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
);
292 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
295 rmap_item
->mm
= NULL
; /* debug safety */
296 kmem_cache_free(rmap_item_cache
, rmap_item
);
299 static inline struct stable_node
*alloc_stable_node(void)
301 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
);
304 static inline void free_stable_node(struct stable_node
*stable_node
)
306 kmem_cache_free(stable_node_cache
, stable_node
);
309 static inline struct mm_slot
*alloc_mm_slot(void)
311 if (!mm_slot_cache
) /* initialization failed */
313 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
316 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
318 kmem_cache_free(mm_slot_cache
, mm_slot
);
321 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
323 struct mm_slot
*slot
;
325 hash_for_each_possible(mm_slots_hash
, slot
, link
, (unsigned long)mm
)
332 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
333 struct mm_slot
*mm_slot
)
336 hash_add(mm_slots_hash
, &mm_slot
->link
, (unsigned long)mm
);
340 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
341 * page tables after it has passed through ksm_exit() - which, if necessary,
342 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
343 * a special flag: they can just back out as soon as mm_users goes to zero.
344 * ksm_test_exit() is used throughout to make this test for exit: in some
345 * places for correctness, in some places just to avoid unnecessary work.
347 static inline bool ksm_test_exit(struct mm_struct
*mm
)
349 return atomic_read(&mm
->mm_users
) == 0;
353 * We use break_ksm to break COW on a ksm page: it's a stripped down
355 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
358 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
359 * in case the application has unmapped and remapped mm,addr meanwhile.
360 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
361 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
363 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
370 page
= follow_page(vma
, addr
, FOLL_GET
| FOLL_MIGRATION
);
371 if (IS_ERR_OR_NULL(page
))
374 ret
= handle_mm_fault(vma
->vm_mm
, vma
, addr
,
377 ret
= VM_FAULT_WRITE
;
379 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_OOM
)));
381 * We must loop because handle_mm_fault() may back out if there's
382 * any difficulty e.g. if pte accessed bit gets updated concurrently.
384 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
385 * COW has been broken, even if the vma does not permit VM_WRITE;
386 * but note that a concurrent fault might break PageKsm for us.
388 * VM_FAULT_SIGBUS could occur if we race with truncation of the
389 * backing file, which also invalidates anonymous pages: that's
390 * okay, that truncation will have unmapped the PageKsm for us.
392 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
393 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
394 * current task has TIF_MEMDIE set, and will be OOM killed on return
395 * to user; and ksmd, having no mm, would never be chosen for that.
397 * But if the mm is in a limited mem_cgroup, then the fault may fail
398 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
399 * even ksmd can fail in this way - though it's usually breaking ksm
400 * just to undo a merge it made a moment before, so unlikely to oom.
402 * That's a pity: we might therefore have more kernel pages allocated
403 * than we're counting as nodes in the stable tree; but ksm_do_scan
404 * will retry to break_cow on each pass, so should recover the page
405 * in due course. The important thing is to not let VM_MERGEABLE
406 * be cleared while any such pages might remain in the area.
408 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
411 static struct vm_area_struct
*find_mergeable_vma(struct mm_struct
*mm
,
414 struct vm_area_struct
*vma
;
415 if (ksm_test_exit(mm
))
417 vma
= find_vma(mm
, addr
);
418 if (!vma
|| vma
->vm_start
> addr
)
420 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
425 static void break_cow(struct rmap_item
*rmap_item
)
427 struct mm_struct
*mm
= rmap_item
->mm
;
428 unsigned long addr
= rmap_item
->address
;
429 struct vm_area_struct
*vma
;
432 * It is not an accident that whenever we want to break COW
433 * to undo, we also need to drop a reference to the anon_vma.
435 put_anon_vma(rmap_item
->anon_vma
);
437 down_read(&mm
->mmap_sem
);
438 vma
= find_mergeable_vma(mm
, addr
);
440 break_ksm(vma
, addr
);
441 up_read(&mm
->mmap_sem
);
444 static struct page
*page_trans_compound_anon(struct page
*page
)
446 if (PageTransCompound(page
)) {
447 struct page
*head
= compound_trans_head(page
);
449 * head may actually be splitted and freed from under
450 * us but it's ok here.
458 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
460 struct mm_struct
*mm
= rmap_item
->mm
;
461 unsigned long addr
= rmap_item
->address
;
462 struct vm_area_struct
*vma
;
465 down_read(&mm
->mmap_sem
);
466 vma
= find_mergeable_vma(mm
, addr
);
470 page
= follow_page(vma
, addr
, FOLL_GET
);
471 if (IS_ERR_OR_NULL(page
))
473 if (PageAnon(page
) || page_trans_compound_anon(page
)) {
474 flush_anon_page(vma
, page
, addr
);
475 flush_dcache_page(page
);
480 up_read(&mm
->mmap_sem
);
485 * This helper is used for getting right index into array of tree roots.
486 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
487 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
488 * every node has its own stable and unstable tree.
490 static inline int get_kpfn_nid(unsigned long kpfn
)
492 return ksm_merge_across_nodes
? 0 : pfn_to_nid(kpfn
);
495 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
497 struct rmap_item
*rmap_item
;
499 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
500 if (rmap_item
->hlist
.next
)
504 put_anon_vma(rmap_item
->anon_vma
);
505 rmap_item
->address
&= PAGE_MASK
;
509 if (stable_node
->head
== &migrate_nodes
)
510 list_del(&stable_node
->list
);
512 rb_erase(&stable_node
->node
,
513 root_stable_tree
+ NUMA(stable_node
->nid
));
514 free_stable_node(stable_node
);
518 * get_ksm_page: checks if the page indicated by the stable node
519 * is still its ksm page, despite having held no reference to it.
520 * In which case we can trust the content of the page, and it
521 * returns the gotten page; but if the page has now been zapped,
522 * remove the stale node from the stable tree and return NULL.
523 * But beware, the stable node's page might be being migrated.
525 * You would expect the stable_node to hold a reference to the ksm page.
526 * But if it increments the page's count, swapping out has to wait for
527 * ksmd to come around again before it can free the page, which may take
528 * seconds or even minutes: much too unresponsive. So instead we use a
529 * "keyhole reference": access to the ksm page from the stable node peeps
530 * out through its keyhole to see if that page still holds the right key,
531 * pointing back to this stable node. This relies on freeing a PageAnon
532 * page to reset its page->mapping to NULL, and relies on no other use of
533 * a page to put something that might look like our key in page->mapping.
534 * is on its way to being freed; but it is an anomaly to bear in mind.
536 static struct page
*get_ksm_page(struct stable_node
*stable_node
, bool lock_it
)
539 void *expected_mapping
;
542 expected_mapping
= (void *)stable_node
+
543 (PAGE_MAPPING_ANON
| PAGE_MAPPING_KSM
);
545 kpfn
= ACCESS_ONCE(stable_node
->kpfn
);
546 page
= pfn_to_page(kpfn
);
549 * page is computed from kpfn, so on most architectures reading
550 * page->mapping is naturally ordered after reading node->kpfn,
551 * but on Alpha we need to be more careful.
553 smp_read_barrier_depends();
554 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
)
558 * We cannot do anything with the page while its refcount is 0.
559 * Usually 0 means free, or tail of a higher-order page: in which
560 * case this node is no longer referenced, and should be freed;
561 * however, it might mean that the page is under page_freeze_refs().
562 * The __remove_mapping() case is easy, again the node is now stale;
563 * but if page is swapcache in migrate_page_move_mapping(), it might
564 * still be our page, in which case it's essential to keep the node.
566 while (!get_page_unless_zero(page
)) {
568 * Another check for page->mapping != expected_mapping would
569 * work here too. We have chosen the !PageSwapCache test to
570 * optimize the common case, when the page is or is about to
571 * be freed: PageSwapCache is cleared (under spin_lock_irq)
572 * in the freeze_refs section of __remove_mapping(); but Anon
573 * page->mapping reset to NULL later, in free_pages_prepare().
575 if (!PageSwapCache(page
))
580 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
587 if (ACCESS_ONCE(page
->mapping
) != expected_mapping
) {
597 * We come here from above when page->mapping or !PageSwapCache
598 * suggests that the node is stale; but it might be under migration.
599 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
600 * before checking whether node->kpfn has been changed.
603 if (ACCESS_ONCE(stable_node
->kpfn
) != kpfn
)
605 remove_node_from_stable_tree(stable_node
);
610 * Removing rmap_item from stable or unstable tree.
611 * This function will clean the information from the stable/unstable tree.
613 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
615 if (rmap_item
->address
& STABLE_FLAG
) {
616 struct stable_node
*stable_node
;
619 stable_node
= rmap_item
->head
;
620 page
= get_ksm_page(stable_node
, true);
624 hlist_del(&rmap_item
->hlist
);
628 if (stable_node
->hlist
.first
)
633 put_anon_vma(rmap_item
->anon_vma
);
634 rmap_item
->address
&= PAGE_MASK
;
636 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
639 * Usually ksmd can and must skip the rb_erase, because
640 * root_unstable_tree was already reset to RB_ROOT.
641 * But be careful when an mm is exiting: do the rb_erase
642 * if this rmap_item was inserted by this scan, rather
643 * than left over from before.
645 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
648 rb_erase(&rmap_item
->node
,
649 root_unstable_tree
+ NUMA(rmap_item
->nid
));
650 ksm_pages_unshared
--;
651 rmap_item
->address
&= PAGE_MASK
;
654 cond_resched(); /* we're called from many long loops */
657 static void remove_trailing_rmap_items(struct mm_slot
*mm_slot
,
658 struct rmap_item
**rmap_list
)
661 struct rmap_item
*rmap_item
= *rmap_list
;
662 *rmap_list
= rmap_item
->rmap_list
;
663 remove_rmap_item_from_tree(rmap_item
);
664 free_rmap_item(rmap_item
);
669 * Though it's very tempting to unmerge rmap_items from stable tree rather
670 * than check every pte of a given vma, the locking doesn't quite work for
671 * that - an rmap_item is assigned to the stable tree after inserting ksm
672 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
673 * rmap_items from parent to child at fork time (so as not to waste time
674 * if exit comes before the next scan reaches it).
676 * Similarly, although we'd like to remove rmap_items (so updating counts
677 * and freeing memory) when unmerging an area, it's easier to leave that
678 * to the next pass of ksmd - consider, for example, how ksmd might be
679 * in cmp_and_merge_page on one of the rmap_items we would be removing.
681 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
682 unsigned long start
, unsigned long end
)
687 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
688 if (ksm_test_exit(vma
->vm_mm
))
690 if (signal_pending(current
))
693 err
= break_ksm(vma
, addr
);
700 * Only called through the sysfs control interface:
702 static int remove_stable_node(struct stable_node
*stable_node
)
707 page
= get_ksm_page(stable_node
, true);
710 * get_ksm_page did remove_node_from_stable_tree itself.
715 if (WARN_ON_ONCE(page_mapped(page
))) {
717 * This should not happen: but if it does, just refuse to let
718 * merge_across_nodes be switched - there is no need to panic.
723 * The stable node did not yet appear stale to get_ksm_page(),
724 * since that allows for an unmapped ksm page to be recognized
725 * right up until it is freed; but the node is safe to remove.
726 * This page might be in a pagevec waiting to be freed,
727 * or it might be PageSwapCache (perhaps under writeback),
728 * or it might have been removed from swapcache a moment ago.
730 set_page_stable_node(page
, NULL
);
731 remove_node_from_stable_tree(stable_node
);
740 static int remove_all_stable_nodes(void)
742 struct stable_node
*stable_node
;
743 struct list_head
*this, *next
;
747 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
748 while (root_stable_tree
[nid
].rb_node
) {
749 stable_node
= rb_entry(root_stable_tree
[nid
].rb_node
,
750 struct stable_node
, node
);
751 if (remove_stable_node(stable_node
)) {
753 break; /* proceed to next nid */
758 list_for_each_safe(this, next
, &migrate_nodes
) {
759 stable_node
= list_entry(this, struct stable_node
, list
);
760 if (remove_stable_node(stable_node
))
767 static int unmerge_and_remove_all_rmap_items(void)
769 struct mm_slot
*mm_slot
;
770 struct mm_struct
*mm
;
771 struct vm_area_struct
*vma
;
774 spin_lock(&ksm_mmlist_lock
);
775 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
776 struct mm_slot
, mm_list
);
777 spin_unlock(&ksm_mmlist_lock
);
779 for (mm_slot
= ksm_scan
.mm_slot
;
780 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
782 down_read(&mm
->mmap_sem
);
783 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
784 if (ksm_test_exit(mm
))
786 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
788 err
= unmerge_ksm_pages(vma
,
789 vma
->vm_start
, vma
->vm_end
);
794 remove_trailing_rmap_items(mm_slot
, &mm_slot
->rmap_list
);
796 spin_lock(&ksm_mmlist_lock
);
797 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
798 struct mm_slot
, mm_list
);
799 if (ksm_test_exit(mm
)) {
800 hash_del(&mm_slot
->link
);
801 list_del(&mm_slot
->mm_list
);
802 spin_unlock(&ksm_mmlist_lock
);
804 free_mm_slot(mm_slot
);
805 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
806 up_read(&mm
->mmap_sem
);
809 spin_unlock(&ksm_mmlist_lock
);
810 up_read(&mm
->mmap_sem
);
814 /* Clean up stable nodes, but don't worry if some are still busy */
815 remove_all_stable_nodes();
820 up_read(&mm
->mmap_sem
);
821 spin_lock(&ksm_mmlist_lock
);
822 ksm_scan
.mm_slot
= &ksm_mm_head
;
823 spin_unlock(&ksm_mmlist_lock
);
826 #endif /* CONFIG_SYSFS */
828 static u32
calc_checksum(struct page
*page
)
831 void *addr
= kmap_atomic(page
);
832 checksum
= jhash2(addr
, PAGE_SIZE
/ 4, 17);
837 static int memcmp_pages(struct page
*page1
, struct page
*page2
)
842 addr1
= kmap_atomic(page1
);
843 addr2
= kmap_atomic(page2
);
844 ret
= memcmp(addr1
, addr2
, PAGE_SIZE
);
845 kunmap_atomic(addr2
);
846 kunmap_atomic(addr1
);
850 static inline int pages_identical(struct page
*page1
, struct page
*page2
)
852 return !memcmp_pages(page1
, page2
);
855 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
858 struct mm_struct
*mm
= vma
->vm_mm
;
864 unsigned long mmun_start
; /* For mmu_notifiers */
865 unsigned long mmun_end
; /* For mmu_notifiers */
867 addr
= page_address_in_vma(page
, vma
);
871 BUG_ON(PageTransCompound(page
));
874 mmun_end
= addr
+ PAGE_SIZE
;
875 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
877 ptep
= page_check_address(page
, mm
, addr
, &ptl
, 0);
881 if (pte_write(*ptep
) || pte_dirty(*ptep
)) {
884 swapped
= PageSwapCache(page
);
885 flush_cache_page(vma
, addr
, page_to_pfn(page
));
887 * Ok this is tricky, when get_user_pages_fast() run it doesn't
888 * take any lock, therefore the check that we are going to make
889 * with the pagecount against the mapcount is racey and
890 * O_DIRECT can happen right after the check.
891 * So we clear the pte and flush the tlb before the check
892 * this assure us that no O_DIRECT can happen after the check
893 * or in the middle of the check.
895 entry
= ptep_clear_flush(vma
, addr
, ptep
);
897 * Check that no O_DIRECT or similar I/O is in progress on the
900 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
901 set_pte_at(mm
, addr
, ptep
, entry
);
904 if (pte_dirty(entry
))
905 set_page_dirty(page
);
906 entry
= pte_mkclean(pte_wrprotect(entry
));
907 set_pte_at_notify(mm
, addr
, ptep
, entry
);
913 pte_unmap_unlock(ptep
, ptl
);
915 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
921 * replace_page - replace page in vma by new ksm page
922 * @vma: vma that holds the pte pointing to page
923 * @page: the page we are replacing by kpage
924 * @kpage: the ksm page we replace page by
925 * @orig_pte: the original value of the pte
927 * Returns 0 on success, -EFAULT on failure.
929 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
930 struct page
*kpage
, pte_t orig_pte
)
932 struct mm_struct
*mm
= vma
->vm_mm
;
938 unsigned long mmun_start
; /* For mmu_notifiers */
939 unsigned long mmun_end
; /* For mmu_notifiers */
941 addr
= page_address_in_vma(page
, vma
);
945 pmd
= mm_find_pmd(mm
, addr
);
948 BUG_ON(pmd_trans_huge(*pmd
));
951 mmun_end
= addr
+ PAGE_SIZE
;
952 mmu_notifier_invalidate_range_start(mm
, mmun_start
, mmun_end
);
954 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
955 if (!pte_same(*ptep
, orig_pte
)) {
956 pte_unmap_unlock(ptep
, ptl
);
961 page_add_anon_rmap(kpage
, vma
, addr
);
963 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
964 ptep_clear_flush(vma
, addr
, ptep
);
965 set_pte_at_notify(mm
, addr
, ptep
, mk_pte(kpage
, vma
->vm_page_prot
));
967 page_remove_rmap(page
);
968 if (!page_mapped(page
))
969 try_to_free_swap(page
);
972 pte_unmap_unlock(ptep
, ptl
);
975 mmu_notifier_invalidate_range_end(mm
, mmun_start
, mmun_end
);
980 static int page_trans_compound_anon_split(struct page
*page
)
983 struct page
*transhuge_head
= page_trans_compound_anon(page
);
984 if (transhuge_head
) {
985 /* Get the reference on the head to split it. */
986 if (get_page_unless_zero(transhuge_head
)) {
988 * Recheck we got the reference while the head
989 * was still anonymous.
991 if (PageAnon(transhuge_head
))
992 ret
= split_huge_page(transhuge_head
);
995 * Retry later if split_huge_page run
999 put_page(transhuge_head
);
1001 /* Retry later if split_huge_page run from under us. */
1008 * try_to_merge_one_page - take two pages and merge them into one
1009 * @vma: the vma that holds the pte pointing to page
1010 * @page: the PageAnon page that we want to replace with kpage
1011 * @kpage: the PageKsm page that we want to map instead of page,
1012 * or NULL the first time when we want to use page as kpage.
1014 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1016 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
1017 struct page
*page
, struct page
*kpage
)
1019 pte_t orig_pte
= __pte(0);
1022 if (page
== kpage
) /* ksm page forked */
1025 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1027 if (PageTransCompound(page
) && page_trans_compound_anon_split(page
))
1029 BUG_ON(PageTransCompound(page
));
1030 if (!PageAnon(page
))
1034 * We need the page lock to read a stable PageSwapCache in
1035 * write_protect_page(). We use trylock_page() instead of
1036 * lock_page() because we don't want to wait here - we
1037 * prefer to continue scanning and merging different pages,
1038 * then come back to this page when it is unlocked.
1040 if (!trylock_page(page
))
1043 * If this anonymous page is mapped only here, its pte may need
1044 * to be write-protected. If it's mapped elsewhere, all of its
1045 * ptes are necessarily already write-protected. But in either
1046 * case, we need to lock and check page_count is not raised.
1048 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
1051 * While we hold page lock, upgrade page from
1052 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1053 * stable_tree_insert() will update stable_node.
1055 set_page_stable_node(page
, NULL
);
1056 mark_page_accessed(page
);
1058 } else if (pages_identical(page
, kpage
))
1059 err
= replace_page(vma
, page
, kpage
, orig_pte
);
1062 if ((vma
->vm_flags
& VM_LOCKED
) && kpage
&& !err
) {
1063 munlock_vma_page(page
);
1064 if (!PageMlocked(kpage
)) {
1067 mlock_vma_page(kpage
);
1068 page
= kpage
; /* for final unlock */
1078 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1079 * but no new kernel page is allocated: kpage must already be a ksm page.
1081 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1083 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
1084 struct page
*page
, struct page
*kpage
)
1086 struct mm_struct
*mm
= rmap_item
->mm
;
1087 struct vm_area_struct
*vma
;
1090 down_read(&mm
->mmap_sem
);
1091 if (ksm_test_exit(mm
))
1093 vma
= find_vma(mm
, rmap_item
->address
);
1094 if (!vma
|| vma
->vm_start
> rmap_item
->address
)
1097 err
= try_to_merge_one_page(vma
, page
, kpage
);
1101 /* Unstable nid is in union with stable anon_vma: remove first */
1102 remove_rmap_item_from_tree(rmap_item
);
1104 /* Must get reference to anon_vma while still holding mmap_sem */
1105 rmap_item
->anon_vma
= vma
->anon_vma
;
1106 get_anon_vma(vma
->anon_vma
);
1108 up_read(&mm
->mmap_sem
);
1113 * try_to_merge_two_pages - take two identical pages and prepare them
1114 * to be merged into one page.
1116 * This function returns the kpage if we successfully merged two identical
1117 * pages into one ksm page, NULL otherwise.
1119 * Note that this function upgrades page to ksm page: if one of the pages
1120 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1122 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
1124 struct rmap_item
*tree_rmap_item
,
1125 struct page
*tree_page
)
1129 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
1131 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
1134 * If that fails, we have a ksm page with only one pte
1135 * pointing to it: so break it.
1138 break_cow(rmap_item
);
1140 return err
? NULL
: page
;
1144 * stable_tree_search - search for page inside the stable tree
1146 * This function checks if there is a page inside the stable tree
1147 * with identical content to the page that we are scanning right now.
1149 * This function returns the stable tree node of identical content if found,
1152 static struct page
*stable_tree_search(struct page
*page
)
1155 struct rb_root
*root
;
1156 struct rb_node
**new;
1157 struct rb_node
*parent
;
1158 struct stable_node
*stable_node
;
1159 struct stable_node
*page_node
;
1161 page_node
= page_stable_node(page
);
1162 if (page_node
&& page_node
->head
!= &migrate_nodes
) {
1163 /* ksm page forked */
1168 nid
= get_kpfn_nid(page_to_pfn(page
));
1169 root
= root_stable_tree
+ nid
;
1171 new = &root
->rb_node
;
1175 struct page
*tree_page
;
1179 stable_node
= rb_entry(*new, struct stable_node
, node
);
1180 tree_page
= get_ksm_page(stable_node
, false);
1184 ret
= memcmp_pages(page
, tree_page
);
1185 put_page(tree_page
);
1189 new = &parent
->rb_left
;
1191 new = &parent
->rb_right
;
1194 * Lock and unlock the stable_node's page (which
1195 * might already have been migrated) so that page
1196 * migration is sure to notice its raised count.
1197 * It would be more elegant to return stable_node
1198 * than kpage, but that involves more changes.
1200 tree_page
= get_ksm_page(stable_node
, true);
1202 unlock_page(tree_page
);
1203 if (get_kpfn_nid(stable_node
->kpfn
) !=
1204 NUMA(stable_node
->nid
)) {
1205 put_page(tree_page
);
1211 * There is now a place for page_node, but the tree may
1212 * have been rebalanced, so re-evaluate parent and new.
1223 list_del(&page_node
->list
);
1224 DO_NUMA(page_node
->nid
= nid
);
1225 rb_link_node(&page_node
->node
, parent
, new);
1226 rb_insert_color(&page_node
->node
, root
);
1232 list_del(&page_node
->list
);
1233 DO_NUMA(page_node
->nid
= nid
);
1234 rb_replace_node(&stable_node
->node
, &page_node
->node
, root
);
1237 rb_erase(&stable_node
->node
, root
);
1240 stable_node
->head
= &migrate_nodes
;
1241 list_add(&stable_node
->list
, stable_node
->head
);
1246 * stable_tree_insert - insert stable tree node pointing to new ksm page
1247 * into the stable tree.
1249 * This function returns the stable tree node just allocated on success,
1252 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1256 struct rb_root
*root
;
1257 struct rb_node
**new;
1258 struct rb_node
*parent
= NULL
;
1259 struct stable_node
*stable_node
;
1261 kpfn
= page_to_pfn(kpage
);
1262 nid
= get_kpfn_nid(kpfn
);
1263 root
= root_stable_tree
+ nid
;
1264 new = &root
->rb_node
;
1267 struct page
*tree_page
;
1271 stable_node
= rb_entry(*new, struct stable_node
, node
);
1272 tree_page
= get_ksm_page(stable_node
, false);
1276 ret
= memcmp_pages(kpage
, tree_page
);
1277 put_page(tree_page
);
1281 new = &parent
->rb_left
;
1283 new = &parent
->rb_right
;
1286 * It is not a bug that stable_tree_search() didn't
1287 * find this node: because at that time our page was
1288 * not yet write-protected, so may have changed since.
1294 stable_node
= alloc_stable_node();
1298 INIT_HLIST_HEAD(&stable_node
->hlist
);
1299 stable_node
->kpfn
= kpfn
;
1300 set_page_stable_node(kpage
, stable_node
);
1301 DO_NUMA(stable_node
->nid
= nid
);
1302 rb_link_node(&stable_node
->node
, parent
, new);
1303 rb_insert_color(&stable_node
->node
, root
);
1309 * unstable_tree_search_insert - search for identical page,
1310 * else insert rmap_item into the unstable tree.
1312 * This function searches for a page in the unstable tree identical to the
1313 * page currently being scanned; and if no identical page is found in the
1314 * tree, we insert rmap_item as a new object into the unstable tree.
1316 * This function returns pointer to rmap_item found to be identical
1317 * to the currently scanned page, NULL otherwise.
1319 * This function does both searching and inserting, because they share
1320 * the same walking algorithm in an rbtree.
1323 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1325 struct page
**tree_pagep
)
1327 struct rb_node
**new;
1328 struct rb_root
*root
;
1329 struct rb_node
*parent
= NULL
;
1332 nid
= get_kpfn_nid(page_to_pfn(page
));
1333 root
= root_unstable_tree
+ nid
;
1334 new = &root
->rb_node
;
1337 struct rmap_item
*tree_rmap_item
;
1338 struct page
*tree_page
;
1342 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1343 tree_page
= get_mergeable_page(tree_rmap_item
);
1344 if (IS_ERR_OR_NULL(tree_page
))
1348 * Don't substitute a ksm page for a forked page.
1350 if (page
== tree_page
) {
1351 put_page(tree_page
);
1355 ret
= memcmp_pages(page
, tree_page
);
1359 put_page(tree_page
);
1360 new = &parent
->rb_left
;
1361 } else if (ret
> 0) {
1362 put_page(tree_page
);
1363 new = &parent
->rb_right
;
1364 } else if (!ksm_merge_across_nodes
&&
1365 page_to_nid(tree_page
) != nid
) {
1367 * If tree_page has been migrated to another NUMA node,
1368 * it will be flushed out and put in the right unstable
1369 * tree next time: only merge with it when across_nodes.
1371 put_page(tree_page
);
1374 *tree_pagep
= tree_page
;
1375 return tree_rmap_item
;
1379 rmap_item
->address
|= UNSTABLE_FLAG
;
1380 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1381 DO_NUMA(rmap_item
->nid
= nid
);
1382 rb_link_node(&rmap_item
->node
, parent
, new);
1383 rb_insert_color(&rmap_item
->node
, root
);
1385 ksm_pages_unshared
++;
1390 * stable_tree_append - add another rmap_item to the linked list of
1391 * rmap_items hanging off a given node of the stable tree, all sharing
1392 * the same ksm page.
1394 static void stable_tree_append(struct rmap_item
*rmap_item
,
1395 struct stable_node
*stable_node
)
1397 rmap_item
->head
= stable_node
;
1398 rmap_item
->address
|= STABLE_FLAG
;
1399 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
1401 if (rmap_item
->hlist
.next
)
1402 ksm_pages_sharing
++;
1408 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1409 * if not, compare checksum to previous and if it's the same, see if page can
1410 * be inserted into the unstable tree, or merged with a page already there and
1411 * both transferred to the stable tree.
1413 * @page: the page that we are searching identical page to.
1414 * @rmap_item: the reverse mapping into the virtual address of this page
1416 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
1418 struct rmap_item
*tree_rmap_item
;
1419 struct page
*tree_page
= NULL
;
1420 struct stable_node
*stable_node
;
1422 unsigned int checksum
;
1425 stable_node
= page_stable_node(page
);
1427 if (stable_node
->head
!= &migrate_nodes
&&
1428 get_kpfn_nid(stable_node
->kpfn
) != NUMA(stable_node
->nid
)) {
1429 rb_erase(&stable_node
->node
,
1430 root_stable_tree
+ NUMA(stable_node
->nid
));
1431 stable_node
->head
= &migrate_nodes
;
1432 list_add(&stable_node
->list
, stable_node
->head
);
1434 if (stable_node
->head
!= &migrate_nodes
&&
1435 rmap_item
->head
== stable_node
)
1439 /* We first start with searching the page inside the stable tree */
1440 kpage
= stable_tree_search(page
);
1441 if (kpage
== page
&& rmap_item
->head
== stable_node
) {
1446 remove_rmap_item_from_tree(rmap_item
);
1449 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
1452 * The page was successfully merged:
1453 * add its rmap_item to the stable tree.
1456 stable_tree_append(rmap_item
, page_stable_node(kpage
));
1464 * If the hash value of the page has changed from the last time
1465 * we calculated it, this page is changing frequently: therefore we
1466 * don't want to insert it in the unstable tree, and we don't want
1467 * to waste our time searching for something identical to it there.
1469 checksum
= calc_checksum(page
);
1470 if (rmap_item
->oldchecksum
!= checksum
) {
1471 rmap_item
->oldchecksum
= checksum
;
1476 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
1477 if (tree_rmap_item
) {
1478 kpage
= try_to_merge_two_pages(rmap_item
, page
,
1479 tree_rmap_item
, tree_page
);
1480 put_page(tree_page
);
1483 * The pages were successfully merged: insert new
1484 * node in the stable tree and add both rmap_items.
1487 stable_node
= stable_tree_insert(kpage
);
1489 stable_tree_append(tree_rmap_item
, stable_node
);
1490 stable_tree_append(rmap_item
, stable_node
);
1495 * If we fail to insert the page into the stable tree,
1496 * we will have 2 virtual addresses that are pointing
1497 * to a ksm page left outside the stable tree,
1498 * in which case we need to break_cow on both.
1501 break_cow(tree_rmap_item
);
1502 break_cow(rmap_item
);
1508 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
1509 struct rmap_item
**rmap_list
,
1512 struct rmap_item
*rmap_item
;
1514 while (*rmap_list
) {
1515 rmap_item
= *rmap_list
;
1516 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
1518 if (rmap_item
->address
> addr
)
1520 *rmap_list
= rmap_item
->rmap_list
;
1521 remove_rmap_item_from_tree(rmap_item
);
1522 free_rmap_item(rmap_item
);
1525 rmap_item
= alloc_rmap_item();
1527 /* It has already been zeroed */
1528 rmap_item
->mm
= mm_slot
->mm
;
1529 rmap_item
->address
= addr
;
1530 rmap_item
->rmap_list
= *rmap_list
;
1531 *rmap_list
= rmap_item
;
1536 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
1538 struct mm_struct
*mm
;
1539 struct mm_slot
*slot
;
1540 struct vm_area_struct
*vma
;
1541 struct rmap_item
*rmap_item
;
1544 if (list_empty(&ksm_mm_head
.mm_list
))
1547 slot
= ksm_scan
.mm_slot
;
1548 if (slot
== &ksm_mm_head
) {
1550 * A number of pages can hang around indefinitely on per-cpu
1551 * pagevecs, raised page count preventing write_protect_page
1552 * from merging them. Though it doesn't really matter much,
1553 * it is puzzling to see some stuck in pages_volatile until
1554 * other activity jostles them out, and they also prevented
1555 * LTP's KSM test from succeeding deterministically; so drain
1556 * them here (here rather than on entry to ksm_do_scan(),
1557 * so we don't IPI too often when pages_to_scan is set low).
1559 lru_add_drain_all();
1562 * Whereas stale stable_nodes on the stable_tree itself
1563 * get pruned in the regular course of stable_tree_search(),
1564 * those moved out to the migrate_nodes list can accumulate:
1565 * so prune them once before each full scan.
1567 if (!ksm_merge_across_nodes
) {
1568 struct stable_node
*stable_node
;
1569 struct list_head
*this, *next
;
1572 list_for_each_safe(this, next
, &migrate_nodes
) {
1573 stable_node
= list_entry(this,
1574 struct stable_node
, list
);
1575 page
= get_ksm_page(stable_node
, false);
1582 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++)
1583 root_unstable_tree
[nid
] = RB_ROOT
;
1585 spin_lock(&ksm_mmlist_lock
);
1586 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
1587 ksm_scan
.mm_slot
= slot
;
1588 spin_unlock(&ksm_mmlist_lock
);
1590 * Although we tested list_empty() above, a racing __ksm_exit
1591 * of the last mm on the list may have removed it since then.
1593 if (slot
== &ksm_mm_head
)
1596 ksm_scan
.address
= 0;
1597 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1601 down_read(&mm
->mmap_sem
);
1602 if (ksm_test_exit(mm
))
1605 vma
= find_vma(mm
, ksm_scan
.address
);
1607 for (; vma
; vma
= vma
->vm_next
) {
1608 if (!(vma
->vm_flags
& VM_MERGEABLE
))
1610 if (ksm_scan
.address
< vma
->vm_start
)
1611 ksm_scan
.address
= vma
->vm_start
;
1613 ksm_scan
.address
= vma
->vm_end
;
1615 while (ksm_scan
.address
< vma
->vm_end
) {
1616 if (ksm_test_exit(mm
))
1618 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
1619 if (IS_ERR_OR_NULL(*page
)) {
1620 ksm_scan
.address
+= PAGE_SIZE
;
1624 if (PageAnon(*page
) ||
1625 page_trans_compound_anon(*page
)) {
1626 flush_anon_page(vma
, *page
, ksm_scan
.address
);
1627 flush_dcache_page(*page
);
1628 rmap_item
= get_next_rmap_item(slot
,
1629 ksm_scan
.rmap_list
, ksm_scan
.address
);
1631 ksm_scan
.rmap_list
=
1632 &rmap_item
->rmap_list
;
1633 ksm_scan
.address
+= PAGE_SIZE
;
1636 up_read(&mm
->mmap_sem
);
1640 ksm_scan
.address
+= PAGE_SIZE
;
1645 if (ksm_test_exit(mm
)) {
1646 ksm_scan
.address
= 0;
1647 ksm_scan
.rmap_list
= &slot
->rmap_list
;
1650 * Nuke all the rmap_items that are above this current rmap:
1651 * because there were no VM_MERGEABLE vmas with such addresses.
1653 remove_trailing_rmap_items(slot
, ksm_scan
.rmap_list
);
1655 spin_lock(&ksm_mmlist_lock
);
1656 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
1657 struct mm_slot
, mm_list
);
1658 if (ksm_scan
.address
== 0) {
1660 * We've completed a full scan of all vmas, holding mmap_sem
1661 * throughout, and found no VM_MERGEABLE: so do the same as
1662 * __ksm_exit does to remove this mm from all our lists now.
1663 * This applies either when cleaning up after __ksm_exit
1664 * (but beware: we can reach here even before __ksm_exit),
1665 * or when all VM_MERGEABLE areas have been unmapped (and
1666 * mmap_sem then protects against race with MADV_MERGEABLE).
1668 hash_del(&slot
->link
);
1669 list_del(&slot
->mm_list
);
1670 spin_unlock(&ksm_mmlist_lock
);
1673 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1674 up_read(&mm
->mmap_sem
);
1677 spin_unlock(&ksm_mmlist_lock
);
1678 up_read(&mm
->mmap_sem
);
1681 /* Repeat until we've completed scanning the whole list */
1682 slot
= ksm_scan
.mm_slot
;
1683 if (slot
!= &ksm_mm_head
)
1691 * ksm_do_scan - the ksm scanner main worker function.
1692 * @scan_npages - number of pages we want to scan before we return.
1694 static void ksm_do_scan(unsigned int scan_npages
)
1696 struct rmap_item
*rmap_item
;
1697 struct page
*uninitialized_var(page
);
1699 while (scan_npages
-- && likely(!freezing(current
))) {
1701 rmap_item
= scan_get_next_rmap_item(&page
);
1704 cmp_and_merge_page(page
, rmap_item
);
1709 static int ksmd_should_run(void)
1711 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
1714 static int ksm_scan_thread(void *nothing
)
1717 set_user_nice(current
, 5);
1719 while (!kthread_should_stop()) {
1720 mutex_lock(&ksm_thread_mutex
);
1721 wait_while_offlining();
1722 if (ksmd_should_run())
1723 ksm_do_scan(ksm_thread_pages_to_scan
);
1724 mutex_unlock(&ksm_thread_mutex
);
1728 if (ksmd_should_run()) {
1729 schedule_timeout_interruptible(
1730 msecs_to_jiffies(ksm_thread_sleep_millisecs
));
1732 wait_event_freezable(ksm_thread_wait
,
1733 ksmd_should_run() || kthread_should_stop());
1739 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
1740 unsigned long end
, int advice
, unsigned long *vm_flags
)
1742 struct mm_struct
*mm
= vma
->vm_mm
;
1746 case MADV_MERGEABLE
:
1748 * Be somewhat over-protective for now!
1750 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
1751 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
1752 VM_HUGETLB
| VM_NONLINEAR
| VM_MIXEDMAP
))
1753 return 0; /* just ignore the advice */
1756 if (*vm_flags
& VM_SAO
)
1760 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
1761 err
= __ksm_enter(mm
);
1766 *vm_flags
|= VM_MERGEABLE
;
1769 case MADV_UNMERGEABLE
:
1770 if (!(*vm_flags
& VM_MERGEABLE
))
1771 return 0; /* just ignore the advice */
1773 if (vma
->anon_vma
) {
1774 err
= unmerge_ksm_pages(vma
, start
, end
);
1779 *vm_flags
&= ~VM_MERGEABLE
;
1786 int __ksm_enter(struct mm_struct
*mm
)
1788 struct mm_slot
*mm_slot
;
1791 mm_slot
= alloc_mm_slot();
1795 /* Check ksm_run too? Would need tighter locking */
1796 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
1798 spin_lock(&ksm_mmlist_lock
);
1799 insert_to_mm_slots_hash(mm
, mm_slot
);
1801 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1802 * insert just behind the scanning cursor, to let the area settle
1803 * down a little; when fork is followed by immediate exec, we don't
1804 * want ksmd to waste time setting up and tearing down an rmap_list.
1806 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1807 * scanning cursor, otherwise KSM pages in newly forked mms will be
1808 * missed: then we might as well insert at the end of the list.
1810 if (ksm_run
& KSM_RUN_UNMERGE
)
1811 list_add_tail(&mm_slot
->mm_list
, &ksm_mm_head
.mm_list
);
1813 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
1814 spin_unlock(&ksm_mmlist_lock
);
1816 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1817 atomic_inc(&mm
->mm_count
);
1820 wake_up_interruptible(&ksm_thread_wait
);
1825 void __ksm_exit(struct mm_struct
*mm
)
1827 struct mm_slot
*mm_slot
;
1828 int easy_to_free
= 0;
1831 * This process is exiting: if it's straightforward (as is the
1832 * case when ksmd was never running), free mm_slot immediately.
1833 * But if it's at the cursor or has rmap_items linked to it, use
1834 * mmap_sem to synchronize with any break_cows before pagetables
1835 * are freed, and leave the mm_slot on the list for ksmd to free.
1836 * Beware: ksm may already have noticed it exiting and freed the slot.
1839 spin_lock(&ksm_mmlist_lock
);
1840 mm_slot
= get_mm_slot(mm
);
1841 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
1842 if (!mm_slot
->rmap_list
) {
1843 hash_del(&mm_slot
->link
);
1844 list_del(&mm_slot
->mm_list
);
1847 list_move(&mm_slot
->mm_list
,
1848 &ksm_scan
.mm_slot
->mm_list
);
1851 spin_unlock(&ksm_mmlist_lock
);
1854 free_mm_slot(mm_slot
);
1855 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1857 } else if (mm_slot
) {
1858 down_write(&mm
->mmap_sem
);
1859 up_write(&mm
->mmap_sem
);
1863 struct page
*ksm_might_need_to_copy(struct page
*page
,
1864 struct vm_area_struct
*vma
, unsigned long address
)
1866 struct anon_vma
*anon_vma
= page_anon_vma(page
);
1867 struct page
*new_page
;
1869 if (PageKsm(page
)) {
1870 if (page_stable_node(page
) &&
1871 !(ksm_run
& KSM_RUN_UNMERGE
))
1872 return page
; /* no need to copy it */
1873 } else if (!anon_vma
) {
1874 return page
; /* no need to copy it */
1875 } else if (anon_vma
->root
== vma
->anon_vma
->root
&&
1876 page
->index
== linear_page_index(vma
, address
)) {
1877 return page
; /* still no need to copy it */
1879 if (!PageUptodate(page
))
1880 return page
; /* let do_swap_page report the error */
1882 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
1884 copy_user_highpage(new_page
, page
, address
, vma
);
1886 SetPageDirty(new_page
);
1887 __SetPageUptodate(new_page
);
1888 __set_page_locked(new_page
);
1894 int page_referenced_ksm(struct page
*page
, struct mem_cgroup
*memcg
,
1895 unsigned long *vm_flags
)
1897 struct stable_node
*stable_node
;
1898 struct rmap_item
*rmap_item
;
1899 unsigned int mapcount
= page_mapcount(page
);
1901 int search_new_forks
= 0;
1903 VM_BUG_ON(!PageKsm(page
));
1904 VM_BUG_ON(!PageLocked(page
));
1906 stable_node
= page_stable_node(page
);
1910 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
1911 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1912 struct anon_vma_chain
*vmac
;
1913 struct vm_area_struct
*vma
;
1915 anon_vma_lock_read(anon_vma
);
1916 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1919 if (rmap_item
->address
< vma
->vm_start
||
1920 rmap_item
->address
>= vma
->vm_end
)
1923 * Initially we examine only the vma which covers this
1924 * rmap_item; but later, if there is still work to do,
1925 * we examine covering vmas in other mms: in case they
1926 * were forked from the original since ksmd passed.
1928 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1931 if (memcg
&& !mm_match_cgroup(vma
->vm_mm
, memcg
))
1934 referenced
+= page_referenced_one(page
, vma
,
1935 rmap_item
->address
, &mapcount
, vm_flags
);
1936 if (!search_new_forks
|| !mapcount
)
1939 anon_vma_unlock_read(anon_vma
);
1943 if (!search_new_forks
++)
1949 int try_to_unmap_ksm(struct page
*page
, enum ttu_flags flags
)
1951 struct stable_node
*stable_node
;
1952 struct rmap_item
*rmap_item
;
1953 int ret
= SWAP_AGAIN
;
1954 int search_new_forks
= 0;
1956 VM_BUG_ON(!PageKsm(page
));
1957 VM_BUG_ON(!PageLocked(page
));
1959 stable_node
= page_stable_node(page
);
1963 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
1964 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
1965 struct anon_vma_chain
*vmac
;
1966 struct vm_area_struct
*vma
;
1968 anon_vma_lock_read(anon_vma
);
1969 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
1972 if (rmap_item
->address
< vma
->vm_start
||
1973 rmap_item
->address
>= vma
->vm_end
)
1976 * Initially we examine only the vma which covers this
1977 * rmap_item; but later, if there is still work to do,
1978 * we examine covering vmas in other mms: in case they
1979 * were forked from the original since ksmd passed.
1981 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
1984 ret
= try_to_unmap_one(page
, vma
,
1985 rmap_item
->address
, flags
);
1986 if (ret
!= SWAP_AGAIN
|| !page_mapped(page
)) {
1987 anon_vma_unlock_read(anon_vma
);
1991 anon_vma_unlock_read(anon_vma
);
1993 if (!search_new_forks
++)
1999 #ifdef CONFIG_MIGRATION
2000 int rmap_walk_ksm(struct page
*page
, int (*rmap_one
)(struct page
*,
2001 struct vm_area_struct
*, unsigned long, void *), void *arg
)
2003 struct stable_node
*stable_node
;
2004 struct rmap_item
*rmap_item
;
2005 int ret
= SWAP_AGAIN
;
2006 int search_new_forks
= 0;
2008 VM_BUG_ON(!PageKsm(page
));
2009 VM_BUG_ON(!PageLocked(page
));
2011 stable_node
= page_stable_node(page
);
2015 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
2016 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
2017 struct anon_vma_chain
*vmac
;
2018 struct vm_area_struct
*vma
;
2020 anon_vma_lock_read(anon_vma
);
2021 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
2024 if (rmap_item
->address
< vma
->vm_start
||
2025 rmap_item
->address
>= vma
->vm_end
)
2028 * Initially we examine only the vma which covers this
2029 * rmap_item; but later, if there is still work to do,
2030 * we examine covering vmas in other mms: in case they
2031 * were forked from the original since ksmd passed.
2033 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
2036 ret
= rmap_one(page
, vma
, rmap_item
->address
, arg
);
2037 if (ret
!= SWAP_AGAIN
) {
2038 anon_vma_unlock_read(anon_vma
);
2042 anon_vma_unlock_read(anon_vma
);
2044 if (!search_new_forks
++)
2050 void ksm_migrate_page(struct page
*newpage
, struct page
*oldpage
)
2052 struct stable_node
*stable_node
;
2054 VM_BUG_ON(!PageLocked(oldpage
));
2055 VM_BUG_ON(!PageLocked(newpage
));
2056 VM_BUG_ON(newpage
->mapping
!= oldpage
->mapping
);
2058 stable_node
= page_stable_node(newpage
);
2060 VM_BUG_ON(stable_node
->kpfn
!= page_to_pfn(oldpage
));
2061 stable_node
->kpfn
= page_to_pfn(newpage
);
2063 * newpage->mapping was set in advance; now we need smp_wmb()
2064 * to make sure that the new stable_node->kpfn is visible
2065 * to get_ksm_page() before it can see that oldpage->mapping
2066 * has gone stale (or that PageSwapCache has been cleared).
2069 set_page_stable_node(oldpage
, NULL
);
2072 #endif /* CONFIG_MIGRATION */
2074 #ifdef CONFIG_MEMORY_HOTREMOVE
2075 static int just_wait(void *word
)
2081 static void wait_while_offlining(void)
2083 while (ksm_run
& KSM_RUN_OFFLINE
) {
2084 mutex_unlock(&ksm_thread_mutex
);
2085 wait_on_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
),
2086 just_wait
, TASK_UNINTERRUPTIBLE
);
2087 mutex_lock(&ksm_thread_mutex
);
2091 static void ksm_check_stable_tree(unsigned long start_pfn
,
2092 unsigned long end_pfn
)
2094 struct stable_node
*stable_node
;
2095 struct list_head
*this, *next
;
2096 struct rb_node
*node
;
2099 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
2100 node
= rb_first(root_stable_tree
+ nid
);
2102 stable_node
= rb_entry(node
, struct stable_node
, node
);
2103 if (stable_node
->kpfn
>= start_pfn
&&
2104 stable_node
->kpfn
< end_pfn
) {
2106 * Don't get_ksm_page, page has already gone:
2107 * which is why we keep kpfn instead of page*
2109 remove_node_from_stable_tree(stable_node
);
2110 node
= rb_first(root_stable_tree
+ nid
);
2112 node
= rb_next(node
);
2116 list_for_each_safe(this, next
, &migrate_nodes
) {
2117 stable_node
= list_entry(this, struct stable_node
, list
);
2118 if (stable_node
->kpfn
>= start_pfn
&&
2119 stable_node
->kpfn
< end_pfn
)
2120 remove_node_from_stable_tree(stable_node
);
2125 static int ksm_memory_callback(struct notifier_block
*self
,
2126 unsigned long action
, void *arg
)
2128 struct memory_notify
*mn
= arg
;
2131 case MEM_GOING_OFFLINE
:
2133 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2134 * and remove_all_stable_nodes() while memory is going offline:
2135 * it is unsafe for them to touch the stable tree at this time.
2136 * But unmerge_ksm_pages(), rmap lookups and other entry points
2137 * which do not need the ksm_thread_mutex are all safe.
2139 mutex_lock(&ksm_thread_mutex
);
2140 ksm_run
|= KSM_RUN_OFFLINE
;
2141 mutex_unlock(&ksm_thread_mutex
);
2146 * Most of the work is done by page migration; but there might
2147 * be a few stable_nodes left over, still pointing to struct
2148 * pages which have been offlined: prune those from the tree,
2149 * otherwise get_ksm_page() might later try to access a
2150 * non-existent struct page.
2152 ksm_check_stable_tree(mn
->start_pfn
,
2153 mn
->start_pfn
+ mn
->nr_pages
);
2156 case MEM_CANCEL_OFFLINE
:
2157 mutex_lock(&ksm_thread_mutex
);
2158 ksm_run
&= ~KSM_RUN_OFFLINE
;
2159 mutex_unlock(&ksm_thread_mutex
);
2161 smp_mb(); /* wake_up_bit advises this */
2162 wake_up_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
));
2168 static void wait_while_offlining(void)
2171 #endif /* CONFIG_MEMORY_HOTREMOVE */
2175 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2178 #define KSM_ATTR_RO(_name) \
2179 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2180 #define KSM_ATTR(_name) \
2181 static struct kobj_attribute _name##_attr = \
2182 __ATTR(_name, 0644, _name##_show, _name##_store)
2184 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
2185 struct kobj_attribute
*attr
, char *buf
)
2187 return sprintf(buf
, "%u\n", ksm_thread_sleep_millisecs
);
2190 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
2191 struct kobj_attribute
*attr
,
2192 const char *buf
, size_t count
)
2194 unsigned long msecs
;
2197 err
= strict_strtoul(buf
, 10, &msecs
);
2198 if (err
|| msecs
> UINT_MAX
)
2201 ksm_thread_sleep_millisecs
= msecs
;
2205 KSM_ATTR(sleep_millisecs
);
2207 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
2208 struct kobj_attribute
*attr
, char *buf
)
2210 return sprintf(buf
, "%u\n", ksm_thread_pages_to_scan
);
2213 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
2214 struct kobj_attribute
*attr
,
2215 const char *buf
, size_t count
)
2218 unsigned long nr_pages
;
2220 err
= strict_strtoul(buf
, 10, &nr_pages
);
2221 if (err
|| nr_pages
> UINT_MAX
)
2224 ksm_thread_pages_to_scan
= nr_pages
;
2228 KSM_ATTR(pages_to_scan
);
2230 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2233 return sprintf(buf
, "%lu\n", ksm_run
);
2236 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2237 const char *buf
, size_t count
)
2240 unsigned long flags
;
2242 err
= strict_strtoul(buf
, 10, &flags
);
2243 if (err
|| flags
> UINT_MAX
)
2245 if (flags
> KSM_RUN_UNMERGE
)
2249 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2250 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2251 * breaking COW to free the pages_shared (but leaves mm_slots
2252 * on the list for when ksmd may be set running again).
2255 mutex_lock(&ksm_thread_mutex
);
2256 wait_while_offlining();
2257 if (ksm_run
!= flags
) {
2259 if (flags
& KSM_RUN_UNMERGE
) {
2260 set_current_oom_origin();
2261 err
= unmerge_and_remove_all_rmap_items();
2262 clear_current_oom_origin();
2264 ksm_run
= KSM_RUN_STOP
;
2269 mutex_unlock(&ksm_thread_mutex
);
2271 if (flags
& KSM_RUN_MERGE
)
2272 wake_up_interruptible(&ksm_thread_wait
);
2279 static ssize_t
merge_across_nodes_show(struct kobject
*kobj
,
2280 struct kobj_attribute
*attr
, char *buf
)
2282 return sprintf(buf
, "%u\n", ksm_merge_across_nodes
);
2285 static ssize_t
merge_across_nodes_store(struct kobject
*kobj
,
2286 struct kobj_attribute
*attr
,
2287 const char *buf
, size_t count
)
2292 err
= kstrtoul(buf
, 10, &knob
);
2298 mutex_lock(&ksm_thread_mutex
);
2299 wait_while_offlining();
2300 if (ksm_merge_across_nodes
!= knob
) {
2301 if (ksm_pages_shared
|| remove_all_stable_nodes())
2303 else if (root_stable_tree
== one_stable_tree
) {
2304 struct rb_root
*buf
;
2306 * This is the first time that we switch away from the
2307 * default of merging across nodes: must now allocate
2308 * a buffer to hold as many roots as may be needed.
2309 * Allocate stable and unstable together:
2310 * MAXSMP NODES_SHIFT 10 will use 16kB.
2312 buf
= kcalloc(nr_node_ids
+ nr_node_ids
,
2313 sizeof(*buf
), GFP_KERNEL
| __GFP_ZERO
);
2314 /* Let us assume that RB_ROOT is NULL is zero */
2318 root_stable_tree
= buf
;
2319 root_unstable_tree
= buf
+ nr_node_ids
;
2320 /* Stable tree is empty but not the unstable */
2321 root_unstable_tree
[0] = one_unstable_tree
[0];
2325 ksm_merge_across_nodes
= knob
;
2326 ksm_nr_node_ids
= knob
? 1 : nr_node_ids
;
2329 mutex_unlock(&ksm_thread_mutex
);
2331 return err
? err
: count
;
2333 KSM_ATTR(merge_across_nodes
);
2336 static ssize_t
pages_shared_show(struct kobject
*kobj
,
2337 struct kobj_attribute
*attr
, char *buf
)
2339 return sprintf(buf
, "%lu\n", ksm_pages_shared
);
2341 KSM_ATTR_RO(pages_shared
);
2343 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
2344 struct kobj_attribute
*attr
, char *buf
)
2346 return sprintf(buf
, "%lu\n", ksm_pages_sharing
);
2348 KSM_ATTR_RO(pages_sharing
);
2350 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
2351 struct kobj_attribute
*attr
, char *buf
)
2353 return sprintf(buf
, "%lu\n", ksm_pages_unshared
);
2355 KSM_ATTR_RO(pages_unshared
);
2357 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
2358 struct kobj_attribute
*attr
, char *buf
)
2360 long ksm_pages_volatile
;
2362 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
2363 - ksm_pages_sharing
- ksm_pages_unshared
;
2365 * It was not worth any locking to calculate that statistic,
2366 * but it might therefore sometimes be negative: conceal that.
2368 if (ksm_pages_volatile
< 0)
2369 ksm_pages_volatile
= 0;
2370 return sprintf(buf
, "%ld\n", ksm_pages_volatile
);
2372 KSM_ATTR_RO(pages_volatile
);
2374 static ssize_t
full_scans_show(struct kobject
*kobj
,
2375 struct kobj_attribute
*attr
, char *buf
)
2377 return sprintf(buf
, "%lu\n", ksm_scan
.seqnr
);
2379 KSM_ATTR_RO(full_scans
);
2381 static struct attribute
*ksm_attrs
[] = {
2382 &sleep_millisecs_attr
.attr
,
2383 &pages_to_scan_attr
.attr
,
2385 &pages_shared_attr
.attr
,
2386 &pages_sharing_attr
.attr
,
2387 &pages_unshared_attr
.attr
,
2388 &pages_volatile_attr
.attr
,
2389 &full_scans_attr
.attr
,
2391 &merge_across_nodes_attr
.attr
,
2396 static struct attribute_group ksm_attr_group
= {
2400 #endif /* CONFIG_SYSFS */
2402 static int __init
ksm_init(void)
2404 struct task_struct
*ksm_thread
;
2407 err
= ksm_slab_init();
2411 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
2412 if (IS_ERR(ksm_thread
)) {
2413 printk(KERN_ERR
"ksm: creating kthread failed\n");
2414 err
= PTR_ERR(ksm_thread
);
2419 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
2421 printk(KERN_ERR
"ksm: register sysfs failed\n");
2422 kthread_stop(ksm_thread
);
2426 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
2428 #endif /* CONFIG_SYSFS */
2430 #ifdef CONFIG_MEMORY_HOTREMOVE
2431 /* There is no significance to this priority 100 */
2432 hotplug_memory_notifier(ksm_memory_callback
, 100);
2441 module_init(ksm_init
)