);
1412 stable_node
->head
= &migrate_nodes
;
1413 list_add(&stable_node
->list
, stable_node
->head
);
1415 if (stable_node
->head
!= &migrate_nodes
&&
1416 rmap_item
->head
== stable_node
)
1420 /* We first start with searching the page inside the stable tree */
1421 kpage
= stable_tree_search(page
);
1422 if (kpage
== page
&& rmap_item
->head
== stable_node
) {
1427 remove_rmap_item_from_tree(rmap_item
);
1430 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
1433 * The page was successfully merged:
1434 * add its rmap_item to the stable tree.
1437 stable_tree_append(rmap_item
, page_stable_node(kpage
));
1445 * If the hash value of the page has changed from the last time
1446 * we calculated it, this page is changing frequently: therefore we
1447 * don't want to insert it in the unstable tree, and we don't want
1448 * to waste our time searching for something identical to it there.
1450 checksum
= calc_checksum(page
);
1451 if (rmap_item
->oldchecksum
!= checksum
) {
1452 rmap_item
->oldchecksum
= checksum
;
1457 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
1458 if (tree_rmap_item
) {
1459 kpage
= try_to_merge_two_pages(rmap_item
, page
,
1460 tree_rmap_item
, tree_page
);
1461 put_page(tree_page
);
1463 * As soon as we merge this page, we want to remove the
1464 * rmap_item of the page we have merged with from the unstable
1465 * tree, and insert it instead as new node in the stable tree.
1468 remove_rmap_item_from_tree(tree_rmap_item
);
1471 stable_node
= stable_tree_insert(kpage
);
1473 stable_tree_append(tree_rmap_item
, stable_node
);
1474 stable_tree_append(rmap_item
, stable_node
);
1479 * If we fail to insert the page into the stable tree,
1480 * we will have 2 virtual addresses that are pointing
1481 * to a ksm page left outside the stable tree,
1482 * in which case we need to break_cow on both.
1485 break_cow(tree_rmap_item
);
1486 break_cow(rmap_item
);
1492 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
1493 struct rmap_item
**rmap_list
,
1496 struct rmap_item
*rmap_item
;
1498 while (*rmap_list
) {
1499 rmap_item
= *rmap_list
;
1500 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
1502 if (rmap_item
->address
> addr
)
1504 *rmap_list
= rmap_item
->rmap_list
;
1505 remove_rmap_item_from_tree(rmap_item
);
1506 free_rmap_item(rmap_item
);
1509 rmap_item
= alloc_rmap_item();
1511 /* It has already been zeroed */
1512 rmap_item
->mm
= mm_slot
->mm
;
1513 rmap_item
->address
= addr
;
1514 rmap_item
->rmap_list
= *rmap_list
;
1515 *rmap_list
= rmap_item
;
1520 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
1522 struct mm_struct
*mm
;
1523 struct mm_slot
*slot
;
1524 struct vm_area_struct
*vma
;
1525 struct rmap_item
*rmap_item
;
1528 if (list_empty(&ksm_mm_head
.mm_list
))
1531 slot
= ksm_scan
.mm_slot
;
1532 if (slot
== &ksm_mm_head
) {
1534 * A number of pages can hang around indefinitely on per-cpu
1535 * pagevecs, raised page count preventing write_protect_page
1536 * from merging them. Though it doesn't really matter much,
1537 * it is puzzling to see some stuck in pages_volatile until
1538 * other activity jostles them out, and they also prevented
1539 * LTP's KSM test from succeeding deterministically; so drain
1540 * them here (here rather than on entry to ksm_do_scan(),
1541 * so we don't IPI too often when pages_to_scan is set low).
1543 lru_add_drain_all();
1546 * Whereas stale stable_nodes on the stable_tree itself
1547 * get pruned in the regular course of stable_tree_search(),
1548 * those moved out to the migrate_nodes list can accumulate:
1549 * so prune them once before each full scan.
1551 if (!ksm_merge_across_nodes
) {
1552 struct stable_node
*stable_node
;
1553 struct list_head
*this, *next
;
1556 list_for_each_safe(this, next
, &migrate_nodes
) {
1557 stable_node
= list_entry(this,
1558 struct stable_node
, list
);
1559 page
= get_ksm_page(stable_node
, false);
1566 for (nid
= 0; nid
< nr_node_ids
; nid
++)
1567 root_unstable_tree
[nid
] = RB_ROOT
;
1569 spin_lock(&ksm_mmlist_lock
);
1570 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
1571 ksm_scan
.mm_slot
= slot
;
1572 spin_unlock(&ksm_mmlist_lock
);
1574 * Although we tested list_empty() above, a racing __ksm_exit
1575 * of the last mm on the list may have removed it since then.
1577 if (slot
== &ksm_mm_head
)
1580 ksm_scan
.address
= 0;
1581 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1585 down_read(&mm
->mmap_sem
);
1586 if (ksm_test_exit(mm
))
1589 vma
= find_vma(mm
, ksm_scan
.address
);
1591 for (; vma
; vma
= vma
->vm_next
) {
1592 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1594 if (ksm_scan
.address
< vma
->vm_start
)
1595 ksm_scan
.address
= vma
->vm_start
;
1597 ksm_scan
.address
= vma
->vm_end
;
1599 while (ksm_scan
.address
< vma
->vm_end
) {
1600 if (ksm_test_exit(mm
))
1602 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
1603 if (IS_ERR_OR_NULL(*page
)) {
1604 ksm_scan
.address
+= PAGE_SIZE
;
1608 if (PageAnon(*page
) ||
1609 page_trans_compound_anon(*page
)) {
1610 flush_anon_page(vma
, *page
, ksm_scan
.address
);
1611 flush_dcache_page(*page
);
1612 rmap_item
= get_next_rmap_item(slot
,
1613 ksm_scan
.rmap_list
, ksm_scan
.address
);
1615 ksm_scan
.rmap_list
=
1616 &rmap_item
->rmap_list
;
1617 ksm_scan
.address
+= PAGE_SIZE
;
1620 up_read(&mm
->mmap_sem
);
1624 ksm_scan
.address
+= PAGE_SIZE
;
1629 if (ksm_test_exit(mm
)) {
1630 ksm_scan
.address
= 0;
1631 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1634 * Nuke all the rmap_items that are above this current rmap:
1635 * because there were no VM_MERGEABLE vmas with such addresses.
1637 remove_trailing_rmap_items(slot
, ksm_scan
.rmap_list
);
1639 spin_lock(&ksm_mmlist_lock
);
1640 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
1641 struct mm_slot
, mm_list
);
1642 if (ksm_scan
.address
== 0) {
1644 * We've completed a full scan of all vmas, holding mmap_sem
1645 * throughout, and found no VM_MERGEABLE: so do the same as
1646 * __ksm_exit does to remove this mm from all our lists now.
1647 * This applies either when cleaning up after __ksm_exit
1648 * (but beware: we can reach here even before __ksm_exit),
1649 * or when all VM_MERGEABLE areas have been unmapped (and
1650 * mmap_sem then protects against race with MADV_MERGEABLE).
1652 hash_del(&slot
->link
);
1653 list_del(&slot
->mm_list
);
1654 spin_unlock(&ksm_mmlist_lock
);
1657 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1658 up_read(&mm
->mmap_sem
);
1661 spin_unlock(&ksm_mmlist_lock
);
1662 up_read(&mm
->mmap_sem
);
1665 /* Repeat until we've completed scanning the whole list */
1666 slot
= ksm_scan
.mm_slot
;
1667 if (slot
!= &ksm_mm_head
)
1675 * ksm_do_scan - the ksm scanner main worker function.
1676 * @scan_npages - number of pages we want to scan before we return.
1678 static void ksm_do_scan(unsigned int scan_npages
)
1680 struct rmap_item
*rmap_item
;
1681 struct page
*uninitialized_var(page
);
1683 while (scan_npages
-- && likely(!freezing(current
))) {
1685 rmap_item
= scan_get_next_rmap_item(&page
);
1688 cmp_and_merge_page(page
, rmap_item
);
1693 static int ksmd_should_run(void)
1695 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
1698 static int ksm_scan_thread(void *nothing
)
1701 set_user_nice(current
, 5);
1703 while (!kthread_should_stop()) {
1704 mutex_lock(&ksm_thread_mutex
);
1705 wait_while_offlining();
1706 if (ksmd_should_run())
1707 ksm_do_scan(ksm_thread_pages_to_scan
);
1708 mutex_unlock(&ksm_thread_mutex
);
1712 if (ksmd_should_run()) {
1713 schedule_timeout_interruptible(
1714 msecs_to_jiffies(ksm_thread_sleep_millisecs
));
1716 wait_event_freezable(ksm_thread_wait
,
1717 ksmd_should_run() || kthread_should_stop());
1723 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
1724 unsigned long end
, int advice
, unsigned long *vm_flags
)
1726 struct mm_struct
*mm
= vma
->vm_mm
;
1730 case MADV_MERGEABLE
:
1732 * Be somewhat over-protective for now!
1734 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
1735 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
1736 VM_HUGETLB
| VM_NONLINEAR
| VM_MIXEDMAP
))
1737 return 0; /* just ignore the advice */
1740 if (*vm_flags
& VM_SAO
)
1744 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
1745 err
= __ksm_enter(mm
);
1750 *vm_flags
|= VM_MERGEABLE
;
1753 case MADV_UNMERGEABLE
:
1754 if (!(*vm_flags
& VM_MERGEABLE
))
1755 return 0; /* just ignore the advice */
1757 if (vma
->anon_vma
) {
1758 err
= unmerge_ksm_pages(vma
, start
, end
);
1763 *vm_flags
&= ~VM_MERGEABLE
;
1770 int __ksm_enter(struct mm_struct
*mm
)
1772 struct mm_slot
*mm_slot
;
1775 mm_slot
= alloc_mm_slot();
1779 /* Check ksm_run too? Would need tighter locking */
1780 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
1782 spin_lock(&ksm_mmlist_lock
);
1783 insert_to_mm_slots_hash(mm
, mm_slot
);
1785 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1786 * insert just behind the scanning cursor, to let the area settle
1787 * down a little; when fork is followed by immediate exec, we don't
1788 * want ksmd to waste time setting up and tearing down an rmap_list.
1790 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1791 * scanning cursor, otherwise KSM pages in newly forked mms will be
1792 * missed: then we might as well insert at the end of the list.
1794 if (ksm_run
& KSM_RUN_UNMERGE
)
1795 list_add_tail(&mm_slot
->mm_list
, &ksm_mm_head
.mm_list
);
1797 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
1798 spin_unlock(&ksm_mmlist_lock
);
1800 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1801 atomic_inc(&mm
->mm_count
);
1804 wake_up_interruptible(&ksm_thread_wait
);
1809 void __ksm_exit(struct mm_struct
*mm
)
1811 struct mm_slot
*mm_slot
;
1812 int easy_to_free
= 0;
1815 * This process is exiting: if it's straightforward (as is the
1816 * case when ksmd was never running), free mm_slot immediately.
1817 * But if it's at the cursor or has rmap_items linked to it, use
1818 * mmap_sem to synchronize with any break_cows before pagetables
1819 * are freed, and leave the mm_slot on the list for ksmd to free.
1820 * Beware: ksm may already have noticed it exiting and freed the slot.
1823 spin_lock(&ksm_mmlist_lock
);
1824 mm_slot
= get_mm_slot(mm
);
1825 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
1826 if (!mm_slot
->rmap_list
) {
1827 hash_del(&mm_slot
->link
);
1828 list_del(&mm_slot
->mm_list
);
1831 list_move(&mm_slot
->mm_list
,
1832 &ksm_scan
.mm_slot
->mm_list
);
1835 spin_unlock(&ksm_mmlist_lock
);
1838 free_mm_slot(mm_slot
);
1839 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1841 } else if (mm_slot
) {
1842 down_write(&mm
->mmap_sem
);
1843 up_write(&mm
->mmap_sem
);
1847 struct page
*ksm_might_need_to_copy(struct page
*page
,
1848 struct vm_area_struct
*vma
, unsigned long address
)
1850 struct anon_vma
*anon_vma
= page_anon_vma(page
);
1851 struct page
*new_page
;
1853 if (PageKsm(page
)) {
1854 if (page_stable_node(page
) &&
1855 !(ksm_run
& KSM_RUN_UNMERGE
))
1856 return page
; /* no need to copy it */
1857 } else if (!anon_vma
) {
1858 return page
; /* no need to copy it */
1859 } else if (anon_vma
->root
== vma
->anon_vma
->root
&&
1860 page
->index
== linear_page_index(vma
, address
)) {
1861 return page
; /* still no need to copy it */
1863 if (!PageUptodate(page
))
1864 return page
; /* let do_swap_page report the error */
1866 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
1868 copy_user_highpage(new_page
, page
, address
, vma
);
1870 SetPageDirty(new_page
);
1871 __SetPageUptodate(new_page
);
1872 __set_page_locked(new_page
);
1878 int page_referenced_ksm(struct page
*page
, struct mem_cgroup
*memcg
,
1879 unsigned long *vm_flags
)
1881 struct stable_node
*stable_node
;
1882 struct rmap_item
*rmap_item
;
1883 struct hlist_node
*hlist
;
1884 unsigned int mapcount
= page_mapcount(page
);
1886 int search_new_forks
= 0;
1888 VM_BUG_ON(!PageKsm(page
));
1889 VM_BUG_ON(!PageLocked(page
));
1891 stable_node
= page_stable_node(page
);
1895 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
1896 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1897 struct anon_vma_chain
*vmac
;
1898 struct vm_area_struct
*vma
;
1900 anon_vma_lock_read(anon_vma
);
1901 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1904 if (rmap_item
->address
< vma
->vm_start
||
1905 rmap_item
->address
>= vma
->vm_end
)
1908 * Initially we examine only the vma which covers this
1909 * rmap_item; but later, if there is still work to do,
1910 * we examine covering vmas in other mms: in case they
1911 * were forked from the original since ksmd passed.
1913 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1916 if (memcg
&& !mm_match_cgroup(vma
->vm_mm
, memcg
))
1919 referenced
+= page_referenced_one(page
, vma
,
1920 rmap_item
->address
, &mapcount
, vm_flags
);
1921 if (!search_new_forks
|| !mapcount
)
1924 anon_vma_unlock_read(anon_vma
);
1928 if (!search_new_forks
++)
1934 int try_to_unmap_ksm(struct page
*page
, enum ttu_flags flags
)
1936 struct stable_node
*stable_node
;
1937 struct hlist_node
*hlist
;
1938 struct rmap_item
*rmap_item
;
1939 int ret
= SWAP_AGAIN
;
1940 int search_new_forks
= 0;
1942 VM_BUG_ON(!PageKsm(page
));
1943 VM_BUG_ON(!PageLocked(page
));
1945 stable_node
= page_stable_node(page
);
1949 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
1950 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1951 struct anon_vma_chain
*vmac
;
1952 struct vm_area_struct
*vma
;
1954 anon_vma_lock_read(anon_vma
);
1955 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1958 if (rmap_item
->address
< vma
->vm_start
||
1959 rmap_item
->address
>= vma
->vm_end
)
1962 * Initially we examine only the vma which covers this
1963 * rmap_item; but later, if there is still work to do,
1964 * we examine covering vmas in other mms: in case they
1965 * were forked from the original since ksmd passed.
1967 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1970 ret
= try_to_unmap_one(page
, vma
,
1971 rmap_item
->address
, flags
);
1972 if (ret
!= SWAP_AGAIN
|| !page_mapped(page
)) {
1973 anon_vma_unlock_read(anon_vma
);
1977 anon_vma_unlock_read(anon_vma
);
1979 if (!search_new_forks
++)
1985 #ifdef CONFIG_MIGRATION
1986 int rmap_walk_ksm(struct page
*page
, int (*rmap_one
)(struct page
*,
1987 struct vm_area_struct
*, unsigned long, void *), void *arg
)
1989 struct stable_node
*stable_node
;
1990 struct hlist_node
*hlist
;
1991 struct rmap_item
*rmap_item
;
1992 int ret
= SWAP_AGAIN
;
1993 int search_new_forks
= 0;
1995 VM_BUG_ON(!PageKsm(page
));
1996 VM_BUG_ON(!PageLocked(page
));
1998 stable_node
= page_stable_node(page
);
2002 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
2003 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
2004 struct anon_vma_chain
*vmac
;
2005 struct vm_area_struct
*vma
;
2007 anon_vma_lock_read(anon_vma
);
2008 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
2011 if (rmap_item
->address
< vma
->vm_start
||
2012 rmap_item
->address
>= vma
->vm_end
)
2015 * Initially we examine only the vma which covers this
2016 * rmap_item; but later, if there is still work to do,
2017 * we examine covering vmas in other mms: in case they
2018 * were forked from the original since ksmd passed.
2020 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
2023 ret
= rmap_one(page
, vma
, rmap_item
->address
, arg
);
2024 if (ret
!= SWAP_AGAIN
) {
2025 anon_vma_unlock_read(anon_vma
);
2029 anon_vma_unlock_read(anon_vma
);
2031 if (!search_new_forks
++)
2037 void ksm_migrate_page(struct page
*newpage
, struct page
*oldpage
)
2039 struct stable_node
*stable_node
;
2041 VM_BUG_ON(!PageLocked(oldpage
));
2042 VM_BUG_ON(!PageLocked(newpage
));
2043 VM_BUG_ON(newpage
->mapping
!= oldpage
->mapping
);
2045 stable_node
= page_stable_node(newpage
);
2047 VM_BUG_ON(stable_node
->kpfn
!= page_to_pfn(oldpage
));
2048 stable_node
->kpfn
= page_to_pfn(newpage
);
2050 * newpage->mapping was set in advance; now we need smp_wmb()
2051 * to make sure that the new stable_node->kpfn is visible
2052 * to get_ksm_page() before it can see that oldpage->mapping
2053 * has gone stale (or that PageSwapCache has been cleared).
2056 set_page_stable_node(oldpage
, NULL
);
2059 #endif /* CONFIG_MIGRATION */
2061 #ifdef CONFIG_MEMORY_HOTREMOVE
2062 static int just_wait(void *word
)
2068 static void wait_while_offlining(void)
2070 while (ksm_run
& KSM_RUN_OFFLINE
) {
2071 mutex_unlock(&ksm_thread_mutex
);
2072 wait_on_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
),
2073 just_wait
, TASK_UNINTERRUPTIBLE
);
2074 mutex_lock(&ksm_thread_mutex
);
2078 static void ksm_check_stable_tree(unsigned long start_pfn
,
2079 unsigned long end_pfn
)
2081 struct stable_node
*stable_node
;
2082 struct list_head
*this, *next
;
2083 struct rb_node
*node
;
2086 for (nid
= 0; nid
< nr_node_ids
; nid
++) {
2087 node
= rb_first(&root_stable_tree
[nid
]);
2089 stable_node
= rb_entry(node
, struct stable_node
, node
);
2090 if (stable_node
->kpfn
>= start_pfn
&&
2091 stable_node
->kpfn
< end_pfn
) {
2093 * Don't get_ksm_page, page has already gone:
2094 * which is why we keep kpfn instead of page*
2096 remove_node_from_stable_tree(stable_node
);
2097 node
= rb_first(&root_stable_tree
[nid
]);
2099 node
= rb_next(node
);
2103 list_for_each_safe(this, next
, &migrate_nodes
) {
2104 stable_node
= list_entry(this, struct stable_node
, list
);
2105 if (stable_node
->kpfn
>= start_pfn
&&
2106 stable_node
->kpfn
< end_pfn
)
2107 remove_node_from_stable_tree(stable_node
);
2112 static int ksm_memory_callback(struct notifier_block
*self
,
2113 unsigned long action
, void *arg
)
2115 struct memory_notify
*mn
= arg
;
2118 case MEM_GOING_OFFLINE
:
2120 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2121 * and remove_all_stable_nodes() while memory is going offline:
2122 * it is unsafe for them to touch the stable tree at this time.
2123 * But unmerge_ksm_pages(), rmap lookups and other entry points
2124 * which do not need the ksm_thread_mutex are all safe.
2126 mutex_lock(&ksm_thread_mutex
);
2127 ksm_run
|= KSM_RUN_OFFLINE
;
2128 mutex_unlock(&ksm_thread_mutex
);
2133 * Most of the work is done by page migration; but there might
2134 * be a few stable_nodes left over, still pointing to struct
2135 * pages which have been offlined: prune those from the tree,
2136 * otherwise get_ksm_page() might later try to access a
2137 * non-existent struct page.
2139 ksm_check_stable_tree(mn
->start_pfn
,
2140 mn
->start_pfn
+ mn
->nr_pages
);
2143 case MEM_CANCEL_OFFLINE
:
2144 mutex_lock(&ksm_thread_mutex
);
2145 ksm_run
&= ~KSM_RUN_OFFLINE
;
2146 mutex_unlock(&ksm_thread_mutex
);
2148 smp_mb(); /* wake_up_bit advises this */
2149 wake_up_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
));
2155 static void wait_while_offlining(void)
2158 #endif /* CONFIG_MEMORY_HOTREMOVE */
2162 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2165 #define KSM_ATTR_RO(_name) \
2166 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2167 #define KSM_ATTR(_name) \
2168 static struct kobj_attribute _name##_attr = \
2169 __ATTR(_name, 0644, _name##_show, _name##_store)
2171 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
2172 struct kobj_attribute
*attr
, char *buf
)
2174 return sprintf(buf
, "%u\n", ksm_thread_sleep_millisecs
);
2177 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
2178 struct kobj_attribute
*attr
,
2179 const char *buf
, size_t count
)
2181 unsigned long msecs
;
2184 err
= strict_strtoul(buf
, 10, &msecs
);
2185 if (err
|| msecs
> UINT_MAX
)
2188 ksm_thread_sleep_millisecs
= msecs
;
2192 KSM_ATTR(sleep_millisecs
);
2194 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
2195 struct kobj_attribute
*attr
, char *buf
)
2197 return sprintf(buf
, "%u\n", ksm_thread_pages_to_scan
);
2200 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
2201 struct kobj_attribute
*attr
,
2202 const char *buf
, size_t count
)
2205 unsigned long nr_pages
;
2207 err
= strict_strtoul(buf
, 10, &nr_pages
);
2208 if (err
|| nr_pages
> UINT_MAX
)
2211 ksm_thread_pages_to_scan
= nr_pages
;
2215 KSM_ATTR(pages_to_scan
);
2217 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2220 return sprintf(buf
, "%lu\n", ksm_run
);
2223 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2224 const char *buf
, size_t count
)
2227 unsigned long flags
;
2229 err
= strict_strtoul(buf
, 10, &flags
);
2230 if (err
|| flags
> UINT_MAX
)
2232 if (flags
> KSM_RUN_UNMERGE
)
2236 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2237 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2238 * breaking COW to free the pages_shared (but leaves mm_slots
2239 * on the list for when ksmd may be set running again).
2242 mutex_lock(&ksm_thread_mutex
);
2243 wait_while_offlining();
2244 if (ksm_run
!= flags
) {
2246 if (flags
& KSM_RUN_UNMERGE
) {
2247 set_current_oom_origin();
2248 err
= unmerge_and_remove_all_rmap_items();
2249 clear_current_oom_origin();
2251 ksm_run
= KSM_RUN_STOP
;
2256 mutex_unlock(&ksm_thread_mutex
);
2258 if (flags
& KSM_RUN_MERGE
)
2259 wake_up_interruptible(&ksm_thread_wait
);
2266 static ssize_t
merge_across_nodes_show(struct kobject
*kobj
,
2267 struct kobj_attribute
*attr
, char *buf
)
2269 return sprintf(buf
, "%u\n", ksm_merge_across_nodes
);
2272 static ssize_t
merge_across_nodes_store(struct kobject
*kobj
,
2273 struct kobj_attribute
*attr
,
2274 const char *buf
, size_t count
)
2279 err
= kstrtoul(buf
, 10, &knob
);
2285 mutex_lock(&ksm_thread_mutex
);
2286 wait_while_offlining();
2287 if (ksm_merge_across_nodes
!= knob
) {
2288 if (ksm_pages_shared
|| remove_all_stable_nodes())
2291 ksm_merge_across_nodes
= knob
;
2293 mutex_unlock(&ksm_thread_mutex
);
2295 return err
? err
: count
;
2297 KSM_ATTR(merge_across_nodes
);
2300 static ssize_t
pages_shared_show(struct kobject
*kobj
,
2301 struct kobj_attribute
*attr
, char *buf
)
2303 return sprintf(buf
, "%lu\n", ksm_pages_shared
);
2305 KSM_ATTR_RO(pages_shared
);
2307 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
2308 struct kobj_attribute
*attr
, char *buf
)
2310 return sprintf(buf
, "%lu\n", ksm_pages_sharing
);
2312 KSM_ATTR_RO(pages_sharing
);
2314 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
2315 struct kobj_attribute
*attr
, char *buf
)
2317 return sprintf(buf
, "%lu\n", ksm_pages_unshared
);
2319 KSM_ATTR_RO(pages_unshared
);
2321 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
2322 struct kobj_attribute
*attr
, char *buf
)
2324 long ksm_pages_volatile
;
2326 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
2327 - ksm_pages_sharing
- ksm_pages_unshared
;
2329 * It was not worth any locking to calculate that statistic,
2330 * but it might therefore sometimes be negative: conceal that.
2332 if (ksm_pages_volatile
< 0)
2333 ksm_pages_volatile
= 0;
2334 return sprintf(buf
, "%ld\n", ksm_pages_volatile
);
2336 KSM_ATTR_RO(pages_volatile
);
2338 static ssize_t
full_scans_show(struct kobject
*kobj
,
2339 struct kobj_attribute
*attr
, char *buf
)
2341 return sprintf(buf
, "%lu\n", ksm_scan
.seqnr
);
2343 KSM_ATTR_RO(full_scans
);
2345 static struct attribute
*ksm_attrs
[] = {
2346 &sleep_millisecs_attr
.attr
,
2347 &pages_to_scan_attr
.attr
,
2349 &pages_shared_attr
.attr
,
2350 &pages_sharing_attr
.attr
,
2351 &pages_unshared_attr
.attr
,
2352 &pages_volatile_attr
.attr
,
2353 &full_scans_attr
.attr
,
2355 &merge_across_nodes_attr
.attr
,
2360 static struct attribute_group ksm_attr_group
= {
2364 #endif /* CONFIG_SYSFS */
2366 static int __init
ksm_init(void)
2368 struct task_struct
*ksm_thread
;
2372 err
= ksm_slab_init();
2376 for (nid
= 0; nid
< nr_node_ids
; nid
++)
2377 root_stable_tree
[nid
] = RB_ROOT
;
2379 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
2380 if (IS_ERR(ksm_thread
)) {
2381 printk(KERN_ERR
"ksm: creating kthread failed\n");
2382 err
= PTR_ERR(ksm_thread
);
2387 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
2389 printk(KERN_ERR
"ksm: register sysfs failed\n");
2390 kthread_stop(ksm_thread
);
2394 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
2396 #endif /* CONFIG_SYSFS */
2398 #ifdef CONFIG_MEMORY_HOTREMOVE
2399 /* There is no significance to this priority 100 */
2400 hotplug_memory_notifier(ksm_memory_callback
, 100);
2409 module_init(ksm_init
)