1 // SPDX-License-Identifier: GPL-2.0-only
3 * Memory merging support.
5 * This code enables dynamic sharing of identical pages found in different
6 * memory areas, even if they are not shared by fork()
8 * Copyright (C) 2008-2009 Red Hat, Inc.
16 #include <linux/errno.h>
18 #include <linux/mm_inline.h>
20 #include <linux/mman.h>
21 #include <linux/sched.h>
22 #include <linux/sched/mm.h>
23 #include <linux/sched/coredump.h>
24 #include <linux/rwsem.h>
25 #include <linux/pagemap.h>
26 #include <linux/rmap.h>
27 #include <linux/spinlock.h>
28 #include <linux/xxhash.h>
29 #include <linux/delay.h>
30 #include <linux/kthread.h>
31 #include <linux/wait.h>
32 #include <linux/slab.h>
33 #include <linux/rbtree.h>
34 #include <linux/memory.h>
35 #include <linux/mmu_notifier.h>
36 #include <linux/swap.h>
37 #include <linux/ksm.h>
38 #include <linux/hashtable.h>
39 #include <linux/freezer.h>
40 #include <linux/oom.h>
41 #include <linux/numa.h>
43 #include <asm/tlbflush.h>
48 #define DO_NUMA(x) do { (x); } while (0)
51 #define DO_NUMA(x) do { } while (0)
57 * A few notes about the KSM scanning process,
58 * to make it easier to understand the data structures below:
60 * In order to reduce excessive scanning, KSM sorts the memory pages by their
61 * contents into a data structure that holds pointers to the pages' locations.
63 * Since the contents of the pages may change at any moment, KSM cannot just
64 * insert the pages into a normal sorted tree and expect it to find anything.
65 * Therefore KSM uses two data structures - the stable and the unstable tree.
67 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
68 * by their contents. Because each such page is write-protected, searching on
69 * this tree is fully assured to be working (except when pages are unmapped),
70 * and therefore this tree is called the stable tree.
72 * The stable tree node includes information required for reverse
73 * mapping from a KSM page to virtual addresses that map this page.
75 * In order to avoid large latencies of the rmap walks on KSM pages,
76 * KSM maintains two types of nodes in the stable tree:
78 * * the regular nodes that keep the reverse mapping structures in a
80 * * the "chains" that link nodes ("dups") that represent the same
81 * write protected memory content, but each "dup" corresponds to a
82 * different KSM page copy of that content
84 * Internally, the regular nodes, "dups" and "chains" are represented
85 * using the same struct stable_node structure.
87 * In addition to the stable tree, KSM uses a second data structure called the
88 * unstable tree: this tree holds pointers to pages which have been found to
89 * be "unchanged for a period of time". The unstable tree sorts these pages
90 * by their contents, but since they are not write-protected, KSM cannot rely
91 * upon the unstable tree to work correctly - the unstable tree is liable to
92 * be corrupted as its contents are modified, and so it is called unstable.
94 * KSM solves this problem by several techniques:
96 * 1) The unstable tree is flushed every time KSM completes scanning all
97 * memory areas, and then the tree is rebuilt again from the beginning.
98 * 2) KSM will only insert into the unstable tree, pages whose hash value
99 * has not changed since the previous scan of all memory areas.
100 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
101 * colors of the nodes and not on their contents, assuring that even when
102 * the tree gets "corrupted" it won't get out of balance, so scanning time
103 * remains the same (also, searching and inserting nodes in an rbtree uses
104 * the same algorithm, so we have no overhead when we flush and rebuild).
105 * 4) KSM never flushes the stable tree, which means that even if it were to
106 * take 10 attempts to find a page in the unstable tree, once it is found,
107 * it is secured in the stable tree. (When we scan a new page, we first
108 * compare it against the stable tree, and then against the unstable tree.)
110 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
111 * stable trees and multiple unstable trees: one of each for each NUMA node.
115 * struct mm_slot - ksm information per mm that is being scanned
116 * @link: link to the mm_slots hash list
117 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
118 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
119 * @mm: the mm that this information is valid for
122 struct hlist_node link
;
123 struct list_head mm_list
;
124 struct rmap_item
*rmap_list
;
125 struct mm_struct
*mm
;
129 * struct ksm_scan - cursor for scanning
130 * @mm_slot: the current mm_slot we are scanning
131 * @address: the next address inside that to be scanned
132 * @rmap_list: link to the next rmap to be scanned in the rmap_list
133 * @seqnr: count of completed full scans (needed when removing unstable node)
135 * There is only the one ksm_scan instance of this cursor structure.
138 struct mm_slot
*mm_slot
;
139 unsigned long address
;
140 struct rmap_item
**rmap_list
;
145 * struct stable_node - node of the stable rbtree
146 * @node: rb node of this ksm page in the stable tree
147 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
148 * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
149 * @list: linked into migrate_nodes, pending placement in the proper node tree
150 * @hlist: hlist head of rmap_items using this ksm page
151 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
152 * @chain_prune_time: time of the last full garbage collection
153 * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
154 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
158 struct rb_node node
; /* when node of stable tree */
159 struct { /* when listed for migration */
160 struct list_head
*head
;
162 struct hlist_node hlist_dup
;
163 struct list_head list
;
167 struct hlist_head hlist
;
170 unsigned long chain_prune_time
;
173 * STABLE_NODE_CHAIN can be any negative number in
174 * rmap_hlist_len negative range, but better not -1 to be able
175 * to reliably detect underflows.
177 #define STABLE_NODE_CHAIN -1024
185 * struct rmap_item - reverse mapping item for virtual addresses
186 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
187 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
188 * @nid: NUMA node id of unstable tree in which linked (may not match page)
189 * @mm: the memory structure this rmap_item is pointing into
190 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
191 * @oldchecksum: previous checksum of the page at that virtual address
192 * @node: rb node of this rmap_item in the unstable tree
193 * @head: pointer to stable_node heading this list in the stable tree
194 * @hlist: link into hlist of rmap_items hanging off that stable_node
197 struct rmap_item
*rmap_list
;
199 struct anon_vma
*anon_vma
; /* when stable */
201 int nid
; /* when node of unstable tree */
204 struct mm_struct
*mm
;
205 unsigned long address
; /* + low bits used for flags below */
206 unsigned int oldchecksum
; /* when unstable */
208 struct rb_node node
; /* when node of unstable tree */
209 struct { /* when listed from stable tree */
210 struct stable_node
*head
;
211 struct hlist_node hlist
;
216 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
217 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
218 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
220 /* The stable and unstable tree heads */
221 static struct rb_root one_stable_tree
[1] = { RB_ROOT
};
222 static struct rb_root one_unstable_tree
[1] = { RB_ROOT
};
223 static struct rb_root
*root_stable_tree
= one_stable_tree
;
224 static struct rb_root
*root_unstable_tree
= one_unstable_tree
;
226 /* Recently migrated nodes of stable tree, pending proper placement */
227 static LIST_HEAD(migrate_nodes
);
228 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
230 #define MM_SLOTS_HASH_BITS 10
231 static DEFINE_HASHTABLE(mm_slots_hash
, MM_SLOTS_HASH_BITS
);
233 static struct mm_slot ksm_mm_head
= {
234 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
236 static struct ksm_scan ksm_scan
= {
237 .mm_slot
= &ksm_mm_head
,
240 static struct kmem_cache
*rmap_item_cache
;
241 static struct kmem_cache
*stable_node_cache
;
242 static struct kmem_cache
*mm_slot_cache
;
244 /* The number of nodes in the stable tree */
245 static unsigned long ksm_pages_shared
;
247 /* The number of page slots additionally sharing those nodes */
248 static unsigned long ksm_pages_sharing
;
250 /* The number of nodes in the unstable tree */
251 static unsigned long ksm_pages_unshared
;
253 /* The number of rmap_items in use: to calculate pages_volatile */
254 static unsigned long ksm_rmap_items
;
256 /* The number of stable_node chains */
257 static unsigned long ksm_stable_node_chains
;
259 /* The number of stable_node dups linked to the stable_node chains */
260 static unsigned long ksm_stable_node_dups
;
262 /* Delay in pruning stale stable_node_dups in the stable_node_chains */
263 static unsigned int ksm_stable_node_chains_prune_millisecs
= 2000;
265 /* Maximum number of page slots sharing a stable node */
266 static int ksm_max_page_sharing
= 256;
268 /* Number of pages ksmd should scan in one batch */
269 static unsigned int ksm_thread_pages_to_scan
= 100;
271 /* Milliseconds ksmd should sleep between batches */
272 static unsigned int ksm_thread_sleep_millisecs
= 20;
274 /* Checksum of an empty (zeroed) page */
275 static unsigned int zero_checksum __read_mostly
;
277 /* Whether to merge empty (zeroed) pages with actual zero pages */
278 static bool ksm_use_zero_pages __read_mostly
;
281 /* Zeroed when merging across nodes is not allowed */
282 static unsigned int ksm_merge_across_nodes
= 1;
283 static int ksm_nr_node_ids
= 1;
285 #define ksm_merge_across_nodes 1U
286 #define ksm_nr_node_ids 1
289 #define KSM_RUN_STOP 0
290 #define KSM_RUN_MERGE 1
291 #define KSM_RUN_UNMERGE 2
292 #define KSM_RUN_OFFLINE 4
293 static unsigned long ksm_run
= KSM_RUN_STOP
;
294 static void wait_while_offlining(void);
296 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
297 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait
);
298 static DEFINE_MUTEX(ksm_thread_mutex
);
299 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
301 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
302 sizeof(struct __struct), __alignof__(struct __struct),\
305 static int __init
ksm_slab_init(void)
307 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
308 if (!rmap_item_cache
)
311 stable_node_cache
= KSM_KMEM_CACHE(stable_node
, 0);
312 if (!stable_node_cache
)
315 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
322 kmem_cache_destroy(stable_node_cache
);
324 kmem_cache_destroy(rmap_item_cache
);
329 static void __init
ksm_slab_free(void)
331 kmem_cache_destroy(mm_slot_cache
);
332 kmem_cache_destroy(stable_node_cache
);
333 kmem_cache_destroy(rmap_item_cache
);
334 mm_slot_cache
= NULL
;
337 static __always_inline
bool is_stable_node_chain(struct stable_node
*chain
)
339 return chain
->rmap_hlist_len
== STABLE_NODE_CHAIN
;
342 static __always_inline
bool is_stable_node_dup(struct stable_node
*dup
)
344 return dup
->head
== STABLE_NODE_DUP_HEAD
;
347 static inline void stable_node_chain_add_dup(struct stable_node
*dup
,
348 struct stable_node
*chain
)
350 VM_BUG_ON(is_stable_node_dup(dup
));
351 dup
->head
= STABLE_NODE_DUP_HEAD
;
352 VM_BUG_ON(!is_stable_node_chain(chain
));
353 hlist_add_head(&dup
->hlist_dup
, &chain
->hlist
);
354 ksm_stable_node_dups
++;
357 static inline void __stable_node_dup_del(struct stable_node
*dup
)
359 VM_BUG_ON(!is_stable_node_dup(dup
));
360 hlist_del(&dup
->hlist_dup
);
361 ksm_stable_node_dups
--;
364 static inline void stable_node_dup_del(struct stable_node
*dup
)
366 VM_BUG_ON(is_stable_node_chain(dup
));
367 if (is_stable_node_dup(dup
))
368 __stable_node_dup_del(dup
);
370 rb_erase(&dup
->node
, root_stable_tree
+ NUMA(dup
->nid
));
371 #ifdef CONFIG_DEBUG_VM
376 static inline struct rmap_item
*alloc_rmap_item(void)
378 struct rmap_item
*rmap_item
;
380 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
|
381 __GFP_NORETRY
| __GFP_NOWARN
);
387 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
390 rmap_item
->mm
= NULL
; /* debug safety */
391 kmem_cache_free(rmap_item_cache
, rmap_item
);
394 static inline struct stable_node
*alloc_stable_node(void)
397 * The allocation can take too long with GFP_KERNEL when memory is under
398 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
399 * grants access to memory reserves, helping to avoid this problem.
401 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
| __GFP_HIGH
);
404 static inline void free_stable_node(struct stable_node
*stable_node
)
406 VM_BUG_ON(stable_node
->rmap_hlist_len
&&
407 !is_stable_node_chain(stable_node
));
408 kmem_cache_free(stable_node_cache
, stable_node
);
411 static inline struct mm_slot
*alloc_mm_slot(void)
413 if (!mm_slot_cache
) /* initialization failed */
415 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
418 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
420 kmem_cache_free(mm_slot_cache
, mm_slot
);
423 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
425 struct mm_slot
*slot
;
427 hash_for_each_possible(mm_slots_hash
, slot
, link
, (unsigned long)mm
)
434 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
435 struct mm_slot
*mm_slot
)
438 hash_add(mm_slots_hash
, &mm_slot
->link
, (unsigned long)mm
);
442 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
443 * page tables after it has passed through ksm_exit() - which, if necessary,
444 * takes mmap_lock briefly to serialize against them. ksm_exit() does not set
445 * a special flag: they can just back out as soon as mm_users goes to zero.
446 * ksm_test_exit() is used throughout to make this test for exit: in some
447 * places for correctness, in some places just to avoid unnecessary work.
449 static inline bool ksm_test_exit(struct mm_struct
*mm
)
451 return atomic_read(&mm
->mm_users
) == 0;
455 * We use break_ksm to break COW on a ksm page: it's a stripped down
457 * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
460 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
461 * in case the application has unmapped and remapped mm,addr meanwhile.
462 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
463 * mmap of /dev/mem, where we would not want to touch it.
465 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
466 * of the process that owns 'vma'. We also do not want to enforce
467 * protection keys here anyway.
469 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
476 page
= follow_page(vma
, addr
,
477 FOLL_GET
| FOLL_MIGRATION
| FOLL_REMOTE
);
478 if (IS_ERR_OR_NULL(page
) || is_zone_device_page(page
))
481 ret
= handle_mm_fault(vma
, addr
,
482 FAULT_FLAG_WRITE
| FAULT_FLAG_REMOTE
,
485 ret
= VM_FAULT_WRITE
;
487 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_SIGSEGV
| VM_FAULT_OOM
)));
489 * We must loop because handle_mm_fault() may back out if there's
490 * any difficulty e.g. if pte accessed bit gets updated concurrently.
492 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
493 * COW has been broken, even if the vma does not permit VM_WRITE;
494 * but note that a concurrent fault might break PageKsm for us.
496 * VM_FAULT_SIGBUS could occur if we race with truncation of the
497 * backing file, which also invalidates anonymous pages: that's
498 * okay, that truncation will have unmapped the PageKsm for us.
500 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
501 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
502 * current task has TIF_MEMDIE set, and will be OOM killed on return
503 * to user; and ksmd, having no mm, would never be chosen for that.
505 * But if the mm is in a limited mem_cgroup, then the fault may fail
506 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
507 * even ksmd can fail in this way - though it's usually breaking ksm
508 * just to undo a merge it made a moment before, so unlikely to oom.
510 * That's a pity: we might therefore have more kernel pages allocated
511 * than we're counting as nodes in the stable tree; but ksm_do_scan
512 * will retry to break_cow on each pass, so should recover the page
513 * in due course. The important thing is to not let VM_MERGEABLE
514 * be cleared while any such pages might remain in the area.
516 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
519 static struct vm_area_struct
*find_mergeable_vma(struct mm_struct
*mm
,
522 struct vm_area_struct
*vma
;
523 if (ksm_test_exit(mm
))
525 vma
= vma_lookup(mm
, addr
);
526 if (!vma
|| !(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
531 static void break_cow(struct rmap_item
*rmap_item
)
533 struct mm_struct
*mm
= rmap_item
->mm
;
534 unsigned long addr
= rmap_item
->address
;
535 struct vm_area_struct
*vma
;
538 * It is not an accident that whenever we want to break COW
539 * to undo, we also need to drop a reference to the anon_vma.
541 put_anon_vma(rmap_item
->anon_vma
);
544 vma
= find_mergeable_vma(mm
, addr
);
546 break_ksm(vma
, addr
);
547 mmap_read_unlock(mm
);
550 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
552 struct mm_struct
*mm
= rmap_item
->mm
;
553 unsigned long addr
= rmap_item
->address
;
554 struct vm_area_struct
*vma
;
558 vma
= find_mergeable_vma(mm
, addr
);
562 page
= follow_page(vma
, addr
, FOLL_GET
);
563 if (IS_ERR_OR_NULL(page
) || is_zone_device_page(page
))
565 if (PageAnon(page
)) {
566 flush_anon_page(vma
, page
, addr
);
567 flush_dcache_page(page
);
573 mmap_read_unlock(mm
);
578 * This helper is used for getting right index into array of tree roots.
579 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
580 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
581 * every node has its own stable and unstable tree.
583 static inline int get_kpfn_nid(unsigned long kpfn
)
585 return ksm_merge_across_nodes
? 0 : NUMA(pfn_to_nid(kpfn
));
588 static struct stable_node
*alloc_stable_node_chain(struct stable_node
*dup
,
589 struct rb_root
*root
)
591 struct stable_node
*chain
= alloc_stable_node();
592 VM_BUG_ON(is_stable_node_chain(dup
));
594 INIT_HLIST_HEAD(&chain
->hlist
);
595 chain
->chain_prune_time
= jiffies
;
596 chain
->rmap_hlist_len
= STABLE_NODE_CHAIN
;
597 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
598 chain
->nid
= NUMA_NO_NODE
; /* debug */
600 ksm_stable_node_chains
++;
603 * Put the stable node chain in the first dimension of
604 * the stable tree and at the same time remove the old
607 rb_replace_node(&dup
->node
, &chain
->node
, root
);
610 * Move the old stable node to the second dimension
611 * queued in the hlist_dup. The invariant is that all
612 * dup stable_nodes in the chain->hlist point to pages
613 * that are write protected and have the exact same
616 stable_node_chain_add_dup(dup
, chain
);
621 static inline void free_stable_node_chain(struct stable_node
*chain
,
622 struct rb_root
*root
)
624 rb_erase(&chain
->node
, root
);
625 free_stable_node(chain
);
626 ksm_stable_node_chains
--;
629 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
631 struct rmap_item
*rmap_item
;
633 /* check it's not STABLE_NODE_CHAIN or negative */
634 BUG_ON(stable_node
->rmap_hlist_len
< 0);
636 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
637 if (rmap_item
->hlist
.next
)
642 rmap_item
->mm
->ksm_merging_pages
--;
644 VM_BUG_ON(stable_node
->rmap_hlist_len
<= 0);
645 stable_node
->rmap_hlist_len
--;
646 put_anon_vma(rmap_item
->anon_vma
);
647 rmap_item
->address
&= PAGE_MASK
;
652 * We need the second aligned pointer of the migrate_nodes
653 * list_head to stay clear from the rb_parent_color union
654 * (aligned and different than any node) and also different
655 * from &migrate_nodes. This will verify that future list.h changes
656 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
658 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD
<= &migrate_nodes
);
659 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD
>= &migrate_nodes
+ 1);
661 if (stable_node
->head
== &migrate_nodes
)
662 list_del(&stable_node
->list
);
664 stable_node_dup_del(stable_node
);
665 free_stable_node(stable_node
);
668 enum get_ksm_page_flags
{
675 * get_ksm_page: checks if the page indicated by the stable node
676 * is still its ksm page, despite having held no reference to it.
677 * In which case we can trust the content of the page, and it
678 * returns the gotten page; but if the page has now been zapped,
679 * remove the stale node from the stable tree and return NULL.
680 * But beware, the stable node's page might be being migrated.
682 * You would expect the stable_node to hold a reference to the ksm page.
683 * But if it increments the page's count, swapping out has to wait for
684 * ksmd to come around again before it can free the page, which may take
685 * seconds or even minutes: much too unresponsive. So instead we use a
686 * "keyhole reference": access to the ksm page from the stable node peeps
687 * out through its keyhole to see if that page still holds the right key,
688 * pointing back to this stable node. This relies on freeing a PageAnon
689 * page to reset its page->mapping to NULL, and relies on no other use of
690 * a page to put something that might look like our key in page->mapping.
691 * is on its way to being freed; but it is an anomaly to bear in mind.
693 static struct page
*get_ksm_page(struct stable_node
*stable_node
,
694 enum get_ksm_page_flags flags
)
697 void *expected_mapping
;
700 expected_mapping
= (void *)((unsigned long)stable_node
|
703 kpfn
= READ_ONCE(stable_node
->kpfn
); /* Address dependency. */
704 page
= pfn_to_page(kpfn
);
705 if (READ_ONCE(page
->mapping
) != expected_mapping
)
709 * We cannot do anything with the page while its refcount is 0.
710 * Usually 0 means free, or tail of a higher-order page: in which
711 * case this node is no longer referenced, and should be freed;
712 * however, it might mean that the page is under page_ref_freeze().
713 * The __remove_mapping() case is easy, again the node is now stale;
714 * the same is in reuse_ksm_page() case; but if page is swapcache
715 * in folio_migrate_mapping(), it might still be our page,
716 * in which case it's essential to keep the node.
718 while (!get_page_unless_zero(page
)) {
720 * Another check for page->mapping != expected_mapping would
721 * work here too. We have chosen the !PageSwapCache test to
722 * optimize the common case, when the page is or is about to
723 * be freed: PageSwapCache is cleared (under spin_lock_irq)
724 * in the ref_freeze section of __remove_mapping(); but Anon
725 * page->mapping reset to NULL later, in free_pages_prepare().
727 if (!PageSwapCache(page
))
732 if (READ_ONCE(page
->mapping
) != expected_mapping
) {
737 if (flags
== GET_KSM_PAGE_TRYLOCK
) {
738 if (!trylock_page(page
)) {
740 return ERR_PTR(-EBUSY
);
742 } else if (flags
== GET_KSM_PAGE_LOCK
)
745 if (flags
!= GET_KSM_PAGE_NOLOCK
) {
746 if (READ_ONCE(page
->mapping
) != expected_mapping
) {
756 * We come here from above when page->mapping or !PageSwapCache
757 * suggests that the node is stale; but it might be under migration.
758 * We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),
759 * before checking whether node->kpfn has been changed.
762 if (READ_ONCE(stable_node
->kpfn
) != kpfn
)
764 remove_node_from_stable_tree(stable_node
);
769 * Removing rmap_item from stable or unstable tree.
770 * This function will clean the information from the stable/unstable tree.
772 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
774 if (rmap_item
->address
& STABLE_FLAG
) {
775 struct stable_node
*stable_node
;
778 stable_node
= rmap_item
->head
;
779 page
= get_ksm_page(stable_node
, GET_KSM_PAGE_LOCK
);
783 hlist_del(&rmap_item
->hlist
);
787 if (!hlist_empty(&stable_node
->hlist
))
792 rmap_item
->mm
->ksm_merging_pages
--;
794 VM_BUG_ON(stable_node
->rmap_hlist_len
<= 0);
795 stable_node
->rmap_hlist_len
--;
797 put_anon_vma(rmap_item
->anon_vma
);
798 rmap_item
->head
= NULL
;
799 rmap_item
->address
&= PAGE_MASK
;
801 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
804 * Usually ksmd can and must skip the rb_erase, because
805 * root_unstable_tree was already reset to RB_ROOT.
806 * But be careful when an mm is exiting: do the rb_erase
807 * if this rmap_item was inserted by this scan, rather
808 * than left over from before.
810 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
813 rb_erase(&rmap_item
->node
,
814 root_unstable_tree
+ NUMA(rmap_item
->nid
));
815 ksm_pages_unshared
--;
816 rmap_item
->address
&= PAGE_MASK
;
819 cond_resched(); /* we're called from many long loops */
822 static void remove_trailing_rmap_items(struct rmap_item
**rmap_list
)
825 struct rmap_item
*rmap_item
= *rmap_list
;
826 *rmap_list
= rmap_item
->rmap_list
;
827 remove_rmap_item_from_tree(rmap_item
);
828 free_rmap_item(rmap_item
);
833 * Though it's very tempting to unmerge rmap_items from stable tree rather
834 * than check every pte of a given vma, the locking doesn't quite work for
835 * that - an rmap_item is assigned to the stable tree after inserting ksm
836 * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
837 * rmap_items from parent to child at fork time (so as not to waste time
838 * if exit comes before the next scan reaches it).
840 * Similarly, although we'd like to remove rmap_items (so updating counts
841 * and freeing memory) when unmerging an area, it's easier to leave that
842 * to the next pass of ksmd - consider, for example, how ksmd might be
843 * in cmp_and_merge_page on one of the rmap_items we would be removing.
845 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
846 unsigned long start
, unsigned long end
)
851 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
852 if (ksm_test_exit(vma
->vm_mm
))
854 if (signal_pending(current
))
857 err
= break_ksm(vma
, addr
);
862 static inline struct stable_node
*folio_stable_node(struct folio
*folio
)
864 return folio_test_ksm(folio
) ? folio_raw_mapping(folio
) : NULL
;
867 static inline struct stable_node
*page_stable_node(struct page
*page
)
869 return folio_stable_node(page_folio(page
));
872 static inline void set_page_stable_node(struct page
*page
,
873 struct stable_node
*stable_node
)
875 VM_BUG_ON_PAGE(PageAnon(page
) && PageAnonExclusive(page
), page
);
876 page
->mapping
= (void *)((unsigned long)stable_node
| PAGE_MAPPING_KSM
);
881 * Only called through the sysfs control interface:
883 static int remove_stable_node(struct stable_node
*stable_node
)
888 page
= get_ksm_page(stable_node
, GET_KSM_PAGE_LOCK
);
891 * get_ksm_page did remove_node_from_stable_tree itself.
897 * Page could be still mapped if this races with __mmput() running in
898 * between ksm_exit() and exit_mmap(). Just refuse to let
899 * merge_across_nodes/max_page_sharing be switched.
902 if (!page_mapped(page
)) {
904 * The stable node did not yet appear stale to get_ksm_page(),
905 * since that allows for an unmapped ksm page to be recognized
906 * right up until it is freed; but the node is safe to remove.
907 * This page might be in a pagevec waiting to be freed,
908 * or it might be PageSwapCache (perhaps under writeback),
909 * or it might have been removed from swapcache a moment ago.
911 set_page_stable_node(page
, NULL
);
912 remove_node_from_stable_tree(stable_node
);
921 static int remove_stable_node_chain(struct stable_node
*stable_node
,
922 struct rb_root
*root
)
924 struct stable_node
*dup
;
925 struct hlist_node
*hlist_safe
;
927 if (!is_stable_node_chain(stable_node
)) {
928 VM_BUG_ON(is_stable_node_dup(stable_node
));
929 if (remove_stable_node(stable_node
))
935 hlist_for_each_entry_safe(dup
, hlist_safe
,
936 &stable_node
->hlist
, hlist_dup
) {
937 VM_BUG_ON(!is_stable_node_dup(dup
));
938 if (remove_stable_node(dup
))
941 BUG_ON(!hlist_empty(&stable_node
->hlist
));
942 free_stable_node_chain(stable_node
, root
);
946 static int remove_all_stable_nodes(void)
948 struct stable_node
*stable_node
, *next
;
952 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
953 while (root_stable_tree
[nid
].rb_node
) {
954 stable_node
= rb_entry(root_stable_tree
[nid
].rb_node
,
955 struct stable_node
, node
);
956 if (remove_stable_node_chain(stable_node
,
957 root_stable_tree
+ nid
)) {
959 break; /* proceed to next nid */
964 list_for_each_entry_safe(stable_node
, next
, &migrate_nodes
, list
) {
965 if (remove_stable_node(stable_node
))
972 static int unmerge_and_remove_all_rmap_items(void)
974 struct mm_slot
*mm_slot
;
975 struct mm_struct
*mm
;
976 struct vm_area_struct
*vma
;
979 spin_lock(&ksm_mmlist_lock
);
980 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
981 struct mm_slot
, mm_list
);
982 spin_unlock(&ksm_mmlist_lock
);
984 for (mm_slot
= ksm_scan
.mm_slot
;
985 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
988 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
989 if (ksm_test_exit(mm
))
991 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
993 err
= unmerge_ksm_pages(vma
,
994 vma
->vm_start
, vma
->vm_end
);
999 remove_trailing_rmap_items(&mm_slot
->rmap_list
);
1000 mmap_read_unlock(mm
);
1002 spin_lock(&ksm_mmlist_lock
);
1003 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
1004 struct mm_slot
, mm_list
);
1005 if (ksm_test_exit(mm
)) {
1006 hash_del(&mm_slot
->link
);
1007 list_del(&mm_slot
->mm_list
);
1008 spin_unlock(&ksm_mmlist_lock
);
1010 free_mm_slot(mm_slot
);
1011 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1014 spin_unlock(&ksm_mmlist_lock
);
1017 /* Clean up stable nodes, but don't worry if some are still busy */
1018 remove_all_stable_nodes();
1023 mmap_read_unlock(mm
);
1024 spin_lock(&ksm_mmlist_lock
);
1025 ksm_scan
.mm_slot
= &ksm_mm_head
;
1026 spin_unlock(&ksm_mmlist_lock
);
1029 #endif /* CONFIG_SYSFS */
1031 static u32
calc_checksum(struct page
*page
)
1034 void *addr
= kmap_atomic(page
);
1035 checksum
= xxhash(addr
, PAGE_SIZE
, 0);
1036 kunmap_atomic(addr
);
1040 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
1043 struct mm_struct
*mm
= vma
->vm_mm
;
1044 DEFINE_PAGE_VMA_WALK(pvmw
, page
, vma
, 0, 0);
1047 struct mmu_notifier_range range
;
1048 bool anon_exclusive
;
1050 pvmw
.address
= page_address_in_vma(page
, vma
);
1051 if (pvmw
.address
== -EFAULT
)
1054 BUG_ON(PageTransCompound(page
));
1056 mmu_notifier_range_init(&range
, MMU_NOTIFY_CLEAR
, 0, vma
, mm
,
1058 pvmw
.address
+ PAGE_SIZE
);
1059 mmu_notifier_invalidate_range_start(&range
);
1061 if (!page_vma_mapped_walk(&pvmw
))
1063 if (WARN_ONCE(!pvmw
.pte
, "Unexpected PMD mapping?"))
1066 anon_exclusive
= PageAnonExclusive(page
);
1067 if (pte_write(*pvmw
.pte
) || pte_dirty(*pvmw
.pte
) ||
1068 (pte_protnone(*pvmw
.pte
) && pte_savedwrite(*pvmw
.pte
)) ||
1069 anon_exclusive
|| mm_tlb_flush_pending(mm
)) {
1072 swapped
= PageSwapCache(page
);
1073 flush_cache_page(vma
, pvmw
.address
, page_to_pfn(page
));
1075 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1076 * take any lock, therefore the check that we are going to make
1077 * with the pagecount against the mapcount is racy and
1078 * O_DIRECT can happen right after the check.
1079 * So we clear the pte and flush the tlb before the check
1080 * this assure us that no O_DIRECT can happen after the check
1081 * or in the middle of the check.
1083 * No need to notify as we are downgrading page table to read
1084 * only not changing it to point to a new page.
1086 * See Documentation/mm/mmu_notifier.rst
1088 entry
= ptep_clear_flush(vma
, pvmw
.address
, pvmw
.pte
);
1090 * Check that no O_DIRECT or similar I/O is in progress on the
1093 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
1094 set_pte_at(mm
, pvmw
.address
, pvmw
.pte
, entry
);
1098 if (anon_exclusive
&& page_try_share_anon_rmap(page
)) {
1099 set_pte_at(mm
, pvmw
.address
, pvmw
.pte
, entry
);
1103 if (pte_dirty(entry
))
1104 set_page_dirty(page
);
1106 if (pte_protnone(entry
))
1107 entry
= pte_mkclean(pte_clear_savedwrite(entry
));
1109 entry
= pte_mkclean(pte_wrprotect(entry
));
1110 set_pte_at_notify(mm
, pvmw
.address
, pvmw
.pte
, entry
);
1112 *orig_pte
= *pvmw
.pte
;
1116 page_vma_mapped_walk_done(&pvmw
);
1118 mmu_notifier_invalidate_range_end(&range
);
1124 * replace_page - replace page in vma by new ksm page
1125 * @vma: vma that holds the pte pointing to page
1126 * @page: the page we are replacing by kpage
1127 * @kpage: the ksm page we replace page by
1128 * @orig_pte: the original value of the pte
1130 * Returns 0 on success, -EFAULT on failure.
1132 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
1133 struct page
*kpage
, pte_t orig_pte
)
1135 struct mm_struct
*mm
= vma
->vm_mm
;
1142 struct mmu_notifier_range range
;
1144 addr
= page_address_in_vma(page
, vma
);
1145 if (addr
== -EFAULT
)
1148 pmd
= mm_find_pmd(mm
, addr
);
1152 mmu_notifier_range_init(&range
, MMU_NOTIFY_CLEAR
, 0, vma
, mm
, addr
,
1154 mmu_notifier_invalidate_range_start(&range
);
1156 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
1157 if (!pte_same(*ptep
, orig_pte
)) {
1158 pte_unmap_unlock(ptep
, ptl
);
1161 VM_BUG_ON_PAGE(PageAnonExclusive(page
), page
);
1162 VM_BUG_ON_PAGE(PageAnon(kpage
) && PageAnonExclusive(kpage
), kpage
);
1165 * No need to check ksm_use_zero_pages here: we can only have a
1166 * zero_page here if ksm_use_zero_pages was enabled already.
1168 if (!is_zero_pfn(page_to_pfn(kpage
))) {
1170 page_add_anon_rmap(kpage
, vma
, addr
, RMAP_NONE
);
1171 newpte
= mk_pte(kpage
, vma
->vm_page_prot
);
1173 newpte
= pte_mkspecial(pfn_pte(page_to_pfn(kpage
),
1174 vma
->vm_page_prot
));
1176 * We're replacing an anonymous page with a zero page, which is
1177 * not anonymous. We need to do proper accounting otherwise we
1178 * will get wrong values in /proc, and a BUG message in dmesg
1179 * when tearing down the mm.
1181 dec_mm_counter(mm
, MM_ANONPAGES
);
1184 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
1186 * No need to notify as we are replacing a read only page with another
1187 * read only page with the same content.
1189 * See Documentation/mm/mmu_notifier.rst
1191 ptep_clear_flush(vma
, addr
, ptep
);
1192 set_pte_at_notify(mm
, addr
, ptep
, newpte
);
1194 page_remove_rmap(page
, vma
, false);
1195 if (!page_mapped(page
))
1196 try_to_free_swap(page
);
1199 pte_unmap_unlock(ptep
, ptl
);
1202 mmu_notifier_invalidate_range_end(&range
);
1208 * try_to_merge_one_page - take two pages and merge them into one
1209 * @vma: the vma that holds the pte pointing to page
1210 * @page: the PageAnon page that we want to replace with kpage
1211 * @kpage: the PageKsm page that we want to map instead of page,
1212 * or NULL the first time when we want to use page as kpage.
1214 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1216 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
1217 struct page
*page
, struct page
*kpage
)
1219 pte_t orig_pte
= __pte(0);
1222 if (page
== kpage
) /* ksm page forked */
1225 if (!PageAnon(page
))
1229 * We need the page lock to read a stable PageSwapCache in
1230 * write_protect_page(). We use trylock_page() instead of
1231 * lock_page() because we don't want to wait here - we
1232 * prefer to continue scanning and merging different pages,
1233 * then come back to this page when it is unlocked.
1235 if (!trylock_page(page
))
1238 if (PageTransCompound(page
)) {
1239 if (split_huge_page(page
))
1244 * If this anonymous page is mapped only here, its pte may need
1245 * to be write-protected. If it's mapped elsewhere, all of its
1246 * ptes are necessarily already write-protected. But in either
1247 * case, we need to lock and check page_count is not raised.
1249 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
1252 * While we hold page lock, upgrade page from
1253 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1254 * stable_tree_insert() will update stable_node.
1256 set_page_stable_node(page
, NULL
);
1257 mark_page_accessed(page
);
1259 * Page reclaim just frees a clean page with no dirty
1260 * ptes: make sure that the ksm page would be swapped.
1262 if (!PageDirty(page
))
1265 } else if (pages_identical(page
, kpage
))
1266 err
= replace_page(vma
, page
, kpage
, orig_pte
);
1276 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1277 * but no new kernel page is allocated: kpage must already be a ksm page.
1279 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1281 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
1282 struct page
*page
, struct page
*kpage
)
1284 struct mm_struct
*mm
= rmap_item
->mm
;
1285 struct vm_area_struct
*vma
;
1289 vma
= find_mergeable_vma(mm
, rmap_item
->address
);
1293 err
= try_to_merge_one_page(vma
, page
, kpage
);
1297 /* Unstable nid is in union with stable anon_vma: remove first */
1298 remove_rmap_item_from_tree(rmap_item
);
1300 /* Must get reference to anon_vma while still holding mmap_lock */
1301 rmap_item
->anon_vma
= vma
->anon_vma
;
1302 get_anon_vma(vma
->anon_vma
);
1304 mmap_read_unlock(mm
);
1309 * try_to_merge_two_pages - take two identical pages and prepare them
1310 * to be merged into one page.
1312 * This function returns the kpage if we successfully merged two identical
1313 * pages into one ksm page, NULL otherwise.
1315 * Note that this function upgrades page to ksm page: if one of the pages
1316 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1318 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
1320 struct rmap_item
*tree_rmap_item
,
1321 struct page
*tree_page
)
1325 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
1327 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
1330 * If that fails, we have a ksm page with only one pte
1331 * pointing to it: so break it.
1334 break_cow(rmap_item
);
1336 return err
? NULL
: page
;
1339 static __always_inline
1340 bool __is_page_sharing_candidate(struct stable_node
*stable_node
, int offset
)
1342 VM_BUG_ON(stable_node
->rmap_hlist_len
< 0);
1344 * Check that at least one mapping still exists, otherwise
1345 * there's no much point to merge and share with this
1346 * stable_node, as the underlying tree_page of the other
1347 * sharer is going to be freed soon.
1349 return stable_node
->rmap_hlist_len
&&
1350 stable_node
->rmap_hlist_len
+ offset
< ksm_max_page_sharing
;
1353 static __always_inline
1354 bool is_page_sharing_candidate(struct stable_node
*stable_node
)
1356 return __is_page_sharing_candidate(stable_node
, 0);
1359 static struct page
*stable_node_dup(struct stable_node
**_stable_node_dup
,
1360 struct stable_node
**_stable_node
,
1361 struct rb_root
*root
,
1362 bool prune_stale_stable_nodes
)
1364 struct stable_node
*dup
, *found
= NULL
, *stable_node
= *_stable_node
;
1365 struct hlist_node
*hlist_safe
;
1366 struct page
*_tree_page
, *tree_page
= NULL
;
1368 int found_rmap_hlist_len
;
1370 if (!prune_stale_stable_nodes
||
1371 time_before(jiffies
, stable_node
->chain_prune_time
+
1373 ksm_stable_node_chains_prune_millisecs
)))
1374 prune_stale_stable_nodes
= false;
1376 stable_node
->chain_prune_time
= jiffies
;
1378 hlist_for_each_entry_safe(dup
, hlist_safe
,
1379 &stable_node
->hlist
, hlist_dup
) {
1382 * We must walk all stable_node_dup to prune the stale
1383 * stable nodes during lookup.
1385 * get_ksm_page can drop the nodes from the
1386 * stable_node->hlist if they point to freed pages
1387 * (that's why we do a _safe walk). The "dup"
1388 * stable_node parameter itself will be freed from
1389 * under us if it returns NULL.
1391 _tree_page
= get_ksm_page(dup
, GET_KSM_PAGE_NOLOCK
);
1395 if (is_page_sharing_candidate(dup
)) {
1397 dup
->rmap_hlist_len
> found_rmap_hlist_len
) {
1399 put_page(tree_page
);
1401 found_rmap_hlist_len
= found
->rmap_hlist_len
;
1402 tree_page
= _tree_page
;
1404 /* skip put_page for found dup */
1405 if (!prune_stale_stable_nodes
)
1410 put_page(_tree_page
);
1415 * nr is counting all dups in the chain only if
1416 * prune_stale_stable_nodes is true, otherwise we may
1417 * break the loop at nr == 1 even if there are
1420 if (prune_stale_stable_nodes
&& nr
== 1) {
1422 * If there's not just one entry it would
1423 * corrupt memory, better BUG_ON. In KSM
1424 * context with no lock held it's not even
1427 BUG_ON(stable_node
->hlist
.first
->next
);
1430 * There's just one entry and it is below the
1431 * deduplication limit so drop the chain.
1433 rb_replace_node(&stable_node
->node
, &found
->node
,
1435 free_stable_node(stable_node
);
1436 ksm_stable_node_chains
--;
1437 ksm_stable_node_dups
--;
1439 * NOTE: the caller depends on the stable_node
1440 * to be equal to stable_node_dup if the chain
1443 *_stable_node
= found
;
1445 * Just for robustness, as stable_node is
1446 * otherwise left as a stable pointer, the
1447 * compiler shall optimize it away at build
1451 } else if (stable_node
->hlist
.first
!= &found
->hlist_dup
&&
1452 __is_page_sharing_candidate(found
, 1)) {
1454 * If the found stable_node dup can accept one
1455 * more future merge (in addition to the one
1456 * that is underway) and is not at the head of
1457 * the chain, put it there so next search will
1458 * be quicker in the !prune_stale_stable_nodes
1461 * NOTE: it would be inaccurate to use nr > 1
1462 * instead of checking the hlist.first pointer
1463 * directly, because in the
1464 * prune_stale_stable_nodes case "nr" isn't
1465 * the position of the found dup in the chain,
1466 * but the total number of dups in the chain.
1468 hlist_del(&found
->hlist_dup
);
1469 hlist_add_head(&found
->hlist_dup
,
1470 &stable_node
->hlist
);
1474 *_stable_node_dup
= found
;
1478 static struct stable_node
*stable_node_dup_any(struct stable_node
*stable_node
,
1479 struct rb_root
*root
)
1481 if (!is_stable_node_chain(stable_node
))
1483 if (hlist_empty(&stable_node
->hlist
)) {
1484 free_stable_node_chain(stable_node
, root
);
1487 return hlist_entry(stable_node
->hlist
.first
,
1488 typeof(*stable_node
), hlist_dup
);
1492 * Like for get_ksm_page, this function can free the *_stable_node and
1493 * *_stable_node_dup if the returned tree_page is NULL.
1495 * It can also free and overwrite *_stable_node with the found
1496 * stable_node_dup if the chain is collapsed (in which case
1497 * *_stable_node will be equal to *_stable_node_dup like if the chain
1498 * never existed). It's up to the caller to verify tree_page is not
1499 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1501 * *_stable_node_dup is really a second output parameter of this
1502 * function and will be overwritten in all cases, the caller doesn't
1503 * need to initialize it.
1505 static struct page
*__stable_node_chain(struct stable_node
**_stable_node_dup
,
1506 struct stable_node
**_stable_node
,
1507 struct rb_root
*root
,
1508 bool prune_stale_stable_nodes
)
1510 struct stable_node
*stable_node
= *_stable_node
;
1511 if (!is_stable_node_chain(stable_node
)) {
1512 if (is_page_sharing_candidate(stable_node
)) {
1513 *_stable_node_dup
= stable_node
;
1514 return get_ksm_page(stable_node
, GET_KSM_PAGE_NOLOCK
);
1517 * _stable_node_dup set to NULL means the stable_node
1518 * reached the ksm_max_page_sharing limit.
1520 *_stable_node_dup
= NULL
;
1523 return stable_node_dup(_stable_node_dup
, _stable_node
, root
,
1524 prune_stale_stable_nodes
);
1527 static __always_inline
struct page
*chain_prune(struct stable_node
**s_n_d
,
1528 struct stable_node
**s_n
,
1529 struct rb_root
*root
)
1531 return __stable_node_chain(s_n_d
, s_n
, root
, true);
1534 static __always_inline
struct page
*chain(struct stable_node
**s_n_d
,
1535 struct stable_node
*s_n
,
1536 struct rb_root
*root
)
1538 struct stable_node
*old_stable_node
= s_n
;
1539 struct page
*tree_page
;
1541 tree_page
= __stable_node_chain(s_n_d
, &s_n
, root
, false);
1542 /* not pruning dups so s_n cannot have changed */
1543 VM_BUG_ON(s_n
!= old_stable_node
);
1548 * stable_tree_search - search for page inside the stable tree
1550 * This function checks if there is a page inside the stable tree
1551 * with identical content to the page that we are scanning right now.
1553 * This function returns the stable tree node of identical content if found,
1556 static struct page
*stable_tree_search(struct page
*page
)
1559 struct rb_root
*root
;
1560 struct rb_node
**new;
1561 struct rb_node
*parent
;
1562 struct stable_node
*stable_node
, *stable_node_dup
, *stable_node_any
;
1563 struct stable_node
*page_node
;
1565 page_node
= page_stable_node(page
);
1566 if (page_node
&& page_node
->head
!= &migrate_nodes
) {
1567 /* ksm page forked */
1572 nid
= get_kpfn_nid(page_to_pfn(page
));
1573 root
= root_stable_tree
+ nid
;
1575 new = &root
->rb_node
;
1579 struct page
*tree_page
;
1583 stable_node
= rb_entry(*new, struct stable_node
, node
);
1584 stable_node_any
= NULL
;
1585 tree_page
= chain_prune(&stable_node_dup
, &stable_node
, root
);
1587 * NOTE: stable_node may have been freed by
1588 * chain_prune() if the returned stable_node_dup is
1589 * not NULL. stable_node_dup may have been inserted in
1590 * the rbtree instead as a regular stable_node (in
1591 * order to collapse the stable_node chain if a single
1592 * stable_node dup was found in it). In such case the
1593 * stable_node is overwritten by the callee to point
1594 * to the stable_node_dup that was collapsed in the
1595 * stable rbtree and stable_node will be equal to
1596 * stable_node_dup like if the chain never existed.
1598 if (!stable_node_dup
) {
1600 * Either all stable_node dups were full in
1601 * this stable_node chain, or this chain was
1602 * empty and should be rb_erased.
1604 stable_node_any
= stable_node_dup_any(stable_node
,
1606 if (!stable_node_any
) {
1607 /* rb_erase just run */
1611 * Take any of the stable_node dups page of
1612 * this stable_node chain to let the tree walk
1613 * continue. All KSM pages belonging to the
1614 * stable_node dups in a stable_node chain
1615 * have the same content and they're
1616 * write protected at all times. Any will work
1617 * fine to continue the walk.
1619 tree_page
= get_ksm_page(stable_node_any
,
1620 GET_KSM_PAGE_NOLOCK
);
1622 VM_BUG_ON(!stable_node_dup
^ !!stable_node_any
);
1625 * If we walked over a stale stable_node,
1626 * get_ksm_page() will call rb_erase() and it
1627 * may rebalance the tree from under us. So
1628 * restart the search from scratch. Returning
1629 * NULL would be safe too, but we'd generate
1630 * false negative insertions just because some
1631 * stable_node was stale.
1636 ret
= memcmp_pages(page
, tree_page
);
1637 put_page(tree_page
);
1641 new = &parent
->rb_left
;
1643 new = &parent
->rb_right
;
1646 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1648 * Test if the migrated page should be merged
1649 * into a stable node dup. If the mapcount is
1650 * 1 we can migrate it with another KSM page
1651 * without adding it to the chain.
1653 if (page_mapcount(page
) > 1)
1657 if (!stable_node_dup
) {
1659 * If the stable_node is a chain and
1660 * we got a payload match in memcmp
1661 * but we cannot merge the scanned
1662 * page in any of the existing
1663 * stable_node dups because they're
1664 * all full, we need to wait the
1665 * scanned page to find itself a match
1666 * in the unstable tree to create a
1667 * brand new KSM page to add later to
1668 * the dups of this stable_node.
1674 * Lock and unlock the stable_node's page (which
1675 * might already have been migrated) so that page
1676 * migration is sure to notice its raised count.
1677 * It would be more elegant to return stable_node
1678 * than kpage, but that involves more changes.
1680 tree_page
= get_ksm_page(stable_node_dup
,
1681 GET_KSM_PAGE_TRYLOCK
);
1683 if (PTR_ERR(tree_page
) == -EBUSY
)
1684 return ERR_PTR(-EBUSY
);
1686 if (unlikely(!tree_page
))
1688 * The tree may have been rebalanced,
1689 * so re-evaluate parent and new.
1692 unlock_page(tree_page
);
1694 if (get_kpfn_nid(stable_node_dup
->kpfn
) !=
1695 NUMA(stable_node_dup
->nid
)) {
1696 put_page(tree_page
);
1706 list_del(&page_node
->list
);
1707 DO_NUMA(page_node
->nid
= nid
);
1708 rb_link_node(&page_node
->node
, parent
, new);
1709 rb_insert_color(&page_node
->node
, root
);
1711 if (is_page_sharing_candidate(page_node
)) {
1719 * If stable_node was a chain and chain_prune collapsed it,
1720 * stable_node has been updated to be the new regular
1721 * stable_node. A collapse of the chain is indistinguishable
1722 * from the case there was no chain in the stable
1723 * rbtree. Otherwise stable_node is the chain and
1724 * stable_node_dup is the dup to replace.
1726 if (stable_node_dup
== stable_node
) {
1727 VM_BUG_ON(is_stable_node_chain(stable_node_dup
));
1728 VM_BUG_ON(is_stable_node_dup(stable_node_dup
));
1729 /* there is no chain */
1731 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1732 list_del(&page_node
->list
);
1733 DO_NUMA(page_node
->nid
= nid
);
1734 rb_replace_node(&stable_node_dup
->node
,
1737 if (is_page_sharing_candidate(page_node
))
1742 rb_erase(&stable_node_dup
->node
, root
);
1746 VM_BUG_ON(!is_stable_node_chain(stable_node
));
1747 __stable_node_dup_del(stable_node_dup
);
1749 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1750 list_del(&page_node
->list
);
1751 DO_NUMA(page_node
->nid
= nid
);
1752 stable_node_chain_add_dup(page_node
, stable_node
);
1753 if (is_page_sharing_candidate(page_node
))
1761 stable_node_dup
->head
= &migrate_nodes
;
1762 list_add(&stable_node_dup
->list
, stable_node_dup
->head
);
1766 /* stable_node_dup could be null if it reached the limit */
1767 if (!stable_node_dup
)
1768 stable_node_dup
= stable_node_any
;
1770 * If stable_node was a chain and chain_prune collapsed it,
1771 * stable_node has been updated to be the new regular
1772 * stable_node. A collapse of the chain is indistinguishable
1773 * from the case there was no chain in the stable
1774 * rbtree. Otherwise stable_node is the chain and
1775 * stable_node_dup is the dup to replace.
1777 if (stable_node_dup
== stable_node
) {
1778 VM_BUG_ON(is_stable_node_dup(stable_node_dup
));
1779 /* chain is missing so create it */
1780 stable_node
= alloc_stable_node_chain(stable_node_dup
,
1786 * Add this stable_node dup that was
1787 * migrated to the stable_node chain
1788 * of the current nid for this page
1791 VM_BUG_ON(!is_stable_node_dup(stable_node_dup
));
1792 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1793 list_del(&page_node
->list
);
1794 DO_NUMA(page_node
->nid
= nid
);
1795 stable_node_chain_add_dup(page_node
, stable_node
);
1800 * stable_tree_insert - insert stable tree node pointing to new ksm page
1801 * into the stable tree.
1803 * This function returns the stable tree node just allocated on success,
1806 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1810 struct rb_root
*root
;
1811 struct rb_node
**new;
1812 struct rb_node
*parent
;
1813 struct stable_node
*stable_node
, *stable_node_dup
, *stable_node_any
;
1814 bool need_chain
= false;
1816 kpfn
= page_to_pfn(kpage
);
1817 nid
= get_kpfn_nid(kpfn
);
1818 root
= root_stable_tree
+ nid
;
1821 new = &root
->rb_node
;
1824 struct page
*tree_page
;
1828 stable_node
= rb_entry(*new, struct stable_node
, node
);
1829 stable_node_any
= NULL
;
1830 tree_page
= chain(&stable_node_dup
, stable_node
, root
);
1831 if (!stable_node_dup
) {
1833 * Either all stable_node dups were full in
1834 * this stable_node chain, or this chain was
1835 * empty and should be rb_erased.
1837 stable_node_any
= stable_node_dup_any(stable_node
,
1839 if (!stable_node_any
) {
1840 /* rb_erase just run */
1844 * Take any of the stable_node dups page of
1845 * this stable_node chain to let the tree walk
1846 * continue. All KSM pages belonging to the
1847 * stable_node dups in a stable_node chain
1848 * have the same content and they're
1849 * write protected at all times. Any will work
1850 * fine to continue the walk.
1852 tree_page
= get_ksm_page(stable_node_any
,
1853 GET_KSM_PAGE_NOLOCK
);
1855 VM_BUG_ON(!stable_node_dup
^ !!stable_node_any
);
1858 * If we walked over a stale stable_node,
1859 * get_ksm_page() will call rb_erase() and it
1860 * may rebalance the tree from under us. So
1861 * restart the search from scratch. Returning
1862 * NULL would be safe too, but we'd generate
1863 * false negative insertions just because some
1864 * stable_node was stale.
1869 ret
= memcmp_pages(kpage
, tree_page
);
1870 put_page(tree_page
);
1874 new = &parent
->rb_left
;
1876 new = &parent
->rb_right
;
1883 stable_node_dup
= alloc_stable_node();
1884 if (!stable_node_dup
)
1887 INIT_HLIST_HEAD(&stable_node_dup
->hlist
);
1888 stable_node_dup
->kpfn
= kpfn
;
1889 set_page_stable_node(kpage
, stable_node_dup
);
1890 stable_node_dup
->rmap_hlist_len
= 0;
1891 DO_NUMA(stable_node_dup
->nid
= nid
);
1893 rb_link_node(&stable_node_dup
->node
, parent
, new);
1894 rb_insert_color(&stable_node_dup
->node
, root
);
1896 if (!is_stable_node_chain(stable_node
)) {
1897 struct stable_node
*orig
= stable_node
;
1898 /* chain is missing so create it */
1899 stable_node
= alloc_stable_node_chain(orig
, root
);
1901 free_stable_node(stable_node_dup
);
1905 stable_node_chain_add_dup(stable_node_dup
, stable_node
);
1908 return stable_node_dup
;
1912 * unstable_tree_search_insert - search for identical page,
1913 * else insert rmap_item into the unstable tree.
1915 * This function searches for a page in the unstable tree identical to the
1916 * page currently being scanned; and if no identical page is found in the
1917 * tree, we insert rmap_item as a new object into the unstable tree.
1919 * This function returns pointer to rmap_item found to be identical
1920 * to the currently scanned page, NULL otherwise.
1922 * This function does both searching and inserting, because they share
1923 * the same walking algorithm in an rbtree.
1926 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1928 struct page
**tree_pagep
)
1930 struct rb_node
**new;
1931 struct rb_root
*root
;
1932 struct rb_node
*parent
= NULL
;
1935 nid
= get_kpfn_nid(page_to_pfn(page
));
1936 root
= root_unstable_tree
+ nid
;
1937 new = &root
->rb_node
;
1940 struct rmap_item
*tree_rmap_item
;
1941 struct page
*tree_page
;
1945 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1946 tree_page
= get_mergeable_page(tree_rmap_item
);
1951 * Don't substitute a ksm page for a forked page.
1953 if (page
== tree_page
) {
1954 put_page(tree_page
);
1958 ret
= memcmp_pages(page
, tree_page
);
1962 put_page(tree_page
);
1963 new = &parent
->rb_left
;
1964 } else if (ret
> 0) {
1965 put_page(tree_page
);
1966 new = &parent
->rb_right
;
1967 } else if (!ksm_merge_across_nodes
&&
1968 page_to_nid(tree_page
) != nid
) {
1970 * If tree_page has been migrated to another NUMA node,
1971 * it will be flushed out and put in the right unstable
1972 * tree next time: only merge with it when across_nodes.
1974 put_page(tree_page
);
1977 *tree_pagep
= tree_page
;
1978 return tree_rmap_item
;
1982 rmap_item
->address
|= UNSTABLE_FLAG
;
1983 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1984 DO_NUMA(rmap_item
->nid
= nid
);
1985 rb_link_node(&rmap_item
->node
, parent
, new);
1986 rb_insert_color(&rmap_item
->node
, root
);
1988 ksm_pages_unshared
++;
1993 * stable_tree_append - add another rmap_item to the linked list of
1994 * rmap_items hanging off a given node of the stable tree, all sharing
1995 * the same ksm page.
1997 static void stable_tree_append(struct rmap_item
*rmap_item
,
1998 struct stable_node
*stable_node
,
1999 bool max_page_sharing_bypass
)
2002 * rmap won't find this mapping if we don't insert the
2003 * rmap_item in the right stable_node
2004 * duplicate. page_migration could break later if rmap breaks,
2005 * so we can as well crash here. We really need to check for
2006 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2007 * for other negative values as an underflow if detected here
2008 * for the first time (and not when decreasing rmap_hlist_len)
2009 * would be sign of memory corruption in the stable_node.
2011 BUG_ON(stable_node
->rmap_hlist_len
< 0);
2013 stable_node
->rmap_hlist_len
++;
2014 if (!max_page_sharing_bypass
)
2015 /* possibly non fatal but unexpected overflow, only warn */
2016 WARN_ON_ONCE(stable_node
->rmap_hlist_len
>
2017 ksm_max_page_sharing
);
2019 rmap_item
->head
= stable_node
;
2020 rmap_item
->address
|= STABLE_FLAG
;
2021 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
2023 if (rmap_item
->hlist
.next
)
2024 ksm_pages_sharing
++;
2028 rmap_item
->mm
->ksm_merging_pages
++;
2032 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2033 * if not, compare checksum to previous and if it's the same, see if page can
2034 * be inserted into the unstable tree, or merged with a page already there and
2035 * both transferred to the stable tree.
2037 * @page: the page that we are searching identical page to.
2038 * @rmap_item: the reverse mapping into the virtual address of this page
2040 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
2042 struct mm_struct
*mm
= rmap_item
->mm
;
2043 struct rmap_item
*tree_rmap_item
;
2044 struct page
*tree_page
= NULL
;
2045 struct stable_node
*stable_node
;
2047 unsigned int checksum
;
2049 bool max_page_sharing_bypass
= false;
2051 stable_node
= page_stable_node(page
);
2053 if (stable_node
->head
!= &migrate_nodes
&&
2054 get_kpfn_nid(READ_ONCE(stable_node
->kpfn
)) !=
2055 NUMA(stable_node
->nid
)) {
2056 stable_node_dup_del(stable_node
);
2057 stable_node
->head
= &migrate_nodes
;
2058 list_add(&stable_node
->list
, stable_node
->head
);
2060 if (stable_node
->head
!= &migrate_nodes
&&
2061 rmap_item
->head
== stable_node
)
2064 * If it's a KSM fork, allow it to go over the sharing limit
2067 if (!is_page_sharing_candidate(stable_node
))
2068 max_page_sharing_bypass
= true;
2071 /* We first start with searching the page inside the stable tree */
2072 kpage
= stable_tree_search(page
);
2073 if (kpage
== page
&& rmap_item
->head
== stable_node
) {
2078 remove_rmap_item_from_tree(rmap_item
);
2081 if (PTR_ERR(kpage
) == -EBUSY
)
2084 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
2087 * The page was successfully merged:
2088 * add its rmap_item to the stable tree.
2091 stable_tree_append(rmap_item
, page_stable_node(kpage
),
2092 max_page_sharing_bypass
);
2100 * If the hash value of the page has changed from the last time
2101 * we calculated it, this page is changing frequently: therefore we
2102 * don't want to insert it in the unstable tree, and we don't want
2103 * to waste our time searching for something identical to it there.
2105 checksum
= calc_checksum(page
);
2106 if (rmap_item
->oldchecksum
!= checksum
) {
2107 rmap_item
->oldchecksum
= checksum
;
2112 * Same checksum as an empty page. We attempt to merge it with the
2113 * appropriate zero page if the user enabled this via sysfs.
2115 if (ksm_use_zero_pages
&& (checksum
== zero_checksum
)) {
2116 struct vm_area_struct
*vma
;
2119 vma
= find_mergeable_vma(mm
, rmap_item
->address
);
2121 err
= try_to_merge_one_page(vma
, page
,
2122 ZERO_PAGE(rmap_item
->address
));
2125 * If the vma is out of date, we do not need to
2130 mmap_read_unlock(mm
);
2132 * In case of failure, the page was not really empty, so we
2133 * need to continue. Otherwise we're done.
2139 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
2140 if (tree_rmap_item
) {
2143 kpage
= try_to_merge_two_pages(rmap_item
, page
,
2144 tree_rmap_item
, tree_page
);
2146 * If both pages we tried to merge belong to the same compound
2147 * page, then we actually ended up increasing the reference
2148 * count of the same compound page twice, and split_huge_page
2150 * Here we set a flag if that happened, and we use it later to
2151 * try split_huge_page again. Since we call put_page right
2152 * afterwards, the reference count will be correct and
2153 * split_huge_page should succeed.
2155 split
= PageTransCompound(page
)
2156 && compound_head(page
) == compound_head(tree_page
);
2157 put_page(tree_page
);
2160 * The pages were successfully merged: insert new
2161 * node in the stable tree and add both rmap_items.
2164 stable_node
= stable_tree_insert(kpage
);
2166 stable_tree_append(tree_rmap_item
, stable_node
,
2168 stable_tree_append(rmap_item
, stable_node
,
2174 * If we fail to insert the page into the stable tree,
2175 * we will have 2 virtual addresses that are pointing
2176 * to a ksm page left outside the stable tree,
2177 * in which case we need to break_cow on both.
2180 break_cow(tree_rmap_item
);
2181 break_cow(rmap_item
);
2185 * We are here if we tried to merge two pages and
2186 * failed because they both belonged to the same
2187 * compound page. We will split the page now, but no
2188 * merging will take place.
2189 * We do not want to add the cost of a full lock; if
2190 * the page is locked, it is better to skip it and
2191 * perhaps try again later.
2193 if (!trylock_page(page
))
2195 split_huge_page(page
);
2201 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
2202 struct rmap_item
**rmap_list
,
2205 struct rmap_item
*rmap_item
;
2207 while (*rmap_list
) {
2208 rmap_item
= *rmap_list
;
2209 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
2211 if (rmap_item
->address
> addr
)
2213 *rmap_list
= rmap_item
->rmap_list
;
2214 remove_rmap_item_from_tree(rmap_item
);
2215 free_rmap_item(rmap_item
);
2218 rmap_item
= alloc_rmap_item();
2220 /* It has already been zeroed */
2221 rmap_item
->mm
= mm_slot
->mm
;
2222 rmap_item
->address
= addr
;
2223 rmap_item
->rmap_list
= *rmap_list
;
2224 *rmap_list
= rmap_item
;
2229 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
2231 struct mm_struct
*mm
;
2232 struct mm_slot
*slot
;
2233 struct vm_area_struct
*vma
;
2234 struct rmap_item
*rmap_item
;
2237 if (list_empty(&ksm_mm_head
.mm_list
))
2240 slot
= ksm_scan
.mm_slot
;
2241 if (slot
== &ksm_mm_head
) {
2243 * A number of pages can hang around indefinitely on per-cpu
2244 * pagevecs, raised page count preventing write_protect_page
2245 * from merging them. Though it doesn't really matter much,
2246 * it is puzzling to see some stuck in pages_volatile until
2247 * other activity jostles them out, and they also prevented
2248 * LTP's KSM test from succeeding deterministically; so drain
2249 * them here (here rather than on entry to ksm_do_scan(),
2250 * so we don't IPI too often when pages_to_scan is set low).
2252 lru_add_drain_all();
2255 * Whereas stale stable_nodes on the stable_tree itself
2256 * get pruned in the regular course of stable_tree_search(),
2257 * those moved out to the migrate_nodes list can accumulate:
2258 * so prune them once before each full scan.
2260 if (!ksm_merge_across_nodes
) {
2261 struct stable_node
*stable_node
, *next
;
2264 list_for_each_entry_safe(stable_node
, next
,
2265 &migrate_nodes
, list
) {
2266 page
= get_ksm_page(stable_node
,
2267 GET_KSM_PAGE_NOLOCK
);
2274 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++)
2275 root_unstable_tree
[nid
] = RB_ROOT
;
2277 spin_lock(&ksm_mmlist_lock
);
2278 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
2279 ksm_scan
.mm_slot
= slot
;
2280 spin_unlock(&ksm_mmlist_lock
);
2282 * Although we tested list_empty() above, a racing __ksm_exit
2283 * of the last mm on the list may have removed it since then.
2285 if (slot
== &ksm_mm_head
)
2288 ksm_scan
.address
= 0;
2289 ksm_scan
.rmap_list
= &slot
->rmap_list
;
2294 if (ksm_test_exit(mm
))
2297 vma
= find_vma(mm
, ksm_scan
.address
);
2299 for (; vma
; vma
= vma
->vm_next
) {
2300 if (!(vma
->vm_flags
& VM_MERGEABLE
))
2302 if (ksm_scan
.address
< vma
->vm_start
)
2303 ksm_scan
.address
= vma
->vm_start
;
2305 ksm_scan
.address
= vma
->vm_end
;
2307 while (ksm_scan
.address
< vma
->vm_end
) {
2308 if (ksm_test_exit(mm
))
2310 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
2311 if (IS_ERR_OR_NULL(*page
) || is_zone_device_page(*page
)) {
2312 ksm_scan
.address
+= PAGE_SIZE
;
2316 if (PageAnon(*page
)) {
2317 flush_anon_page(vma
, *page
, ksm_scan
.address
);
2318 flush_dcache_page(*page
);
2319 rmap_item
= get_next_rmap_item(slot
,
2320 ksm_scan
.rmap_list
, ksm_scan
.address
);
2322 ksm_scan
.rmap_list
=
2323 &rmap_item
->rmap_list
;
2324 ksm_scan
.address
+= PAGE_SIZE
;
2327 mmap_read_unlock(mm
);
2331 ksm_scan
.address
+= PAGE_SIZE
;
2336 if (ksm_test_exit(mm
)) {
2337 ksm_scan
.address
= 0;
2338 ksm_scan
.rmap_list
= &slot
->rmap_list
;
2341 * Nuke all the rmap_items that are above this current rmap:
2342 * because there were no VM_MERGEABLE vmas with such addresses.
2344 remove_trailing_rmap_items(ksm_scan
.rmap_list
);
2346 spin_lock(&ksm_mmlist_lock
);
2347 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
2348 struct mm_slot
, mm_list
);
2349 if (ksm_scan
.address
== 0) {
2351 * We've completed a full scan of all vmas, holding mmap_lock
2352 * throughout, and found no VM_MERGEABLE: so do the same as
2353 * __ksm_exit does to remove this mm from all our lists now.
2354 * This applies either when cleaning up after __ksm_exit
2355 * (but beware: we can reach here even before __ksm_exit),
2356 * or when all VM_MERGEABLE areas have been unmapped (and
2357 * mmap_lock then protects against race with MADV_MERGEABLE).
2359 hash_del(&slot
->link
);
2360 list_del(&slot
->mm_list
);
2361 spin_unlock(&ksm_mmlist_lock
);
2364 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2365 mmap_read_unlock(mm
);
2368 mmap_read_unlock(mm
);
2370 * mmap_read_unlock(mm) first because after
2371 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2372 * already have been freed under us by __ksm_exit()
2373 * because the "mm_slot" is still hashed and
2374 * ksm_scan.mm_slot doesn't point to it anymore.
2376 spin_unlock(&ksm_mmlist_lock
);
2379 /* Repeat until we've completed scanning the whole list */
2380 slot
= ksm_scan
.mm_slot
;
2381 if (slot
!= &ksm_mm_head
)
2389 * ksm_do_scan - the ksm scanner main worker function.
2390 * @scan_npages: number of pages we want to scan before we return.
2392 static void ksm_do_scan(unsigned int scan_npages
)
2394 struct rmap_item
*rmap_item
;
2397 while (scan_npages
-- && likely(!freezing(current
))) {
2399 rmap_item
= scan_get_next_rmap_item(&page
);
2402 cmp_and_merge_page(page
, rmap_item
);
2407 static int ksmd_should_run(void)
2409 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
2412 static int ksm_scan_thread(void *nothing
)
2414 unsigned int sleep_ms
;
2417 set_user_nice(current
, 5);
2419 while (!kthread_should_stop()) {
2420 mutex_lock(&ksm_thread_mutex
);
2421 wait_while_offlining();
2422 if (ksmd_should_run())
2423 ksm_do_scan(ksm_thread_pages_to_scan
);
2424 mutex_unlock(&ksm_thread_mutex
);
2428 if (ksmd_should_run()) {
2429 sleep_ms
= READ_ONCE(ksm_thread_sleep_millisecs
);
2430 wait_event_interruptible_timeout(ksm_iter_wait
,
2431 sleep_ms
!= READ_ONCE(ksm_thread_sleep_millisecs
),
2432 msecs_to_jiffies(sleep_ms
));
2434 wait_event_freezable(ksm_thread_wait
,
2435 ksmd_should_run() || kthread_should_stop());
2441 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
2442 unsigned long end
, int advice
, unsigned long *vm_flags
)
2444 struct mm_struct
*mm
= vma
->vm_mm
;
2448 case MADV_MERGEABLE
:
2450 * Be somewhat over-protective for now!
2452 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
2453 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
2454 VM_HUGETLB
| VM_MIXEDMAP
))
2455 return 0; /* just ignore the advice */
2457 if (vma_is_dax(vma
))
2461 if (*vm_flags
& VM_SAO
)
2465 if (*vm_flags
& VM_SPARC_ADI
)
2469 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
2470 err
= __ksm_enter(mm
);
2475 *vm_flags
|= VM_MERGEABLE
;
2478 case MADV_UNMERGEABLE
:
2479 if (!(*vm_flags
& VM_MERGEABLE
))
2480 return 0; /* just ignore the advice */
2482 if (vma
->anon_vma
) {
2483 err
= unmerge_ksm_pages(vma
, start
, end
);
2488 *vm_flags
&= ~VM_MERGEABLE
;
2494 EXPORT_SYMBOL_GPL(ksm_madvise
);
2496 int __ksm_enter(struct mm_struct
*mm
)
2498 struct mm_slot
*mm_slot
;
2501 mm_slot
= alloc_mm_slot();
2505 /* Check ksm_run too? Would need tighter locking */
2506 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
2508 spin_lock(&ksm_mmlist_lock
);
2509 insert_to_mm_slots_hash(mm
, mm_slot
);
2511 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2512 * insert just behind the scanning cursor, to let the area settle
2513 * down a little; when fork is followed by immediate exec, we don't
2514 * want ksmd to waste time setting up and tearing down an rmap_list.
2516 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2517 * scanning cursor, otherwise KSM pages in newly forked mms will be
2518 * missed: then we might as well insert at the end of the list.
2520 if (ksm_run
& KSM_RUN_UNMERGE
)
2521 list_add_tail(&mm_slot
->mm_list
, &ksm_mm_head
.mm_list
);
2523 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
2524 spin_unlock(&ksm_mmlist_lock
);
2526 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2530 wake_up_interruptible(&ksm_thread_wait
);
2535 void __ksm_exit(struct mm_struct
*mm
)
2537 struct mm_slot
*mm_slot
;
2538 int easy_to_free
= 0;
2541 * This process is exiting: if it's straightforward (as is the
2542 * case when ksmd was never running), free mm_slot immediately.
2543 * But if it's at the cursor or has rmap_items linked to it, use
2544 * mmap_lock to synchronize with any break_cows before pagetables
2545 * are freed, and leave the mm_slot on the list for ksmd to free.
2546 * Beware: ksm may already have noticed it exiting and freed the slot.
2549 spin_lock(&ksm_mmlist_lock
);
2550 mm_slot
= get_mm_slot(mm
);
2551 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
2552 if (!mm_slot
->rmap_list
) {
2553 hash_del(&mm_slot
->link
);
2554 list_del(&mm_slot
->mm_list
);
2557 list_move(&mm_slot
->mm_list
,
2558 &ksm_scan
.mm_slot
->mm_list
);
2561 spin_unlock(&ksm_mmlist_lock
);
2564 free_mm_slot(mm_slot
);
2565 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2567 } else if (mm_slot
) {
2568 mmap_write_lock(mm
);
2569 mmap_write_unlock(mm
);
2573 struct page
*ksm_might_need_to_copy(struct page
*page
,
2574 struct vm_area_struct
*vma
, unsigned long address
)
2576 struct folio
*folio
= page_folio(page
);
2577 struct anon_vma
*anon_vma
= folio_anon_vma(folio
);
2578 struct page
*new_page
;
2580 if (PageKsm(page
)) {
2581 if (page_stable_node(page
) &&
2582 !(ksm_run
& KSM_RUN_UNMERGE
))
2583 return page
; /* no need to copy it */
2584 } else if (!anon_vma
) {
2585 return page
; /* no need to copy it */
2586 } else if (page
->index
== linear_page_index(vma
, address
) &&
2587 anon_vma
->root
== vma
->anon_vma
->root
) {
2588 return page
; /* still no need to copy it */
2590 if (!PageUptodate(page
))
2591 return page
; /* let do_swap_page report the error */
2593 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
2595 mem_cgroup_charge(page_folio(new_page
), vma
->vm_mm
, GFP_KERNEL
)) {
2600 copy_user_highpage(new_page
, page
, address
, vma
);
2602 SetPageDirty(new_page
);
2603 __SetPageUptodate(new_page
);
2604 __SetPageLocked(new_page
);
2606 count_vm_event(KSM_SWPIN_COPY
);
2613 void rmap_walk_ksm(struct folio
*folio
, struct rmap_walk_control
*rwc
)
2615 struct stable_node
*stable_node
;
2616 struct rmap_item
*rmap_item
;
2617 int search_new_forks
= 0;
2619 VM_BUG_ON_FOLIO(!folio_test_ksm(folio
), folio
);
2622 * Rely on the page lock to protect against concurrent modifications
2623 * to that page's node of the stable tree.
2625 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
2627 stable_node
= folio_stable_node(folio
);
2631 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
2632 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
2633 struct anon_vma_chain
*vmac
;
2634 struct vm_area_struct
*vma
;
2637 if (!anon_vma_trylock_read(anon_vma
)) {
2638 if (rwc
->try_lock
) {
2639 rwc
->contended
= true;
2642 anon_vma_lock_read(anon_vma
);
2644 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
2651 /* Ignore the stable/unstable/sqnr flags */
2652 addr
= rmap_item
->address
& PAGE_MASK
;
2654 if (addr
< vma
->vm_start
|| addr
>= vma
->vm_end
)
2657 * Initially we examine only the vma which covers this
2658 * rmap_item; but later, if there is still work to do,
2659 * we examine covering vmas in other mms: in case they
2660 * were forked from the original since ksmd passed.
2662 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
2665 if (rwc
->invalid_vma
&& rwc
->invalid_vma(vma
, rwc
->arg
))
2668 if (!rwc
->rmap_one(folio
, vma
, addr
, rwc
->arg
)) {
2669 anon_vma_unlock_read(anon_vma
);
2672 if (rwc
->done
&& rwc
->done(folio
)) {
2673 anon_vma_unlock_read(anon_vma
);
2677 anon_vma_unlock_read(anon_vma
);
2679 if (!search_new_forks
++)
2683 #ifdef CONFIG_MIGRATION
2684 void folio_migrate_ksm(struct folio
*newfolio
, struct folio
*folio
)
2686 struct stable_node
*stable_node
;
2688 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
2689 VM_BUG_ON_FOLIO(!folio_test_locked(newfolio
), newfolio
);
2690 VM_BUG_ON_FOLIO(newfolio
->mapping
!= folio
->mapping
, newfolio
);
2692 stable_node
= folio_stable_node(folio
);
2694 VM_BUG_ON_FOLIO(stable_node
->kpfn
!= folio_pfn(folio
), folio
);
2695 stable_node
->kpfn
= folio_pfn(newfolio
);
2697 * newfolio->mapping was set in advance; now we need smp_wmb()
2698 * to make sure that the new stable_node->kpfn is visible
2699 * to get_ksm_page() before it can see that folio->mapping
2700 * has gone stale (or that folio_test_swapcache has been cleared).
2703 set_page_stable_node(&folio
->page
, NULL
);
2706 #endif /* CONFIG_MIGRATION */
2708 #ifdef CONFIG_MEMORY_HOTREMOVE
2709 static void wait_while_offlining(void)
2711 while (ksm_run
& KSM_RUN_OFFLINE
) {
2712 mutex_unlock(&ksm_thread_mutex
);
2713 wait_on_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
),
2714 TASK_UNINTERRUPTIBLE
);
2715 mutex_lock(&ksm_thread_mutex
);
2719 static bool stable_node_dup_remove_range(struct stable_node
*stable_node
,
2720 unsigned long start_pfn
,
2721 unsigned long end_pfn
)
2723 if (stable_node
->kpfn
>= start_pfn
&&
2724 stable_node
->kpfn
< end_pfn
) {
2726 * Don't get_ksm_page, page has already gone:
2727 * which is why we keep kpfn instead of page*
2729 remove_node_from_stable_tree(stable_node
);
2735 static bool stable_node_chain_remove_range(struct stable_node
*stable_node
,
2736 unsigned long start_pfn
,
2737 unsigned long end_pfn
,
2738 struct rb_root
*root
)
2740 struct stable_node
*dup
;
2741 struct hlist_node
*hlist_safe
;
2743 if (!is_stable_node_chain(stable_node
)) {
2744 VM_BUG_ON(is_stable_node_dup(stable_node
));
2745 return stable_node_dup_remove_range(stable_node
, start_pfn
,
2749 hlist_for_each_entry_safe(dup
, hlist_safe
,
2750 &stable_node
->hlist
, hlist_dup
) {
2751 VM_BUG_ON(!is_stable_node_dup(dup
));
2752 stable_node_dup_remove_range(dup
, start_pfn
, end_pfn
);
2754 if (hlist_empty(&stable_node
->hlist
)) {
2755 free_stable_node_chain(stable_node
, root
);
2756 return true; /* notify caller that tree was rebalanced */
2761 static void ksm_check_stable_tree(unsigned long start_pfn
,
2762 unsigned long end_pfn
)
2764 struct stable_node
*stable_node
, *next
;
2765 struct rb_node
*node
;
2768 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
2769 node
= rb_first(root_stable_tree
+ nid
);
2771 stable_node
= rb_entry(node
, struct stable_node
, node
);
2772 if (stable_node_chain_remove_range(stable_node
,
2776 node
= rb_first(root_stable_tree
+ nid
);
2778 node
= rb_next(node
);
2782 list_for_each_entry_safe(stable_node
, next
, &migrate_nodes
, list
) {
2783 if (stable_node
->kpfn
>= start_pfn
&&
2784 stable_node
->kpfn
< end_pfn
)
2785 remove_node_from_stable_tree(stable_node
);
2790 static int ksm_memory_callback(struct notifier_block
*self
,
2791 unsigned long action
, void *arg
)
2793 struct memory_notify
*mn
= arg
;
2796 case MEM_GOING_OFFLINE
:
2798 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2799 * and remove_all_stable_nodes() while memory is going offline:
2800 * it is unsafe for them to touch the stable tree at this time.
2801 * But unmerge_ksm_pages(), rmap lookups and other entry points
2802 * which do not need the ksm_thread_mutex are all safe.
2804 mutex_lock(&ksm_thread_mutex
);
2805 ksm_run
|= KSM_RUN_OFFLINE
;
2806 mutex_unlock(&ksm_thread_mutex
);
2811 * Most of the work is done by page migration; but there might
2812 * be a few stable_nodes left over, still pointing to struct
2813 * pages which have been offlined: prune those from the tree,
2814 * otherwise get_ksm_page() might later try to access a
2815 * non-existent struct page.
2817 ksm_check_stable_tree(mn
->start_pfn
,
2818 mn
->start_pfn
+ mn
->nr_pages
);
2820 case MEM_CANCEL_OFFLINE
:
2821 mutex_lock(&ksm_thread_mutex
);
2822 ksm_run
&= ~KSM_RUN_OFFLINE
;
2823 mutex_unlock(&ksm_thread_mutex
);
2825 smp_mb(); /* wake_up_bit advises this */
2826 wake_up_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
));
2832 static void wait_while_offlining(void)
2835 #endif /* CONFIG_MEMORY_HOTREMOVE */
2839 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2842 #define KSM_ATTR_RO(_name) \
2843 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2844 #define KSM_ATTR(_name) \
2845 static struct kobj_attribute _name##_attr = __ATTR_RW(_name)
2847 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
2848 struct kobj_attribute
*attr
, char *buf
)
2850 return sysfs_emit(buf
, "%u\n", ksm_thread_sleep_millisecs
);
2853 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
2854 struct kobj_attribute
*attr
,
2855 const char *buf
, size_t count
)
2860 err
= kstrtouint(buf
, 10, &msecs
);
2864 ksm_thread_sleep_millisecs
= msecs
;
2865 wake_up_interruptible(&ksm_iter_wait
);
2869 KSM_ATTR(sleep_millisecs
);
2871 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
2872 struct kobj_attribute
*attr
, char *buf
)
2874 return sysfs_emit(buf
, "%u\n", ksm_thread_pages_to_scan
);
2877 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
2878 struct kobj_attribute
*attr
,
2879 const char *buf
, size_t count
)
2881 unsigned int nr_pages
;
2884 err
= kstrtouint(buf
, 10, &nr_pages
);
2888 ksm_thread_pages_to_scan
= nr_pages
;
2892 KSM_ATTR(pages_to_scan
);
2894 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2897 return sysfs_emit(buf
, "%lu\n", ksm_run
);
2900 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2901 const char *buf
, size_t count
)
2906 err
= kstrtouint(buf
, 10, &flags
);
2909 if (flags
> KSM_RUN_UNMERGE
)
2913 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2914 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2915 * breaking COW to free the pages_shared (but leaves mm_slots
2916 * on the list for when ksmd may be set running again).
2919 mutex_lock(&ksm_thread_mutex
);
2920 wait_while_offlining();
2921 if (ksm_run
!= flags
) {
2923 if (flags
& KSM_RUN_UNMERGE
) {
2924 set_current_oom_origin();
2925 err
= unmerge_and_remove_all_rmap_items();
2926 clear_current_oom_origin();
2928 ksm_run
= KSM_RUN_STOP
;
2933 mutex_unlock(&ksm_thread_mutex
);
2935 if (flags
& KSM_RUN_MERGE
)
2936 wake_up_interruptible(&ksm_thread_wait
);
2943 static ssize_t
merge_across_nodes_show(struct kobject
*kobj
,
2944 struct kobj_attribute
*attr
, char *buf
)
2946 return sysfs_emit(buf
, "%u\n", ksm_merge_across_nodes
);
2949 static ssize_t
merge_across_nodes_store(struct kobject
*kobj
,
2950 struct kobj_attribute
*attr
,
2951 const char *buf
, size_t count
)
2956 err
= kstrtoul(buf
, 10, &knob
);
2962 mutex_lock(&ksm_thread_mutex
);
2963 wait_while_offlining();
2964 if (ksm_merge_across_nodes
!= knob
) {
2965 if (ksm_pages_shared
|| remove_all_stable_nodes())
2967 else if (root_stable_tree
== one_stable_tree
) {
2968 struct rb_root
*buf
;
2970 * This is the first time that we switch away from the
2971 * default of merging across nodes: must now allocate
2972 * a buffer to hold as many roots as may be needed.
2973 * Allocate stable and unstable together:
2974 * MAXSMP NODES_SHIFT 10 will use 16kB.
2976 buf
= kcalloc(nr_node_ids
+ nr_node_ids
, sizeof(*buf
),
2978 /* Let us assume that RB_ROOT is NULL is zero */
2982 root_stable_tree
= buf
;
2983 root_unstable_tree
= buf
+ nr_node_ids
;
2984 /* Stable tree is empty but not the unstable */
2985 root_unstable_tree
[0] = one_unstable_tree
[0];
2989 ksm_merge_across_nodes
= knob
;
2990 ksm_nr_node_ids
= knob
? 1 : nr_node_ids
;
2993 mutex_unlock(&ksm_thread_mutex
);
2995 return err
? err
: count
;
2997 KSM_ATTR(merge_across_nodes
);
3000 static ssize_t
use_zero_pages_show(struct kobject
*kobj
,
3001 struct kobj_attribute
*attr
, char *buf
)
3003 return sysfs_emit(buf
, "%u\n", ksm_use_zero_pages
);
3005 static ssize_t
use_zero_pages_store(struct kobject
*kobj
,
3006 struct kobj_attribute
*attr
,
3007 const char *buf
, size_t count
)
3012 err
= kstrtobool(buf
, &value
);
3016 ksm_use_zero_pages
= value
;
3020 KSM_ATTR(use_zero_pages
);
3022 static ssize_t
max_page_sharing_show(struct kobject
*kobj
,
3023 struct kobj_attribute
*attr
, char *buf
)
3025 return sysfs_emit(buf
, "%u\n", ksm_max_page_sharing
);
3028 static ssize_t
max_page_sharing_store(struct kobject
*kobj
,
3029 struct kobj_attribute
*attr
,
3030 const char *buf
, size_t count
)
3035 err
= kstrtoint(buf
, 10, &knob
);
3039 * When a KSM page is created it is shared by 2 mappings. This
3040 * being a signed comparison, it implicitly verifies it's not
3046 if (READ_ONCE(ksm_max_page_sharing
) == knob
)
3049 mutex_lock(&ksm_thread_mutex
);
3050 wait_while_offlining();
3051 if (ksm_max_page_sharing
!= knob
) {
3052 if (ksm_pages_shared
|| remove_all_stable_nodes())
3055 ksm_max_page_sharing
= knob
;
3057 mutex_unlock(&ksm_thread_mutex
);
3059 return err
? err
: count
;
3061 KSM_ATTR(max_page_sharing
);
3063 static ssize_t
pages_shared_show(struct kobject
*kobj
,
3064 struct kobj_attribute
*attr
, char *buf
)
3066 return sysfs_emit(buf
, "%lu\n", ksm_pages_shared
);
3068 KSM_ATTR_RO(pages_shared
);
3070 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
3071 struct kobj_attribute
*attr
, char *buf
)
3073 return sysfs_emit(buf
, "%lu\n", ksm_pages_sharing
);
3075 KSM_ATTR_RO(pages_sharing
);
3077 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
3078 struct kobj_attribute
*attr
, char *buf
)
3080 return sysfs_emit(buf
, "%lu\n", ksm_pages_unshared
);
3082 KSM_ATTR_RO(pages_unshared
);
3084 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
3085 struct kobj_attribute
*attr
, char *buf
)
3087 long ksm_pages_volatile
;
3089 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
3090 - ksm_pages_sharing
- ksm_pages_unshared
;
3092 * It was not worth any locking to calculate that statistic,
3093 * but it might therefore sometimes be negative: conceal that.
3095 if (ksm_pages_volatile
< 0)
3096 ksm_pages_volatile
= 0;
3097 return sysfs_emit(buf
, "%ld\n", ksm_pages_volatile
);
3099 KSM_ATTR_RO(pages_volatile
);
3101 static ssize_t
stable_node_dups_show(struct kobject
*kobj
,
3102 struct kobj_attribute
*attr
, char *buf
)
3104 return sysfs_emit(buf
, "%lu\n", ksm_stable_node_dups
);
3106 KSM_ATTR_RO(stable_node_dups
);
3108 static ssize_t
stable_node_chains_show(struct kobject
*kobj
,
3109 struct kobj_attribute
*attr
, char *buf
)
3111 return sysfs_emit(buf
, "%lu\n", ksm_stable_node_chains
);
3113 KSM_ATTR_RO(stable_node_chains
);
3116 stable_node_chains_prune_millisecs_show(struct kobject
*kobj
,
3117 struct kobj_attribute
*attr
,
3120 return sysfs_emit(buf
, "%u\n", ksm_stable_node_chains_prune_millisecs
);
3124 stable_node_chains_prune_millisecs_store(struct kobject
*kobj
,
3125 struct kobj_attribute
*attr
,
3126 const char *buf
, size_t count
)
3131 err
= kstrtouint(buf
, 10, &msecs
);
3135 ksm_stable_node_chains_prune_millisecs
= msecs
;
3139 KSM_ATTR(stable_node_chains_prune_millisecs
);
3141 static ssize_t
full_scans_show(struct kobject
*kobj
,
3142 struct kobj_attribute
*attr
, char *buf
)
3144 return sysfs_emit(buf
, "%lu\n", ksm_scan
.seqnr
);
3146 KSM_ATTR_RO(full_scans
);
3148 static struct attribute
*ksm_attrs
[] = {
3149 &sleep_millisecs_attr
.attr
,
3150 &pages_to_scan_attr
.attr
,
3152 &pages_shared_attr
.attr
,
3153 &pages_sharing_attr
.attr
,
3154 &pages_unshared_attr
.attr
,
3155 &pages_volatile_attr
.attr
,
3156 &full_scans_attr
.attr
,
3158 &merge_across_nodes_attr
.attr
,
3160 &max_page_sharing_attr
.attr
,
3161 &stable_node_chains_attr
.attr
,
3162 &stable_node_dups_attr
.attr
,
3163 &stable_node_chains_prune_millisecs_attr
.attr
,
3164 &use_zero_pages_attr
.attr
,
3168 static const struct attribute_group ksm_attr_group
= {
3172 #endif /* CONFIG_SYSFS */
3174 static int __init
ksm_init(void)
3176 struct task_struct
*ksm_thread
;
3179 /* The correct value depends on page size and endianness */
3180 zero_checksum
= calc_checksum(ZERO_PAGE(0));
3181 /* Default to false for backwards compatibility */
3182 ksm_use_zero_pages
= false;
3184 err
= ksm_slab_init();
3188 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
3189 if (IS_ERR(ksm_thread
)) {
3190 pr_err("ksm: creating kthread failed\n");
3191 err
= PTR_ERR(ksm_thread
);
3196 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
3198 pr_err("ksm: register sysfs failed\n");
3199 kthread_stop(ksm_thread
);
3203 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
3205 #endif /* CONFIG_SYSFS */
3207 #ifdef CONFIG_MEMORY_HOTREMOVE
3208 /* There is no significance to this priority 100 */
3209 hotplug_memory_notifier(ksm_memory_callback
, 100);
3218 subsys_initcall(ksm_init
);