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1 | /* |
2 | * Memory merging support. |
3 | * |
4 | * This code enables dynamic sharing of identical pages found in different |
5 | * memory areas, even if they are not shared by fork() |
6 | * |
7 | * Copyright (C) 2008-2009 Red Hat, Inc. |
8 | * Authors: |
9 | * Izik Eidus |
10 | * Andrea Arcangeli |
11 | * Chris Wright |
12 | * Hugh Dickins |
13 | * |
14 | * This work is licensed under the terms of the GNU GPL, version 2. |
15 | */ |
16 | |
17 | #include <linux/errno.h> |
18 | #include <linux/mm.h> |
19 | #include <linux/fs.h> |
20 | #include <linux/mman.h> |
21 | #include <linux/sched.h> |
22 | #include <linux/rwsem.h> |
23 | #include <linux/pagemap.h> |
24 | #include <linux/rmap.h> |
25 | #include <linux/spinlock.h> |
26 | #include <linux/jhash.h> |
27 | #include <linux/delay.h> |
28 | #include <linux/kthread.h> |
29 | #include <linux/wait.h> |
30 | #include <linux/slab.h> |
31 | #include <linux/rbtree.h> |
32 | #include <linux/memory.h> |
33 | #include <linux/mmu_notifier.h> |
34 | #include <linux/swap.h> |
35 | #include <linux/ksm.h> |
36 | #include <linux/hash.h> |
37 | |
38 | #include <asm/tlbflush.h> |
39 | #include "internal.h" |
40 | |
41 | /* |
42 | * A few notes about the KSM scanning process, |
43 | * to make it easier to understand the data structures below: |
44 | * |
45 | * In order to reduce excessive scanning, KSM sorts the memory pages by their |
46 | * contents into a data structure that holds pointers to the pages' locations. |
47 | * |
48 | * Since the contents of the pages may change at any moment, KSM cannot just |
49 | * insert the pages into a normal sorted tree and expect it to find anything. |
50 | * Therefore KSM uses two data structures - the stable and the unstable tree. |
51 | * |
52 | * The stable tree holds pointers to all the merged pages (ksm pages), sorted |
53 | * by their contents. Because each such page is write-protected, searching on |
54 | * this tree is fully assured to be working (except when pages are unmapped), |
55 | * and therefore this tree is called the stable tree. |
56 | * |
57 | * In addition to the stable tree, KSM uses a second data structure called the |
58 | * unstable tree: this tree holds pointers to pages which have been found to |
59 | * be "unchanged for a period of time". The unstable tree sorts these pages |
60 | * by their contents, but since they are not write-protected, KSM cannot rely |
61 | * upon the unstable tree to work correctly - the unstable tree is liable to |
62 | * be corrupted as its contents are modified, and so it is called unstable. |
63 | * |
64 | * KSM solves this problem by several techniques: |
65 | * |
66 | * 1) The unstable tree is flushed every time KSM completes scanning all |
67 | * memory areas, and then the tree is rebuilt again from the beginning. |
68 | * 2) KSM will only insert into the unstable tree, pages whose hash value |
69 | * has not changed since the previous scan of all memory areas. |
70 | * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the |
71 | * colors of the nodes and not on their contents, assuring that even when |
72 | * the tree gets "corrupted" it won't get out of balance, so scanning time |
73 | * remains the same (also, searching and inserting nodes in an rbtree uses |
74 | * the same algorithm, so we have no overhead when we flush and rebuild). |
75 | * 4) KSM never flushes the stable tree, which means that even if it were to |
76 | * take 10 attempts to find a page in the unstable tree, once it is found, |
77 | * it is secured in the stable tree. (When we scan a new page, we first |
78 | * compare it against the stable tree, and then against the unstable tree.) |
79 | */ |
80 | |
81 | /** |
82 | * struct mm_slot - ksm information per mm that is being scanned |
83 | * @link: link to the mm_slots hash list |
84 | * @mm_list: link into the mm_slots list, rooted in ksm_mm_head |
85 | * @rmap_list: head for this mm_slot's singly-linked list of rmap_items |
86 | * @mm: the mm that this information is valid for |
87 | */ |
88 | struct mm_slot { |
89 | struct hlist_node link; |
90 | struct list_head mm_list; |
91 | struct rmap_item *rmap_list; |
92 | struct mm_struct *mm; |
93 | }; |
94 | |
95 | /** |
96 | * struct ksm_scan - cursor for scanning |
97 | * @mm_slot: the current mm_slot we are scanning |
98 | * @address: the next address inside that to be scanned |
99 | * @rmap_list: link to the next rmap to be scanned in the rmap_list |
100 | * @seqnr: count of completed full scans (needed when removing unstable node) |
101 | * |
102 | * There is only the one ksm_scan instance of this cursor structure. |
103 | */ |
104 | struct ksm_scan { |
105 | struct mm_slot *mm_slot; |
106 | unsigned long address; |
107 | struct rmap_item **rmap_list; |
108 | unsigned long seqnr; |
109 | }; |
110 | |
111 | /** |
112 | * struct stable_node - node of the stable rbtree |
113 | * @node: rb node of this ksm page in the stable tree |
114 | * @hlist: hlist head of rmap_items using this ksm page |
115 | * @kpfn: page frame number of this ksm page |
116 | */ |
117 | struct stable_node { |
118 | struct rb_node node; |
119 | struct hlist_head hlist; |
120 | unsigned long kpfn; |
121 | }; |
122 | |
123 | /** |
124 | * struct rmap_item - reverse mapping item for virtual addresses |
125 | * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list |
126 | * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree |
127 | * @mm: the memory structure this rmap_item is pointing into |
128 | * @address: the virtual address this rmap_item tracks (+ flags in low bits) |
129 | * @oldchecksum: previous checksum of the page at that virtual address |
130 | * @node: rb node of this rmap_item in the unstable tree |
131 | * @head: pointer to stable_node heading this list in the stable tree |
132 | * @hlist: link into hlist of rmap_items hanging off that stable_node |
133 | */ |
134 | struct rmap_item { |
135 | struct rmap_item *rmap_list; |
136 | struct anon_vma *anon_vma; /* when stable */ |
137 | struct mm_struct *mm; |
138 | unsigned long address; /* + low bits used for flags below */ |
139 | unsigned int oldchecksum; /* when unstable */ |
140 | union { |
141 | struct rb_node node; /* when node of unstable tree */ |
142 | struct { /* when listed from stable tree */ |
143 | struct stable_node *head; |
144 | struct hlist_node hlist; |
145 | }; |
146 | }; |
147 | }; |
148 | |
149 | #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ |
150 | #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ |
151 | #define STABLE_FLAG 0x200 /* is listed from the stable tree */ |
152 | |
153 | /* The stable and unstable tree heads */ |
154 | static struct rb_root root_stable_tree = RB_ROOT; |
155 | static struct rb_root root_unstable_tree = RB_ROOT; |
156 | |
157 | #define MM_SLOTS_HASH_SHIFT 10 |
158 | #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT) |
159 | static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS]; |
160 | |
161 | static struct mm_slot ksm_mm_head = { |
162 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), |
163 | }; |
164 | static struct ksm_scan ksm_scan = { |
165 | .mm_slot = &ksm_mm_head, |
166 | }; |
167 | |
168 | static struct kmem_cache *rmap_item_cache; |
169 | static struct kmem_cache *stable_node_cache; |
170 | static struct kmem_cache *mm_slot_cache; |
171 | |
172 | /* The number of nodes in the stable tree */ |
173 | static unsigned long ksm_pages_shared; |
174 | |
175 | /* The number of page slots additionally sharing those nodes */ |
176 | static unsigned long ksm_pages_sharing; |
177 | |
178 | /* The number of nodes in the unstable tree */ |
179 | static unsigned long ksm_pages_unshared; |
180 | |
181 | /* The number of rmap_items in use: to calculate pages_volatile */ |
182 | static unsigned long ksm_rmap_items; |
183 | |
184 | /* Number of pages ksmd should scan in one batch */ |
185 | static unsigned int ksm_thread_pages_to_scan = 100; |
186 | |
187 | /* Milliseconds ksmd should sleep between batches */ |
188 | static unsigned int ksm_thread_sleep_millisecs = 20; |
189 | |
190 | #define KSM_RUN_STOP 0 |
191 | #define KSM_RUN_MERGE 1 |
192 | #define KSM_RUN_UNMERGE 2 |
193 | static unsigned int ksm_run = KSM_RUN_STOP; |
194 | |
195 | static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); |
196 | static DEFINE_MUTEX(ksm_thread_mutex); |
197 | static DEFINE_SPINLOCK(ksm_mmlist_lock); |
198 | |
199 | #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ |
200 | sizeof(struct __struct), __alignof__(struct __struct),\ |
201 | (__flags), NULL) |
202 | |
203 | static int __init ksm_slab_init(void) |
204 | { |
205 | rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); |
206 | if (!rmap_item_cache) |
207 | goto out; |
208 | |
209 | stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); |
210 | if (!stable_node_cache) |
211 | goto out_free1; |
212 | |
213 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); |
214 | if (!mm_slot_cache) |
215 | goto out_free2; |
216 | |
217 | return 0; |
218 | |
219 | out_free2: |
220 | kmem_cache_destroy(stable_node_cache); |
221 | out_free1: |
222 | kmem_cache_destroy(rmap_item_cache); |
223 | out: |
224 | return -ENOMEM; |
225 | } |
226 | |
227 | static void __init ksm_slab_free(void) |
228 | { |
229 | kmem_cache_destroy(mm_slot_cache); |
230 | kmem_cache_destroy(stable_node_cache); |
231 | kmem_cache_destroy(rmap_item_cache); |
232 | mm_slot_cache = NULL; |
233 | } |
234 | |
235 | static inline struct rmap_item *alloc_rmap_item(void) |
236 | { |
237 | struct rmap_item *rmap_item; |
238 | |
239 | rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); |
240 | if (rmap_item) |
241 | ksm_rmap_items++; |
242 | return rmap_item; |
243 | } |
244 | |
245 | static inline void free_rmap_item(struct rmap_item *rmap_item) |
246 | { |
247 | ksm_rmap_items--; |
248 | rmap_item->mm = NULL; /* debug safety */ |
249 | kmem_cache_free(rmap_item_cache, rmap_item); |
250 | } |
251 | |
252 | static inline struct stable_node *alloc_stable_node(void) |
253 | { |
254 | return kmem_cache_alloc(stable_node_cache, GFP_KERNEL); |
255 | } |
256 | |
257 | static inline void free_stable_node(struct stable_node *stable_node) |
258 | { |
259 | kmem_cache_free(stable_node_cache, stable_node); |
260 | } |
261 | |
262 | static inline struct mm_slot *alloc_mm_slot(void) |
263 | { |
264 | if (!mm_slot_cache) /* initialization failed */ |
265 | return NULL; |
266 | return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); |
267 | } |
268 | |
269 | static inline void free_mm_slot(struct mm_slot *mm_slot) |
270 | { |
271 | kmem_cache_free(mm_slot_cache, mm_slot); |
272 | } |
273 | |
274 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) |
275 | { |
276 | struct mm_slot *mm_slot; |
277 | struct hlist_head *bucket; |
278 | struct hlist_node *node; |
279 | |
280 | bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)]; |
281 | hlist_for_each_entry(mm_slot, node, bucket, link) { |
282 | if (mm == mm_slot->mm) |
283 | return mm_slot; |
284 | } |
285 | return NULL; |
286 | } |
287 | |
288 | static void insert_to_mm_slots_hash(struct mm_struct *mm, |
289 | struct mm_slot *mm_slot) |
290 | { |
291 | struct hlist_head *bucket; |
292 | |
293 | bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)]; |
294 | mm_slot->mm = mm; |
295 | hlist_add_head(&mm_slot->link, bucket); |
296 | } |
297 | |
298 | static inline int in_stable_tree(struct rmap_item *rmap_item) |
299 | { |
300 | return rmap_item->address & STABLE_FLAG; |
301 | } |
302 | |
303 | static void hold_anon_vma(struct rmap_item *rmap_item, |
304 | struct anon_vma *anon_vma) |
305 | { |
306 | rmap_item->anon_vma = anon_vma; |
307 | get_anon_vma(anon_vma); |
308 | } |
309 | |
310 | static void ksm_drop_anon_vma(struct rmap_item *rmap_item) |
311 | { |
312 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
313 | |
314 | drop_anon_vma(anon_vma); |
315 | } |
316 | |
317 | /* |
318 | * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's |
319 | * page tables after it has passed through ksm_exit() - which, if necessary, |
320 | * takes mmap_sem briefly to serialize against them. ksm_exit() does not set |
321 | * a special flag: they can just back out as soon as mm_users goes to zero. |
322 | * ksm_test_exit() is used throughout to make this test for exit: in some |
323 | * places for correctness, in some places just to avoid unnecessary work. |
324 | */ |
325 | static inline bool ksm_test_exit(struct mm_struct *mm) |
326 | { |
327 | return atomic_read(&mm->mm_users) == 0; |
328 | } |
329 | |
330 | /* |
331 | * We use break_ksm to break COW on a ksm page: it's a stripped down |
332 | * |
333 | * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) |
334 | * put_page(page); |
335 | * |
336 | * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, |
337 | * in case the application has unmapped and remapped mm,addr meanwhile. |
338 | * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP |
339 | * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. |
340 | */ |
341 | static int break_ksm(struct vm_area_struct *vma, unsigned long addr) |
342 | { |
343 | struct page *page; |
344 | int ret = 0; |
345 | |
346 | do { |
347 | cond_resched(); |
348 | page = follow_page(vma, addr, FOLL_GET); |
349 | if (IS_ERR_OR_NULL(page)) |
350 | break; |
351 | if (PageKsm(page)) |
352 | ret = handle_mm_fault(vma->vm_mm, vma, addr, |
353 | FAULT_FLAG_WRITE); |
354 | else |
355 | ret = VM_FAULT_WRITE; |
356 | put_page(page); |
357 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM))); |
358 | /* |
359 | * We must loop because handle_mm_fault() may back out if there's |
360 | * any difficulty e.g. if pte accessed bit gets updated concurrently. |
361 | * |
362 | * VM_FAULT_WRITE is what we have been hoping for: it indicates that |
363 | * COW has been broken, even if the vma does not permit VM_WRITE; |
364 | * but note that a concurrent fault might break PageKsm for us. |
365 | * |
366 | * VM_FAULT_SIGBUS could occur if we race with truncation of the |
367 | * backing file, which also invalidates anonymous pages: that's |
368 | * okay, that truncation will have unmapped the PageKsm for us. |
369 | * |
370 | * VM_FAULT_OOM: at the time of writing (late July 2009), setting |
371 | * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the |
372 | * current task has TIF_MEMDIE set, and will be OOM killed on return |
373 | * to user; and ksmd, having no mm, would never be chosen for that. |
374 | * |
375 | * But if the mm is in a limited mem_cgroup, then the fault may fail |
376 | * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and |
377 | * even ksmd can fail in this way - though it's usually breaking ksm |
378 | * just to undo a merge it made a moment before, so unlikely to oom. |
379 | * |
380 | * That's a pity: we might therefore have more kernel pages allocated |
381 | * than we're counting as nodes in the stable tree; but ksm_do_scan |
382 | * will retry to break_cow on each pass, so should recover the page |
383 | * in due course. The important thing is to not let VM_MERGEABLE |
384 | * be cleared while any such pages might remain in the area. |
385 | */ |
386 | return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; |
387 | } |
388 | |
389 | static void break_cow(struct rmap_item *rmap_item) |
390 | { |
391 | struct mm_struct *mm = rmap_item->mm; |
392 | unsigned long addr = rmap_item->address; |
393 | struct vm_area_struct *vma; |
394 | |
395 | /* |
396 | * It is not an accident that whenever we want to break COW |
397 | * to undo, we also need to drop a reference to the anon_vma. |
398 | */ |
399 | ksm_drop_anon_vma(rmap_item); |
400 | |
401 | down_read(&mm->mmap_sem); |
402 | if (ksm_test_exit(mm)) |
403 | goto out; |
404 | vma = find_vma(mm, addr); |
405 | if (!vma || vma->vm_start > addr) |
406 | goto out; |
407 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
408 | goto out; |
409 | break_ksm(vma, addr); |
410 | out: |
411 | up_read(&mm->mmap_sem); |
412 | } |
413 | |
414 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) |
415 | { |
416 | struct mm_struct *mm = rmap_item->mm; |
417 | unsigned long addr = rmap_item->address; |
418 | struct vm_area_struct *vma; |
419 | struct page *page; |
420 | |
421 | down_read(&mm->mmap_sem); |
422 | if (ksm_test_exit(mm)) |
423 | goto out; |
424 | vma = find_vma(mm, addr); |
425 | if (!vma || vma->vm_start > addr) |
426 | goto out; |
427 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
428 | goto out; |
429 | |
430 | page = follow_page(vma, addr, FOLL_GET); |
431 | if (IS_ERR_OR_NULL(page)) |
432 | goto out; |
433 | if (PageAnon(page)) { |
434 | flush_anon_page(vma, page, addr); |
435 | flush_dcache_page(page); |
436 | } else { |
437 | put_page(page); |
438 | out: page = NULL; |
439 | } |
440 | up_read(&mm->mmap_sem); |
441 | return page; |
442 | } |
443 | |
444 | static void remove_node_from_stable_tree(struct stable_node *stable_node) |
445 | { |
446 | struct rmap_item *rmap_item; |
447 | struct hlist_node *hlist; |
448 | |
449 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
450 | if (rmap_item->hlist.next) |
451 | ksm_pages_sharing--; |
452 | else |
453 | ksm_pages_shared--; |
454 | ksm_drop_anon_vma(rmap_item); |
455 | rmap_item->address &= PAGE_MASK; |
456 | cond_resched(); |
457 | } |
458 | |
459 | rb_erase(&stable_node->node, &root_stable_tree); |
460 | free_stable_node(stable_node); |
461 | } |
462 | |
463 | /* |
464 | * get_ksm_page: checks if the page indicated by the stable node |
465 | * is still its ksm page, despite having held no reference to it. |
466 | * In which case we can trust the content of the page, and it |
467 | * returns the gotten page; but if the page has now been zapped, |
468 | * remove the stale node from the stable tree and return NULL. |
469 | * |
470 | * You would expect the stable_node to hold a reference to the ksm page. |
471 | * But if it increments the page's count, swapping out has to wait for |
472 | * ksmd to come around again before it can free the page, which may take |
473 | * seconds or even minutes: much too unresponsive. So instead we use a |
474 | * "keyhole reference": access to the ksm page from the stable node peeps |
475 | * out through its keyhole to see if that page still holds the right key, |
476 | * pointing back to this stable node. This relies on freeing a PageAnon |
477 | * page to reset its page->mapping to NULL, and relies on no other use of |
478 | * a page to put something that might look like our key in page->mapping. |
479 | * |
480 | * include/linux/pagemap.h page_cache_get_speculative() is a good reference, |
481 | * but this is different - made simpler by ksm_thread_mutex being held, but |
482 | * interesting for assuming that no other use of the struct page could ever |
483 | * put our expected_mapping into page->mapping (or a field of the union which |
484 | * coincides with page->mapping). The RCU calls are not for KSM at all, but |
485 | * to keep the page_count protocol described with page_cache_get_speculative. |
486 | * |
487 | * Note: it is possible that get_ksm_page() will return NULL one moment, |
488 | * then page the next, if the page is in between page_freeze_refs() and |
489 | * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page |
490 | * is on its way to being freed; but it is an anomaly to bear in mind. |
491 | */ |
492 | static struct page *get_ksm_page(struct stable_node *stable_node) |
493 | { |
494 | struct page *page; |
495 | void *expected_mapping; |
496 | |
497 | page = pfn_to_page(stable_node->kpfn); |
498 | expected_mapping = (void *)stable_node + |
499 | (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM); |
500 | rcu_read_lock(); |
501 | if (page->mapping != expected_mapping) |
502 | goto stale; |
503 | if (!get_page_unless_zero(page)) |
504 | goto stale; |
505 | if (page->mapping != expected_mapping) { |
506 | put_page(page); |
507 | goto stale; |
508 | } |
509 | rcu_read_unlock(); |
510 | return page; |
511 | stale: |
512 | rcu_read_unlock(); |
513 | remove_node_from_stable_tree(stable_node); |
514 | return NULL; |
515 | } |
516 | |
517 | /* |
518 | * Removing rmap_item from stable or unstable tree. |
519 | * This function will clean the information from the stable/unstable tree. |
520 | */ |
521 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) |
522 | { |
523 | if (rmap_item->address & STABLE_FLAG) { |
524 | struct stable_node *stable_node; |
525 | struct page *page; |
526 | |
527 | stable_node = rmap_item->head; |
528 | page = get_ksm_page(stable_node); |
529 | if (!page) |
530 | goto out; |
531 | |
532 | lock_page(page); |
533 | hlist_del(&rmap_item->hlist); |
534 | unlock_page(page); |
535 | put_page(page); |
536 | |
537 | if (stable_node->hlist.first) |
538 | ksm_pages_sharing--; |
539 | else |
540 | ksm_pages_shared--; |
541 | |
542 | ksm_drop_anon_vma(rmap_item); |
543 | rmap_item->address &= PAGE_MASK; |
544 | |
545 | } else if (rmap_item->address & UNSTABLE_FLAG) { |
546 | unsigned char age; |
547 | /* |
548 | * Usually ksmd can and must skip the rb_erase, because |
549 | * root_unstable_tree was already reset to RB_ROOT. |
550 | * But be careful when an mm is exiting: do the rb_erase |
551 | * if this rmap_item was inserted by this scan, rather |
552 | * than left over from before. |
553 | */ |
554 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); |
555 | BUG_ON(age > 1); |
556 | if (!age) |
557 | rb_erase(&rmap_item->node, &root_unstable_tree); |
558 | |
559 | ksm_pages_unshared--; |
560 | rmap_item->address &= PAGE_MASK; |
561 | } |
562 | out: |
563 | cond_resched(); /* we're called from many long loops */ |
564 | } |
565 | |
566 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, |
567 | struct rmap_item **rmap_list) |
568 | { |
569 | while (*rmap_list) { |
570 | struct rmap_item *rmap_item = *rmap_list; |
571 | *rmap_list = rmap_item->rmap_list; |
572 | remove_rmap_item_from_tree(rmap_item); |
573 | free_rmap_item(rmap_item); |
574 | } |
575 | } |
576 | |
577 | /* |
578 | * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather |
579 | * than check every pte of a given vma, the locking doesn't quite work for |
580 | * that - an rmap_item is assigned to the stable tree after inserting ksm |
581 | * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing |
582 | * rmap_items from parent to child at fork time (so as not to waste time |
583 | * if exit comes before the next scan reaches it). |
584 | * |
585 | * Similarly, although we'd like to remove rmap_items (so updating counts |
586 | * and freeing memory) when unmerging an area, it's easier to leave that |
587 | * to the next pass of ksmd - consider, for example, how ksmd might be |
588 | * in cmp_and_merge_page on one of the rmap_items we would be removing. |
589 | */ |
590 | static int unmerge_ksm_pages(struct vm_area_struct *vma, |
591 | unsigned long start, unsigned long end) |
592 | { |
593 | unsigned long addr; |
594 | int err = 0; |
595 | |
596 | for (addr = start; addr < end && !err; addr += PAGE_SIZE) { |
597 | if (ksm_test_exit(vma->vm_mm)) |
598 | break; |
599 | if (signal_pending(current)) |
600 | err = -ERESTARTSYS; |
601 | else |
602 | err = break_ksm(vma, addr); |
603 | } |
604 | return err; |
605 | } |
606 | |
607 | #ifdef CONFIG_SYSFS |
608 | /* |
609 | * Only called through the sysfs control interface: |
610 | */ |
611 | static int unmerge_and_remove_all_rmap_items(void) |
612 | { |
613 | struct mm_slot *mm_slot; |
614 | struct mm_struct *mm; |
615 | struct vm_area_struct *vma; |
616 | int err = 0; |
617 | |
618 | spin_lock(&ksm_mmlist_lock); |
619 | ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, |
620 | struct mm_slot, mm_list); |
621 | spin_unlock(&ksm_mmlist_lock); |
622 | |
623 | for (mm_slot = ksm_scan.mm_slot; |
624 | mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { |
625 | mm = mm_slot->mm; |
626 | down_read(&mm->mmap_sem); |
627 | for (vma = mm->mmap; vma; vma = vma->vm_next) { |
628 | if (ksm_test_exit(mm)) |
629 | break; |
630 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
631 | continue; |
632 | err = unmerge_ksm_pages(vma, |
633 | vma->vm_start, vma->vm_end); |
634 | if (err) |
635 | goto error; |
636 | } |
637 | |
638 | remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); |
639 | |
640 | spin_lock(&ksm_mmlist_lock); |
641 | ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, |
642 | struct mm_slot, mm_list); |
643 | if (ksm_test_exit(mm)) { |
644 | hlist_del(&mm_slot->link); |
645 | list_del(&mm_slot->mm_list); |
646 | spin_unlock(&ksm_mmlist_lock); |
647 | |
648 | free_mm_slot(mm_slot); |
649 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
650 | up_read(&mm->mmap_sem); |
651 | mmdrop(mm); |
652 | } else { |
653 | spin_unlock(&ksm_mmlist_lock); |
654 | up_read(&mm->mmap_sem); |
655 | } |
656 | } |
657 | |
658 | ksm_scan.seqnr = 0; |
659 | return 0; |
660 | |
661 | error: |
662 | up_read(&mm->mmap_sem); |
663 | spin_lock(&ksm_mmlist_lock); |
664 | ksm_scan.mm_slot = &ksm_mm_head; |
665 | spin_unlock(&ksm_mmlist_lock); |
666 | return err; |
667 | } |
668 | #endif /* CONFIG_SYSFS */ |
669 | |
670 | static u32 calc_checksum(struct page *page) |
671 | { |
672 | u32 checksum; |
673 | void *addr = kmap_atomic(page, KM_USER0); |
674 | checksum = jhash2(addr, PAGE_SIZE / 4, 17); |
675 | kunmap_atomic(addr, KM_USER0); |
676 | return checksum; |
677 | } |
678 | |
679 | static int memcmp_pages(struct page *page1, struct page *page2) |
680 | { |
681 | char *addr1, *addr2; |
682 | int ret; |
683 | |
684 | addr1 = kmap_atomic(page1, KM_USER0); |
685 | addr2 = kmap_atomic(page2, KM_USER1); |
686 | ret = memcmp(addr1, addr2, PAGE_SIZE); |
687 | kunmap_atomic(addr2, KM_USER1); |
688 | kunmap_atomic(addr1, KM_USER0); |
689 | return ret; |
690 | } |
691 | |
692 | static inline int pages_identical(struct page *page1, struct page *page2) |
693 | { |
694 | return !memcmp_pages(page1, page2); |
695 | } |
696 | |
697 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, |
698 | pte_t *orig_pte) |
699 | { |
700 | struct mm_struct *mm = vma->vm_mm; |
701 | unsigned long addr; |
702 | pte_t *ptep; |
703 | spinlock_t *ptl; |
704 | int swapped; |
705 | int err = -EFAULT; |
706 | |
707 | addr = page_address_in_vma(page, vma); |
708 | if (addr == -EFAULT) |
709 | goto out; |
710 | |
711 | ptep = page_check_address(page, mm, addr, &ptl, 0); |
712 | if (!ptep) |
713 | goto out; |
714 | |
715 | if (pte_write(*ptep) || pte_dirty(*ptep)) { |
716 | pte_t entry; |
717 | |
718 | swapped = PageSwapCache(page); |
719 | flush_cache_page(vma, addr, page_to_pfn(page)); |
720 | /* |
721 | * Ok this is tricky, when get_user_pages_fast() run it doesnt |
722 | * take any lock, therefore the check that we are going to make |
723 | * with the pagecount against the mapcount is racey and |
724 | * O_DIRECT can happen right after the check. |
725 | * So we clear the pte and flush the tlb before the check |
726 | * this assure us that no O_DIRECT can happen after the check |
727 | * or in the middle of the check. |
728 | */ |
729 | entry = ptep_clear_flush(vma, addr, ptep); |
730 | /* |
731 | * Check that no O_DIRECT or similar I/O is in progress on the |
732 | * page |
733 | */ |
734 | if (page_mapcount(page) + 1 + swapped != page_count(page)) { |
735 | set_pte_at(mm, addr, ptep, entry); |
736 | goto out_unlock; |
737 | } |
738 | if (pte_dirty(entry)) |
739 | set_page_dirty(page); |
740 | entry = pte_mkclean(pte_wrprotect(entry)); |
741 | set_pte_at_notify(mm, addr, ptep, entry); |
742 | } |
743 | *orig_pte = *ptep; |
744 | err = 0; |
745 | |
746 | out_unlock: |
747 | pte_unmap_unlock(ptep, ptl); |
748 | out: |
749 | return err; |
750 | } |
751 | |
752 | /** |
753 | * replace_page - replace page in vma by new ksm page |
754 | * @vma: vma that holds the pte pointing to page |
755 | * @page: the page we are replacing by kpage |
756 | * @kpage: the ksm page we replace page by |
757 | * @orig_pte: the original value of the pte |
758 | * |
759 | * Returns 0 on success, -EFAULT on failure. |
760 | */ |
761 | static int replace_page(struct vm_area_struct *vma, struct page *page, |
762 | struct page *kpage, pte_t orig_pte) |
763 | { |
764 | struct mm_struct *mm = vma->vm_mm; |
765 | pgd_t *pgd; |
766 | pud_t *pud; |
767 | pmd_t *pmd; |
768 | pte_t *ptep; |
769 | spinlock_t *ptl; |
770 | unsigned long addr; |
771 | int err = -EFAULT; |
772 | |
773 | addr = page_address_in_vma(page, vma); |
774 | if (addr == -EFAULT) |
775 | goto out; |
776 | |
777 | pgd = pgd_offset(mm, addr); |
778 | if (!pgd_present(*pgd)) |
779 | goto out; |
780 | |
781 | pud = pud_offset(pgd, addr); |
782 | if (!pud_present(*pud)) |
783 | goto out; |
784 | |
785 | pmd = pmd_offset(pud, addr); |
786 | if (!pmd_present(*pmd)) |
787 | goto out; |
788 | |
789 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); |
790 | if (!pte_same(*ptep, orig_pte)) { |
791 | pte_unmap_unlock(ptep, ptl); |
792 | goto out; |
793 | } |
794 | |
795 | get_page(kpage); |
796 | page_add_anon_rmap(kpage, vma, addr); |
797 | |
798 | flush_cache_page(vma, addr, pte_pfn(*ptep)); |
799 | ptep_clear_flush(vma, addr, ptep); |
800 | set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot)); |
801 | |
802 | page_remove_rmap(page); |
803 | put_page(page); |
804 | |
805 | pte_unmap_unlock(ptep, ptl); |
806 | err = 0; |
807 | out: |
808 | return err; |
809 | } |
810 | |
811 | /* |
812 | * try_to_merge_one_page - take two pages and merge them into one |
813 | * @vma: the vma that holds the pte pointing to page |
814 | * @page: the PageAnon page that we want to replace with kpage |
815 | * @kpage: the PageKsm page that we want to map instead of page, |
816 | * or NULL the first time when we want to use page as kpage. |
817 | * |
818 | * This function returns 0 if the pages were merged, -EFAULT otherwise. |
819 | */ |
820 | static int try_to_merge_one_page(struct vm_area_struct *vma, |
821 | struct page *page, struct page *kpage) |
822 | { |
823 | pte_t orig_pte = __pte(0); |
824 | int err = -EFAULT; |
825 | |
826 | if (page == kpage) /* ksm page forked */ |
827 | return 0; |
828 | |
829 | if (!(vma->vm_flags & VM_MERGEABLE)) |
830 | goto out; |
831 | if (!PageAnon(page)) |
832 | goto out; |
833 | |
834 | /* |
835 | * We need the page lock to read a stable PageSwapCache in |
836 | * write_protect_page(). We use trylock_page() instead of |
837 | * lock_page() because we don't want to wait here - we |
838 | * prefer to continue scanning and merging different pages, |
839 | * then come back to this page when it is unlocked. |
840 | */ |
841 | if (!trylock_page(page)) |
842 | goto out; |
843 | /* |
844 | * If this anonymous page is mapped only here, its pte may need |
845 | * to be write-protected. If it's mapped elsewhere, all of its |
846 | * ptes are necessarily already write-protected. But in either |
847 | * case, we need to lock and check page_count is not raised. |
848 | */ |
849 | if (write_protect_page(vma, page, &orig_pte) == 0) { |
850 | if (!kpage) { |
851 | /* |
852 | * While we hold page lock, upgrade page from |
853 | * PageAnon+anon_vma to PageKsm+NULL stable_node: |
854 | * stable_tree_insert() will update stable_node. |
855 | */ |
856 | set_page_stable_node(page, NULL); |
857 | mark_page_accessed(page); |
858 | err = 0; |
859 | } else if (pages_identical(page, kpage)) |
860 | err = replace_page(vma, page, kpage, orig_pte); |
861 | } |
862 | |
863 | if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { |
864 | munlock_vma_page(page); |
865 | if (!PageMlocked(kpage)) { |
866 | unlock_page(page); |
867 | lock_page(kpage); |
868 | mlock_vma_page(kpage); |
869 | page = kpage; /* for final unlock */ |
870 | } |
871 | } |
872 | |
873 | unlock_page(page); |
874 | out: |
875 | return err; |
876 | } |
877 | |
878 | /* |
879 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, |
880 | * but no new kernel page is allocated: kpage must already be a ksm page. |
881 | * |
882 | * This function returns 0 if the pages were merged, -EFAULT otherwise. |
883 | */ |
884 | static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, |
885 | struct page *page, struct page *kpage) |
886 | { |
887 | struct mm_struct *mm = rmap_item->mm; |
888 | struct vm_area_struct *vma; |
889 | int err = -EFAULT; |
890 | |
891 | down_read(&mm->mmap_sem); |
892 | if (ksm_test_exit(mm)) |
893 | goto out; |
894 | vma = find_vma(mm, rmap_item->address); |
895 | if (!vma || vma->vm_start > rmap_item->address) |
896 | goto out; |
897 | |
898 | err = try_to_merge_one_page(vma, page, kpage); |
899 | if (err) |
900 | goto out; |
901 | |
902 | /* Must get reference to anon_vma while still holding mmap_sem */ |
903 | hold_anon_vma(rmap_item, vma->anon_vma); |
904 | out: |
905 | up_read(&mm->mmap_sem); |
906 | return err; |
907 | } |
908 | |
909 | /* |
910 | * try_to_merge_two_pages - take two identical pages and prepare them |
911 | * to be merged into one page. |
912 | * |
913 | * This function returns the kpage if we successfully merged two identical |
914 | * pages into one ksm page, NULL otherwise. |
915 | * |
916 | * Note that this function upgrades page to ksm page: if one of the pages |
917 | * is already a ksm page, try_to_merge_with_ksm_page should be used. |
918 | */ |
919 | static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, |
920 | struct page *page, |
921 | struct rmap_item *tree_rmap_item, |
922 | struct page *tree_page) |
923 | { |
924 | int err; |
925 | |
926 | err = try_to_merge_with_ksm_page(rmap_item, page, NULL); |
927 | if (!err) { |
928 | err = try_to_merge_with_ksm_page(tree_rmap_item, |
929 | tree_page, page); |
930 | /* |
931 | * If that fails, we have a ksm page with only one pte |
932 | * pointing to it: so break it. |
933 | */ |
934 | if (err) |
935 | break_cow(rmap_item); |
936 | } |
937 | return err ? NULL : page; |
938 | } |
939 | |
940 | /* |
941 | * stable_tree_search - search for page inside the stable tree |
942 | * |
943 | * This function checks if there is a page inside the stable tree |
944 | * with identical content to the page that we are scanning right now. |
945 | * |
946 | * This function returns the stable tree node of identical content if found, |
947 | * NULL otherwise. |
948 | */ |
949 | static struct page *stable_tree_search(struct page *page) |
950 | { |
951 | struct rb_node *node = root_stable_tree.rb_node; |
952 | struct stable_node *stable_node; |
953 | |
954 | stable_node = page_stable_node(page); |
955 | if (stable_node) { /* ksm page forked */ |
956 | get_page(page); |
957 | return page; |
958 | } |
959 | |
960 | while (node) { |
961 | struct page *tree_page; |
962 | int ret; |
963 | |
964 | cond_resched(); |
965 | stable_node = rb_entry(node, struct stable_node, node); |
966 | tree_page = get_ksm_page(stable_node); |
967 | if (!tree_page) |
968 | return NULL; |
969 | |
970 | ret = memcmp_pages(page, tree_page); |
971 | |
972 | if (ret < 0) { |
973 | put_page(tree_page); |
974 | node = node->rb_left; |
975 | } else if (ret > 0) { |
976 | put_page(tree_page); |
977 | node = node->rb_right; |
978 | } else |
979 | return tree_page; |
980 | } |
981 | |
982 | return NULL; |
983 | } |
984 | |
985 | /* |
986 | * stable_tree_insert - insert rmap_item pointing to new ksm page |
987 | * into the stable tree. |
988 | * |
989 | * This function returns the stable tree node just allocated on success, |
990 | * NULL otherwise. |
991 | */ |
992 | static struct stable_node *stable_tree_insert(struct page *kpage) |
993 | { |
994 | struct rb_node **new = &root_stable_tree.rb_node; |
995 | struct rb_node *parent = NULL; |
996 | struct stable_node *stable_node; |
997 | |
998 | while (*new) { |
999 | struct page *tree_page; |
1000 | int ret; |
1001 | |
1002 | cond_resched(); |
1003 | stable_node = rb_entry(*new, struct stable_node, node); |
1004 | tree_page = get_ksm_page(stable_node); |
1005 | if (!tree_page) |
1006 | return NULL; |
1007 | |
1008 | ret = memcmp_pages(kpage, tree_page); |
1009 | put_page(tree_page); |
1010 | |
1011 | parent = *new; |
1012 | if (ret < 0) |
1013 | new = &parent->rb_left; |
1014 | else if (ret > 0) |
1015 | new = &parent->rb_right; |
1016 | else { |
1017 | /* |
1018 | * It is not a bug that stable_tree_search() didn't |
1019 | * find this node: because at that time our page was |
1020 | * not yet write-protected, so may have changed since. |
1021 | */ |
1022 | return NULL; |
1023 | } |
1024 | } |
1025 | |
1026 | stable_node = alloc_stable_node(); |
1027 | if (!stable_node) |
1028 | return NULL; |
1029 | |
1030 | rb_link_node(&stable_node->node, parent, new); |
1031 | rb_insert_color(&stable_node->node, &root_stable_tree); |
1032 | |
1033 | INIT_HLIST_HEAD(&stable_node->hlist); |
1034 | |
1035 | stable_node->kpfn = page_to_pfn(kpage); |
1036 | set_page_stable_node(kpage, stable_node); |
1037 | |
1038 | return stable_node; |
1039 | } |
1040 | |
1041 | /* |
1042 | * unstable_tree_search_insert - search for identical page, |
1043 | * else insert rmap_item into the unstable tree. |
1044 | * |
1045 | * This function searches for a page in the unstable tree identical to the |
1046 | * page currently being scanned; and if no identical page is found in the |
1047 | * tree, we insert rmap_item as a new object into the unstable tree. |
1048 | * |
1049 | * This function returns pointer to rmap_item found to be identical |
1050 | * to the currently scanned page, NULL otherwise. |
1051 | * |
1052 | * This function does both searching and inserting, because they share |
1053 | * the same walking algorithm in an rbtree. |
1054 | */ |
1055 | static |
1056 | struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, |
1057 | struct page *page, |
1058 | struct page **tree_pagep) |
1059 | |
1060 | { |
1061 | struct rb_node **new = &root_unstable_tree.rb_node; |
1062 | struct rb_node *parent = NULL; |
1063 | |
1064 | while (*new) { |
1065 | struct rmap_item *tree_rmap_item; |
1066 | struct page *tree_page; |
1067 | int ret; |
1068 | |
1069 | cond_resched(); |
1070 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
1071 | tree_page = get_mergeable_page(tree_rmap_item); |
1072 | if (IS_ERR_OR_NULL(tree_page)) |
1073 | return NULL; |
1074 | |
1075 | /* |
1076 | * Don't substitute a ksm page for a forked page. |
1077 | */ |
1078 | if (page == tree_page) { |
1079 | put_page(tree_page); |
1080 | return NULL; |
1081 | } |
1082 | |
1083 | ret = memcmp_pages(page, tree_page); |
1084 | |
1085 | parent = *new; |
1086 | if (ret < 0) { |
1087 | put_page(tree_page); |
1088 | new = &parent->rb_left; |
1089 | } else if (ret > 0) { |
1090 | put_page(tree_page); |
1091 | new = &parent->rb_right; |
1092 | } else { |
1093 | *tree_pagep = tree_page; |
1094 | return tree_rmap_item; |
1095 | } |
1096 | } |
1097 | |
1098 | rmap_item->address |= UNSTABLE_FLAG; |
1099 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); |
1100 | rb_link_node(&rmap_item->node, parent, new); |
1101 | rb_insert_color(&rmap_item->node, &root_unstable_tree); |
1102 | |
1103 | ksm_pages_unshared++; |
1104 | return NULL; |
1105 | } |
1106 | |
1107 | /* |
1108 | * stable_tree_append - add another rmap_item to the linked list of |
1109 | * rmap_items hanging off a given node of the stable tree, all sharing |
1110 | * the same ksm page. |
1111 | */ |
1112 | static void stable_tree_append(struct rmap_item *rmap_item, |
1113 | struct stable_node *stable_node) |
1114 | { |
1115 | rmap_item->head = stable_node; |
1116 | rmap_item->address |= STABLE_FLAG; |
1117 | hlist_add_head(&rmap_item->hlist, &stable_node->hlist); |
1118 | |
1119 | if (rmap_item->hlist.next) |
1120 | ksm_pages_sharing++; |
1121 | else |
1122 | ksm_pages_shared++; |
1123 | } |
1124 | |
1125 | /* |
1126 | * cmp_and_merge_page - first see if page can be merged into the stable tree; |
1127 | * if not, compare checksum to previous and if it's the same, see if page can |
1128 | * be inserted into the unstable tree, or merged with a page already there and |
1129 | * both transferred to the stable tree. |
1130 | * |
1131 | * @page: the page that we are searching identical page to. |
1132 | * @rmap_item: the reverse mapping into the virtual address of this page |
1133 | */ |
1134 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) |
1135 | { |
1136 | struct rmap_item *tree_rmap_item; |
1137 | struct page *tree_page = NULL; |
1138 | struct stable_node *stable_node; |
1139 | struct page *kpage; |
1140 | unsigned int checksum; |
1141 | int err; |
1142 | |
1143 | remove_rmap_item_from_tree(rmap_item); |
1144 | |
1145 | /* We first start with searching the page inside the stable tree */ |
1146 | kpage = stable_tree_search(page); |
1147 | if (kpage) { |
1148 | err = try_to_merge_with_ksm_page(rmap_item, page, kpage); |
1149 | if (!err) { |
1150 | /* |
1151 | * The page was successfully merged: |
1152 | * add its rmap_item to the stable tree. |
1153 | */ |
1154 | lock_page(kpage); |
1155 | stable_tree_append(rmap_item, page_stable_node(kpage)); |
1156 | unlock_page(kpage); |
1157 | } |
1158 | put_page(kpage); |
1159 | return; |
1160 | } |
1161 | |
1162 | /* |
1163 | * If the hash value of the page has changed from the last time |
1164 | * we calculated it, this page is changing frequently: therefore we |
1165 | * don't want to insert it in the unstable tree, and we don't want |
1166 | * to waste our time searching for something identical to it there. |
1167 | */ |
1168 | checksum = calc_checksum(page); |
1169 | if (rmap_item->oldchecksum != checksum) { |
1170 | rmap_item->oldchecksum = checksum; |
1171 | return; |
1172 | } |
1173 | |
1174 | tree_rmap_item = |
1175 | unstable_tree_search_insert(rmap_item, page, &tree_page); |
1176 | if (tree_rmap_item) { |
1177 | kpage = try_to_merge_two_pages(rmap_item, page, |
1178 | tree_rmap_item, tree_page); |
1179 | put_page(tree_page); |
1180 | /* |
1181 | * As soon as we merge this page, we want to remove the |
1182 | * rmap_item of the page we have merged with from the unstable |
1183 | * tree, and insert it instead as new node in the stable tree. |
1184 | */ |
1185 | if (kpage) { |
1186 | remove_rmap_item_from_tree(tree_rmap_item); |
1187 | |
1188 | lock_page(kpage); |
1189 | stable_node = stable_tree_insert(kpage); |
1190 | if (stable_node) { |
1191 | stable_tree_append(tree_rmap_item, stable_node); |
1192 | stable_tree_append(rmap_item, stable_node); |
1193 | } |
1194 | unlock_page(kpage); |
1195 | |
1196 | /* |
1197 | * If we fail to insert the page into the stable tree, |
1198 | * we will have 2 virtual addresses that are pointing |
1199 | * to a ksm page left outside the stable tree, |
1200 | * in which case we need to break_cow on both. |
1201 | */ |
1202 | if (!stable_node) { |
1203 | break_cow(tree_rmap_item); |
1204 | break_cow(rmap_item); |
1205 | } |
1206 | } |
1207 | } |
1208 | } |
1209 | |
1210 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, |
1211 | struct rmap_item **rmap_list, |
1212 | unsigned long addr) |
1213 | { |
1214 | struct rmap_item *rmap_item; |
1215 | |
1216 | while (*rmap_list) { |
1217 | rmap_item = *rmap_list; |
1218 | if ((rmap_item->address & PAGE_MASK) == addr) |
1219 | return rmap_item; |
1220 | if (rmap_item->address > addr) |
1221 | break; |
1222 | *rmap_list = rmap_item->rmap_list; |
1223 | remove_rmap_item_from_tree(rmap_item); |
1224 | free_rmap_item(rmap_item); |
1225 | } |
1226 | |
1227 | rmap_item = alloc_rmap_item(); |
1228 | if (rmap_item) { |
1229 | /* It has already been zeroed */ |
1230 | rmap_item->mm = mm_slot->mm; |
1231 | rmap_item->address = addr; |
1232 | rmap_item->rmap_list = *rmap_list; |
1233 | *rmap_list = rmap_item; |
1234 | } |
1235 | return rmap_item; |
1236 | } |
1237 | |
1238 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) |
1239 | { |
1240 | struct mm_struct *mm; |
1241 | struct mm_slot *slot; |
1242 | struct vm_area_struct *vma; |
1243 | struct rmap_item *rmap_item; |
1244 | |
1245 | if (list_empty(&ksm_mm_head.mm_list)) |
1246 | return NULL; |
1247 | |
1248 | slot = ksm_scan.mm_slot; |
1249 | if (slot == &ksm_mm_head) { |
1250 | root_unstable_tree = RB_ROOT; |
1251 | |
1252 | spin_lock(&ksm_mmlist_lock); |
1253 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); |
1254 | ksm_scan.mm_slot = slot; |
1255 | spin_unlock(&ksm_mmlist_lock); |
1256 | next_mm: |
1257 | ksm_scan.address = 0; |
1258 | ksm_scan.rmap_list = &slot->rmap_list; |
1259 | } |
1260 | |
1261 | mm = slot->mm; |
1262 | down_read(&mm->mmap_sem); |
1263 | if (ksm_test_exit(mm)) |
1264 | vma = NULL; |
1265 | else |
1266 | vma = find_vma(mm, ksm_scan.address); |
1267 | |
1268 | for (; vma; vma = vma->vm_next) { |
1269 | if (!(vma->vm_flags & VM_MERGEABLE)) |
1270 | continue; |
1271 | if (ksm_scan.address < vma->vm_start) |
1272 | ksm_scan.address = vma->vm_start; |
1273 | if (!vma->anon_vma) |
1274 | ksm_scan.address = vma->vm_end; |
1275 | |
1276 | while (ksm_scan.address < vma->vm_end) { |
1277 | if (ksm_test_exit(mm)) |
1278 | break; |
1279 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); |
1280 | if (!IS_ERR_OR_NULL(*page) && PageAnon(*page)) { |
1281 | flush_anon_page(vma, *page, ksm_scan.address); |
1282 | flush_dcache_page(*page); |
1283 | rmap_item = get_next_rmap_item(slot, |
1284 | ksm_scan.rmap_list, ksm_scan.address); |
1285 | if (rmap_item) { |
1286 | ksm_scan.rmap_list = |
1287 | &rmap_item->rmap_list; |
1288 | ksm_scan.address += PAGE_SIZE; |
1289 | } else |
1290 | put_page(*page); |
1291 | up_read(&mm->mmap_sem); |
1292 | return rmap_item; |
1293 | } |
1294 | if (!IS_ERR_OR_NULL(*page)) |
1295 | put_page(*page); |
1296 | ksm_scan.address += PAGE_SIZE; |
1297 | cond_resched(); |
1298 | } |
1299 | } |
1300 | |
1301 | if (ksm_test_exit(mm)) { |
1302 | ksm_scan.address = 0; |
1303 | ksm_scan.rmap_list = &slot->rmap_list; |
1304 | } |
1305 | /* |
1306 | * Nuke all the rmap_items that are above this current rmap: |
1307 | * because there were no VM_MERGEABLE vmas with such addresses. |
1308 | */ |
1309 | remove_trailing_rmap_items(slot, ksm_scan.rmap_list); |
1310 | |
1311 | spin_lock(&ksm_mmlist_lock); |
1312 | ksm_scan.mm_slot = list_entry(slot->mm_list.next, |
1313 | struct mm_slot, mm_list); |
1314 | if (ksm_scan.address == 0) { |
1315 | /* |
1316 | * We've completed a full scan of all vmas, holding mmap_sem |
1317 | * throughout, and found no VM_MERGEABLE: so do the same as |
1318 | * __ksm_exit does to remove this mm from all our lists now. |
1319 | * This applies either when cleaning up after __ksm_exit |
1320 | * (but beware: we can reach here even before __ksm_exit), |
1321 | * or when all VM_MERGEABLE areas have been unmapped (and |
1322 | * mmap_sem then protects against race with MADV_MERGEABLE). |
1323 | */ |
1324 | hlist_del(&slot->link); |
1325 | list_del(&slot->mm_list); |
1326 | spin_unlock(&ksm_mmlist_lock); |
1327 | |
1328 | free_mm_slot(slot); |
1329 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
1330 | up_read(&mm->mmap_sem); |
1331 | mmdrop(mm); |
1332 | } else { |
1333 | spin_unlock(&ksm_mmlist_lock); |
1334 | up_read(&mm->mmap_sem); |
1335 | } |
1336 | |
1337 | /* Repeat until we've completed scanning the whole list */ |
1338 | slot = ksm_scan.mm_slot; |
1339 | if (slot != &ksm_mm_head) |
1340 | goto next_mm; |
1341 | |
1342 | ksm_scan.seqnr++; |
1343 | return NULL; |
1344 | } |
1345 | |
1346 | /** |
1347 | * ksm_do_scan - the ksm scanner main worker function. |
1348 | * @scan_npages - number of pages we want to scan before we return. |
1349 | */ |
1350 | static void ksm_do_scan(unsigned int scan_npages) |
1351 | { |
1352 | struct rmap_item *rmap_item; |
1353 | struct page *uninitialized_var(page); |
1354 | |
1355 | while (scan_npages--) { |
1356 | cond_resched(); |
1357 | rmap_item = scan_get_next_rmap_item(&page); |
1358 | if (!rmap_item) |
1359 | return; |
1360 | if (!PageKsm(page) || !in_stable_tree(rmap_item)) |
1361 | cmp_and_merge_page(page, rmap_item); |
1362 | put_page(page); |
1363 | } |
1364 | } |
1365 | |
1366 | static int ksmd_should_run(void) |
1367 | { |
1368 | return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); |
1369 | } |
1370 | |
1371 | static int ksm_scan_thread(void *nothing) |
1372 | { |
1373 | set_user_nice(current, 5); |
1374 | |
1375 | while (!kthread_should_stop()) { |
1376 | mutex_lock(&ksm_thread_mutex); |
1377 | if (ksmd_should_run()) |
1378 | ksm_do_scan(ksm_thread_pages_to_scan); |
1379 | mutex_unlock(&ksm_thread_mutex); |
1380 | |
1381 | if (ksmd_should_run()) { |
1382 | schedule_timeout_interruptible( |
1383 | msecs_to_jiffies(ksm_thread_sleep_millisecs)); |
1384 | } else { |
1385 | wait_event_interruptible(ksm_thread_wait, |
1386 | ksmd_should_run() || kthread_should_stop()); |
1387 | } |
1388 | } |
1389 | return 0; |
1390 | } |
1391 | |
1392 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
1393 | unsigned long end, int advice, unsigned long *vm_flags) |
1394 | { |
1395 | struct mm_struct *mm = vma->vm_mm; |
1396 | int err; |
1397 | |
1398 | switch (advice) { |
1399 | case MADV_MERGEABLE: |
1400 | /* |
1401 | * Be somewhat over-protective for now! |
1402 | */ |
1403 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | |
1404 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | |
1405 | VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | |
1406 | VM_NONLINEAR | VM_MIXEDMAP | VM_SAO)) |
1407 | return 0; /* just ignore the advice */ |
1408 | |
1409 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
1410 | err = __ksm_enter(mm); |
1411 | if (err) |
1412 | return err; |
1413 | } |
1414 | |
1415 | *vm_flags |= VM_MERGEABLE; |
1416 | break; |
1417 | |
1418 | case MADV_UNMERGEABLE: |
1419 | if (!(*vm_flags & VM_MERGEABLE)) |
1420 | return 0; /* just ignore the advice */ |
1421 | |
1422 | if (vma->anon_vma) { |
1423 | err = unmerge_ksm_pages(vma, start, end); |
1424 | if (err) |
1425 | return err; |
1426 | } |
1427 | |
1428 | *vm_flags &= ~VM_MERGEABLE; |
1429 | break; |
1430 | } |
1431 | |
1432 | return 0; |
1433 | } |
1434 | |
1435 | int __ksm_enter(struct mm_struct *mm) |
1436 | { |
1437 | struct mm_slot *mm_slot; |
1438 | int needs_wakeup; |
1439 | |
1440 | mm_slot = alloc_mm_slot(); |
1441 | if (!mm_slot) |
1442 | return -ENOMEM; |
1443 | |
1444 | /* Check ksm_run too? Would need tighter locking */ |
1445 | needs_wakeup = list_empty(&ksm_mm_head.mm_list); |
1446 | |
1447 | spin_lock(&ksm_mmlist_lock); |
1448 | insert_to_mm_slots_hash(mm, mm_slot); |
1449 | /* |
1450 | * Insert just behind the scanning cursor, to let the area settle |
1451 | * down a little; when fork is followed by immediate exec, we don't |
1452 | * want ksmd to waste time setting up and tearing down an rmap_list. |
1453 | */ |
1454 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); |
1455 | spin_unlock(&ksm_mmlist_lock); |
1456 | |
1457 | set_bit(MMF_VM_MERGEABLE, &mm->flags); |
1458 | atomic_inc(&mm->mm_count); |
1459 | |
1460 | if (needs_wakeup) |
1461 | wake_up_interruptible(&ksm_thread_wait); |
1462 | |
1463 | return 0; |
1464 | } |
1465 | |
1466 | void __ksm_exit(struct mm_struct *mm) |
1467 | { |
1468 | struct mm_slot *mm_slot; |
1469 | int easy_to_free = 0; |
1470 | |
1471 | /* |
1472 | * This process is exiting: if it's straightforward (as is the |
1473 | * case when ksmd was never running), free mm_slot immediately. |
1474 | * But if it's at the cursor or has rmap_items linked to it, use |
1475 | * mmap_sem to synchronize with any break_cows before pagetables |
1476 | * are freed, and leave the mm_slot on the list for ksmd to free. |
1477 | * Beware: ksm may already have noticed it exiting and freed the slot. |
1478 | */ |
1479 | |
1480 | spin_lock(&ksm_mmlist_lock); |
1481 | mm_slot = get_mm_slot(mm); |
1482 | if (mm_slot && ksm_scan.mm_slot != mm_slot) { |
1483 | if (!mm_slot->rmap_list) { |
1484 | hlist_del(&mm_slot->link); |
1485 | list_del(&mm_slot->mm_list); |
1486 | easy_to_free = 1; |
1487 | } else { |
1488 | list_move(&mm_slot->mm_list, |
1489 | &ksm_scan.mm_slot->mm_list); |
1490 | } |
1491 | } |
1492 | spin_unlock(&ksm_mmlist_lock); |
1493 | |
1494 | if (easy_to_free) { |
1495 | free_mm_slot(mm_slot); |
1496 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
1497 | mmdrop(mm); |
1498 | } else if (mm_slot) { |
1499 | down_write(&mm->mmap_sem); |
1500 | up_write(&mm->mmap_sem); |
1501 | } |
1502 | } |
1503 | |
1504 | struct page *ksm_does_need_to_copy(struct page *page, |
1505 | struct vm_area_struct *vma, unsigned long address) |
1506 | { |
1507 | struct page *new_page; |
1508 | |
1509 | new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); |
1510 | if (new_page) { |
1511 | copy_user_highpage(new_page, page, address, vma); |
1512 | |
1513 | SetPageDirty(new_page); |
1514 | __SetPageUptodate(new_page); |
1515 | SetPageSwapBacked(new_page); |
1516 | __set_page_locked(new_page); |
1517 | |
1518 | if (page_evictable(new_page, vma)) |
1519 | lru_cache_add_lru(new_page, LRU_ACTIVE_ANON); |
1520 | else |
1521 | add_page_to_unevictable_list(new_page); |
1522 | } |
1523 | |
1524 | return new_page; |
1525 | } |
1526 | |
1527 | int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg, |
1528 | unsigned long *vm_flags) |
1529 | { |
1530 | struct stable_node *stable_node; |
1531 | struct rmap_item *rmap_item; |
1532 | struct hlist_node *hlist; |
1533 | unsigned int mapcount = page_mapcount(page); |
1534 | int referenced = 0; |
1535 | int search_new_forks = 0; |
1536 | |
1537 | VM_BUG_ON(!PageKsm(page)); |
1538 | VM_BUG_ON(!PageLocked(page)); |
1539 | |
1540 | stable_node = page_stable_node(page); |
1541 | if (!stable_node) |
1542 | return 0; |
1543 | again: |
1544 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
1545 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1546 | struct anon_vma_chain *vmac; |
1547 | struct vm_area_struct *vma; |
1548 | |
1549 | anon_vma_lock(anon_vma); |
1550 | list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) { |
1551 | vma = vmac->vma; |
1552 | if (rmap_item->address < vma->vm_start || |
1553 | rmap_item->address >= vma->vm_end) |
1554 | continue; |
1555 | /* |
1556 | * Initially we examine only the vma which covers this |
1557 | * rmap_item; but later, if there is still work to do, |
1558 | * we examine covering vmas in other mms: in case they |
1559 | * were forked from the original since ksmd passed. |
1560 | */ |
1561 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) |
1562 | continue; |
1563 | |
1564 | if (memcg && !mm_match_cgroup(vma->vm_mm, memcg)) |
1565 | continue; |
1566 | |
1567 | referenced += page_referenced_one(page, vma, |
1568 | rmap_item->address, &mapcount, vm_flags); |
1569 | if (!search_new_forks || !mapcount) |
1570 | break; |
1571 | } |
1572 | anon_vma_unlock(anon_vma); |
1573 | if (!mapcount) |
1574 | goto out; |
1575 | } |
1576 | if (!search_new_forks++) |
1577 | goto again; |
1578 | out: |
1579 | return referenced; |
1580 | } |
1581 | |
1582 | int try_to_unmap_ksm(struct page *page, enum ttu_flags flags) |
1583 | { |
1584 | struct stable_node *stable_node; |
1585 | struct hlist_node *hlist; |
1586 | struct rmap_item *rmap_item; |
1587 | int ret = SWAP_AGAIN; |
1588 | int search_new_forks = 0; |
1589 | |
1590 | VM_BUG_ON(!PageKsm(page)); |
1591 | VM_BUG_ON(!PageLocked(page)); |
1592 | |
1593 | stable_node = page_stable_node(page); |
1594 | if (!stable_node) |
1595 | return SWAP_FAIL; |
1596 | again: |
1597 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
1598 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1599 | struct anon_vma_chain *vmac; |
1600 | struct vm_area_struct *vma; |
1601 | |
1602 | anon_vma_lock(anon_vma); |
1603 | list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) { |
1604 | vma = vmac->vma; |
1605 | if (rmap_item->address < vma->vm_start || |
1606 | rmap_item->address >= vma->vm_end) |
1607 | continue; |
1608 | /* |
1609 | * Initially we examine only the vma which covers this |
1610 | * rmap_item; but later, if there is still work to do, |
1611 | * we examine covering vmas in other mms: in case they |
1612 | * were forked from the original since ksmd passed. |
1613 | */ |
1614 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) |
1615 | continue; |
1616 | |
1617 | ret = try_to_unmap_one(page, vma, |
1618 | rmap_item->address, flags); |
1619 | if (ret != SWAP_AGAIN || !page_mapped(page)) { |
1620 | anon_vma_unlock(anon_vma); |
1621 | goto out; |
1622 | } |
1623 | } |
1624 | anon_vma_unlock(anon_vma); |
1625 | } |
1626 | if (!search_new_forks++) |
1627 | goto again; |
1628 | out: |
1629 | return ret; |
1630 | } |
1631 | |
1632 | #ifdef CONFIG_MIGRATION |
1633 | int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *, |
1634 | struct vm_area_struct *, unsigned long, void *), void *arg) |
1635 | { |
1636 | struct stable_node *stable_node; |
1637 | struct hlist_node *hlist; |
1638 | struct rmap_item *rmap_item; |
1639 | int ret = SWAP_AGAIN; |
1640 | int search_new_forks = 0; |
1641 | |
1642 | VM_BUG_ON(!PageKsm(page)); |
1643 | VM_BUG_ON(!PageLocked(page)); |
1644 | |
1645 | stable_node = page_stable_node(page); |
1646 | if (!stable_node) |
1647 | return ret; |
1648 | again: |
1649 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
1650 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1651 | struct anon_vma_chain *vmac; |
1652 | struct vm_area_struct *vma; |
1653 | |
1654 | anon_vma_lock(anon_vma); |
1655 | list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) { |
1656 | vma = vmac->vma; |
1657 | if (rmap_item->address < vma->vm_start || |
1658 | rmap_item->address >= vma->vm_end) |
1659 | continue; |
1660 | /* |
1661 | * Initially we examine only the vma which covers this |
1662 | * rmap_item; but later, if there is still work to do, |
1663 | * we examine covering vmas in other mms: in case they |
1664 | * were forked from the original since ksmd passed. |
1665 | */ |
1666 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) |
1667 | continue; |
1668 | |
1669 | ret = rmap_one(page, vma, rmap_item->address, arg); |
1670 | if (ret != SWAP_AGAIN) { |
1671 | anon_vma_unlock(anon_vma); |
1672 | goto out; |
1673 | } |
1674 | } |
1675 | anon_vma_unlock(anon_vma); |
1676 | } |
1677 | if (!search_new_forks++) |
1678 | goto again; |
1679 | out: |
1680 | return ret; |
1681 | } |
1682 | |
1683 | void ksm_migrate_page(struct page *newpage, struct page *oldpage) |
1684 | { |
1685 | struct stable_node *stable_node; |
1686 | |
1687 | VM_BUG_ON(!PageLocked(oldpage)); |
1688 | VM_BUG_ON(!PageLocked(newpage)); |
1689 | VM_BUG_ON(newpage->mapping != oldpage->mapping); |
1690 | |
1691 | stable_node = page_stable_node(newpage); |
1692 | if (stable_node) { |
1693 | VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage)); |
1694 | stable_node->kpfn = page_to_pfn(newpage); |
1695 | } |
1696 | } |
1697 | #endif /* CONFIG_MIGRATION */ |
1698 | |
1699 | #ifdef CONFIG_MEMORY_HOTREMOVE |
1700 | static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn, |
1701 | unsigned long end_pfn) |
1702 | { |
1703 | struct rb_node *node; |
1704 | |
1705 | for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) { |
1706 | struct stable_node *stable_node; |
1707 | |
1708 | stable_node = rb_entry(node, struct stable_node, node); |
1709 | if (stable_node->kpfn >= start_pfn && |
1710 | stable_node->kpfn < end_pfn) |
1711 | return stable_node; |
1712 | } |
1713 | return NULL; |
1714 | } |
1715 | |
1716 | static int ksm_memory_callback(struct notifier_block *self, |
1717 | unsigned long action, void *arg) |
1718 | { |
1719 | struct memory_notify *mn = arg; |
1720 | struct stable_node *stable_node; |
1721 | |
1722 | switch (action) { |
1723 | case MEM_GOING_OFFLINE: |
1724 | /* |
1725 | * Keep it very simple for now: just lock out ksmd and |
1726 | * MADV_UNMERGEABLE while any memory is going offline. |
1727 | */ |
1728 | mutex_lock(&ksm_thread_mutex); |
1729 | break; |
1730 | |
1731 | case MEM_OFFLINE: |
1732 | /* |
1733 | * Most of the work is done by page migration; but there might |
1734 | * be a few stable_nodes left over, still pointing to struct |
1735 | * pages which have been offlined: prune those from the tree. |
1736 | */ |
1737 | while ((stable_node = ksm_check_stable_tree(mn->start_pfn, |
1738 | mn->start_pfn + mn->nr_pages)) != NULL) |
1739 | remove_node_from_stable_tree(stable_node); |
1740 | /* fallthrough */ |
1741 | |
1742 | case MEM_CANCEL_OFFLINE: |
1743 | mutex_unlock(&ksm_thread_mutex); |
1744 | break; |
1745 | } |
1746 | return NOTIFY_OK; |
1747 | } |
1748 | #endif /* CONFIG_MEMORY_HOTREMOVE */ |
1749 | |
1750 | #ifdef CONFIG_SYSFS |
1751 | /* |
1752 | * This all compiles without CONFIG_SYSFS, but is a waste of space. |
1753 | */ |
1754 | |
1755 | #define KSM_ATTR_RO(_name) \ |
1756 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) |
1757 | #define KSM_ATTR(_name) \ |
1758 | static struct kobj_attribute _name##_attr = \ |
1759 | __ATTR(_name, 0644, _name##_show, _name##_store) |
1760 | |
1761 | static ssize_t sleep_millisecs_show(struct kobject *kobj, |
1762 | struct kobj_attribute *attr, char *buf) |
1763 | { |
1764 | return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); |
1765 | } |
1766 | |
1767 | static ssize_t sleep_millisecs_store(struct kobject *kobj, |
1768 | struct kobj_attribute *attr, |
1769 | const char *buf, size_t count) |
1770 | { |
1771 | unsigned long msecs; |
1772 | int err; |
1773 | |
1774 | err = strict_strtoul(buf, 10, &msecs); |
1775 | if (err || msecs > UINT_MAX) |
1776 | return -EINVAL; |
1777 | |
1778 | ksm_thread_sleep_millisecs = msecs; |
1779 | |
1780 | return count; |
1781 | } |
1782 | KSM_ATTR(sleep_millisecs); |
1783 | |
1784 | static ssize_t pages_to_scan_show(struct kobject *kobj, |
1785 | struct kobj_attribute *attr, char *buf) |
1786 | { |
1787 | return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); |
1788 | } |
1789 | |
1790 | static ssize_t pages_to_scan_store(struct kobject *kobj, |
1791 | struct kobj_attribute *attr, |
1792 | const char *buf, size_t count) |
1793 | { |
1794 | int err; |
1795 | unsigned long nr_pages; |
1796 | |
1797 | err = strict_strtoul(buf, 10, &nr_pages); |
1798 | if (err || nr_pages > UINT_MAX) |
1799 | return -EINVAL; |
1800 | |
1801 | ksm_thread_pages_to_scan = nr_pages; |
1802 | |
1803 | return count; |
1804 | } |
1805 | KSM_ATTR(pages_to_scan); |
1806 | |
1807 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, |
1808 | char *buf) |
1809 | { |
1810 | return sprintf(buf, "%u\n", ksm_run); |
1811 | } |
1812 | |
1813 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, |
1814 | const char *buf, size_t count) |
1815 | { |
1816 | int err; |
1817 | unsigned long flags; |
1818 | |
1819 | err = strict_strtoul(buf, 10, &flags); |
1820 | if (err || flags > UINT_MAX) |
1821 | return -EINVAL; |
1822 | if (flags > KSM_RUN_UNMERGE) |
1823 | return -EINVAL; |
1824 | |
1825 | /* |
1826 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. |
1827 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, |
1828 | * breaking COW to free the pages_shared (but leaves mm_slots |
1829 | * on the list for when ksmd may be set running again). |
1830 | */ |
1831 | |
1832 | mutex_lock(&ksm_thread_mutex); |
1833 | if (ksm_run != flags) { |
1834 | ksm_run = flags; |
1835 | if (flags & KSM_RUN_UNMERGE) { |
1836 | current->flags |= PF_OOM_ORIGIN; |
1837 | err = unmerge_and_remove_all_rmap_items(); |
1838 | current->flags &= ~PF_OOM_ORIGIN; |
1839 | if (err) { |
1840 | ksm_run = KSM_RUN_STOP; |
1841 | count = err; |
1842 | } |
1843 | } |
1844 | } |
1845 | mutex_unlock(&ksm_thread_mutex); |
1846 | |
1847 | if (flags & KSM_RUN_MERGE) |
1848 | wake_up_interruptible(&ksm_thread_wait); |
1849 | |
1850 | return count; |
1851 | } |
1852 | KSM_ATTR(run); |
1853 | |
1854 | static ssize_t pages_shared_show(struct kobject *kobj, |
1855 | struct kobj_attribute *attr, char *buf) |
1856 | { |
1857 | return sprintf(buf, "%lu\n", ksm_pages_shared); |
1858 | } |
1859 | KSM_ATTR_RO(pages_shared); |
1860 | |
1861 | static ssize_t pages_sharing_show(struct kobject *kobj, |
1862 | struct kobj_attribute *attr, char *buf) |
1863 | { |
1864 | return sprintf(buf, "%lu\n", ksm_pages_sharing); |
1865 | } |
1866 | KSM_ATTR_RO(pages_sharing); |
1867 | |
1868 | static ssize_t pages_unshared_show(struct kobject *kobj, |
1869 | struct kobj_attribute *attr, char *buf) |
1870 | { |
1871 | return sprintf(buf, "%lu\n", ksm_pages_unshared); |
1872 | } |
1873 | KSM_ATTR_RO(pages_unshared); |
1874 | |
1875 | static ssize_t pages_volatile_show(struct kobject *kobj, |
1876 | struct kobj_attribute *attr, char *buf) |
1877 | { |
1878 | long ksm_pages_volatile; |
1879 | |
1880 | ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared |
1881 | - ksm_pages_sharing - ksm_pages_unshared; |
1882 | /* |
1883 | * It was not worth any locking to calculate that statistic, |
1884 | * but it might therefore sometimes be negative: conceal that. |
1885 | */ |
1886 | if (ksm_pages_volatile < 0) |
1887 | ksm_pages_volatile = 0; |
1888 | return sprintf(buf, "%ld\n", ksm_pages_volatile); |
1889 | } |
1890 | KSM_ATTR_RO(pages_volatile); |
1891 | |
1892 | static ssize_t full_scans_show(struct kobject *kobj, |
1893 | struct kobj_attribute *attr, char *buf) |
1894 | { |
1895 | return sprintf(buf, "%lu\n", ksm_scan.seqnr); |
1896 | } |
1897 | KSM_ATTR_RO(full_scans); |
1898 | |
1899 | static struct attribute *ksm_attrs[] = { |
1900 | &sleep_millisecs_attr.attr, |
1901 | &pages_to_scan_attr.attr, |
1902 | &run_attr.attr, |
1903 | &pages_shared_attr.attr, |
1904 | &pages_sharing_attr.attr, |
1905 | &pages_unshared_attr.attr, |
1906 | &pages_volatile_attr.attr, |
1907 | &full_scans_attr.attr, |
1908 | NULL, |
1909 | }; |
1910 | |
1911 | static struct attribute_group ksm_attr_group = { |
1912 | .attrs = ksm_attrs, |
1913 | .name = "ksm", |
1914 | }; |
1915 | #endif /* CONFIG_SYSFS */ |
1916 | |
1917 | static int __init ksm_init(void) |
1918 | { |
1919 | struct task_struct *ksm_thread; |
1920 | int err; |
1921 | |
1922 | err = ksm_slab_init(); |
1923 | if (err) |
1924 | goto out; |
1925 | |
1926 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); |
1927 | if (IS_ERR(ksm_thread)) { |
1928 | printk(KERN_ERR "ksm: creating kthread failed\n"); |
1929 | err = PTR_ERR(ksm_thread); |
1930 | goto out_free; |
1931 | } |
1932 | |
1933 | #ifdef CONFIG_SYSFS |
1934 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); |
1935 | if (err) { |
1936 | printk(KERN_ERR "ksm: register sysfs failed\n"); |
1937 | kthread_stop(ksm_thread); |
1938 | goto out_free; |
1939 | } |
1940 | #else |
1941 | ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ |
1942 | |
1943 | #endif /* CONFIG_SYSFS */ |
1944 | |
1945 | #ifdef CONFIG_MEMORY_HOTREMOVE |
1946 | /* |
1947 | * Choose a high priority since the callback takes ksm_thread_mutex: |
1948 | * later callbacks could only be taking locks which nest within that. |
1949 | */ |
1950 | hotplug_memory_notifier(ksm_memory_callback, 100); |
1951 | #endif |
1952 | return 0; |
1953 | |
1954 | out_free: |
1955 | ksm_slab_free(); |
1956 | out: |
1957 | return err; |
1958 | } |
1959 | module_init(ksm_init) |
1960 |
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