2 * Memory merging support.
4 * This code enables dynamic sharing of identical pages found in different
5 * memory areas, even if they are not shared by fork()
7 * Copyright (C) 2008-2009 Red Hat, Inc.
14 * This work is licensed under the terms of the GNU GPL, version 2.
17 #include <linux/errno.h>
20 #include <linux/mman.h>
21 #include <linux/sched.h>
22 #include <linux/rwsem.h>
23 #include <linux/pagemap.h>
24 #include <linux/rmap.h>
25 #include <linux/spinlock.h>
26 #include <linux/jhash.h>
27 #include <linux/delay.h>
28 #include <linux/kthread.h>
29 #include <linux/wait.h>
30 #include <linux/slab.h>
31 #include <linux/rbtree.h>
32 #include <linux/memory.h>
33 #include <linux/mmu_notifier.h>
34 #include <linux/swap.h>
35 #include <linux/ksm.h>
36 #include <linux/hashtable.h>
37 #include <linux/freezer.h>
38 #include <linux/oom.h>
39 #include <linux/numa.h>
41 #include <asm/tlbflush.h>
46 #define DO_NUMA(x) do { (x); } while (0)
49 #define DO_NUMA(x) do { } while (0)
53 * A few notes about the KSM scanning process,
54 * to make it easier to understand the data structures below:
56 * In order to reduce excessive scanning, KSM sorts the memory pages by their
57 * contents into a data structure that holds pointers to the pages' locations.
59 * Since the contents of the pages may change at any moment, KSM cannot just
60 * insert the pages into a normal sorted tree and expect it to find anything.
61 * Therefore KSM uses two data structures - the stable and the unstable tree.
63 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
64 * by their contents. Because each such page is write-protected, searching on
65 * this tree is fully assured to be working (except when pages are unmapped),
66 * and therefore this tree is called the stable tree.
68 * In addition to the stable tree, KSM uses a second data structure called the
69 * unstable tree: this tree holds pointers to pages which have been found to
70 * be "unchanged for a period of time". The unstable tree sorts these pages
71 * by their contents, but since they are not write-protected, KSM cannot rely
72 * upon the unstable tree to work correctly - the unstable tree is liable to
73 * be corrupted as its contents are modified, and so it is called unstable.
75 * KSM solves this problem by several techniques:
77 * 1) The unstable tree is flushed every time KSM completes scanning all
78 * memory areas, and then the tree is rebuilt again from the beginning.
79 * 2) KSM will only insert into the unstable tree, pages whose hash value
80 * has not changed since the previous scan of all memory areas.
81 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
82 * colors of the nodes and not on their contents, assuring that even when
83 * the tree gets "corrupted" it won't get out of balance, so scanning time
84 * remains the same (also, searching and inserting nodes in an rbtree uses
85 * the same algorithm, so we have no overhead when we flush and rebuild).
86 * 4) KSM never flushes the stable tree, which means that even if it were to
87 * take 10 attempts to find a page in the unstable tree, once it is found,
88 * it is secured in the stable tree. (When we scan a new page, we first
89 * compare it against the stable tree, and then against the unstable tree.)
91 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
92 * stable trees and multiple unstable trees: one of each for each NUMA node.
96 * struct mm_slot - ksm information per mm that is being scanned
97 * @link: link to the mm_slots hash list
98 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
99 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
100 * @mm: the mm that this information is valid for
103 struct hlist_node link
;
104 struct list_head mm_list
;
105 struct rmap_item
*rmap_list
;
106 struct mm_struct
*mm
;
110 * struct ksm_scan - cursor for scanning
111 * @mm_slot: the current mm_slot we are scanning
112 * @address: the next address inside that to be scanned
113 * @rmap_list: link to the next rmap to be scanned in the rmap_list
114 * @seqnr: count of completed full scans (needed when removing unstable node)
116 * There is only the one ksm_scan instance of this cursor structure.
119 struct mm_slot
*mm_slot
;
120 unsigned long address
;
121 struct rmap_item
**rmap_list
;
126 * struct stable_node - node of the stable rbtree
127 * @node: rb node of this ksm page in the stable tree
128 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129 * @list: linked into migrate_nodes, pending placement in the proper node tree
130 * @hlist: hlist head of rmap_items using this ksm page
131 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
132 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
136 struct rb_node node
; /* when node of stable tree */
137 struct { /* when listed for migration */
138 struct list_head
*head
;
139 struct list_head list
;
142 struct hlist_head hlist
;
150 * struct rmap_item - reverse mapping item for virtual addresses
151 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
152 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
154 * @mm: the memory structure this rmap_item is pointing into
155 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
156 * @oldchecksum: previous checksum of the page at that virtual address
157 * @node: rb node of this rmap_item in the unstable tree
158 * @head: pointer to stable_node heading this list in the stable tree
159 * @hlist: link into hlist of rmap_items hanging off that stable_node
162 struct rmap_item
*rmap_list
;
164 struct anon_vma
*anon_vma
; /* when stable */
166 int nid
; /* when node of unstable tree */
169 struct mm_struct
*mm
;
170 unsigned long address
; /* + low bits used for flags below */
171 unsigned int oldchecksum
; /* when unstable */
173 struct rb_node node
; /* when node of unstable tree */
174 struct { /* when listed from stable tree */
175 struct stable_node
*head
;
176 struct hlist_node hlist
;
181 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
182 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
183 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
185 /* The stable and unstable tree heads */
186 static struct rb_root one_stable_tree
[1] = { RB_ROOT
};
187 static struct rb_root one_unstable_tree
[1] = { RB_ROOT
};
188 static struct rb_root
*root_stable_tree
= one_stable_tree
;
189 static struct rb_root
*root_unstable_tree
= one_unstable_tree
;
191 /* Recently migrated nodes of stable tree, pending proper placement */
192 static LIST_HEAD(migrate_nodes
);
194 #define MM_SLOTS_HASH_BITS 10
195 static DEFINE_HASHTABLE(mm_slots_hash
, MM_SLOTS_HASH_BITS
);
197 static struct mm_slot ksm_mm_head
= {
198 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
200 static struct ksm_scan ksm_scan
= {
201 .mm_slot
= &ksm_mm_head
,
204 static struct kmem_cache
*rmap_item_cache
;
205 static struct kmem_cache
*stable_node_cache
;
206 static struct kmem_cache
*mm_slot_cache
;
208 /* The number of nodes in the stable tree */
209 static unsigned long ksm_pages_shared
;
211 /* The number of page slots additionally sharing those nodes */
212 static unsigned long ksm_pages_sharing
;
214 /* The number of nodes in the unstable tree */
215 static unsigned long ksm_pages_unshared
;
217 /* The number of rmap_items in use: to calculate pages_volatile */
218 static unsigned long ksm_rmap_items
;
220 /* Number of pages ksmd should scan in one batch */
221 static unsigned int ksm_thread_pages_to_scan
= 100;
223 /* Milliseconds ksmd should sleep between batches */
224 static unsigned int ksm_thread_sleep_millisecs
= 20;
227 /* Zeroed when merging across nodes is not allowed */
228 static unsigned int ksm_merge_across_nodes
= 1;
229 static int ksm_nr_node_ids
= 1;
231 #define ksm_merge_across_nodes 1U
232 #define ksm_nr_node_ids 1
235 #define KSM_RUN_STOP 0
236 #define KSM_RUN_MERGE 1
237 #define KSM_RUN_UNMERGE 2
238 #define KSM_RUN_OFFLINE 4
239 static unsigned long ksm_run
= KSM_RUN_STOP
;
240 static void wait_while_offlining(void);
242 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
243 static DEFINE_MUTEX(ksm_thread_mutex
);
244 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
246 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247 sizeof(struct __struct), __alignof__(struct __struct),\
250 static int __init
ksm_slab_init(void)
252 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
253 if (!rmap_item_cache
)
256 stable_node_cache
= KSM_KMEM_CACHE(stable_node
, 0);
257 if (!stable_node_cache
)
260 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
267 kmem_cache_destroy(stable_node_cache
);
269 kmem_cache_destroy(rmap_item_cache
);
274 static void __init
ksm_slab_free(void)
276 kmem_cache_destroy(mm_slot_cache
);
277 kmem_cache_destroy(stable_node_cache
);
278 kmem_cache_destroy(rmap_item_cache
);
279 mm_slot_cache
= NULL
;
282 static inline struct rmap_item
*alloc_rmap_item(void)
284 struct rmap_item
*rmap_item
;
286 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
|
287 __GFP_NORETRY
| __GFP_NOWARN
);
293 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
296 rmap_item
->mm
= NULL
; /* debug safety */
297 kmem_cache_free(rmap_item_cache
, rmap_item
);
300 static inline struct stable_node
*alloc_stable_node(void)
302 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
);
305 static inline void free_stable_node(struct stable_node
*stable_node
)
307 kmem_cache_free(stable_node_cache
, stable_node
);
310 static inline struct mm_slot
*alloc_mm_slot(void)
312 if (!mm_slot_cache
) /* initialization failed */
314 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
317 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
319 kmem_cache_free(mm_slot_cache
, mm_slot
);
322 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
324 struct mm_slot
*slot
;
326 hash_for_each_possible(mm_slots_hash
, slot
, link
, (unsigned long)mm
)
333 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
334 struct mm_slot
*mm_slot
)
337 hash_add(mm_slots_hash
, &mm_slot
->link
, (unsigned long)mm
);
341 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
342 * page tables after it has passed through ksm_exit() - which, if necessary,
343 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
344 * a special flag: they can just back out as soon as mm_users goes to zero.
345 * ksm_test_exit() is used throughout to make this test for exit: in some
346 * places for correctness, in some places just to avoid unnecessary work.
348 static inline bool ksm_test_exit(struct mm_struct
*mm
)
350 return atomic_read(&mm
->mm_users
) == 0;
354 * We use break_ksm to break COW on a ksm page: it's a stripped down
356 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
359 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
360 * in case the application has unmapped and remapped mm,addr meanwhile.
361 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
362 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
364 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
371 page
= follow_page(vma
, addr
, FOLL_GET
| FOLL_MIGRATION
);
372 if (IS_ERR_OR_NULL(page
))
375 ret
= handle_mm_fault(vma
->vm_mm
, vma
, addr
,
378 ret
= VM_FAULT_WRITE
;
380 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_SIGSEGV
| VM_FAULT_OOM
)));
382 * We must loop because handle_mm_fault() may back out if there's
383 * any difficulty e.g. if pte accessed bit gets updated concurrently.
385 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
386 * COW has been broken, even if the vma does not permit VM_WRITE;
387 * but note that a concurrent fault might break PageKsm for us.
389 * VM_FAULT_SIGBUS could occur if we race with truncation of the
390 * backing file, which also invalidates anonymous pages: that's
391 * okay, that truncation will have unmapped the PageKsm for us.
393 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
394 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
395 * current task has TIF_MEMDIE set, and will be OOM killed on return
396 * to user; and ksmd, having no mm, would never be chosen for that.
398 * But if the mm is in a limited mem_cgroup, then the fault may fail
399 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
400 * even ksmd can fail in this way - though it's usually breaking ksm
401 * just to undo a merge it made a moment before, so unlikely to oom.
403 * That's a pity: we might therefore have more kernel pages allocated
404 * than we're counting as nodes in the stable tree; but ksm_do_scan
405 * will retry to break_cow on each pass, so should recover the page
406 * in due course. The important thing is to not let VM_MERGEABLE
407 * be cleared while any such pages might remain in the area.
409 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
412 static struct vm_area_struct
*find_mergeable_vma(struct mm_struct
*mm
,
415 struct vm_area_struct
*vma
;
416 if (ksm_test_exit(mm
))
418 vma
= find_vma(mm
, addr
);
419 if (!vma
|| vma
->vm_start
> addr
)
421 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
426 static void break_cow(struct rmap_item
*rmap_item
)
428 struct mm_struct
*mm
= rmap_item
->mm
;
429 unsigned long addr
= rmap_item
->address
;
430 struct vm_area_struct
*vma
;
433 * It is not an accident that whenever we want to break COW
434 * to undo, we also need to drop a reference to the anon_vma.
436 put_anon_vma(rmap_item
->anon_vma
);
438 down_read(&mm
->mmap_sem
);
439 vma
= find_mergeable_vma(mm
, addr
);
441 break_ksm(vma
, addr
);
442 up_read(&mm
->mmap_sem
);
445 static struct page
*page_trans_compound_anon(struct page
*page
)
447 if (PageTransCompound(page
)) {
448 struct page
*head
= compound_head(page
);
450 * head may actually be splitted and freed from under
451 * us but it's ok here.
459 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
461 struct mm_struct
*mm
= rmap_item
->mm
;
462 unsigned long addr
= rmap_item
->address
;
463 struct vm_area_struct
*vma
;
466 down_read(&mm
->mmap_sem
);
467 vma
= find_mergeable_vma(mm
, addr
);
471 page
= follow_page(vma
, addr
, FOLL_GET
);
472 if (IS_ERR_OR_NULL(page
))
474 if (PageAnon(page
) || page_trans_compound_anon(page
)) {
475 flush_anon_page(vma
, page
, addr
);
476 flush_dcache_page(page
);
481 up_read(&mm
->mmap_sem
);
486 * This helper is used for getting right index into array of tree roots.
487 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
488 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
489 * every node has its own stable and unstable tree.
491 static inline int get_kpfn_nid(unsigned long kpfn
)
493 return ksm_merge_across_nodes
? 0 : NUMA(pfn_to_nid(kpfn
));
496 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
498 struct rmap_item
*rmap_item
;
500 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
501 if (rmap_item
->hlist
.next
)
505 put_anon_vma(rmap_item
->anon_vma
);
506 rmap_item
->address
&= PAGE_MASK
;
510 if (stable_node
->head
== &migrate_nodes
)
511 list_del(&stable_node
->list
);
513 rb_erase(&stable_node
->node
,
514 root_stable_tree
+ NUMA(stable_node
->nid
));
515 free_stable_node(stable_node
);
519 * get_ksm_page: checks if the page indicated by the stable node
520 * is still its ksm page, despite having held no reference to it.
521 * In which case we can trust the content of the page, and it
522 * returns the gotten page; but if the page has now been zapped,
523 * remove the stale node from the stable tree and return NULL.
524 * But beware, the stable node's page might be being migrated.
526 * You would expect the stable_node to hold a reference to the ksm page.
527 * But if it increments the page's count, swapping out has to wait for
528 * ksmd to come around again before it can free the page, which may take
529 * seconds or even minutes: much too unresponsive. So instead we use a
530 * "keyhole reference": access to the ksm page from the stable node peeps
531 * out through its keyhole to see if that page still holds the right key,
532 * pointing back to this stable node. This relies on freeing a PageAnon
533 * page to reset its page->mapping to NULL, and relies on no other use of
534 * a page to put something that might look like our key in page->mapping.
535 * is on its way to being freed; but it is an anomaly to bear in mind.
537 static struct page
*get_ksm_page(struct stable_node
*stable_node
, bool lock_it
)
540 void *expected_mapping
;
543 expected_mapping
= (void *)stable_node
+
544 (PAGE_MAPPING_ANON
| PAGE_MAPPING_KSM
);
546 kpfn
= ACCESS_ONCE(stable_node
->kpfn
);
547 page
= pfn_to_page(kpfn
);
550 * page is computed from kpfn, so on most architectures reading
551 * page->mapping is naturally ordered after reading node->kpfn,
552 * but on Alpha we need to be more careful.
554 smp_read_barrier_depends();
555 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
)
559 * We cannot do anything with the page while its refcount is 0.
560 * Usually 0 means free, or tail of a higher-order page: in which
561 * case this node is no longer referenced, and should be freed;
562 * however, it might mean that the page is under page_freeze_refs().
563 * The __remove_mapping() case is easy, again the node is now stale;
564 * but if page is swapcache in migrate_page_move_mapping(), it might
565 * still be our page, in which case it's essential to keep the node.
567 while (!get_page_unless_zero(page
)) {
569 * Another check for page->mapping != expected_mapping would
570 * work here too. We have chosen the !PageSwapCache test to
571 * optimize the common case, when the page is or is about to
572 * be freed: PageSwapCache is cleared (under spin_lock_irq)
573 * in the freeze_refs section of __remove_mapping(); but Anon
574 * page->mapping reset to NULL later, in free_pages_prepare().
576 if (!PageSwapCache(page
))
581 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
588 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
598 * We come here from above when page->mapping or !PageSwapCache
599 * suggests that the node is stale; but it might be under migration.
600 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
601 * before checking whether node->kpfn has been changed.
604 if (ACCESS_ONCE(stable_node
->kpfn
) != kpfn
)
606 remove_node_from_stable_tree(stable_node
);
611 * Removing rmap_item from stable or unstable tree.
612 * This function will clean the information from the stable/unstable tree.
614 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
616 if (rmap_item
->address
& STABLE_FLAG
) {
617 struct stable_node
*stable_node
;
620 stable_node
= rmap_item
->head
;
621 page
= get_ksm_page(stable_node
, true);
625 hlist_del(&rmap_item
->hlist
);
629 if (stable_node
->hlist
.first
)
634 put_anon_vma(rmap_item
->anon_vma
);
635 rmap_item
->address
&= PAGE_MASK
;
637 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
640 * Usually ksmd can and must skip the rb_erase, because
641 * root_unstable_tree was already reset to RB_ROOT.
642 * But be careful when an mm is exiting: do the rb_erase
643 * if this rmap_item was inserted by this scan, rather
644 * than left over from before.
646 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
649 rb_erase(&rmap_item
->node
,
650 root_unstable_tree
+ NUMA(rmap_item
->nid
));
651 ksm_pages_unshared
--;
652 rmap_item
->address
&= PAGE_MASK
;
655 cond_resched(); /* we're called from many long loops */
658 static void remove_trailing_rmap_items(struct mm_slot
*mm_slot
,
659 struct rmap_item
**rmap_list
)
662 struct rmap_item
*rmap_item
= *rmap_list
;
663 *rmap_list
= rmap_item
->rmap_list
;
664 remove_rmap_item_from_tree(rmap_item
);
665 free_rmap_item(rmap_item
);
670 * Though it's very tempting to unmerge rmap_items from stable tree rather
671 * than check every pte of a given vma, the locking doesn't quite work for
672 * that - an rmap_item is assigned to the stable tree after inserting ksm
673 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
674 * rmap_items from parent to child at fork time (so as not to waste time
675 * if exit comes before the next scan reaches it).
677 * Similarly, although we'd like to remove rmap_items (so updating counts
678 * and freeing memory) when unmerging an area, it's easier to leave that
679 * to the next pass of ksmd - consider, for example, how ksmd might be
680 * in cmp_and_merge_page on one of the rmap_items we would be removing.
682 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
683 unsigned long start
, unsigned long end
)
688 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
689 if (ksm_test_exit(vma
->vm_mm
))
691 if (signal_pending(current
))
694 err
= break_ksm(vma
, addr
);
701 * Only called through the sysfs control interface:
703 static int remove_stable_node(struct stable_node
*stable_node
)
708 page
= get_ksm_page(stable_node
, true);
711 * get_ksm_page did remove_node_from_stable_tree itself.
716 if (WARN_ON_ONCE(page_mapped(page
))) {
718 * This should not happen: but if it does, just refuse to let
719 * merge_across_nodes be switched - there is no need to panic.
724 * The stable node did not yet appear stale to get_ksm_page(),
725 * since that allows for an unmapped ksm page to be recognized
726 * right up until it is freed; but the node is safe to remove.
727 * This page might be in a pagevec waiting to be freed,
728 * or it might be PageSwapCache (perhaps under writeback),
729 * or it might have been removed from swapcache a moment ago.
731 set_page_stable_node(page
, NULL
);
732 remove_node_from_stable_tree(stable_node
);
741 static int remove_all_stable_nodes(void)
743 struct stable_node
*stable_node
;
744 struct list_head
*this, *next
;
748 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
749 while (root_stable_tree
[nid
].rb_node
) {
750 stable_node
= rb_entry(root_stable_tree
[nid
].rb_node
,
751 struct stable_node
, node
);
752 if (remove_stable_node(stable_node
)) {
754 break; /* proceed to next nid */
759 list_for_each_safe(this, next
, &migrate_nodes
) {
760 stable_node
= list_entry(this, struct stable_node
, list
);
761 if (remove_stable_node(stable_node
))
768 static int unmerge_and_remove_all_rmap_items(void)
770 struct mm_slot
*mm_slot
;
771 struct mm_struct
*mm
;
772 struct vm_area_struct
*vma
;
775 spin_lock(&ksm_mmlist_lock
);
776 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
777 struct mm_slot
, mm_list
);
778 spin_unlock(&ksm_mmlist_lock
);
780 for (mm_slot
= ksm_scan
.mm_slot
;
781 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
783 down_read(&mm
->mmap_sem
);
784 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
785 if (ksm_test_exit(mm
))
787 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
789 err
= unmerge_ksm_pages(vma
,
790 vma
->vm_start
, vma
->vm_end
);
795 remove_trailing_rmap_items(mm_slot
, &mm_slot
->rmap_list
);
797 spin_lock(&ksm_mmlist_lock
);
798 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
799 struct mm_slot
, mm_list
);
800 if (ksm_test_exit(mm
)) {
801 hash_del(&mm_slot
->link
);
802 list_del(&mm_slot
->mm_list
);
803 spin_unlock(&ksm_mmlist_lock
);
805 free_mm_slot(mm_slot
);
806 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
807 up_read(&mm
->mmap_sem
);
810 spin_unlock(&ksm_mmlist_lock
);
811 up_read(&mm
->mmap_sem
);
815 /* Clean up stable nodes, but don't worry if some are still busy */
816 remove_all_stable_nodes();
821 up_read(&mm
->mmap_sem
);
822 spin_lock(&ksm_mmlist_lock
);
823 ksm_scan
.mm_slot
= &ksm_mm_head
;
824 spin_unlock(&ksm_mmlist_lock
);
827 #endif /* CONFIG_SYSFS */
829 static u32
calc_checksum(struct page
*page
)
832 void *addr
= kmap_atomic(page
);
833 checksum
= jhash2(addr
, PAGE_SIZE
/ 4, 17);
838 static int memcmp_pages(struct page
*page1
, struct page
*page2
)
843 addr1
= kmap_atomic(page1
);
844 addr2
= kmap_atomic(page2
);
845 ret
= memcmp(addr1
, addr2
, PAGE_SIZE
);
846 kunmap_atomic(addr2
);
847 kunmap_atomic(addr1
);
851 static inline int pages_identical(struct page
*page1
, struct page
*page2
)
853 return !memcmp_pages(page1
, page2
);
856 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
859 struct mm_struct
*mm
= vma
->vm_mm
;
865 unsigned long mmun_start
; /* For mmu_notifiers */
866 unsigned long mmun_end
; /* For mmu_notifiers */
868 addr
= page_address_in_vma(page
, vma
);
872 BUG_ON(PageTransCompound(page
));
875 mmun_end
= addr
+ PAGE_SIZE
;
876 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
878 ptep
= page_check_address(page
, mm
, addr
, &ptl
, 0);
882 if (pte_write(*ptep
) || pte_dirty(*ptep
)) {
885 swapped
= PageSwapCache(page
);
886 flush_cache_page(vma
, addr
, page_to_pfn(page
));
888 * Ok this is tricky, when get_user_pages_fast() run it doesn't
889 * take any lock, therefore the check that we are going to make
890 * with the pagecount against the mapcount is racey and
891 * O_DIRECT can happen right after the check.
892 * So we clear the pte and flush the tlb before the check
893 * this assure us that no O_DIRECT can happen after the check
894 * or in the middle of the check.
896 entry
= ptep_clear_flush(vma
, addr
, ptep
);
898 * Check that no O_DIRECT or similar I/O is in progress on the
901 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
902 set_pte_at(mm
, addr
, ptep
, entry
);
905 if (pte_dirty(entry
))
906 set_page_dirty(page
);
907 entry
= pte_mkclean(pte_wrprotect(entry
));
908 set_pte_at_notify(mm
, addr
, ptep
, entry
);
914 pte_unmap_unlock(ptep
, ptl
);
916 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
922 * replace_page - replace page in vma by new ksm page
923 * @vma: vma that holds the pte pointing to page
924 * @page: the page we are replacing by kpage
925 * @kpage: the ksm page we replace page by
926 * @orig_pte: the original value of the pte
928 * Returns 0 on success, -EFAULT on failure.
930 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
931 struct page
*kpage
, pte_t orig_pte
)
933 struct mm_struct
*mm
= vma
->vm_mm
;
939 unsigned long mmun_start
; /* For mmu_notifiers */
940 unsigned long mmun_end
; /* For mmu_notifiers */
942 addr
= page_address_in_vma(page
, vma
);
946 pmd
= mm_find_pmd(mm
, addr
);
949 BUG_ON(pmd_trans_huge(*pmd
));
952 mmun_end
= addr
+ PAGE_SIZE
;
953 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
955 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
956 if (!pte_same(*ptep
, orig_pte
)) {
957 pte_unmap_unlock(ptep
, ptl
);
962 page_add_anon_rmap(kpage
, vma
, addr
);
964 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
965 ptep_clear_flush(vma
, addr
, ptep
);
966 set_pte_at_notify(mm
, addr
, ptep
, mk_pte(kpage
, vma
->vm_page_prot
));
968 page_remove_rmap(page
);
969 if (!page_mapped(page
))
970 try_to_free_swap(page
);
973 pte_unmap_unlock(ptep
, ptl
);
976 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
981 static int page_trans_compound_anon_split(struct page
*page
)
984 struct page
*transhuge_head
= page_trans_compound_anon(page
);
985 if (transhuge_head
) {
986 /* Get the reference on the head to split it. */
987 if (get_page_unless_zero(transhuge_head
)) {
989 * Recheck we got the reference while the head
990 * was still anonymous.
992 if (PageAnon(transhuge_head
))
993 ret
= split_huge_page(transhuge_head
);
996 * Retry later if split_huge_page run
1000 put_page(transhuge_head
);
1002 /* Retry later if split_huge_page run from under us. */
1009 * try_to_merge_one_page - take two pages and merge them into one
1010 * @vma: the vma that holds the pte pointing to page
1011 * @page: the PageAnon page that we want to replace with kpage
1012 * @kpage: the PageKsm page that we want to map instead of page,
1013 * or NULL the first time when we want to use page as kpage.
1015 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1017 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
1018 struct page
*page
, struct page
*kpage
)
1020 pte_t orig_pte
= __pte(0);
1023 if (page
== kpage
) /* ksm page forked */
1026 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1028 if (PageTransCompound(page
) && page_trans_compound_anon_split(page
))
1030 BUG_ON(PageTransCompound(page
));
1031 if (!PageAnon(page
))
1035 * We need the page lock to read a stable PageSwapCache in
1036 * write_protect_page(). We use trylock_page() instead of
1037 * lock_page() because we don't want to wait here - we
1038 * prefer to continue scanning and merging different pages,
1039 * then come back to this page when it is unlocked.
1041 if (!trylock_page(page
))
1044 * If this anonymous page is mapped only here, its pte may need
1045 * to be write-protected. If it's mapped elsewhere, all of its
1046 * ptes are necessarily already write-protected. But in either
1047 * case, we need to lock and check page_count is not raised.
1049 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
1052 * While we hold page lock, upgrade page from
1053 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1054 * stable_tree_insert() will update stable_node.
1056 set_page_stable_node(page
, NULL
);
1057 mark_page_accessed(page
);
1059 } else if (pages_identical(page
, kpage
))
1060 err
= replace_page(vma
, page
, kpage
, orig_pte
);
1063 if ((vma
->vm_flags
& VM_LOCKED
) && kpage
&& !err
) {
1064 munlock_vma_page(page
);
1065 if (!PageMlocked(kpage
)) {
1068 mlock_vma_page(kpage
);
1069 page
= kpage
; /* for final unlock */
1079 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1080 * but no new kernel page is allocated: kpage must already be a ksm page.
1082 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1084 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
1085 struct page
*page
, struct page
*kpage
)
1087 struct mm_struct
*mm
= rmap_item
->mm
;
1088 struct vm_area_struct
*vma
;
1091 down_read(&mm
->mmap_sem
);
1092 if (ksm_test_exit(mm
))
1094 vma
= find_vma(mm
, rmap_item
->address
);
1095 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
1098 err
= try_to_merge_one_page(vma
, page
, kpage
);
1102 /* Unstable nid is in union with stable anon_vma: remove first */
1103 remove_rmap_item_from_tree(rmap_item
);
1105 /* Must get reference to anon_vma while still holding mmap_sem */
1106 rmap_item
->anon_vma
= vma
->anon_vma
;
1107 get_anon_vma(vma
->anon_vma
);
1109 up_read(&mm
->mmap_sem
);
1114 * try_to_merge_two_pages - take two identical pages and prepare them
1115 * to be merged into one page.
1117 * This function returns the kpage if we successfully merged two identical
1118 * pages into one ksm page, NULL otherwise.
1120 * Note that this function upgrades page to ksm page: if one of the pages
1121 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1123 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
1125 struct rmap_item
*tree_rmap_item
,
1126 struct page
*tree_page
)
1130 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
1132 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
1135 * If that fails, we have a ksm page with only one pte
1136 * pointing to it: so break it.
1139 break_cow(rmap_item
);
1141 return err
? NULL
: page
;
1145 * stable_tree_search - search for page inside the stable tree
1147 * This function checks if there is a page inside the stable tree
1148 * with identical content to the page that we are scanning right now.
1150 * This function returns the stable tree node of identical content if found,
1153 static struct page
*stable_tree_search(struct page
*page
)
1156 struct rb_root
*root
;
1157 struct rb_node
**new;
1158 struct rb_node
*parent
;
1159 struct stable_node
*stable_node
;
1160 struct stable_node
*page_node
;
1162 page_node
= page_stable_node(page
);
1163 if (page_node
&& page_node
->head
!= &migrate_nodes
) {
1164 /* ksm page forked */
1169 nid
= get_kpfn_nid(page_to_pfn(page
));
1170 root
= root_stable_tree
+ nid
;
1172 new = &root
->rb_node
;
1176 struct page
*tree_page
;
1180 stable_node
= rb_entry(*new, struct stable_node
, node
);
1181 tree_page
= get_ksm_page(stable_node
, false);
1185 ret
= memcmp_pages(page
, tree_page
);
1186 put_page(tree_page
);
1190 new = &parent
->rb_left
;
1192 new = &parent
->rb_right
;
1195 * Lock and unlock the stable_node's page (which
1196 * might already have been migrated) so that page
1197 * migration is sure to notice its raised count.
1198 * It would be more elegant to return stable_node
1199 * than kpage, but that involves more changes.
1201 tree_page
= get_ksm_page(stable_node
, true);
1203 unlock_page(tree_page
);
1204 if (get_kpfn_nid(stable_node
->kpfn
) !=
1205 NUMA(stable_node
->nid
)) {
1206 put_page(tree_page
);
1212 * There is now a place for page_node, but the tree may
1213 * have been rebalanced, so re-evaluate parent and new.
1224 list_del(&page_node
->list
);
1225 DO_NUMA(page_node
->nid
= nid
);
1226 rb_link_node(&page_node
->node
, parent
, new);
1227 rb_insert_color(&page_node
->node
, root
);
1233 list_del(&page_node
->list
);
1234 DO_NUMA(page_node
->nid
= nid
);
1235 rb_replace_node(&stable_node
->node
, &page_node
->node
, root
);
1238 rb_erase(&stable_node
->node
, root
);
1241 stable_node
->head
= &migrate_nodes
;
1242 list_add(&stable_node
->list
, stable_node
->head
);
1247 * stable_tree_insert - insert stable tree node pointing to new ksm page
1248 * into the stable tree.
1250 * This function returns the stable tree node just allocated on success,
1253 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1257 struct rb_root
*root
;
1258 struct rb_node
**new;
1259 struct rb_node
*parent
= NULL
;
1260 struct stable_node
*stable_node
;
1262 kpfn
= page_to_pfn(kpage
);
1263 nid
= get_kpfn_nid(kpfn
);
1264 root
= root_stable_tree
+ nid
;
1265 new = &root
->rb_node
;
1268 struct page
*tree_page
;
1272 stable_node
= rb_entry(*new, struct stable_node
, node
);
1273 tree_page
= get_ksm_page(stable_node
, false);
1277 ret
= memcmp_pages(kpage
, tree_page
);
1278 put_page(tree_page
);
1282 new = &parent
->rb_left
;
1284 new = &parent
->rb_right
;
1287 * It is not a bug that stable_tree_search() didn't
1288 * find this node: because at that time our page was
1289 * not yet write-protected, so may have changed since.
1295 stable_node
= alloc_stable_node();
1299 INIT_HLIST_HEAD(&stable_node
->hlist
);
1300 stable_node
->kpfn
= kpfn
;
1301 set_page_stable_node(kpage
, stable_node
);
1302 DO_NUMA(stable_node
->nid
= nid
);
1303 rb_link_node(&stable_node
->node
, parent
, new);
1304 rb_insert_color(&stable_node
->node
, root
);
1310 * unstable_tree_search_insert - search for identical page,
1311 * else insert rmap_item into the unstable tree.
1313 * This function searches for a page in the unstable tree identical to the
1314 * page currently being scanned; and if no identical page is found in the
1315 * tree, we insert rmap_item as a new object into the unstable tree.
1317 * This function returns pointer to rmap_item found to be identical
1318 * to the currently scanned page, NULL otherwise.
1320 * This function does both searching and inserting, because they share
1321 * the same walking algorithm in an rbtree.
1324 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1326 struct page
**tree_pagep
)
1328 struct rb_node
**new;
1329 struct rb_root
*root
;
1330 struct rb_node
*parent
= NULL
;
1333 nid
= get_kpfn_nid(page_to_pfn(page
));
1334 root
= root_unstable_tree
+ nid
;
1335 new = &root
->rb_node
;
1338 struct rmap_item
*tree_rmap_item
;
1339 struct page
*tree_page
;
1343 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1344 tree_page
= get_mergeable_page(tree_rmap_item
);
1345 if (IS_ERR_OR_NULL(tree_page
))
1349 * Don't substitute a ksm page for a forked page.
1351 if (page
== tree_page
) {
1352 put_page(tree_page
);
1356 ret
= memcmp_pages(page
, tree_page
);
1360 put_page(tree_page
);
1361 new = &parent
->rb_left
;
1362 } else if (ret
> 0) {
1363 put_page(tree_page
);
1364 new = &parent
->rb_right
;
1365 } else if (!ksm_merge_across_nodes
&&
1366 page_to_nid(tree_page
) != nid
) {
1368 * If tree_page has been migrated to another NUMA node,
1369 * it will be flushed out and put in the right unstable
1370 * tree next time: only merge with it when across_nodes.
1372 put_page(tree_page
);
1375 *tree_pagep
= tree_page
;
1376 return tree_rmap_item
;
1380 rmap_item
->address
|= UNSTABLE_FLAG
;
1381 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1382 DO_NUMA(rmap_item
->nid
= nid
);
1383 rb_link_node(&rmap_item
->node
, parent
, new);
1384 rb_insert_color(&rmap_item
->node
, root
);
1386 ksm_pages_unshared
++;
1391 * stable_tree_append - add another rmap_item to the linked list of
1392 * rmap_items hanging off a given node of the stable tree, all sharing
1393 * the same ksm page.
1395 static void stable_tree_append(struct rmap_item
*rmap_item
,
1396 struct stable_node
*stable_node
)
1398 rmap_item
->head
= stable_node
;
1399 rmap_item
->address
|= STABLE_FLAG
;
1400 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
1402 if (rmap_item
->hlist
.next
)
1403 ksm_pages_sharing
++;
1409 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1410 * if not, compare checksum to previous and if it's the same, see if page can
1411 * be inserted into the unstable tree, or merged with a page already there and
1412 * both transferred to the stable tree.
1414 * @page: the page that we are searching identical page to.
1415 * @rmap_item: the reverse mapping into the virtual address of this page
1417 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
1419 struct rmap_item
*tree_rmap_item
;
1420 struct page
*tree_page
= NULL
;
1421 struct stable_node
*stable_node
;
1423 unsigned int checksum
;
1426 stable_node
= page_stable_node(page
);
1428 if (stable_node
->head
!= &migrate_nodes
&&
1429 get_kpfn_nid(stable_node
->kpfn
) != NUMA(stable_node
->nid
)) {
1430 rb_erase(&stable_node
->node
,
1431 root_stable_tree
+ NUMA(stable_node
->nid
));
1432 stable_node
->head
= &migrate_nodes
;
1433 list_add(&stable_node
->list
, stable_node
->head
);
1435 if (stable_node
->head
!= &migrate_nodes
&&
1436 rmap_item
->head
== stable_node
)
1440 /* We first start with searching the page inside the stable tree */
1441 kpage
= stable_tree_search(page
);
1442 if (kpage
== page
&& rmap_item
->head
== stable_node
) {
1447 remove_rmap_item_from_tree(rmap_item
);
1450 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
1453 * The page was successfully merged:
1454 * add its rmap_item to the stable tree.
1457 stable_tree_append(rmap_item
, page_stable_node(kpage
));
1465 * If the hash value of the page has changed from the last time
1466 * we calculated it, this page is changing frequently: therefore we
1467 * don't want to insert it in the unstable tree, and we don't want
1468 * to waste our time searching for something identical to it there.
1470 checksum
= calc_checksum(page
);
1471 if (rmap_item
->oldchecksum
!= checksum
) {
1472 rmap_item
->oldchecksum
= checksum
;
1477 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
1478 if (tree_rmap_item
) {
1479 kpage
= try_to_merge_two_pages(rmap_item
, page
,
1480 tree_rmap_item
, tree_page
);
1481 put_page(tree_page
);
1484 * The pages were successfully merged: insert new
1485 * node in the stable tree and add both rmap_items.
1488 stable_node
= stable_tree_insert(kpage
);
1490 stable_tree_append(tree_rmap_item
, stable_node
);
1491 stable_tree_append(rmap_item
, stable_node
);
1496 * If we fail to insert the page into the stable tree,
1497 * we will have 2 virtual addresses that are pointing
1498 * to a ksm page left outside the stable tree,
1499 * in which case we need to break_cow on both.
1502 break_cow(tree_rmap_item
);
1503 break_cow(rmap_item
);
1509 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
1510 struct rmap_item
**rmap_list
,
1513 struct rmap_item
*rmap_item
;
1515 while (*rmap_list
) {
1516 rmap_item
= *rmap_list
;
1517 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
1519 if (rmap_item
->address
> addr
)
1521 *rmap_list
= rmap_item
->rmap_list
;
1522 remove_rmap_item_from_tree(rmap_item
);
1523 free_rmap_item(rmap_item
);
1526 rmap_item
= alloc_rmap_item();
1528 /* It has already been zeroed */
1529 rmap_item
->mm
= mm_slot
->mm
;
1530 rmap_item
->address
= addr
;
1531 rmap_item
->rmap_list
= *rmap_list
;
1532 *rmap_list
= rmap_item
;
1537 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
1539 struct mm_struct
*mm
;
1540 struct mm_slot
*slot
;
1541 struct vm_area_struct
*vma
;
1542 struct rmap_item
*rmap_item
;
1545 if (list_empty(&ksm_mm_head
.mm_list
))
1548 slot
= ksm_scan
.mm_slot
;
1549 if (slot
== &ksm_mm_head
) {
1551 * A number of pages can hang around indefinitely on per-cpu
1552 * pagevecs, raised page count preventing write_protect_page
1553 * from merging them. Though it doesn't really matter much,
1554 * it is puzzling to see some stuck in pages_volatile until
1555 * other activity jostles them out, and they also prevented
1556 * LTP's KSM test from succeeding deterministically; so drain
1557 * them here (here rather than on entry to ksm_do_scan(),
1558 * so we don't IPI too often when pages_to_scan is set low).
1560 lru_add_drain_all();
1563 * Whereas stale stable_nodes on the stable_tree itself
1564 * get pruned in the regular course of stable_tree_search(),
1565 * those moved out to the migrate_nodes list can accumulate:
1566 * so prune them once before each full scan.
1568 if (!ksm_merge_across_nodes
) {
1569 struct stable_node
*stable_node
;
1570 struct list_head
*this, *next
;
1573 list_for_each_safe(this, next
, &migrate_nodes
) {
1574 stable_node
= list_entry(this,
1575 struct stable_node
, list
);
1576 page
= get_ksm_page(stable_node
, false);
1583 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++)
1584 root_unstable_tree
[nid
] = RB_ROOT
;
1586 spin_lock(&ksm_mmlist_lock
);
1587 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
1588 ksm_scan
.mm_slot
= slot
;
1589 spin_unlock(&ksm_mmlist_lock
);
1591 * Although we tested list_empty() above, a racing __ksm_exit
1592 * of the last mm on the list may have removed it since then.
1594 if (slot
== &ksm_mm_head
)
1597 ksm_scan
.address
= 0;
1598 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1602 down_read(&mm
->mmap_sem
);
1603 if (ksm_test_exit(mm
))
1606 vma
= find_vma(mm
, ksm_scan
.address
);
1608 for (; vma
; vma
= vma
->vm_next
) {
1609 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1611 if (ksm_scan
.address
< vma
->vm_start
)
1612 ksm_scan
.address
= vma
->vm_start
;
1614 ksm_scan
.address
= vma
->vm_end
;
1616 while (ksm_scan
.address
< vma
->vm_end
) {
1617 if (ksm_test_exit(mm
))
1619 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
1620 if (IS_ERR_OR_NULL(*page
)) {
1621 ksm_scan
.address
+= PAGE_SIZE
;
1625 if (PageAnon(*page
) ||
1626 page_trans_compound_anon(*page
)) {
1627 flush_anon_page(vma
, *page
, ksm_scan
.address
);
1628 flush_dcache_page(*page
);
1629 rmap_item
= get_next_rmap_item(slot
,
1630 ksm_scan
.rmap_list
, ksm_scan
.address
);
1632 ksm_scan
.rmap_list
=
1633 &rmap_item
->rmap_list
;
1634 ksm_scan
.address
+= PAGE_SIZE
;
1637 up_read(&mm
->mmap_sem
);
1641 ksm_scan
.address
+= PAGE_SIZE
;
1646 if (ksm_test_exit(mm
)) {
1647 ksm_scan
.address
= 0;
1648 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1651 * Nuke all the rmap_items that are above this current rmap:
1652 * because there were no VM_MERGEABLE vmas with such addresses.
1654 remove_trailing_rmap_items(slot
, ksm_scan
.rmap_list
);
1656 spin_lock(&ksm_mmlist_lock
);
1657 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
1658 struct mm_slot
, mm_list
);
1659 if (ksm_scan
.address
== 0) {
1661 * We've completed a full scan of all vmas, holding mmap_sem
1662 * throughout, and found no VM_MERGEABLE: so do the same as
1663 * __ksm_exit does to remove this mm from all our lists now.
1664 * This applies either when cleaning up after __ksm_exit
1665 * (but beware: we can reach here even before __ksm_exit),
1666 * or when all VM_MERGEABLE areas have been unmapped (and
1667 * mmap_sem then protects against race with MADV_MERGEABLE).
1669 hash_del(&slot
->link
);
1670 list_del(&slot
->mm_list
);
1671 spin_unlock(&ksm_mmlist_lock
);
1674 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1675 up_read(&mm
->mmap_sem
);
1678 spin_unlock(&ksm_mmlist_lock
);
1679 up_read(&mm
->mmap_sem
);
1682 /* Repeat until we've completed scanning the whole list */
1683 slot
= ksm_scan
.mm_slot
;
1684 if (slot
!= &ksm_mm_head
)
1692 * ksm_do_scan - the ksm scanner main worker function.
1693 * @scan_npages - number of pages we want to scan before we return.
1695 static void ksm_do_scan(unsigned int scan_npages
)
1697 struct rmap_item
*rmap_item
;
1698 struct page
*uninitialized_var(page
);
1700 while (scan_npages
-- && likely(!freezing(current
))) {
1702 rmap_item
= scan_get_next_rmap_item(&page
);
1705 cmp_and_merge_page(page
, rmap_item
);
1710 static int ksmd_should_run(void)
1712 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
1715 static int ksm_scan_thread(void *nothing
)
1718 set_user_nice(current
, 5);
1720 while (!kthread_should_stop()) {
1721 mutex_lock(&ksm_thread_mutex
);
1722 wait_while_offlining();
1723 if (ksmd_should_run())
1724 ksm_do_scan(ksm_thread_pages_to_scan
);
1725 mutex_unlock(&ksm_thread_mutex
);
1729 if (ksmd_should_run()) {
1730 schedule_timeout_interruptible(
1731 msecs_to_jiffies(ksm_thread_sleep_millisecs
));
1733 wait_event_freezable(ksm_thread_wait
,
1734 ksmd_should_run() || kthread_should_stop());
1740 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
1741 unsigned long end
, int advice
, unsigned long *vm_flags
)
1743 struct mm_struct
*mm
= vma
->vm_mm
;
1747 case MADV_MERGEABLE
:
1749 * Be somewhat over-protective for now!
1751 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
1752 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
1753 VM_HUGETLB
| VM_NONLINEAR
| VM_MIXEDMAP
))
1754 return 0; /* just ignore the advice */
1757 if (*vm_flags
& VM_SAO
)
1761 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
1762 err
= __ksm_enter(mm
);
1767 *vm_flags
|= VM_MERGEABLE
;
1770 case MADV_UNMERGEABLE
:
1771 if (!(*vm_flags
& VM_MERGEABLE
))
1772 return 0; /* just ignore the advice */
1774 if (vma
->anon_vma
) {
1775 err
= unmerge_ksm_pages(vma
, start
, end
);
1780 *vm_flags
&= ~VM_MERGEABLE
;
1787 int __ksm_enter(struct mm_struct
*mm
)
1789 struct mm_slot
*mm_slot
;
1792 mm_slot
= alloc_mm_slot();
1796 /* Check ksm_run too? Would need tighter locking */
1797 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
1799 spin_lock(&ksm_mmlist_lock
);
1800 insert_to_mm_slots_hash(mm
, mm_slot
);
1802 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1803 * insert just behind the scanning cursor, to let the area settle
1804 * down a little; when fork is followed by immediate exec, we don't
1805 * want ksmd to waste time setting up and tearing down an rmap_list.
1807 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1808 * scanning cursor, otherwise KSM pages in newly forked mms will be
1809 * missed: then we might as well insert at the end of the list.
1811 if (ksm_run
& KSM_RUN_UNMERGE
)
1812 list_add_tail(&mm_slot
->mm_list
, &ksm_mm_head
.mm_list
);
1814 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
1815 spin_unlock(&ksm_mmlist_lock
);
1817 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1818 atomic_inc(&mm
->mm_count
);
1821 wake_up_interruptible(&ksm_thread_wait
);
1826 void __ksm_exit(struct mm_struct
*mm
)
1828 struct mm_slot
*mm_slot
;
1829 int easy_to_free
= 0;
1832 * This process is exiting: if it's straightforward (as is the
1833 * case when ksmd was never running), free mm_slot immediately.
1834 * But if it's at the cursor or has rmap_items linked to it, use
1835 * mmap_sem to synchronize with any break_cows before pagetables
1836 * are freed, and leave the mm_slot on the list for ksmd to free.
1837 * Beware: ksm may already have noticed it exiting and freed the slot.
1840 spin_lock(&ksm_mmlist_lock
);
1841 mm_slot
= get_mm_slot(mm
);
1842 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
1843 if (!mm_slot
->rmap_list
) {
1844 hash_del(&mm_slot
->link
);
1845 list_del(&mm_slot
->mm_list
);
1848 list_move(&mm_slot
->mm_list
,
1849 &ksm_scan
.mm_slot
->mm_list
);
1852 spin_unlock(&ksm_mmlist_lock
);
1855 free_mm_slot(mm_slot
);
1856 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1858 } else if (mm_slot
) {
1859 down_write(&mm
->mmap_sem
);
1860 up_write(&mm
->mmap_sem
);
1864 struct page
*ksm_might_need_to_copy(struct page
*page
,
1865 struct vm_area_struct
*vma
, unsigned long address
)
1867 struct anon_vma
*anon_vma
= page_anon_vma(page
);
1868 struct page
*new_page
;
1870 if (PageKsm(page
)) {
1871 if (page_stable_node(page
) &&
1872 !(ksm_run
& KSM_RUN_UNMERGE
))
1873 return page
; /* no need to copy it */
1874 } else if (!anon_vma
) {
1875 return page
; /* no need to copy it */
1876 } else if (anon_vma
->root
== vma
->anon_vma
->root
&&
1877 page
->index
== linear_page_index(vma
, address
)) {
1878 return page
; /* still no need to copy it */
1880 if (!PageUptodate(page
))
1881 return page
; /* let do_swap_page report the error */
1883 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
1885 copy_user_highpage(new_page
, page
, address
, vma
);
1887 SetPageDirty(new_page
);
1888 __SetPageUptodate(new_page
);
1889 __set_page_locked(new_page
);
1895 int page_referenced_ksm(struct page
*page
, struct mem_cgroup
*memcg
,
1896 unsigned long *vm_flags
)
1898 struct stable_node
*stable_node
;
1899 struct rmap_item
*rmap_item
;
1900 unsigned int mapcount
= page_mapcount(page
);
1902 int search_new_forks
= 0;
1904 VM_BUG_ON(!PageKsm(page
));
1905 VM_BUG_ON(!PageLocked(page
));
1907 stable_node
= page_stable_node(page
);
1911 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
1912 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1913 struct anon_vma_chain
*vmac
;
1914 struct vm_area_struct
*vma
;
1916 anon_vma_lock_read(anon_vma
);
1917 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1920 if (rmap_item
->address
< vma
->vm_start
||
1921 rmap_item
->address
>= vma
->vm_end
)
1924 * Initially we examine only the vma which covers this
1925 * rmap_item; but later, if there is still work to do,
1926 * we examine covering vmas in other mms: in case they
1927 * were forked from the original since ksmd passed.
1929 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1932 if (memcg
&& !mm_match_cgroup(vma
->vm_mm
, memcg
))
1935 referenced
+= page_referenced_one(page
, vma
,
1936 rmap_item
->address
, &mapcount
, vm_flags
);
1937 if (!search_new_forks
|| !mapcount
)
1940 anon_vma_unlock_read(anon_vma
);
1944 if (!search_new_forks
++)
1950 int try_to_unmap_ksm(struct page
*page
, enum ttu_flags flags
)
1952 struct stable_node
*stable_node
;
1953 struct rmap_item
*rmap_item
;
1954 int ret
= SWAP_AGAIN
;
1955 int search_new_forks
= 0;
1957 VM_BUG_ON(!PageKsm(page
));
1958 VM_BUG_ON(!PageLocked(page
));
1960 stable_node
= page_stable_node(page
);
1964 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
1965 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1966 struct anon_vma_chain
*vmac
;
1967 struct vm_area_struct
*vma
;
1969 anon_vma_lock_read(anon_vma
);
1970 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1973 if (rmap_item
->address
< vma
->vm_start
||
1974 rmap_item
->address
>= vma
->vm_end
)
1977 * Initially we examine only the vma which covers this
1978 * rmap_item; but later, if there is still work to do,
1979 * we examine covering vmas in other mms: in case they
1980 * were forked from the original since ksmd passed.
1982 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1985 ret
= try_to_unmap_one(page
, vma
,
1986 rmap_item
->address
, flags
);
1987 if (ret
!= SWAP_AGAIN
|| !page_mapped(page
)) {
1988 anon_vma_unlock_read(anon_vma
);
1992 anon_vma_unlock_read(anon_vma
);
1994 if (!search_new_forks
++)
2000 #ifdef CONFIG_MIGRATION
2001 int rmap_walk_ksm(struct page
*page
, int (*rmap_one
)(struct page
*,
2002 struct vm_area_struct
*, unsigned long, void *), void *arg
)
2004 struct stable_node
*stable_node
;
2005 struct rmap_item
*rmap_item
;
2006 int ret
= SWAP_AGAIN
;
2007 int search_new_forks
= 0;
2009 VM_BUG_ON(!PageKsm(page
));
2010 VM_BUG_ON(!PageLocked(page
));
2012 stable_node
= page_stable_node(page
);
2016 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
2017 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
2018 struct anon_vma_chain
*vmac
;
2019 struct vm_area_struct
*vma
;
2021 anon_vma_lock_read(anon_vma
);
2022 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
2025 if (rmap_item
->address
< vma
->vm_start
||
2026 rmap_item
->address
>= vma
->vm_end
)
2029 * Initially we examine only the vma which covers this
2030 * rmap_item; but later, if there is still work to do,
2031 * we examine covering vmas in other mms: in case they
2032 * were forked from the original since ksmd passed.
2034 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
2037 ret
= rmap_one(page
, vma
, rmap_item
->address
, arg
);
2038 if (ret
!= SWAP_AGAIN
) {
2039 anon_vma_unlock_read(anon_vma
);
2043 anon_vma_unlock_read(anon_vma
);
2045 if (!search_new_forks
++)
2051 void ksm_migrate_page(struct page
*newpage
, struct page
*oldpage
)
2053 struct stable_node
*stable_node
;
2055 VM_BUG_ON(!PageLocked(oldpage
));
2056 VM_BUG_ON(!PageLocked(newpage
));
2057 VM_BUG_ON(newpage
->mapping
!= oldpage
->mapping
);
2059 stable_node
= page_stable_node(newpage
);
2061 VM_BUG_ON(stable_node
->kpfn
!= page_to_pfn(oldpage
));
2062 stable_node
->kpfn
= page_to_pfn(newpage
);
2064 * newpage->mapping was set in advance; now we need smp_wmb()
2065 * to make sure that the new stable_node->kpfn is visible
2066 * to get_ksm_page() before it can see that oldpage->mapping
2067 * has gone stale (or that PageSwapCache has been cleared).
2070 set_page_stable_node(oldpage
, NULL
);
2073 #endif /* CONFIG_MIGRATION */
2075 #ifdef CONFIG_MEMORY_HOTREMOVE
2076 static int just_wait(void *word
)
2082 static void wait_while_offlining(void)
2084 while (ksm_run
& KSM_RUN_OFFLINE
) {
2085 mutex_unlock(&ksm_thread_mutex
);
2086 wait_on_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
),
2087 just_wait
, TASK_UNINTERRUPTIBLE
);
2088 mutex_lock(&ksm_thread_mutex
);
2092 static void ksm_check_stable_tree(unsigned long start_pfn
,
2093 unsigned long end_pfn
)
2095 struct stable_node
*stable_node
;
2096 struct list_head
*this, *next
;
2097 struct rb_node
*node
;
2100 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
2101 node
= rb_first(root_stable_tree
+ nid
);
2103 stable_node
= rb_entry(node
, struct stable_node
, node
);
2104 if (stable_node
->kpfn
>= start_pfn
&&
2105 stable_node
->kpfn
< end_pfn
) {
2107 * Don't get_ksm_page, page has already gone:
2108 * which is why we keep kpfn instead of page*
2110 remove_node_from_stable_tree(stable_node
);
2111 node
= rb_first(root_stable_tree
+ nid
);
2113 node
= rb_next(node
);
2117 list_for_each_safe(this, next
, &migrate_nodes
) {
2118 stable_node
= list_entry(this, struct stable_node
, list
);
2119 if (stable_node
->kpfn
>= start_pfn
&&
2120 stable_node
->kpfn
< end_pfn
)
2121 remove_node_from_stable_tree(stable_node
);
2126 static int ksm_memory_callback(struct notifier_block
*self
,
2127 unsigned long action
, void *arg
)
2129 struct memory_notify
*mn
= arg
;
2132 case MEM_GOING_OFFLINE
:
2134 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2135 * and remove_all_stable_nodes() while memory is going offline:
2136 * it is unsafe for them to touch the stable tree at this time.
2137 * But unmerge_ksm_pages(), rmap lookups and other entry points
2138 * which do not need the ksm_thread_mutex are all safe.
2140 mutex_lock(&ksm_thread_mutex
);
2141 ksm_run
|= KSM_RUN_OFFLINE
;
2142 mutex_unlock(&ksm_thread_mutex
);
2147 * Most of the work is done by page migration; but there might
2148 * be a few stable_nodes left over, still pointing to struct
2149 * pages which have been offlined: prune those from the tree,
2150 * otherwise get_ksm_page() might later try to access a
2151 * non-existent struct page.
2153 ksm_check_stable_tree(mn
->start_pfn
,
2154 mn
->start_pfn
+ mn
->nr_pages
);
2157 case MEM_CANCEL_OFFLINE
:
2158 mutex_lock(&ksm_thread_mutex
);
2159 ksm_run
&= ~KSM_RUN_OFFLINE
;
2160 mutex_unlock(&ksm_thread_mutex
);
2162 smp_mb(); /* wake_up_bit advises this */
2163 wake_up_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
));
2169 static void wait_while_offlining(void)
2172 #endif /* CONFIG_MEMORY_HOTREMOVE */
2176 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2179 #define KSM_ATTR_RO(_name) \
2180 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2181 #define KSM_ATTR(_name) \
2182 static struct kobj_attribute _name##_attr = \
2183 __ATTR(_name, 0644, _name##_show, _name##_store)
2185 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
2186 struct kobj_attribute
*attr
, char *buf
)
2188 return sprintf(buf
, "%u\n", ksm_thread_sleep_millisecs
);
2191 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
2192 struct kobj_attribute
*attr
,
2193 const char *buf
, size_t count
)
2195 unsigned long msecs
;
2198 err
= strict_strtoul(buf
, 10, &msecs
);
2199 if (err
|| msecs
> UINT_MAX
)
2202 ksm_thread_sleep_millisecs
= msecs
;
2206 KSM_ATTR(sleep_millisecs
);
2208 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
2209 struct kobj_attribute
*attr
, char *buf
)
2211 return sprintf(buf
, "%u\n", ksm_thread_pages_to_scan
);
2214 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
2215 struct kobj_attribute
*attr
,
2216 const char *buf
, size_t count
)
2219 unsigned long nr_pages
;
2221 err
= strict_strtoul(buf
, 10, &nr_pages
);
2222 if (err
|| nr_pages
> UINT_MAX
)
2225 ksm_thread_pages_to_scan
= nr_pages
;
2229 KSM_ATTR(pages_to_scan
);
2231 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2234 return sprintf(buf
, "%lu\n", ksm_run
);
2237 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2238 const char *buf
, size_t count
)
2241 unsigned long flags
;
2243 err
= strict_strtoul(buf
, 10, &flags
);
2244 if (err
|| flags
> UINT_MAX
)
2246 if (flags
> KSM_RUN_UNMERGE
)
2250 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2251 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2252 * breaking COW to free the pages_shared (but leaves mm_slots
2253 * on the list for when ksmd may be set running again).
2256 mutex_lock(&ksm_thread_mutex
);
2257 wait_while_offlining();
2258 if (ksm_run
!= flags
) {
2260 if (flags
& KSM_RUN_UNMERGE
) {
2261 set_current_oom_origin();
2262 err
= unmerge_and_remove_all_rmap_items();
2263 clear_current_oom_origin();
2265 ksm_run
= KSM_RUN_STOP
;
2270 mutex_unlock(&ksm_thread_mutex
);
2272 if (flags
& KSM_RUN_MERGE
)
2273 wake_up_interruptible(&ksm_thread_wait
);
2280 static ssize_t
merge_across_nodes_show(struct kobject
*kobj
,
2281 struct kobj_attribute
*attr
, char *buf
)
2283 return sprintf(buf
, "%u\n", ksm_merge_across_nodes
);
2286 static ssize_t
merge_across_nodes_store(struct kobject
*kobj
,
2287 struct kobj_attribute
*attr
,
2288 const char *buf
, size_t count
)
2293 err
= kstrtoul(buf
, 10, &knob
);
2299 mutex_lock(&ksm_thread_mutex
);
2300 wait_while_offlining();
2301 if (ksm_merge_across_nodes
!= knob
) {
2302 if (ksm_pages_shared
|| remove_all_stable_nodes())
2304 else if (root_stable_tree
== one_stable_tree
) {
2305 struct rb_root
*buf
;
2307 * This is the first time that we switch away from the
2308 * default of merging across nodes: must now allocate
2309 * a buffer to hold as many roots as may be needed.
2310 * Allocate stable and unstable together:
2311 * MAXSMP NODES_SHIFT 10 will use 16kB.
2313 buf
= kcalloc(nr_node_ids
+ nr_node_ids
,
2314 sizeof(*buf
), GFP_KERNEL
| __GFP_ZERO
);
2315 /* Let us assume that RB_ROOT is NULL is zero */
2319 root_stable_tree
= buf
;
2320 root_unstable_tree
= buf
+ nr_node_ids
;
2321 /* Stable tree is empty but not the unstable */
2322 root_unstable_tree
[0] = one_unstable_tree
[0];
2326 ksm_merge_across_nodes
= knob
;
2327 ksm_nr_node_ids
= knob
? 1 : nr_node_ids
;
2330 mutex_unlock(&ksm_thread_mutex
);
2332 return err
? err
: count
;
2334 KSM_ATTR(merge_across_nodes
);
2337 static ssize_t
pages_shared_show(struct kobject
*kobj
,
2338 struct kobj_attribute
*attr
, char *buf
)
2340 return sprintf(buf
, "%lu\n", ksm_pages_shared
);
2342 KSM_ATTR_RO(pages_shared
);
2344 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
2345 struct kobj_attribute
*attr
, char *buf
)
2347 return sprintf(buf
, "%lu\n", ksm_pages_sharing
);
2349 KSM_ATTR_RO(pages_sharing
);
2351 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
2352 struct kobj_attribute
*attr
, char *buf
)
2354 return sprintf(buf
, "%lu\n", ksm_pages_unshared
);
2356 KSM_ATTR_RO(pages_unshared
);
2358 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
2359 struct kobj_attribute
*attr
, char *buf
)
2361 long ksm_pages_volatile
;
2363 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
2364 - ksm_pages_sharing
- ksm_pages_unshared
;
2366 * It was not worth any locking to calculate that statistic,
2367 * but it might therefore sometimes be negative: conceal that.
2369 if (ksm_pages_volatile
< 0)
2370 ksm_pages_volatile
= 0;
2371 return sprintf(buf
, "%ld\n", ksm_pages_volatile
);
2373 KSM_ATTR_RO(pages_volatile
);
2375 static ssize_t
full_scans_show(struct kobject
*kobj
,
2376 struct kobj_attribute
*attr
, char *buf
)
2378 return sprintf(buf
, "%lu\n", ksm_scan
.seqnr
);
2380 KSM_ATTR_RO(full_scans
);
2382 static struct attribute
*ksm_attrs
[] = {
2383 &sleep_millisecs_attr
.attr
,
2384 &pages_to_scan_attr
.attr
,
2386 &pages_shared_attr
.attr
,
2387 &pages_sharing_attr
.attr
,
2388 &pages_unshared_attr
.attr
,
2389 &pages_volatile_attr
.attr
,
2390 &full_scans_attr
.attr
,
2392 &merge_across_nodes_attr
.attr
,
2397 static struct attribute_group ksm_attr_group
= {
2401 #endif /* CONFIG_SYSFS */
2403 static int __init
ksm_init(void)
2405 struct task_struct
*ksm_thread
;
2408 err
= ksm_slab_init();
2412 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
2413 if (IS_ERR(ksm_thread
)) {
2414 printk(KERN_ERR
"ksm: creating kthread failed\n");
2415 err
= PTR_ERR(ksm_thread
);
2420 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
2422 printk(KERN_ERR
"ksm: register sysfs failed\n");
2423 kthread_stop(ksm_thread
);
2427 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
2429 #endif /* CONFIG_SYSFS */
2431 #ifdef CONFIG_MEMORY_HOTREMOVE
2432 /* There is no significance to this priority 100 */
2433 hotplug_memory_notifier(ksm_memory_callback
, 100);
2442 module_init(ksm_init
)