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/mmu_notifier.h>
33 #include <linux/swap.h>
34 #include <linux/ksm.h>
36 #include <asm/tlbflush.h>
39 * A few notes about the KSM scanning process,
40 * to make it easier to understand the data structures below:
42 * In order to reduce excessive scanning, KSM sorts the memory pages by their
43 * contents into a data structure that holds pointers to the pages' locations.
45 * Since the contents of the pages may change at any moment, KSM cannot just
46 * insert the pages into a normal sorted tree and expect it to find anything.
47 * Therefore KSM uses two data structures - the stable and the unstable tree.
49 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
50 * by their contents. Because each such page is write-protected, searching on
51 * this tree is fully assured to be working (except when pages are unmapped),
52 * and therefore this tree is called the stable tree.
54 * In addition to the stable tree, KSM uses a second data structure called the
55 * unstable tree: this tree holds pointers to pages which have been found to
56 * be "unchanged for a period of time". The unstable tree sorts these pages
57 * by their contents, but since they are not write-protected, KSM cannot rely
58 * upon the unstable tree to work correctly - the unstable tree is liable to
59 * be corrupted as its contents are modified, and so it is called unstable.
61 * KSM solves this problem by several techniques:
63 * 1) The unstable tree is flushed every time KSM completes scanning all
64 * memory areas, and then the tree is rebuilt again from the beginning.
65 * 2) KSM will only insert into the unstable tree, pages whose hash value
66 * has not changed since the previous scan of all memory areas.
67 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
68 * colors of the nodes and not on their contents, assuring that even when
69 * the tree gets "corrupted" it won't get out of balance, so scanning time
70 * remains the same (also, searching and inserting nodes in an rbtree uses
71 * the same algorithm, so we have no overhead when we flush and rebuild).
72 * 4) KSM never flushes the stable tree, which means that even if it were to
73 * take 10 attempts to find a page in the unstable tree, once it is found,
74 * it is secured in the stable tree. (When we scan a new page, we first
75 * compare it against the stable tree, and then against the unstable tree.)
79 * struct mm_slot - ksm information per mm that is being scanned
80 * @link: link to the mm_slots hash list
81 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
82 * @rmap_list: head for this mm_slot's list of rmap_items
83 * @mm: the mm that this information is valid for
86 struct hlist_node link
;
87 struct list_head mm_list
;
88 struct list_head rmap_list
;
93 * struct ksm_scan - cursor for scanning
94 * @mm_slot: the current mm_slot we are scanning
95 * @address: the next address inside that to be scanned
96 * @rmap_item: the current rmap that we are scanning inside the rmap_list
97 * @seqnr: count of completed full scans (needed when removing unstable node)
99 * There is only the one ksm_scan instance of this cursor structure.
102 struct mm_slot
*mm_slot
;
103 unsigned long address
;
104 struct rmap_item
*rmap_item
;
109 * struct rmap_item - reverse mapping item for virtual addresses
110 * @link: link into mm_slot's rmap_list (rmap_list is per mm)
111 * @mm: the memory structure this rmap_item is pointing into
112 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
113 * @oldchecksum: previous checksum of the page at that virtual address
114 * @node: rb_node of this rmap_item in either unstable or stable tree
115 * @next: next rmap_item hanging off the same node of the stable tree
116 * @prev: previous rmap_item hanging off the same node of the stable tree
119 struct list_head link
;
120 struct mm_struct
*mm
;
121 unsigned long address
; /* + low bits used for flags below */
123 unsigned int oldchecksum
; /* when unstable */
124 struct rmap_item
*next
; /* when stable */
127 struct rb_node node
; /* when tree node */
128 struct rmap_item
*prev
; /* in stable list */
132 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
133 #define NODE_FLAG 0x100 /* is a node of unstable or stable tree */
134 #define STABLE_FLAG 0x200 /* is a node or list item of stable tree */
136 /* The stable and unstable tree heads */
137 static struct rb_root root_stable_tree
= RB_ROOT
;
138 static struct rb_root root_unstable_tree
= RB_ROOT
;
140 #define MM_SLOTS_HASH_HEADS 1024
141 static struct hlist_head
*mm_slots_hash
;
143 static struct mm_slot ksm_mm_head
= {
144 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
146 static struct ksm_scan ksm_scan
= {
147 .mm_slot
= &ksm_mm_head
,
150 static struct kmem_cache
*rmap_item_cache
;
151 static struct kmem_cache
*mm_slot_cache
;
153 /* The number of nodes in the stable tree */
154 static unsigned long ksm_pages_shared
;
156 /* The number of page slots additionally sharing those nodes */
157 static unsigned long ksm_pages_sharing
;
159 /* The number of nodes in the unstable tree */
160 static unsigned long ksm_pages_unshared
;
162 /* The number of rmap_items in use: to calculate pages_volatile */
163 static unsigned long ksm_rmap_items
;
165 /* Limit on the number of unswappable pages used */
166 static unsigned long ksm_max_kernel_pages
;
168 /* Number of pages ksmd should scan in one batch */
169 static unsigned int ksm_thread_pages_to_scan
= 100;
171 /* Milliseconds ksmd should sleep between batches */
172 static unsigned int ksm_thread_sleep_millisecs
= 20;
174 #define KSM_RUN_STOP 0
175 #define KSM_RUN_MERGE 1
176 #define KSM_RUN_UNMERGE 2
177 static unsigned int ksm_run
= KSM_RUN_STOP
;
179 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
180 static DEFINE_MUTEX(ksm_thread_mutex
);
181 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
183 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
184 sizeof(struct __struct), __alignof__(struct __struct),\
187 static int __init
ksm_slab_init(void)
189 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
190 if (!rmap_item_cache
)
193 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
200 kmem_cache_destroy(rmap_item_cache
);
205 static void __init
ksm_slab_free(void)
207 kmem_cache_destroy(mm_slot_cache
);
208 kmem_cache_destroy(rmap_item_cache
);
209 mm_slot_cache
= NULL
;
212 static inline struct rmap_item
*alloc_rmap_item(void)
214 struct rmap_item
*rmap_item
;
216 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
);
222 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
225 rmap_item
->mm
= NULL
; /* debug safety */
226 kmem_cache_free(rmap_item_cache
, rmap_item
);
229 static inline struct mm_slot
*alloc_mm_slot(void)
231 if (!mm_slot_cache
) /* initialization failed */
233 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
236 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
238 kmem_cache_free(mm_slot_cache
, mm_slot
);
241 static int __init
mm_slots_hash_init(void)
243 mm_slots_hash
= kzalloc(MM_SLOTS_HASH_HEADS
* sizeof(struct hlist_head
),
250 static void __init
mm_slots_hash_free(void)
252 kfree(mm_slots_hash
);
255 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
257 struct mm_slot
*mm_slot
;
258 struct hlist_head
*bucket
;
259 struct hlist_node
*node
;
261 bucket
= &mm_slots_hash
[((unsigned long)mm
/ sizeof(struct mm_struct
))
262 % MM_SLOTS_HASH_HEADS
];
263 hlist_for_each_entry(mm_slot
, node
, bucket
, link
) {
264 if (mm
== mm_slot
->mm
)
270 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
271 struct mm_slot
*mm_slot
)
273 struct hlist_head
*bucket
;
275 bucket
= &mm_slots_hash
[((unsigned long)mm
/ sizeof(struct mm_struct
))
276 % MM_SLOTS_HASH_HEADS
];
278 INIT_LIST_HEAD(&mm_slot
->rmap_list
);
279 hlist_add_head(&mm_slot
->link
, bucket
);
282 static inline int in_stable_tree(struct rmap_item
*rmap_item
)
284 return rmap_item
->address
& STABLE_FLAG
;
288 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
289 * page tables after it has passed through ksm_exit() - which, if necessary,
290 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
291 * a special flag: they can just back out as soon as mm_users goes to zero.
292 * ksm_test_exit() is used throughout to make this test for exit: in some
293 * places for correctness, in some places just to avoid unnecessary work.
295 static inline bool ksm_test_exit(struct mm_struct
*mm
)
297 return atomic_read(&mm
->mm_users
) == 0;
301 * We use break_ksm to break COW on a ksm page: it's a stripped down
303 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
306 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
307 * in case the application has unmapped and remapped mm,addr meanwhile.
308 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
309 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
311 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
318 page
= follow_page(vma
, addr
, FOLL_GET
);
322 ret
= handle_mm_fault(vma
->vm_mm
, vma
, addr
,
325 ret
= VM_FAULT_WRITE
;
327 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_OOM
)));
329 * We must loop because handle_mm_fault() may back out if there's
330 * any difficulty e.g. if pte accessed bit gets updated concurrently.
332 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
333 * COW has been broken, even if the vma does not permit VM_WRITE;
334 * but note that a concurrent fault might break PageKsm for us.
336 * VM_FAULT_SIGBUS could occur if we race with truncation of the
337 * backing file, which also invalidates anonymous pages: that's
338 * okay, that truncation will have unmapped the PageKsm for us.
340 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
341 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
342 * current task has TIF_MEMDIE set, and will be OOM killed on return
343 * to user; and ksmd, having no mm, would never be chosen for that.
345 * But if the mm is in a limited mem_cgroup, then the fault may fail
346 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
347 * even ksmd can fail in this way - though it's usually breaking ksm
348 * just to undo a merge it made a moment before, so unlikely to oom.
350 * That's a pity: we might therefore have more kernel pages allocated
351 * than we're counting as nodes in the stable tree; but ksm_do_scan
352 * will retry to break_cow on each pass, so should recover the page
353 * in due course. The important thing is to not let VM_MERGEABLE
354 * be cleared while any such pages might remain in the area.
356 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
359 static void break_cow(struct rmap_item
*rmap_item
)
361 struct mm_struct
*mm
= rmap_item
->mm
;
362 unsigned long addr
= rmap_item
->address
;
363 struct vm_area_struct
*vma
;
365 down_read(&mm
->mmap_sem
);
366 if (ksm_test_exit(mm
))
368 vma
= find_vma(mm
, addr
);
369 if (!vma
|| vma
->vm_start
> addr
)
371 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
373 break_ksm(vma
, addr
);
375 up_read(&mm
->mmap_sem
);
378 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
380 struct mm_struct
*mm
= rmap_item
->mm
;
381 unsigned long addr
= rmap_item
->address
;
382 struct vm_area_struct
*vma
;
385 down_read(&mm
->mmap_sem
);
386 if (ksm_test_exit(mm
))
388 vma
= find_vma(mm
, addr
);
389 if (!vma
|| vma
->vm_start
> addr
)
391 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
394 page
= follow_page(vma
, addr
, FOLL_GET
);
397 if (PageAnon(page
)) {
398 flush_anon_page(vma
, page
, addr
);
399 flush_dcache_page(page
);
404 up_read(&mm
->mmap_sem
);
409 * get_ksm_page: checks if the page at the virtual address in rmap_item
410 * is still PageKsm, in which case we can trust the content of the page,
411 * and it returns the gotten page; but NULL if the page has been zapped.
413 static struct page
*get_ksm_page(struct rmap_item
*rmap_item
)
417 page
= get_mergeable_page(rmap_item
);
418 if (page
&& !PageKsm(page
)) {
426 * Removing rmap_item from stable or unstable tree.
427 * This function will clean the information from the stable/unstable tree.
429 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
431 if (in_stable_tree(rmap_item
)) {
432 struct rmap_item
*next_item
= rmap_item
->next
;
434 if (rmap_item
->address
& NODE_FLAG
) {
436 rb_replace_node(&rmap_item
->node
,
439 next_item
->address
|= NODE_FLAG
;
442 rb_erase(&rmap_item
->node
, &root_stable_tree
);
446 struct rmap_item
*prev_item
= rmap_item
->prev
;
448 BUG_ON(prev_item
->next
!= rmap_item
);
449 prev_item
->next
= next_item
;
451 BUG_ON(next_item
->prev
!= rmap_item
);
452 next_item
->prev
= rmap_item
->prev
;
457 rmap_item
->next
= NULL
;
458 rmap_item
->address
&= PAGE_MASK
;
460 } else if (rmap_item
->address
& NODE_FLAG
) {
463 * Usually ksmd can and must skip the rb_erase, because
464 * root_unstable_tree was already reset to RB_ROOT.
465 * But be careful when an mm is exiting: do the rb_erase
466 * if this rmap_item was inserted by this scan, rather
467 * than left over from before.
469 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
472 rb_erase(&rmap_item
->node
, &root_unstable_tree
);
474 ksm_pages_unshared
--;
475 rmap_item
->address
&= PAGE_MASK
;
478 cond_resched(); /* we're called from many long loops */
481 static void remove_trailing_rmap_items(struct mm_slot
*mm_slot
,
482 struct list_head
*cur
)
484 struct rmap_item
*rmap_item
;
486 while (cur
!= &mm_slot
->rmap_list
) {
487 rmap_item
= list_entry(cur
, struct rmap_item
, link
);
489 remove_rmap_item_from_tree(rmap_item
);
490 list_del(&rmap_item
->link
);
491 free_rmap_item(rmap_item
);
496 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
497 * than check every pte of a given vma, the locking doesn't quite work for
498 * that - an rmap_item is assigned to the stable tree after inserting ksm
499 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
500 * rmap_items from parent to child at fork time (so as not to waste time
501 * if exit comes before the next scan reaches it).
503 * Similarly, although we'd like to remove rmap_items (so updating counts
504 * and freeing memory) when unmerging an area, it's easier to leave that
505 * to the next pass of ksmd - consider, for example, how ksmd might be
506 * in cmp_and_merge_page on one of the rmap_items we would be removing.
508 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
509 unsigned long start
, unsigned long end
)
514 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
515 if (ksm_test_exit(vma
->vm_mm
))
517 if (signal_pending(current
))
520 err
= break_ksm(vma
, addr
);
527 * Only called through the sysfs control interface:
529 static int unmerge_and_remove_all_rmap_items(void)
531 struct mm_slot
*mm_slot
;
532 struct mm_struct
*mm
;
533 struct vm_area_struct
*vma
;
536 spin_lock(&ksm_mmlist_lock
);
537 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
538 struct mm_slot
, mm_list
);
539 spin_unlock(&ksm_mmlist_lock
);
541 for (mm_slot
= ksm_scan
.mm_slot
;
542 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
544 down_read(&mm
->mmap_sem
);
545 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
546 if (ksm_test_exit(mm
))
548 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
550 err
= unmerge_ksm_pages(vma
,
551 vma
->vm_start
, vma
->vm_end
);
556 remove_trailing_rmap_items(mm_slot
, mm_slot
->rmap_list
.next
);
558 spin_lock(&ksm_mmlist_lock
);
559 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
560 struct mm_slot
, mm_list
);
561 if (ksm_test_exit(mm
)) {
562 hlist_del(&mm_slot
->link
);
563 list_del(&mm_slot
->mm_list
);
564 spin_unlock(&ksm_mmlist_lock
);
566 free_mm_slot(mm_slot
);
567 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
568 up_read(&mm
->mmap_sem
);
571 spin_unlock(&ksm_mmlist_lock
);
572 up_read(&mm
->mmap_sem
);
580 up_read(&mm
->mmap_sem
);
581 spin_lock(&ksm_mmlist_lock
);
582 ksm_scan
.mm_slot
= &ksm_mm_head
;
583 spin_unlock(&ksm_mmlist_lock
);
586 #endif /* CONFIG_SYSFS */
588 static u32
calc_checksum(struct page
*page
)
591 void *addr
= kmap_atomic(page
, KM_USER0
);
592 checksum
= jhash2(addr
, PAGE_SIZE
/ 4, 17);
593 kunmap_atomic(addr
, KM_USER0
);
597 static int memcmp_pages(struct page
*page1
, struct page
*page2
)
602 addr1
= kmap_atomic(page1
, KM_USER0
);
603 addr2
= kmap_atomic(page2
, KM_USER1
);
604 ret
= memcmp(addr1
, addr2
, PAGE_SIZE
);
605 kunmap_atomic(addr2
, KM_USER1
);
606 kunmap_atomic(addr1
, KM_USER0
);
610 static inline int pages_identical(struct page
*page1
, struct page
*page2
)
612 return !memcmp_pages(page1
, page2
);
615 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
618 struct mm_struct
*mm
= vma
->vm_mm
;
625 addr
= page_address_in_vma(page
, vma
);
629 ptep
= page_check_address(page
, mm
, addr
, &ptl
, 0);
633 if (pte_write(*ptep
)) {
636 swapped
= PageSwapCache(page
);
637 flush_cache_page(vma
, addr
, page_to_pfn(page
));
639 * Ok this is tricky, when get_user_pages_fast() run it doesnt
640 * take any lock, therefore the check that we are going to make
641 * with the pagecount against the mapcount is racey and
642 * O_DIRECT can happen right after the check.
643 * So we clear the pte and flush the tlb before the check
644 * this assure us that no O_DIRECT can happen after the check
645 * or in the middle of the check.
647 entry
= ptep_clear_flush(vma
, addr
, ptep
);
649 * Check that no O_DIRECT or similar I/O is in progress on the
652 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
653 set_pte_at_notify(mm
, addr
, ptep
, entry
);
656 entry
= pte_wrprotect(entry
);
657 set_pte_at_notify(mm
, addr
, ptep
, entry
);
663 pte_unmap_unlock(ptep
, ptl
);
669 * replace_page - replace page in vma by new ksm page
670 * @vma: vma that holds the pte pointing to page
671 * @page: the page we are replacing by kpage
672 * @kpage: the ksm page we replace page by
673 * @orig_pte: the original value of the pte
675 * Returns 0 on success, -EFAULT on failure.
677 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
678 struct page
*kpage
, pte_t orig_pte
)
680 struct mm_struct
*mm
= vma
->vm_mm
;
689 addr
= page_address_in_vma(page
, vma
);
693 pgd
= pgd_offset(mm
, addr
);
694 if (!pgd_present(*pgd
))
697 pud
= pud_offset(pgd
, addr
);
698 if (!pud_present(*pud
))
701 pmd
= pmd_offset(pud
, addr
);
702 if (!pmd_present(*pmd
))
705 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
706 if (!pte_same(*ptep
, orig_pte
)) {
707 pte_unmap_unlock(ptep
, ptl
);
712 page_add_ksm_rmap(kpage
);
714 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
715 ptep_clear_flush(vma
, addr
, ptep
);
716 set_pte_at_notify(mm
, addr
, ptep
, mk_pte(kpage
, vma
->vm_page_prot
));
718 page_remove_rmap(page
);
721 pte_unmap_unlock(ptep
, ptl
);
728 * try_to_merge_one_page - take two pages and merge them into one
729 * @vma: the vma that holds the pte pointing to page
730 * @page: the PageAnon page that we want to replace with kpage
731 * @kpage: the PageKsm page (or newly allocated page which page_add_ksm_rmap
732 * will make PageKsm) that we want to map instead of page
734 * This function returns 0 if the pages were merged, -EFAULT otherwise.
736 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
737 struct page
*page
, struct page
*kpage
)
739 pte_t orig_pte
= __pte(0);
742 if (!(vma
->vm_flags
& VM_MERGEABLE
))
748 * We need the page lock to read a stable PageSwapCache in
749 * write_protect_page(). We use trylock_page() instead of
750 * lock_page() because we don't want to wait here - we
751 * prefer to continue scanning and merging different pages,
752 * then come back to this page when it is unlocked.
754 if (!trylock_page(page
))
757 * If this anonymous page is mapped only here, its pte may need
758 * to be write-protected. If it's mapped elsewhere, all of its
759 * ptes are necessarily already write-protected. But in either
760 * case, we need to lock and check page_count is not raised.
762 if (write_protect_page(vma
, page
, &orig_pte
) == 0 &&
763 pages_identical(page
, kpage
))
764 err
= replace_page(vma
, page
, kpage
, orig_pte
);
772 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
773 * but no new kernel page is allocated: kpage must already be a ksm page.
775 * This function returns 0 if the pages were merged, -EFAULT otherwise.
777 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
778 struct page
*page
, struct page
*kpage
)
780 struct mm_struct
*mm
= rmap_item
->mm
;
781 struct vm_area_struct
*vma
;
784 down_read(&mm
->mmap_sem
);
785 if (ksm_test_exit(mm
))
787 vma
= find_vma(mm
, rmap_item
->address
);
788 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
791 err
= try_to_merge_one_page(vma
, page
, kpage
);
793 up_read(&mm
->mmap_sem
);
798 * try_to_merge_two_pages - take two identical pages and prepare them
799 * to be merged into one page.
801 * This function returns the kpage if we successfully merged two identical
802 * pages into one ksm page, NULL otherwise.
804 * Note that this function allocates a new kernel page: if one of the pages
805 * is already a ksm page, try_to_merge_with_ksm_page should be used.
807 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
809 struct rmap_item
*tree_rmap_item
,
810 struct page
*tree_page
)
812 struct mm_struct
*mm
= rmap_item
->mm
;
813 struct vm_area_struct
*vma
;
818 * The number of nodes in the stable tree
819 * is the number of kernel pages that we hold.
821 if (ksm_max_kernel_pages
&&
822 ksm_max_kernel_pages
<= ksm_pages_shared
)
825 kpage
= alloc_page(GFP_HIGHUSER
);
829 down_read(&mm
->mmap_sem
);
830 if (ksm_test_exit(mm
))
832 vma
= find_vma(mm
, rmap_item
->address
);
833 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
836 copy_user_highpage(kpage
, page
, rmap_item
->address
, vma
);
837 err
= try_to_merge_one_page(vma
, page
, kpage
);
839 up_read(&mm
->mmap_sem
);
842 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
845 * If that fails, we have a ksm page with only one pte
846 * pointing to it: so break it.
849 break_cow(rmap_item
);
859 * stable_tree_search - search for page inside the stable tree
861 * This function checks if there is a page inside the stable tree
862 * with identical content to the page that we are scanning right now.
864 * This function return rmap_item pointer to the identical item if found,
867 static struct rmap_item
*stable_tree_search(struct page
*page
,
868 struct page
**tree_pagep
)
870 struct rb_node
*node
= root_stable_tree
.rb_node
;
873 struct rmap_item
*tree_rmap_item
, *next_rmap_item
;
874 struct page
*tree_page
;
877 tree_rmap_item
= rb_entry(node
, struct rmap_item
, node
);
878 while (tree_rmap_item
) {
879 BUG_ON(!in_stable_tree(tree_rmap_item
));
881 tree_page
= get_ksm_page(tree_rmap_item
);
884 next_rmap_item
= tree_rmap_item
->next
;
885 remove_rmap_item_from_tree(tree_rmap_item
);
886 tree_rmap_item
= next_rmap_item
;
891 ret
= memcmp_pages(page
, tree_page
);
895 node
= node
->rb_left
;
896 } else if (ret
> 0) {
898 node
= node
->rb_right
;
900 *tree_pagep
= tree_page
;
901 return tree_rmap_item
;
909 * stable_tree_insert - insert rmap_item pointing to new ksm page
910 * into the stable tree.
912 * This function returns rmap_item if success, NULL otherwise.
914 static struct rmap_item
*stable_tree_insert(struct page
*kpage
,
915 struct rmap_item
*rmap_item
)
917 struct rb_node
**new = &root_stable_tree
.rb_node
;
918 struct rb_node
*parent
= NULL
;
921 struct rmap_item
*tree_rmap_item
, *next_rmap_item
;
922 struct page
*tree_page
;
925 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
926 while (tree_rmap_item
) {
927 BUG_ON(!in_stable_tree(tree_rmap_item
));
929 tree_page
= get_ksm_page(tree_rmap_item
);
932 next_rmap_item
= tree_rmap_item
->next
;
933 remove_rmap_item_from_tree(tree_rmap_item
);
934 tree_rmap_item
= next_rmap_item
;
939 ret
= memcmp_pages(kpage
, tree_page
);
944 new = &parent
->rb_left
;
946 new = &parent
->rb_right
;
949 * It is not a bug that stable_tree_search() didn't
950 * find this node: because at that time our page was
951 * not yet write-protected, so may have changed since.
957 rmap_item
->address
|= NODE_FLAG
| STABLE_FLAG
;
958 rmap_item
->next
= NULL
;
959 rb_link_node(&rmap_item
->node
, parent
, new);
960 rb_insert_color(&rmap_item
->node
, &root_stable_tree
);
967 * unstable_tree_search_insert - search for identical page,
968 * else insert rmap_item into the unstable tree.
970 * This function searches for a page in the unstable tree identical to the
971 * page currently being scanned; and if no identical page is found in the
972 * tree, we insert rmap_item as a new object into the unstable tree.
974 * This function returns pointer to rmap_item found to be identical
975 * to the currently scanned page, NULL otherwise.
977 * This function does both searching and inserting, because they share
978 * the same walking algorithm in an rbtree.
981 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
983 struct page
**tree_pagep
)
986 struct rb_node
**new = &root_unstable_tree
.rb_node
;
987 struct rb_node
*parent
= NULL
;
990 struct rmap_item
*tree_rmap_item
;
991 struct page
*tree_page
;
995 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
996 tree_page
= get_mergeable_page(tree_rmap_item
);
1001 * Don't substitute a ksm page for a forked page.
1003 if (page
== tree_page
) {
1004 put_page(tree_page
);
1008 ret
= memcmp_pages(page
, tree_page
);
1012 put_page(tree_page
);
1013 new = &parent
->rb_left
;
1014 } else if (ret
> 0) {
1015 put_page(tree_page
);
1016 new = &parent
->rb_right
;
1018 *tree_pagep
= tree_page
;
1019 return tree_rmap_item
;
1023 rmap_item
->address
|= NODE_FLAG
;
1024 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1025 rb_link_node(&rmap_item
->node
, parent
, new);
1026 rb_insert_color(&rmap_item
->node
, &root_unstable_tree
);
1028 ksm_pages_unshared
++;
1033 * stable_tree_append - add another rmap_item to the linked list of
1034 * rmap_items hanging off a given node of the stable tree, all sharing
1035 * the same ksm page.
1037 static void stable_tree_append(struct rmap_item
*rmap_item
,
1038 struct rmap_item
*tree_rmap_item
)
1040 rmap_item
->next
= tree_rmap_item
->next
;
1041 rmap_item
->prev
= tree_rmap_item
;
1043 if (tree_rmap_item
->next
)
1044 tree_rmap_item
->next
->prev
= rmap_item
;
1046 tree_rmap_item
->next
= rmap_item
;
1047 rmap_item
->address
|= STABLE_FLAG
;
1049 ksm_pages_sharing
++;
1053 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1054 * if not, compare checksum to previous and if it's the same, see if page can
1055 * be inserted into the unstable tree, or merged with a page already there and
1056 * both transferred to the stable tree.
1058 * @page: the page that we are searching identical page to.
1059 * @rmap_item: the reverse mapping into the virtual address of this page
1061 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
1063 struct rmap_item
*tree_rmap_item
;
1064 struct page
*tree_page
= NULL
;
1066 unsigned int checksum
;
1069 remove_rmap_item_from_tree(rmap_item
);
1071 /* We first start with searching the page inside the stable tree */
1072 tree_rmap_item
= stable_tree_search(page
, &tree_page
);
1073 if (tree_rmap_item
) {
1075 if (page
== kpage
) /* forked */
1078 err
= try_to_merge_with_ksm_page(rmap_item
,
1082 * The page was successfully merged:
1083 * add its rmap_item to the stable tree.
1085 stable_tree_append(rmap_item
, tree_rmap_item
);
1092 * A ksm page might have got here by fork, but its other
1093 * references have already been removed from the stable tree.
1094 * Or it might be left over from a break_ksm which failed
1095 * when the mem_cgroup had reached its limit: try again now.
1098 break_cow(rmap_item
);
1101 * In case the hash value of the page was changed from the last time we
1102 * have calculated it, this page to be changed frequely, therefore we
1103 * don't want to insert it to the unstable tree, and we don't want to
1104 * waste our time to search if there is something identical to it there.
1106 checksum
= calc_checksum(page
);
1107 if (rmap_item
->oldchecksum
!= checksum
) {
1108 rmap_item
->oldchecksum
= checksum
;
1113 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
1114 if (tree_rmap_item
) {
1115 kpage
= try_to_merge_two_pages(rmap_item
, page
,
1116 tree_rmap_item
, tree_page
);
1117 put_page(tree_page
);
1119 * As soon as we merge this page, we want to remove the
1120 * rmap_item of the page we have merged with from the unstable
1121 * tree, and insert it instead as new node in the stable tree.
1124 remove_rmap_item_from_tree(tree_rmap_item
);
1127 * If we fail to insert the page into the stable tree,
1128 * we will have 2 virtual addresses that are pointing
1129 * to a ksm page left outside the stable tree,
1130 * in which case we need to break_cow on both.
1132 if (stable_tree_insert(kpage
, tree_rmap_item
))
1133 stable_tree_append(rmap_item
, tree_rmap_item
);
1135 break_cow(tree_rmap_item
);
1136 break_cow(rmap_item
);
1143 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
1144 struct list_head
*cur
,
1147 struct rmap_item
*rmap_item
;
1149 while (cur
!= &mm_slot
->rmap_list
) {
1150 rmap_item
= list_entry(cur
, struct rmap_item
, link
);
1151 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
1153 if (rmap_item
->address
> addr
)
1156 remove_rmap_item_from_tree(rmap_item
);
1157 list_del(&rmap_item
->link
);
1158 free_rmap_item(rmap_item
);
1161 rmap_item
= alloc_rmap_item();
1163 /* It has already been zeroed */
1164 rmap_item
->mm
= mm_slot
->mm
;
1165 rmap_item
->address
= addr
;
1166 list_add_tail(&rmap_item
->link
, cur
);
1171 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
1173 struct mm_struct
*mm
;
1174 struct mm_slot
*slot
;
1175 struct vm_area_struct
*vma
;
1176 struct rmap_item
*rmap_item
;
1178 if (list_empty(&ksm_mm_head
.mm_list
))
1181 slot
= ksm_scan
.mm_slot
;
1182 if (slot
== &ksm_mm_head
) {
1183 root_unstable_tree
= RB_ROOT
;
1185 spin_lock(&ksm_mmlist_lock
);
1186 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
1187 ksm_scan
.mm_slot
= slot
;
1188 spin_unlock(&ksm_mmlist_lock
);
1190 ksm_scan
.address
= 0;
1191 ksm_scan
.rmap_item
= list_entry(&slot
->rmap_list
,
1192 struct rmap_item
, link
);
1196 down_read(&mm
->mmap_sem
);
1197 if (ksm_test_exit(mm
))
1200 vma
= find_vma(mm
, ksm_scan
.address
);
1202 for (; vma
; vma
= vma
->vm_next
) {
1203 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1205 if (ksm_scan
.address
< vma
->vm_start
)
1206 ksm_scan
.address
= vma
->vm_start
;
1208 ksm_scan
.address
= vma
->vm_end
;
1210 while (ksm_scan
.address
< vma
->vm_end
) {
1211 if (ksm_test_exit(mm
))
1213 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
1214 if (*page
&& PageAnon(*page
)) {
1215 flush_anon_page(vma
, *page
, ksm_scan
.address
);
1216 flush_dcache_page(*page
);
1217 rmap_item
= get_next_rmap_item(slot
,
1218 ksm_scan
.rmap_item
->link
.next
,
1221 ksm_scan
.rmap_item
= rmap_item
;
1222 ksm_scan
.address
+= PAGE_SIZE
;
1225 up_read(&mm
->mmap_sem
);
1230 ksm_scan
.address
+= PAGE_SIZE
;
1235 if (ksm_test_exit(mm
)) {
1236 ksm_scan
.address
= 0;
1237 ksm_scan
.rmap_item
= list_entry(&slot
->rmap_list
,
1238 struct rmap_item
, link
);
1241 * Nuke all the rmap_items that are above this current rmap:
1242 * because there were no VM_MERGEABLE vmas with such addresses.
1244 remove_trailing_rmap_items(slot
, ksm_scan
.rmap_item
->link
.next
);
1246 spin_lock(&ksm_mmlist_lock
);
1247 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
1248 struct mm_slot
, mm_list
);
1249 if (ksm_scan
.address
== 0) {
1251 * We've completed a full scan of all vmas, holding mmap_sem
1252 * throughout, and found no VM_MERGEABLE: so do the same as
1253 * __ksm_exit does to remove this mm from all our lists now.
1254 * This applies either when cleaning up after __ksm_exit
1255 * (but beware: we can reach here even before __ksm_exit),
1256 * or when all VM_MERGEABLE areas have been unmapped (and
1257 * mmap_sem then protects against race with MADV_MERGEABLE).
1259 hlist_del(&slot
->link
);
1260 list_del(&slot
->mm_list
);
1261 spin_unlock(&ksm_mmlist_lock
);
1264 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1265 up_read(&mm
->mmap_sem
);
1268 spin_unlock(&ksm_mmlist_lock
);
1269 up_read(&mm
->mmap_sem
);
1272 /* Repeat until we've completed scanning the whole list */
1273 slot
= ksm_scan
.mm_slot
;
1274 if (slot
!= &ksm_mm_head
)
1282 * ksm_do_scan - the ksm scanner main worker function.
1283 * @scan_npages - number of pages we want to scan before we return.
1285 static void ksm_do_scan(unsigned int scan_npages
)
1287 struct rmap_item
*rmap_item
;
1290 while (scan_npages
--) {
1292 rmap_item
= scan_get_next_rmap_item(&page
);
1295 if (!PageKsm(page
) || !in_stable_tree(rmap_item
))
1296 cmp_and_merge_page(page
, rmap_item
);
1297 else if (page_mapcount(page
) == 1) {
1299 * Replace now-unshared ksm page by ordinary page.
1301 break_cow(rmap_item
);
1302 remove_rmap_item_from_tree(rmap_item
);
1303 rmap_item
->oldchecksum
= calc_checksum(page
);
1309 static int ksmd_should_run(void)
1311 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
1314 static int ksm_scan_thread(void *nothing
)
1316 set_user_nice(current
, 5);
1318 while (!kthread_should_stop()) {
1319 mutex_lock(&ksm_thread_mutex
);
1320 if (ksmd_should_run())
1321 ksm_do_scan(ksm_thread_pages_to_scan
);
1322 mutex_unlock(&ksm_thread_mutex
);
1324 if (ksmd_should_run()) {
1325 schedule_timeout_interruptible(
1326 msecs_to_jiffies(ksm_thread_sleep_millisecs
));
1328 wait_event_interruptible(ksm_thread_wait
,
1329 ksmd_should_run() || kthread_should_stop());
1335 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
1336 unsigned long end
, int advice
, unsigned long *vm_flags
)
1338 struct mm_struct
*mm
= vma
->vm_mm
;
1342 case MADV_MERGEABLE
:
1344 * Be somewhat over-protective for now!
1346 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
1347 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
1348 VM_RESERVED
| VM_HUGETLB
| VM_INSERTPAGE
|
1349 VM_MIXEDMAP
| VM_SAO
))
1350 return 0; /* just ignore the advice */
1352 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
1353 err
= __ksm_enter(mm
);
1358 *vm_flags
|= VM_MERGEABLE
;
1361 case MADV_UNMERGEABLE
:
1362 if (!(*vm_flags
& VM_MERGEABLE
))
1363 return 0; /* just ignore the advice */
1365 if (vma
->anon_vma
) {
1366 err
= unmerge_ksm_pages(vma
, start
, end
);
1371 *vm_flags
&= ~VM_MERGEABLE
;
1378 int __ksm_enter(struct mm_struct
*mm
)
1380 struct mm_slot
*mm_slot
;
1383 mm_slot
= alloc_mm_slot();
1387 /* Check ksm_run too? Would need tighter locking */
1388 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
1390 spin_lock(&ksm_mmlist_lock
);
1391 insert_to_mm_slots_hash(mm
, mm_slot
);
1393 * Insert just behind the scanning cursor, to let the area settle
1394 * down a little; when fork is followed by immediate exec, we don't
1395 * want ksmd to waste time setting up and tearing down an rmap_list.
1397 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
1398 spin_unlock(&ksm_mmlist_lock
);
1400 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1401 atomic_inc(&mm
->mm_count
);
1404 wake_up_interruptible(&ksm_thread_wait
);
1409 void __ksm_exit(struct mm_struct
*mm
)
1411 struct mm_slot
*mm_slot
;
1412 int easy_to_free
= 0;
1415 * This process is exiting: if it's straightforward (as is the
1416 * case when ksmd was never running), free mm_slot immediately.
1417 * But if it's at the cursor or has rmap_items linked to it, use
1418 * mmap_sem to synchronize with any break_cows before pagetables
1419 * are freed, and leave the mm_slot on the list for ksmd to free.
1420 * Beware: ksm may already have noticed it exiting and freed the slot.
1423 spin_lock(&ksm_mmlist_lock
);
1424 mm_slot
= get_mm_slot(mm
);
1425 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
1426 if (list_empty(&mm_slot
->rmap_list
)) {
1427 hlist_del(&mm_slot
->link
);
1428 list_del(&mm_slot
->mm_list
);
1431 list_move(&mm_slot
->mm_list
,
1432 &ksm_scan
.mm_slot
->mm_list
);
1435 spin_unlock(&ksm_mmlist_lock
);
1438 free_mm_slot(mm_slot
);
1439 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1441 } else if (mm_slot
) {
1442 down_write(&mm
->mmap_sem
);
1443 up_write(&mm
->mmap_sem
);
1449 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1452 #define KSM_ATTR_RO(_name) \
1453 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1454 #define KSM_ATTR(_name) \
1455 static struct kobj_attribute _name##_attr = \
1456 __ATTR(_name, 0644, _name##_show, _name##_store)
1458 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
1459 struct kobj_attribute
*attr
, char *buf
)
1461 return sprintf(buf
, "%u\n", ksm_thread_sleep_millisecs
);
1464 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
1465 struct kobj_attribute
*attr
,
1466 const char *buf
, size_t count
)
1468 unsigned long msecs
;
1471 err
= strict_strtoul(buf
, 10, &msecs
);
1472 if (err
|| msecs
> UINT_MAX
)
1475 ksm_thread_sleep_millisecs
= msecs
;
1479 KSM_ATTR(sleep_millisecs
);
1481 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
1482 struct kobj_attribute
*attr
, char *buf
)
1484 return sprintf(buf
, "%u\n", ksm_thread_pages_to_scan
);
1487 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
1488 struct kobj_attribute
*attr
,
1489 const char *buf
, size_t count
)
1492 unsigned long nr_pages
;
1494 err
= strict_strtoul(buf
, 10, &nr_pages
);
1495 if (err
|| nr_pages
> UINT_MAX
)
1498 ksm_thread_pages_to_scan
= nr_pages
;
1502 KSM_ATTR(pages_to_scan
);
1504 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
1507 return sprintf(buf
, "%u\n", ksm_run
);
1510 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
1511 const char *buf
, size_t count
)
1514 unsigned long flags
;
1516 err
= strict_strtoul(buf
, 10, &flags
);
1517 if (err
|| flags
> UINT_MAX
)
1519 if (flags
> KSM_RUN_UNMERGE
)
1523 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1524 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1525 * breaking COW to free the unswappable pages_shared (but leaves
1526 * mm_slots on the list for when ksmd may be set running again).
1529 mutex_lock(&ksm_thread_mutex
);
1530 if (ksm_run
!= flags
) {
1532 if (flags
& KSM_RUN_UNMERGE
) {
1533 current
->flags
|= PF_OOM_ORIGIN
;
1534 err
= unmerge_and_remove_all_rmap_items();
1535 current
->flags
&= ~PF_OOM_ORIGIN
;
1537 ksm_run
= KSM_RUN_STOP
;
1542 mutex_unlock(&ksm_thread_mutex
);
1544 if (flags
& KSM_RUN_MERGE
)
1545 wake_up_interruptible(&ksm_thread_wait
);
1551 static ssize_t
max_kernel_pages_store(struct kobject
*kobj
,
1552 struct kobj_attribute
*attr
,
1553 const char *buf
, size_t count
)
1556 unsigned long nr_pages
;
1558 err
= strict_strtoul(buf
, 10, &nr_pages
);
1562 ksm_max_kernel_pages
= nr_pages
;
1567 static ssize_t
max_kernel_pages_show(struct kobject
*kobj
,
1568 struct kobj_attribute
*attr
, char *buf
)
1570 return sprintf(buf
, "%lu\n", ksm_max_kernel_pages
);
1572 KSM_ATTR(max_kernel_pages
);
1574 static ssize_t
pages_shared_show(struct kobject
*kobj
,
1575 struct kobj_attribute
*attr
, char *buf
)
1577 return sprintf(buf
, "%lu\n", ksm_pages_shared
);
1579 KSM_ATTR_RO(pages_shared
);
1581 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
1582 struct kobj_attribute
*attr
, char *buf
)
1584 return sprintf(buf
, "%lu\n", ksm_pages_sharing
);
1586 KSM_ATTR_RO(pages_sharing
);
1588 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
1589 struct kobj_attribute
*attr
, char *buf
)
1591 return sprintf(buf
, "%lu\n", ksm_pages_unshared
);
1593 KSM_ATTR_RO(pages_unshared
);
1595 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
1596 struct kobj_attribute
*attr
, char *buf
)
1598 long ksm_pages_volatile
;
1600 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
1601 - ksm_pages_sharing
- ksm_pages_unshared
;
1603 * It was not worth any locking to calculate that statistic,
1604 * but it might therefore sometimes be negative: conceal that.
1606 if (ksm_pages_volatile
< 0)
1607 ksm_pages_volatile
= 0;
1608 return sprintf(buf
, "%ld\n", ksm_pages_volatile
);
1610 KSM_ATTR_RO(pages_volatile
);
1612 static ssize_t
full_scans_show(struct kobject
*kobj
,
1613 struct kobj_attribute
*attr
, char *buf
)
1615 return sprintf(buf
, "%lu\n", ksm_scan
.seqnr
);
1617 KSM_ATTR_RO(full_scans
);
1619 static struct attribute
*ksm_attrs
[] = {
1620 &sleep_millisecs_attr
.attr
,
1621 &pages_to_scan_attr
.attr
,
1623 &max_kernel_pages_attr
.attr
,
1624 &pages_shared_attr
.attr
,
1625 &pages_sharing_attr
.attr
,
1626 &pages_unshared_attr
.attr
,
1627 &pages_volatile_attr
.attr
,
1628 &full_scans_attr
.attr
,
1632 static struct attribute_group ksm_attr_group
= {
1636 #endif /* CONFIG_SYSFS */
1638 static int __init
ksm_init(void)
1640 struct task_struct
*ksm_thread
;
1643 ksm_max_kernel_pages
= totalram_pages
/ 4;
1645 err
= ksm_slab_init();
1649 err
= mm_slots_hash_init();
1653 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
1654 if (IS_ERR(ksm_thread
)) {
1655 printk(KERN_ERR
"ksm: creating kthread failed\n");
1656 err
= PTR_ERR(ksm_thread
);
1661 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
1663 printk(KERN_ERR
"ksm: register sysfs failed\n");
1664 kthread_stop(ksm_thread
);
1668 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
1670 #endif /* CONFIG_SYSFS */
1675 mm_slots_hash_free();
1681 module_init(ksm_init
)