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/hash.h>
37 #include <linux/freezer.h>
39 #include <asm/tlbflush.h>
43 * A few notes about the KSM scanning process,
44 * to make it easier to understand the data structures below:
46 * In order to reduce excessive scanning, KSM sorts the memory pages by their
47 * contents into a data structure that holds pointers to the pages' locations.
49 * Since the contents of the pages may change at any moment, KSM cannot just
50 * insert the pages into a normal sorted tree and expect it to find anything.
51 * Therefore KSM uses two data structures - the stable and the unstable tree.
53 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
54 * by their contents. Because each such page is write-protected, searching on
55 * this tree is fully assured to be working (except when pages are unmapped),
56 * and therefore this tree is called the stable tree.
58 * In addition to the stable tree, KSM uses a second data structure called the
59 * unstable tree: this tree holds pointers to pages which have been found to
60 * be "unchanged for a period of time". The unstable tree sorts these pages
61 * by their contents, but since they are not write-protected, KSM cannot rely
62 * upon the unstable tree to work correctly - the unstable tree is liable to
63 * be corrupted as its contents are modified, and so it is called unstable.
65 * KSM solves this problem by several techniques:
67 * 1) The unstable tree is flushed every time KSM completes scanning all
68 * memory areas, and then the tree is rebuilt again from the beginning.
69 * 2) KSM will only insert into the unstable tree, pages whose hash value
70 * has not changed since the previous scan of all memory areas.
71 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
72 * colors of the nodes and not on their contents, assuring that even when
73 * the tree gets "corrupted" it won't get out of balance, so scanning time
74 * remains the same (also, searching and inserting nodes in an rbtree uses
75 * the same algorithm, so we have no overhead when we flush and rebuild).
76 * 4) KSM never flushes the stable tree, which means that even if it were to
77 * take 10 attempts to find a page in the unstable tree, once it is found,
78 * it is secured in the stable tree. (When we scan a new page, we first
79 * compare it against the stable tree, and then against the unstable tree.)
83 * struct mm_slot - ksm information per mm that is being scanned
84 * @link: link to the mm_slots hash list
85 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
86 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
87 * @mm: the mm that this information is valid for
90 struct hlist_node link
;
91 struct list_head mm_list
;
92 struct rmap_item
*rmap_list
;
97 * struct ksm_scan - cursor for scanning
98 * @mm_slot: the current mm_slot we are scanning
99 * @address: the next address inside that to be scanned
100 * @rmap_list: link to the next rmap to be scanned in the rmap_list
101 * @seqnr: count of completed full scans (needed when removing unstable node)
103 * There is only the one ksm_scan instance of this cursor structure.
106 struct mm_slot
*mm_slot
;
107 unsigned long address
;
108 struct rmap_item
**rmap_list
;
113 * struct stable_node - node of the stable rbtree
114 * @node: rb node of this ksm page in the stable tree
115 * @hlist: hlist head of rmap_items using this ksm page
116 * @kpfn: page frame number of this ksm page
120 struct hlist_head hlist
;
125 * struct rmap_item - reverse mapping item for virtual addresses
126 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
127 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
128 * @mm: the memory structure this rmap_item is pointing into
129 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
130 * @oldchecksum: previous checksum of the page at that virtual address
131 * @node: rb node of this rmap_item in the unstable tree
132 * @head: pointer to stable_node heading this list in the stable tree
133 * @hlist: link into hlist of rmap_items hanging off that stable_node
136 struct rmap_item
*rmap_list
;
137 struct anon_vma
*anon_vma
; /* when stable */
138 struct mm_struct
*mm
;
139 unsigned long address
; /* + low bits used for flags below */
140 unsigned int oldchecksum
; /* when unstable */
142 struct rb_node node
; /* when node of unstable tree */
143 struct { /* when listed from stable tree */
144 struct stable_node
*head
;
145 struct hlist_node hlist
;
150 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
151 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
152 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
154 /* The stable and unstable tree heads */
155 static struct rb_root root_stable_tree
= RB_ROOT
;
156 static struct rb_root root_unstable_tree
= RB_ROOT
;
158 #define MM_SLOTS_HASH_SHIFT 10
159 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
160 static struct hlist_head mm_slots_hash
[MM_SLOTS_HASH_HEADS
];
162 static struct mm_slot ksm_mm_head
= {
163 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
165 static struct ksm_scan ksm_scan
= {
166 .mm_slot
= &ksm_mm_head
,
169 static struct kmem_cache
*rmap_item_cache
;
170 static struct kmem_cache
*stable_node_cache
;
171 static struct kmem_cache
*mm_slot_cache
;
173 /* The number of nodes in the stable tree */
174 static unsigned long ksm_pages_shared
;
176 /* The number of page slots additionally sharing those nodes */
177 static unsigned long ksm_pages_sharing
;
179 /* The number of nodes in the unstable tree */
180 static unsigned long ksm_pages_unshared
;
182 /* The number of rmap_items in use: to calculate pages_volatile */
183 static unsigned long ksm_rmap_items
;
185 /* Number of pages ksmd should scan in one batch */
186 static unsigned int ksm_thread_pages_to_scan
= 100;
188 /* Milliseconds ksmd should sleep between batches */
189 static unsigned int ksm_thread_sleep_millisecs
= 20;
191 #define KSM_RUN_STOP 0
192 #define KSM_RUN_MERGE 1
193 #define KSM_RUN_UNMERGE 2
194 static unsigned int ksm_run
= KSM_RUN_STOP
;
196 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
197 static DEFINE_MUTEX(ksm_thread_mutex
);
198 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
200 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
201 sizeof(struct __struct), __alignof__(struct __struct),\
204 static int __init
ksm_slab_init(void)
206 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
207 if (!rmap_item_cache
)
210 stable_node_cache
= KSM_KMEM_CACHE(stable_node
, 0);
211 if (!stable_node_cache
)
214 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
221 kmem_cache_destroy(stable_node_cache
);
223 kmem_cache_destroy(rmap_item_cache
);
228 static void __init
ksm_slab_free(void)
230 kmem_cache_destroy(mm_slot_cache
);
231 kmem_cache_destroy(stable_node_cache
);
232 kmem_cache_destroy(rmap_item_cache
);
233 mm_slot_cache
= NULL
;
236 static inline struct rmap_item
*alloc_rmap_item(void)
238 struct rmap_item
*rmap_item
;
240 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
);
246 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
249 rmap_item
->mm
= NULL
; /* debug safety */
250 kmem_cache_free(rmap_item_cache
, rmap_item
);
253 static inline struct stable_node
*alloc_stable_node(void)
255 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
);
258 static inline void free_stable_node(struct stable_node
*stable_node
)
260 kmem_cache_free(stable_node_cache
, stable_node
);
263 static inline struct mm_slot
*alloc_mm_slot(void)
265 if (!mm_slot_cache
) /* initialization failed */
267 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
270 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
272 kmem_cache_free(mm_slot_cache
, mm_slot
);
275 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
277 struct mm_slot
*mm_slot
;
278 struct hlist_head
*bucket
;
279 struct hlist_node
*node
;
281 bucket
= &mm_slots_hash
[hash_ptr(mm
, MM_SLOTS_HASH_SHIFT
)];
282 hlist_for_each_entry(mm_slot
, node
, bucket
, link
) {
283 if (mm
== mm_slot
->mm
)
289 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
290 struct mm_slot
*mm_slot
)
292 struct hlist_head
*bucket
;
294 bucket
= &mm_slots_hash
[hash_ptr(mm
, MM_SLOTS_HASH_SHIFT
)];
296 hlist_add_head(&mm_slot
->link
, bucket
);
299 static inline int in_stable_tree(struct rmap_item
*rmap_item
)
301 return rmap_item
->address
& STABLE_FLAG
;
305 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
306 * page tables after it has passed through ksm_exit() - which, if necessary,
307 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
308 * a special flag: they can just back out as soon as mm_users goes to zero.
309 * ksm_test_exit() is used throughout to make this test for exit: in some
310 * places for correctness, in some places just to avoid unnecessary work.
312 static inline bool ksm_test_exit(struct mm_struct
*mm
)
314 return atomic_read(&mm
->mm_users
) == 0;
318 * We use break_ksm to break COW on a ksm page: it's a stripped down
320 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
323 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
324 * in case the application has unmapped and remapped mm,addr meanwhile.
325 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
326 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
328 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
335 page
= follow_page(vma
, addr
, FOLL_GET
);
336 if (IS_ERR_OR_NULL(page
))
339 ret
= handle_mm_fault(vma
->vm_mm
, vma
, addr
,
342 ret
= VM_FAULT_WRITE
;
344 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_OOM
)));
346 * We must loop because handle_mm_fault() may back out if there's
347 * any difficulty e.g. if pte accessed bit gets updated concurrently.
349 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
350 * COW has been broken, even if the vma does not permit VM_WRITE;
351 * but note that a concurrent fault might break PageKsm for us.
353 * VM_FAULT_SIGBUS could occur if we race with truncation of the
354 * backing file, which also invalidates anonymous pages: that's
355 * okay, that truncation will have unmapped the PageKsm for us.
357 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
358 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
359 * current task has TIF_MEMDIE set, and will be OOM killed on return
360 * to user; and ksmd, having no mm, would never be chosen for that.
362 * But if the mm is in a limited mem_cgroup, then the fault may fail
363 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
364 * even ksmd can fail in this way - though it's usually breaking ksm
365 * just to undo a merge it made a moment before, so unlikely to oom.
367 * That's a pity: we might therefore have more kernel pages allocated
368 * than we're counting as nodes in the stable tree; but ksm_do_scan
369 * will retry to break_cow on each pass, so should recover the page
370 * in due course. The important thing is to not let VM_MERGEABLE
371 * be cleared while any such pages might remain in the area.
373 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
376 static void break_cow(struct rmap_item
*rmap_item
)
378 struct mm_struct
*mm
= rmap_item
->mm
;
379 unsigned long addr
= rmap_item
->address
;
380 struct vm_area_struct
*vma
;
383 * It is not an accident that whenever we want to break COW
384 * to undo, we also need to drop a reference to the anon_vma.
386 put_anon_vma(rmap_item
->anon_vma
);
388 down_read(&mm
->mmap_sem
);
389 if (ksm_test_exit(mm
))
391 vma
= find_vma(mm
, addr
);
392 if (!vma
|| vma
->vm_start
> addr
)
394 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
396 break_ksm(vma
, addr
);
398 up_read(&mm
->mmap_sem
);
401 static struct page
*page_trans_compound_anon(struct page
*page
)
403 if (PageTransCompound(page
)) {
404 struct page
*head
= compound_trans_head(page
);
406 * head may actually be splitted and freed from under
407 * us but it's ok here.
415 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
417 struct mm_struct
*mm
= rmap_item
->mm
;
418 unsigned long addr
= rmap_item
->address
;
419 struct vm_area_struct
*vma
;
422 down_read(&mm
->mmap_sem
);
423 if (ksm_test_exit(mm
))
425 vma
= find_vma(mm
, addr
);
426 if (!vma
|| vma
->vm_start
> addr
)
428 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
431 page
= follow_page(vma
, addr
, FOLL_GET
);
432 if (IS_ERR_OR_NULL(page
))
434 if (PageAnon(page
) || page_trans_compound_anon(page
)) {
435 flush_anon_page(vma
, page
, addr
);
436 flush_dcache_page(page
);
441 up_read(&mm
->mmap_sem
);
445 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
447 struct rmap_item
*rmap_item
;
448 struct hlist_node
*hlist
;
450 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
451 if (rmap_item
->hlist
.next
)
455 put_anon_vma(rmap_item
->anon_vma
);
456 rmap_item
->address
&= PAGE_MASK
;
460 rb_erase(&stable_node
->node
, &root_stable_tree
);
461 free_stable_node(stable_node
);
465 * get_ksm_page: checks if the page indicated by the stable node
466 * is still its ksm page, despite having held no reference to it.
467 * In which case we can trust the content of the page, and it
468 * returns the gotten page; but if the page has now been zapped,
469 * remove the stale node from the stable tree and return NULL.
471 * You would expect the stable_node to hold a reference to the ksm page.
472 * But if it increments the page's count, swapping out has to wait for
473 * ksmd to come around again before it can free the page, which may take
474 * seconds or even minutes: much too unresponsive. So instead we use a
475 * "keyhole reference": access to the ksm page from the stable node peeps
476 * out through its keyhole to see if that page still holds the right key,
477 * pointing back to this stable node. This relies on freeing a PageAnon
478 * page to reset its page->mapping to NULL, and relies on no other use of
479 * a page to put something that might look like our key in page->mapping.
481 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
482 * but this is different - made simpler by ksm_thread_mutex being held, but
483 * interesting for assuming that no other use of the struct page could ever
484 * put our expected_mapping into page->mapping (or a field of the union which
485 * coincides with page->mapping). The RCU calls are not for KSM at all, but
486 * to keep the page_count protocol described with page_cache_get_speculative.
488 * Note: it is possible that get_ksm_page() will return NULL one moment,
489 * then page the next, if the page is in between page_freeze_refs() and
490 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
491 * is on its way to being freed; but it is an anomaly to bear in mind.
493 static struct page
*get_ksm_page(struct stable_node
*stable_node
)
496 void *expected_mapping
;
498 page
= pfn_to_page(stable_node
->kpfn
);
499 expected_mapping
= (void *)stable_node
+
500 (PAGE_MAPPING_ANON
| PAGE_MAPPING_KSM
);
502 if (page
->mapping
!= expected_mapping
)
504 if (!get_page_unless_zero(page
))
506 if (page
->mapping
!= expected_mapping
) {
514 remove_node_from_stable_tree(stable_node
);
519 * Removing rmap_item from stable or unstable tree.
520 * This function will clean the information from the stable/unstable tree.
522 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
524 if (rmap_item
->address
& STABLE_FLAG
) {
525 struct stable_node
*stable_node
;
528 stable_node
= rmap_item
->head
;
529 page
= get_ksm_page(stable_node
);
534 hlist_del(&rmap_item
->hlist
);
538 if (stable_node
->hlist
.first
)
543 put_anon_vma(rmap_item
->anon_vma
);
544 rmap_item
->address
&= PAGE_MASK
;
546 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
549 * Usually ksmd can and must skip the rb_erase, because
550 * root_unstable_tree was already reset to RB_ROOT.
551 * But be careful when an mm is exiting: do the rb_erase
552 * if this rmap_item was inserted by this scan, rather
553 * than left over from before.
555 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
558 rb_erase(&rmap_item
->node
, &root_unstable_tree
);
560 ksm_pages_unshared
--;
561 rmap_item
->address
&= PAGE_MASK
;
564 cond_resched(); /* we're called from many long loops */
567 static void remove_trailing_rmap_items(struct mm_slot
*mm_slot
,
568 struct rmap_item
**rmap_list
)
571 struct rmap_item
*rmap_item
= *rmap_list
;
572 *rmap_list
= rmap_item
->rmap_list
;
573 remove_rmap_item_from_tree(rmap_item
);
574 free_rmap_item(rmap_item
);
579 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
580 * than check every pte of a given vma, the locking doesn't quite work for
581 * that - an rmap_item is assigned to the stable tree after inserting ksm
582 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
583 * rmap_items from parent to child at fork time (so as not to waste time
584 * if exit comes before the next scan reaches it).
586 * Similarly, although we'd like to remove rmap_items (so updating counts
587 * and freeing memory) when unmerging an area, it's easier to leave that
588 * to the next pass of ksmd - consider, for example, how ksmd might be
589 * in cmp_and_merge_page on one of the rmap_items we would be removing.
591 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
592 unsigned long start
, unsigned long end
)
597 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
598 if (ksm_test_exit(vma
->vm_mm
))
600 if (signal_pending(current
))
603 err
= break_ksm(vma
, addr
);
610 * Only called through the sysfs control interface:
612 static int unmerge_and_remove_all_rmap_items(void)
614 struct mm_slot
*mm_slot
;
615 struct mm_struct
*mm
;
616 struct vm_area_struct
*vma
;
619 spin_lock(&ksm_mmlist_lock
);
620 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
621 struct mm_slot
, mm_list
);
622 spin_unlock(&ksm_mmlist_lock
);
624 for (mm_slot
= ksm_scan
.mm_slot
;
625 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
627 down_read(&mm
->mmap_sem
);
628 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
629 if (ksm_test_exit(mm
))
631 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
633 err
= unmerge_ksm_pages(vma
,
634 vma
->vm_start
, vma
->vm_end
);
639 remove_trailing_rmap_items(mm_slot
, &mm_slot
->rmap_list
);
641 spin_lock(&ksm_mmlist_lock
);
642 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
643 struct mm_slot
, mm_list
);
644 if (ksm_test_exit(mm
)) {
645 hlist_del(&mm_slot
->link
);
646 list_del(&mm_slot
->mm_list
);
647 spin_unlock(&ksm_mmlist_lock
);
649 free_mm_slot(mm_slot
);
650 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
651 up_read(&mm
->mmap_sem
);
654 spin_unlock(&ksm_mmlist_lock
);
655 up_read(&mm
->mmap_sem
);
663 up_read(&mm
->mmap_sem
);
664 spin_lock(&ksm_mmlist_lock
);
665 ksm_scan
.mm_slot
= &ksm_mm_head
;
666 spin_unlock(&ksm_mmlist_lock
);
669 #endif /* CONFIG_SYSFS */
671 static u32
calc_checksum(struct page
*page
)
674 void *addr
= kmap_atomic(page
, KM_USER0
);
675 checksum
= jhash2(addr
, PAGE_SIZE
/ 4, 17);
676 kunmap_atomic(addr
, KM_USER0
);
680 static int memcmp_pages(struct page
*page1
, struct page
*page2
)
685 addr1
= kmap_atomic(page1
, KM_USER0
);
686 addr2
= kmap_atomic(page2
, KM_USER1
);
687 ret
= memcmp(addr1
, addr2
, PAGE_SIZE
);
688 kunmap_atomic(addr2
, KM_USER1
);
689 kunmap_atomic(addr1
, KM_USER0
);
693 static inline int pages_identical(struct page
*page1
, struct page
*page2
)
695 return !memcmp_pages(page1
, page2
);
698 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
701 struct mm_struct
*mm
= vma
->vm_mm
;
708 addr
= page_address_in_vma(page
, vma
);
712 BUG_ON(PageTransCompound(page
));
713 ptep
= page_check_address(page
, mm
, addr
, &ptl
, 0);
717 if (pte_write(*ptep
) || pte_dirty(*ptep
)) {
720 swapped
= PageSwapCache(page
);
721 flush_cache_page(vma
, addr
, page_to_pfn(page
));
723 * Ok this is tricky, when get_user_pages_fast() run it doesn't
724 * take any lock, therefore the check that we are going to make
725 * with the pagecount against the mapcount is racey and
726 * O_DIRECT can happen right after the check.
727 * So we clear the pte and flush the tlb before the check
728 * this assure us that no O_DIRECT can happen after the check
729 * or in the middle of the check.
731 entry
= ptep_clear_flush(vma
, addr
, ptep
);
733 * Check that no O_DIRECT or similar I/O is in progress on the
736 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
737 set_pte_at(mm
, addr
, ptep
, entry
);
740 if (pte_dirty(entry
))
741 set_page_dirty(page
);
742 entry
= pte_mkclean(pte_wrprotect(entry
));
743 set_pte_at_notify(mm
, addr
, ptep
, entry
);
749 pte_unmap_unlock(ptep
, ptl
);
755 * replace_page - replace page in vma by new ksm page
756 * @vma: vma that holds the pte pointing to page
757 * @page: the page we are replacing by kpage
758 * @kpage: the ksm page we replace page by
759 * @orig_pte: the original value of the pte
761 * Returns 0 on success, -EFAULT on failure.
763 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
764 struct page
*kpage
, pte_t orig_pte
)
766 struct mm_struct
*mm
= vma
->vm_mm
;
775 addr
= page_address_in_vma(page
, vma
);
779 pgd
= pgd_offset(mm
, addr
);
780 if (!pgd_present(*pgd
))
783 pud
= pud_offset(pgd
, addr
);
784 if (!pud_present(*pud
))
787 pmd
= pmd_offset(pud
, addr
);
788 BUG_ON(pmd_trans_huge(*pmd
));
789 if (!pmd_present(*pmd
))
792 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
793 if (!pte_same(*ptep
, orig_pte
)) {
794 pte_unmap_unlock(ptep
, ptl
);
799 page_add_anon_rmap(kpage
, vma
, addr
);
801 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
802 ptep_clear_flush(vma
, addr
, ptep
);
803 set_pte_at_notify(mm
, addr
, ptep
, mk_pte(kpage
, vma
->vm_page_prot
));
805 page_remove_rmap(page
);
806 if (!page_mapped(page
))
807 try_to_free_swap(page
);
810 pte_unmap_unlock(ptep
, ptl
);
816 static int page_trans_compound_anon_split(struct page
*page
)
819 struct page
*transhuge_head
= page_trans_compound_anon(page
);
820 if (transhuge_head
) {
821 /* Get the reference on the head to split it. */
822 if (get_page_unless_zero(transhuge_head
)) {
824 * Recheck we got the reference while the head
825 * was still anonymous.
827 if (PageAnon(transhuge_head
))
828 ret
= split_huge_page(transhuge_head
);
831 * Retry later if split_huge_page run
835 put_page(transhuge_head
);
837 /* Retry later if split_huge_page run from under us. */
844 * try_to_merge_one_page - take two pages and merge them into one
845 * @vma: the vma that holds the pte pointing to page
846 * @page: the PageAnon page that we want to replace with kpage
847 * @kpage: the PageKsm page that we want to map instead of page,
848 * or NULL the first time when we want to use page as kpage.
850 * This function returns 0 if the pages were merged, -EFAULT otherwise.
852 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
853 struct page
*page
, struct page
*kpage
)
855 pte_t orig_pte
= __pte(0);
858 if (page
== kpage
) /* ksm page forked */
861 if (!(vma
->vm_flags
& VM_MERGEABLE
))
863 if (PageTransCompound(page
) && page_trans_compound_anon_split(page
))
865 BUG_ON(PageTransCompound(page
));
870 * We need the page lock to read a stable PageSwapCache in
871 * write_protect_page(). We use trylock_page() instead of
872 * lock_page() because we don't want to wait here - we
873 * prefer to continue scanning and merging different pages,
874 * then come back to this page when it is unlocked.
876 if (!trylock_page(page
))
879 * If this anonymous page is mapped only here, its pte may need
880 * to be write-protected. If it's mapped elsewhere, all of its
881 * ptes are necessarily already write-protected. But in either
882 * case, we need to lock and check page_count is not raised.
884 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
887 * While we hold page lock, upgrade page from
888 * PageAnon+anon_vma to PageKsm+NULL stable_node:
889 * stable_tree_insert() will update stable_node.
891 set_page_stable_node(page
, NULL
);
892 mark_page_accessed(page
);
894 } else if (pages_identical(page
, kpage
))
895 err
= replace_page(vma
, page
, kpage
, orig_pte
);
898 if ((vma
->vm_flags
& VM_LOCKED
) && kpage
&& !err
) {
899 munlock_vma_page(page
);
900 if (!PageMlocked(kpage
)) {
903 mlock_vma_page(kpage
);
904 page
= kpage
; /* for final unlock */
914 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
915 * but no new kernel page is allocated: kpage must already be a ksm page.
917 * This function returns 0 if the pages were merged, -EFAULT otherwise.
919 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
920 struct page
*page
, struct page
*kpage
)
922 struct mm_struct
*mm
= rmap_item
->mm
;
923 struct vm_area_struct
*vma
;
926 down_read(&mm
->mmap_sem
);
927 if (ksm_test_exit(mm
))
929 vma
= find_vma(mm
, rmap_item
->address
);
930 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
933 err
= try_to_merge_one_page(vma
, page
, kpage
);
937 /* Must get reference to anon_vma while still holding mmap_sem */
938 rmap_item
->anon_vma
= vma
->anon_vma
;
939 get_anon_vma(vma
->anon_vma
);
941 up_read(&mm
->mmap_sem
);
946 * try_to_merge_two_pages - take two identical pages and prepare them
947 * to be merged into one page.
949 * This function returns the kpage if we successfully merged two identical
950 * pages into one ksm page, NULL otherwise.
952 * Note that this function upgrades page to ksm page: if one of the pages
953 * is already a ksm page, try_to_merge_with_ksm_page should be used.
955 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
957 struct rmap_item
*tree_rmap_item
,
958 struct page
*tree_page
)
962 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
964 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
967 * If that fails, we have a ksm page with only one pte
968 * pointing to it: so break it.
971 break_cow(rmap_item
);
973 return err
? NULL
: page
;
977 * stable_tree_search - search for page inside the stable tree
979 * This function checks if there is a page inside the stable tree
980 * with identical content to the page that we are scanning right now.
982 * This function returns the stable tree node of identical content if found,
985 static struct page
*stable_tree_search(struct page
*page
)
987 struct rb_node
*node
= root_stable_tree
.rb_node
;
988 struct stable_node
*stable_node
;
990 stable_node
= page_stable_node(page
);
991 if (stable_node
) { /* ksm page forked */
997 struct page
*tree_page
;
1001 stable_node
= rb_entry(node
, struct stable_node
, node
);
1002 tree_page
= get_ksm_page(stable_node
);
1006 ret
= memcmp_pages(page
, tree_page
);
1009 put_page(tree_page
);
1010 node
= node
->rb_left
;
1011 } else if (ret
> 0) {
1012 put_page(tree_page
);
1013 node
= node
->rb_right
;
1022 * stable_tree_insert - insert rmap_item pointing to new ksm page
1023 * into the stable tree.
1025 * This function returns the stable tree node just allocated on success,
1028 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1030 struct rb_node
**new = &root_stable_tree
.rb_node
;
1031 struct rb_node
*parent
= NULL
;
1032 struct stable_node
*stable_node
;
1035 struct page
*tree_page
;
1039 stable_node
= rb_entry(*new, struct stable_node
, node
);
1040 tree_page
= get_ksm_page(stable_node
);
1044 ret
= memcmp_pages(kpage
, tree_page
);
1045 put_page(tree_page
);
1049 new = &parent
->rb_left
;
1051 new = &parent
->rb_right
;
1054 * It is not a bug that stable_tree_search() didn't
1055 * find this node: because at that time our page was
1056 * not yet write-protected, so may have changed since.
1062 stable_node
= alloc_stable_node();
1066 rb_link_node(&stable_node
->node
, parent
, new);
1067 rb_insert_color(&stable_node
->node
, &root_stable_tree
);
1069 INIT_HLIST_HEAD(&stable_node
->hlist
);
1071 stable_node
->kpfn
= page_to_pfn(kpage
);
1072 set_page_stable_node(kpage
, stable_node
);
1078 * unstable_tree_search_insert - search for identical page,
1079 * else insert rmap_item into the unstable tree.
1081 * This function searches for a page in the unstable tree identical to the
1082 * page currently being scanned; and if no identical page is found in the
1083 * tree, we insert rmap_item as a new object into the unstable tree.
1085 * This function returns pointer to rmap_item found to be identical
1086 * to the currently scanned page, NULL otherwise.
1088 * This function does both searching and inserting, because they share
1089 * the same walking algorithm in an rbtree.
1092 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1094 struct page
**tree_pagep
)
1097 struct rb_node
**new = &root_unstable_tree
.rb_node
;
1098 struct rb_node
*parent
= NULL
;
1101 struct rmap_item
*tree_rmap_item
;
1102 struct page
*tree_page
;
1106 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1107 tree_page
= get_mergeable_page(tree_rmap_item
);
1108 if (IS_ERR_OR_NULL(tree_page
))
1112 * Don't substitute a ksm page for a forked page.
1114 if (page
== tree_page
) {
1115 put_page(tree_page
);
1119 ret
= memcmp_pages(page
, tree_page
);
1123 put_page(tree_page
);
1124 new = &parent
->rb_left
;
1125 } else if (ret
> 0) {
1126 put_page(tree_page
);
1127 new = &parent
->rb_right
;
1129 *tree_pagep
= tree_page
;
1130 return tree_rmap_item
;
1134 rmap_item
->address
|= UNSTABLE_FLAG
;
1135 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1136 rb_link_node(&rmap_item
->node
, parent
, new);
1137 rb_insert_color(&rmap_item
->node
, &root_unstable_tree
);
1139 ksm_pages_unshared
++;
1144 * stable_tree_append - add another rmap_item to the linked list of
1145 * rmap_items hanging off a given node of the stable tree, all sharing
1146 * the same ksm page.
1148 static void stable_tree_append(struct rmap_item
*rmap_item
,
1149 struct stable_node
*stable_node
)
1151 rmap_item
->head
= stable_node
;
1152 rmap_item
->address
|= STABLE_FLAG
;
1153 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
1155 if (rmap_item
->hlist
.next
)
1156 ksm_pages_sharing
++;
1162 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1163 * if not, compare checksum to previous and if it's the same, see if page can
1164 * be inserted into the unstable tree, or merged with a page already there and
1165 * both transferred to the stable tree.
1167 * @page: the page that we are searching identical page to.
1168 * @rmap_item: the reverse mapping into the virtual address of this page
1170 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
1172 struct rmap_item
*tree_rmap_item
;
1173 struct page
*tree_page
= NULL
;
1174 struct stable_node
*stable_node
;
1176 unsigned int checksum
;
1179 remove_rmap_item_from_tree(rmap_item
);
1181 /* We first start with searching the page inside the stable tree */
1182 kpage
= stable_tree_search(page
);
1184 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
1187 * The page was successfully merged:
1188 * add its rmap_item to the stable tree.
1191 stable_tree_append(rmap_item
, page_stable_node(kpage
));
1199 * If the hash value of the page has changed from the last time
1200 * we calculated it, this page is changing frequently: therefore we
1201 * don't want to insert it in the unstable tree, and we don't want
1202 * to waste our time searching for something identical to it there.
1204 checksum
= calc_checksum(page
);
1205 if (rmap_item
->oldchecksum
!= checksum
) {
1206 rmap_item
->oldchecksum
= checksum
;
1211 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
1212 if (tree_rmap_item
) {
1213 kpage
= try_to_merge_two_pages(rmap_item
, page
,
1214 tree_rmap_item
, tree_page
);
1215 put_page(tree_page
);
1217 * As soon as we merge this page, we want to remove the
1218 * rmap_item of the page we have merged with from the unstable
1219 * tree, and insert it instead as new node in the stable tree.
1222 remove_rmap_item_from_tree(tree_rmap_item
);
1225 stable_node
= stable_tree_insert(kpage
);
1227 stable_tree_append(tree_rmap_item
, stable_node
);
1228 stable_tree_append(rmap_item
, stable_node
);
1233 * If we fail to insert the page into the stable tree,
1234 * we will have 2 virtual addresses that are pointing
1235 * to a ksm page left outside the stable tree,
1236 * in which case we need to break_cow on both.
1239 break_cow(tree_rmap_item
);
1240 break_cow(rmap_item
);
1246 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
1247 struct rmap_item
**rmap_list
,
1250 struct rmap_item
*rmap_item
;
1252 while (*rmap_list
) {
1253 rmap_item
= *rmap_list
;
1254 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
1256 if (rmap_item
->address
> addr
)
1258 *rmap_list
= rmap_item
->rmap_list
;
1259 remove_rmap_item_from_tree(rmap_item
);
1260 free_rmap_item(rmap_item
);
1263 rmap_item
= alloc_rmap_item();
1265 /* It has already been zeroed */
1266 rmap_item
->mm
= mm_slot
->mm
;
1267 rmap_item
->address
= addr
;
1268 rmap_item
->rmap_list
= *rmap_list
;
1269 *rmap_list
= rmap_item
;
1274 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
1276 struct mm_struct
*mm
;
1277 struct mm_slot
*slot
;
1278 struct vm_area_struct
*vma
;
1279 struct rmap_item
*rmap_item
;
1281 if (list_empty(&ksm_mm_head
.mm_list
))
1284 slot
= ksm_scan
.mm_slot
;
1285 if (slot
== &ksm_mm_head
) {
1287 * A number of pages can hang around indefinitely on per-cpu
1288 * pagevecs, raised page count preventing write_protect_page
1289 * from merging them. Though it doesn't really matter much,
1290 * it is puzzling to see some stuck in pages_volatile until
1291 * other activity jostles them out, and they also prevented
1292 * LTP's KSM test from succeeding deterministically; so drain
1293 * them here (here rather than on entry to ksm_do_scan(),
1294 * so we don't IPI too often when pages_to_scan is set low).
1296 lru_add_drain_all();
1298 root_unstable_tree
= RB_ROOT
;
1300 spin_lock(&ksm_mmlist_lock
);
1301 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
1302 ksm_scan
.mm_slot
= slot
;
1303 spin_unlock(&ksm_mmlist_lock
);
1305 ksm_scan
.address
= 0;
1306 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1310 down_read(&mm
->mmap_sem
);
1311 if (ksm_test_exit(mm
))
1314 vma
= find_vma(mm
, ksm_scan
.address
);
1316 for (; vma
; vma
= vma
->vm_next
) {
1317 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1319 if (ksm_scan
.address
< vma
->vm_start
)
1320 ksm_scan
.address
= vma
->vm_start
;
1322 ksm_scan
.address
= vma
->vm_end
;
1324 while (ksm_scan
.address
< vma
->vm_end
) {
1325 if (ksm_test_exit(mm
))
1327 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
1328 if (IS_ERR_OR_NULL(*page
)) {
1329 ksm_scan
.address
+= PAGE_SIZE
;
1333 if (PageAnon(*page
) ||
1334 page_trans_compound_anon(*page
)) {
1335 flush_anon_page(vma
, *page
, ksm_scan
.address
);
1336 flush_dcache_page(*page
);
1337 rmap_item
= get_next_rmap_item(slot
,
1338 ksm_scan
.rmap_list
, ksm_scan
.address
);
1340 ksm_scan
.rmap_list
=
1341 &rmap_item
->rmap_list
;
1342 ksm_scan
.address
+= PAGE_SIZE
;
1345 up_read(&mm
->mmap_sem
);
1349 ksm_scan
.address
+= PAGE_SIZE
;
1354 if (ksm_test_exit(mm
)) {
1355 ksm_scan
.address
= 0;
1356 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1359 * Nuke all the rmap_items that are above this current rmap:
1360 * because there were no VM_MERGEABLE vmas with such addresses.
1362 remove_trailing_rmap_items(slot
, ksm_scan
.rmap_list
);
1364 spin_lock(&ksm_mmlist_lock
);
1365 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
1366 struct mm_slot
, mm_list
);
1367 if (ksm_scan
.address
== 0) {
1369 * We've completed a full scan of all vmas, holding mmap_sem
1370 * throughout, and found no VM_MERGEABLE: so do the same as
1371 * __ksm_exit does to remove this mm from all our lists now.
1372 * This applies either when cleaning up after __ksm_exit
1373 * (but beware: we can reach here even before __ksm_exit),
1374 * or when all VM_MERGEABLE areas have been unmapped (and
1375 * mmap_sem then protects against race with MADV_MERGEABLE).
1377 hlist_del(&slot
->link
);
1378 list_del(&slot
->mm_list
);
1379 spin_unlock(&ksm_mmlist_lock
);
1382 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1383 up_read(&mm
->mmap_sem
);
1386 spin_unlock(&ksm_mmlist_lock
);
1387 up_read(&mm
->mmap_sem
);
1390 /* Repeat until we've completed scanning the whole list */
1391 slot
= ksm_scan
.mm_slot
;
1392 if (slot
!= &ksm_mm_head
)
1400 * ksm_do_scan - the ksm scanner main worker function.
1401 * @scan_npages - number of pages we want to scan before we return.
1403 static void ksm_do_scan(unsigned int scan_npages
)
1405 struct rmap_item
*rmap_item
;
1406 struct page
*uninitialized_var(page
);
1408 while (scan_npages
-- && likely(!freezing(current
))) {
1410 rmap_item
= scan_get_next_rmap_item(&page
);
1413 if (!PageKsm(page
) || !in_stable_tree(rmap_item
))
1414 cmp_and_merge_page(page
, rmap_item
);
1419 static int ksmd_should_run(void)
1421 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
1424 static int ksm_scan_thread(void *nothing
)
1427 set_user_nice(current
, 5);
1429 while (!kthread_should_stop()) {
1430 mutex_lock(&ksm_thread_mutex
);
1431 if (ksmd_should_run())
1432 ksm_do_scan(ksm_thread_pages_to_scan
);
1433 mutex_unlock(&ksm_thread_mutex
);
1437 if (ksmd_should_run()) {
1438 schedule_timeout_interruptible(
1439 msecs_to_jiffies(ksm_thread_sleep_millisecs
));
1441 wait_event_freezable(ksm_thread_wait
,
1442 ksmd_should_run() || kthread_should_stop());
1448 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
1449 unsigned long end
, int advice
, unsigned long *vm_flags
)
1451 struct mm_struct
*mm
= vma
->vm_mm
;
1455 case MADV_MERGEABLE
:
1457 * Be somewhat over-protective for now!
1459 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
1460 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
1461 VM_RESERVED
| VM_HUGETLB
| VM_INSERTPAGE
|
1462 VM_NONLINEAR
| VM_MIXEDMAP
| VM_SAO
))
1463 return 0; /* just ignore the advice */
1465 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
1466 err
= __ksm_enter(mm
);
1471 *vm_flags
|= VM_MERGEABLE
;
1474 case MADV_UNMERGEABLE
:
1475 if (!(*vm_flags
& VM_MERGEABLE
))
1476 return 0; /* just ignore the advice */
1478 if (vma
->anon_vma
) {
1479 err
= unmerge_ksm_pages(vma
, start
, end
);
1484 *vm_flags
&= ~VM_MERGEABLE
;
1491 int __ksm_enter(struct mm_struct
*mm
)
1493 struct mm_slot
*mm_slot
;
1496 mm_slot
= alloc_mm_slot();
1500 /* Check ksm_run too? Would need tighter locking */
1501 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
1503 spin_lock(&ksm_mmlist_lock
);
1504 insert_to_mm_slots_hash(mm
, mm_slot
);
1506 * Insert just behind the scanning cursor, to let the area settle
1507 * down a little; when fork is followed by immediate exec, we don't
1508 * want ksmd to waste time setting up and tearing down an rmap_list.
1510 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
1511 spin_unlock(&ksm_mmlist_lock
);
1513 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1514 atomic_inc(&mm
->mm_count
);
1517 wake_up_interruptible(&ksm_thread_wait
);
1522 void __ksm_exit(struct mm_struct
*mm
)
1524 struct mm_slot
*mm_slot
;
1525 int easy_to_free
= 0;
1528 * This process is exiting: if it's straightforward (as is the
1529 * case when ksmd was never running), free mm_slot immediately.
1530 * But if it's at the cursor or has rmap_items linked to it, use
1531 * mmap_sem to synchronize with any break_cows before pagetables
1532 * are freed, and leave the mm_slot on the list for ksmd to free.
1533 * Beware: ksm may already have noticed it exiting and freed the slot.
1536 spin_lock(&ksm_mmlist_lock
);
1537 mm_slot
= get_mm_slot(mm
);
1538 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
1539 if (!mm_slot
->rmap_list
) {
1540 hlist_del(&mm_slot
->link
);
1541 list_del(&mm_slot
->mm_list
);
1544 list_move(&mm_slot
->mm_list
,
1545 &ksm_scan
.mm_slot
->mm_list
);
1548 spin_unlock(&ksm_mmlist_lock
);
1551 free_mm_slot(mm_slot
);
1552 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1554 } else if (mm_slot
) {
1555 down_write(&mm
->mmap_sem
);
1556 up_write(&mm
->mmap_sem
);
1560 struct page
*ksm_does_need_to_copy(struct page
*page
,
1561 struct vm_area_struct
*vma
, unsigned long address
)
1563 struct page
*new_page
;
1565 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
1567 copy_user_highpage(new_page
, page
, address
, vma
);
1569 SetPageDirty(new_page
);
1570 __SetPageUptodate(new_page
);
1571 SetPageSwapBacked(new_page
);
1572 __set_page_locked(new_page
);
1574 if (page_evictable(new_page
, vma
))
1575 lru_cache_add_lru(new_page
, LRU_ACTIVE_ANON
);
1577 add_page_to_unevictable_list(new_page
);
1583 int page_referenced_ksm(struct page
*page
, struct mem_cgroup
*memcg
,
1584 unsigned long *vm_flags
)
1586 struct stable_node
*stable_node
;
1587 struct rmap_item
*rmap_item
;
1588 struct hlist_node
*hlist
;
1589 unsigned int mapcount
= page_mapcount(page
);
1591 int search_new_forks
= 0;
1593 VM_BUG_ON(!PageKsm(page
));
1594 VM_BUG_ON(!PageLocked(page
));
1596 stable_node
= page_stable_node(page
);
1600 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
1601 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1602 struct anon_vma_chain
*vmac
;
1603 struct vm_area_struct
*vma
;
1605 anon_vma_lock(anon_vma
);
1606 list_for_each_entry(vmac
, &anon_vma
->head
, same_anon_vma
) {
1608 if (rmap_item
->address
< vma
->vm_start
||
1609 rmap_item
->address
>= vma
->vm_end
)
1612 * Initially we examine only the vma which covers this
1613 * rmap_item; but later, if there is still work to do,
1614 * we examine covering vmas in other mms: in case they
1615 * were forked from the original since ksmd passed.
1617 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1620 if (memcg
&& !mm_match_cgroup(vma
->vm_mm
, memcg
))
1623 referenced
+= page_referenced_one(page
, vma
,
1624 rmap_item
->address
, &mapcount
, vm_flags
);
1625 if (!search_new_forks
|| !mapcount
)
1628 anon_vma_unlock(anon_vma
);
1632 if (!search_new_forks
++)
1638 int try_to_unmap_ksm(struct page
*page
, enum ttu_flags flags
)
1640 struct stable_node
*stable_node
;
1641 struct hlist_node
*hlist
;
1642 struct rmap_item
*rmap_item
;
1643 int ret
= SWAP_AGAIN
;
1644 int search_new_forks
= 0;
1646 VM_BUG_ON(!PageKsm(page
));
1647 VM_BUG_ON(!PageLocked(page
));
1649 stable_node
= page_stable_node(page
);
1653 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
1654 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1655 struct anon_vma_chain
*vmac
;
1656 struct vm_area_struct
*vma
;
1658 anon_vma_lock(anon_vma
);
1659 list_for_each_entry(vmac
, &anon_vma
->head
, same_anon_vma
) {
1661 if (rmap_item
->address
< vma
->vm_start
||
1662 rmap_item
->address
>= vma
->vm_end
)
1665 * Initially we examine only the vma which covers this
1666 * rmap_item; but later, if there is still work to do,
1667 * we examine covering vmas in other mms: in case they
1668 * were forked from the original since ksmd passed.
1670 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1673 ret
= try_to_unmap_one(page
, vma
,
1674 rmap_item
->address
, flags
);
1675 if (ret
!= SWAP_AGAIN
|| !page_mapped(page
)) {
1676 anon_vma_unlock(anon_vma
);
1680 anon_vma_unlock(anon_vma
);
1682 if (!search_new_forks
++)
1688 #ifdef CONFIG_MIGRATION
1689 int rmap_walk_ksm(struct page
*page
, int (*rmap_one
)(struct page
*,
1690 struct vm_area_struct
*, unsigned long, void *), void *arg
)
1692 struct stable_node
*stable_node
;
1693 struct hlist_node
*hlist
;
1694 struct rmap_item
*rmap_item
;
1695 int ret
= SWAP_AGAIN
;
1696 int search_new_forks
= 0;
1698 VM_BUG_ON(!PageKsm(page
));
1699 VM_BUG_ON(!PageLocked(page
));
1701 stable_node
= page_stable_node(page
);
1705 hlist_for_each_entry(rmap_item
, hlist
, &stable_node
->hlist
, hlist
) {
1706 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1707 struct anon_vma_chain
*vmac
;
1708 struct vm_area_struct
*vma
;
1710 anon_vma_lock(anon_vma
);
1711 list_for_each_entry(vmac
, &anon_vma
->head
, same_anon_vma
) {
1713 if (rmap_item
->address
< vma
->vm_start
||
1714 rmap_item
->address
>= vma
->vm_end
)
1717 * Initially we examine only the vma which covers this
1718 * rmap_item; but later, if there is still work to do,
1719 * we examine covering vmas in other mms: in case they
1720 * were forked from the original since ksmd passed.
1722 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1725 ret
= rmap_one(page
, vma
, rmap_item
->address
, arg
);
1726 if (ret
!= SWAP_AGAIN
) {
1727 anon_vma_unlock(anon_vma
);
1731 anon_vma_unlock(anon_vma
);
1733 if (!search_new_forks
++)
1739 void ksm_migrate_page(struct page
*newpage
, struct page
*oldpage
)
1741 struct stable_node
*stable_node
;
1743 VM_BUG_ON(!PageLocked(oldpage
));
1744 VM_BUG_ON(!PageLocked(newpage
));
1745 VM_BUG_ON(newpage
->mapping
!= oldpage
->mapping
);
1747 stable_node
= page_stable_node(newpage
);
1749 VM_BUG_ON(stable_node
->kpfn
!= page_to_pfn(oldpage
));
1750 stable_node
->kpfn
= page_to_pfn(newpage
);
1753 #endif /* CONFIG_MIGRATION */
1755 #ifdef CONFIG_MEMORY_HOTREMOVE
1756 static struct stable_node
*ksm_check_stable_tree(unsigned long start_pfn
,
1757 unsigned long end_pfn
)
1759 struct rb_node
*node
;
1761 for (node
= rb_first(&root_stable_tree
); node
; node
= rb_next(node
)) {
1762 struct stable_node
*stable_node
;
1764 stable_node
= rb_entry(node
, struct stable_node
, node
);
1765 if (stable_node
->kpfn
>= start_pfn
&&
1766 stable_node
->kpfn
< end_pfn
)
1772 static int ksm_memory_callback(struct notifier_block
*self
,
1773 unsigned long action
, void *arg
)
1775 struct memory_notify
*mn
= arg
;
1776 struct stable_node
*stable_node
;
1779 case MEM_GOING_OFFLINE
:
1781 * Keep it very simple for now: just lock out ksmd and
1782 * MADV_UNMERGEABLE while any memory is going offline.
1783 * mutex_lock_nested() is necessary because lockdep was alarmed
1784 * that here we take ksm_thread_mutex inside notifier chain
1785 * mutex, and later take notifier chain mutex inside
1786 * ksm_thread_mutex to unlock it. But that's safe because both
1787 * are inside mem_hotplug_mutex.
1789 mutex_lock_nested(&ksm_thread_mutex
, SINGLE_DEPTH_NESTING
);
1794 * Most of the work is done by page migration; but there might
1795 * be a few stable_nodes left over, still pointing to struct
1796 * pages which have been offlined: prune those from the tree.
1798 while ((stable_node
= ksm_check_stable_tree(mn
->start_pfn
,
1799 mn
->start_pfn
+ mn
->nr_pages
)) != NULL
)
1800 remove_node_from_stable_tree(stable_node
);
1803 case MEM_CANCEL_OFFLINE
:
1804 mutex_unlock(&ksm_thread_mutex
);
1809 #endif /* CONFIG_MEMORY_HOTREMOVE */
1813 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1816 #define KSM_ATTR_RO(_name) \
1817 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1818 #define KSM_ATTR(_name) \
1819 static struct kobj_attribute _name##_attr = \
1820 __ATTR(_name, 0644, _name##_show, _name##_store)
1822 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
1823 struct kobj_attribute
*attr
, char *buf
)
1825 return sprintf(buf
, "%u\n", ksm_thread_sleep_millisecs
);
1828 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
1829 struct kobj_attribute
*attr
,
1830 const char *buf
, size_t count
)
1832 unsigned long msecs
;
1835 err
= strict_strtoul(buf
, 10, &msecs
);
1836 if (err
|| msecs
> UINT_MAX
)
1839 ksm_thread_sleep_millisecs
= msecs
;
1843 KSM_ATTR(sleep_millisecs
);
1845 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
1846 struct kobj_attribute
*attr
, char *buf
)
1848 return sprintf(buf
, "%u\n", ksm_thread_pages_to_scan
);
1851 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
1852 struct kobj_attribute
*attr
,
1853 const char *buf
, size_t count
)
1856 unsigned long nr_pages
;
1858 err
= strict_strtoul(buf
, 10, &nr_pages
);
1859 if (err
|| nr_pages
> UINT_MAX
)
1862 ksm_thread_pages_to_scan
= nr_pages
;
1866 KSM_ATTR(pages_to_scan
);
1868 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
1871 return sprintf(buf
, "%u\n", ksm_run
);
1874 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
1875 const char *buf
, size_t count
)
1878 unsigned long flags
;
1880 err
= strict_strtoul(buf
, 10, &flags
);
1881 if (err
|| flags
> UINT_MAX
)
1883 if (flags
> KSM_RUN_UNMERGE
)
1887 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1888 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1889 * breaking COW to free the pages_shared (but leaves mm_slots
1890 * on the list for when ksmd may be set running again).
1893 mutex_lock(&ksm_thread_mutex
);
1894 if (ksm_run
!= flags
) {
1896 if (flags
& KSM_RUN_UNMERGE
) {
1897 current
->flags
|= PF_OOM_ORIGIN
;
1898 err
= unmerge_and_remove_all_rmap_items();
1899 current
->flags
&= ~PF_OOM_ORIGIN
;
1901 ksm_run
= KSM_RUN_STOP
;
1906 mutex_unlock(&ksm_thread_mutex
);
1908 if (flags
& KSM_RUN_MERGE
)
1909 wake_up_interruptible(&ksm_thread_wait
);
1915 static ssize_t
pages_shared_show(struct kobject
*kobj
,
1916 struct kobj_attribute
*attr
, char *buf
)
1918 return sprintf(buf
, "%lu\n", ksm_pages_shared
);
1920 KSM_ATTR_RO(pages_shared
);
1922 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
1923 struct kobj_attribute
*attr
, char *buf
)
1925 return sprintf(buf
, "%lu\n", ksm_pages_sharing
);
1927 KSM_ATTR_RO(pages_sharing
);
1929 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
1930 struct kobj_attribute
*attr
, char *buf
)
1932 return sprintf(buf
, "%lu\n", ksm_pages_unshared
);
1934 KSM_ATTR_RO(pages_unshared
);
1936 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
1937 struct kobj_attribute
*attr
, char *buf
)
1939 long ksm_pages_volatile
;
1941 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
1942 - ksm_pages_sharing
- ksm_pages_unshared
;
1944 * It was not worth any locking to calculate that statistic,
1945 * but it might therefore sometimes be negative: conceal that.
1947 if (ksm_pages_volatile
< 0)
1948 ksm_pages_volatile
= 0;
1949 return sprintf(buf
, "%ld\n", ksm_pages_volatile
);
1951 KSM_ATTR_RO(pages_volatile
);
1953 static ssize_t
full_scans_show(struct kobject
*kobj
,
1954 struct kobj_attribute
*attr
, char *buf
)
1956 return sprintf(buf
, "%lu\n", ksm_scan
.seqnr
);
1958 KSM_ATTR_RO(full_scans
);
1960 static struct attribute
*ksm_attrs
[] = {
1961 &sleep_millisecs_attr
.attr
,
1962 &pages_to_scan_attr
.attr
,
1964 &pages_shared_attr
.attr
,
1965 &pages_sharing_attr
.attr
,
1966 &pages_unshared_attr
.attr
,
1967 &pages_volatile_attr
.attr
,
1968 &full_scans_attr
.attr
,
1972 static struct attribute_group ksm_attr_group
= {
1976 #endif /* CONFIG_SYSFS */
1978 static int __init
ksm_init(void)
1980 struct task_struct
*ksm_thread
;
1983 err
= ksm_slab_init();
1987 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
1988 if (IS_ERR(ksm_thread
)) {
1989 printk(KERN_ERR
"ksm: creating kthread failed\n");
1990 err
= PTR_ERR(ksm_thread
);
1995 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
1997 printk(KERN_ERR
"ksm: register sysfs failed\n");
1998 kthread_stop(ksm_thread
);
2002 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
2004 #endif /* CONFIG_SYSFS */
2006 #ifdef CONFIG_MEMORY_HOTREMOVE
2008 * Choose a high priority since the callback takes ksm_thread_mutex:
2009 * later callbacks could only be taking locks which nest within that.
2011 hotplug_memory_notifier(ksm_memory_callback
, 100);
2020 module_init(ksm_init
)