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Commit | Line | Data |
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f8af4da3 | 1 | /* |
31dbd01f IE |
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 | * | |
36b2528d | 7 | * Copyright (C) 2008-2009 Red Hat, Inc. |
31dbd01f IE |
8 | * Authors: |
9 | * Izik Eidus | |
10 | * Andrea Arcangeli | |
11 | * Chris Wright | |
36b2528d | 12 | * Hugh Dickins |
31dbd01f IE |
13 | * |
14 | * This work is licensed under the terms of the GNU GPL, version 2. | |
f8af4da3 HD |
15 | */ |
16 | ||
17 | #include <linux/errno.h> | |
31dbd01f IE |
18 | #include <linux/mm.h> |
19 | #include <linux/fs.h> | |
f8af4da3 | 20 | #include <linux/mman.h> |
31dbd01f IE |
21 | #include <linux/sched.h> |
22 | #include <linux/rwsem.h> | |
23 | #include <linux/pagemap.h> | |
24 | #include <linux/rmap.h> | |
25 | #include <linux/spinlock.h> | |
26 | #include <linux/jhash.h> | |
27 | #include <linux/delay.h> | |
28 | #include <linux/kthread.h> | |
29 | #include <linux/wait.h> | |
30 | #include <linux/slab.h> | |
31 | #include <linux/rbtree.h> | |
32 | #include <linux/mmu_notifier.h> | |
2c6854fd | 33 | #include <linux/swap.h> |
f8af4da3 HD |
34 | #include <linux/ksm.h> |
35 | ||
31dbd01f | 36 | #include <asm/tlbflush.h> |
73848b46 | 37 | #include "internal.h" |
31dbd01f IE |
38 | |
39 | /* | |
40 | * A few notes about the KSM scanning process, | |
41 | * to make it easier to understand the data structures below: | |
42 | * | |
43 | * In order to reduce excessive scanning, KSM sorts the memory pages by their | |
44 | * contents into a data structure that holds pointers to the pages' locations. | |
45 | * | |
46 | * Since the contents of the pages may change at any moment, KSM cannot just | |
47 | * insert the pages into a normal sorted tree and expect it to find anything. | |
48 | * Therefore KSM uses two data structures - the stable and the unstable tree. | |
49 | * | |
50 | * The stable tree holds pointers to all the merged pages (ksm pages), sorted | |
51 | * by their contents. Because each such page is write-protected, searching on | |
52 | * this tree is fully assured to be working (except when pages are unmapped), | |
53 | * and therefore this tree is called the stable tree. | |
54 | * | |
55 | * In addition to the stable tree, KSM uses a second data structure called the | |
56 | * unstable tree: this tree holds pointers to pages which have been found to | |
57 | * be "unchanged for a period of time". The unstable tree sorts these pages | |
58 | * by their contents, but since they are not write-protected, KSM cannot rely | |
59 | * upon the unstable tree to work correctly - the unstable tree is liable to | |
60 | * be corrupted as its contents are modified, and so it is called unstable. | |
61 | * | |
62 | * KSM solves this problem by several techniques: | |
63 | * | |
64 | * 1) The unstable tree is flushed every time KSM completes scanning all | |
65 | * memory areas, and then the tree is rebuilt again from the beginning. | |
66 | * 2) KSM will only insert into the unstable tree, pages whose hash value | |
67 | * has not changed since the previous scan of all memory areas. | |
68 | * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the | |
69 | * colors of the nodes and not on their contents, assuring that even when | |
70 | * the tree gets "corrupted" it won't get out of balance, so scanning time | |
71 | * remains the same (also, searching and inserting nodes in an rbtree uses | |
72 | * the same algorithm, so we have no overhead when we flush and rebuild). | |
73 | * 4) KSM never flushes the stable tree, which means that even if it were to | |
74 | * take 10 attempts to find a page in the unstable tree, once it is found, | |
75 | * it is secured in the stable tree. (When we scan a new page, we first | |
76 | * compare it against the stable tree, and then against the unstable tree.) | |
77 | */ | |
78 | ||
79 | /** | |
80 | * struct mm_slot - ksm information per mm that is being scanned | |
81 | * @link: link to the mm_slots hash list | |
82 | * @mm_list: link into the mm_slots list, rooted in ksm_mm_head | |
6514d511 | 83 | * @rmap_list: head for this mm_slot's singly-linked list of rmap_items |
31dbd01f IE |
84 | * @mm: the mm that this information is valid for |
85 | */ | |
86 | struct mm_slot { | |
87 | struct hlist_node link; | |
88 | struct list_head mm_list; | |
6514d511 | 89 | struct rmap_item *rmap_list; |
31dbd01f IE |
90 | struct mm_struct *mm; |
91 | }; | |
92 | ||
93 | /** | |
94 | * struct ksm_scan - cursor for scanning | |
95 | * @mm_slot: the current mm_slot we are scanning | |
96 | * @address: the next address inside that to be scanned | |
6514d511 | 97 | * @rmap_list: link to the next rmap to be scanned in the rmap_list |
31dbd01f IE |
98 | * @seqnr: count of completed full scans (needed when removing unstable node) |
99 | * | |
100 | * There is only the one ksm_scan instance of this cursor structure. | |
101 | */ | |
102 | struct ksm_scan { | |
103 | struct mm_slot *mm_slot; | |
104 | unsigned long address; | |
6514d511 | 105 | struct rmap_item **rmap_list; |
31dbd01f IE |
106 | unsigned long seqnr; |
107 | }; | |
108 | ||
7b6ba2c7 HD |
109 | /** |
110 | * struct stable_node - node of the stable rbtree | |
08beca44 | 111 | * @page: pointer to struct page of the ksm page |
7b6ba2c7 HD |
112 | * @node: rb node of this ksm page in the stable tree |
113 | * @hlist: hlist head of rmap_items using this ksm page | |
114 | */ | |
115 | struct stable_node { | |
08beca44 | 116 | struct page *page; |
7b6ba2c7 HD |
117 | struct rb_node node; |
118 | struct hlist_head hlist; | |
119 | }; | |
120 | ||
31dbd01f IE |
121 | /** |
122 | * struct rmap_item - reverse mapping item for virtual addresses | |
6514d511 | 123 | * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list |
db114b83 | 124 | * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree |
31dbd01f IE |
125 | * @mm: the memory structure this rmap_item is pointing into |
126 | * @address: the virtual address this rmap_item tracks (+ flags in low bits) | |
127 | * @oldchecksum: previous checksum of the page at that virtual address | |
7b6ba2c7 HD |
128 | * @node: rb node of this rmap_item in the unstable tree |
129 | * @head: pointer to stable_node heading this list in the stable tree | |
130 | * @hlist: link into hlist of rmap_items hanging off that stable_node | |
31dbd01f IE |
131 | */ |
132 | struct rmap_item { | |
6514d511 | 133 | struct rmap_item *rmap_list; |
db114b83 | 134 | struct anon_vma *anon_vma; /* when stable */ |
31dbd01f IE |
135 | struct mm_struct *mm; |
136 | unsigned long address; /* + low bits used for flags below */ | |
7b6ba2c7 | 137 | unsigned int oldchecksum; /* when unstable */ |
31dbd01f | 138 | union { |
7b6ba2c7 HD |
139 | struct rb_node node; /* when node of unstable tree */ |
140 | struct { /* when listed from stable tree */ | |
141 | struct stable_node *head; | |
142 | struct hlist_node hlist; | |
143 | }; | |
31dbd01f IE |
144 | }; |
145 | }; | |
146 | ||
147 | #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ | |
7b6ba2c7 HD |
148 | #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ |
149 | #define STABLE_FLAG 0x200 /* is listed from the stable tree */ | |
31dbd01f IE |
150 | |
151 | /* The stable and unstable tree heads */ | |
152 | static struct rb_root root_stable_tree = RB_ROOT; | |
153 | static struct rb_root root_unstable_tree = RB_ROOT; | |
154 | ||
155 | #define MM_SLOTS_HASH_HEADS 1024 | |
156 | static struct hlist_head *mm_slots_hash; | |
157 | ||
158 | static struct mm_slot ksm_mm_head = { | |
159 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), | |
160 | }; | |
161 | static struct ksm_scan ksm_scan = { | |
162 | .mm_slot = &ksm_mm_head, | |
163 | }; | |
164 | ||
165 | static struct kmem_cache *rmap_item_cache; | |
7b6ba2c7 | 166 | static struct kmem_cache *stable_node_cache; |
31dbd01f IE |
167 | static struct kmem_cache *mm_slot_cache; |
168 | ||
169 | /* The number of nodes in the stable tree */ | |
b4028260 | 170 | static unsigned long ksm_pages_shared; |
31dbd01f | 171 | |
e178dfde | 172 | /* The number of page slots additionally sharing those nodes */ |
b4028260 | 173 | static unsigned long ksm_pages_sharing; |
31dbd01f | 174 | |
473b0ce4 HD |
175 | /* The number of nodes in the unstable tree */ |
176 | static unsigned long ksm_pages_unshared; | |
177 | ||
178 | /* The number of rmap_items in use: to calculate pages_volatile */ | |
179 | static unsigned long ksm_rmap_items; | |
180 | ||
31dbd01f | 181 | /* Limit on the number of unswappable pages used */ |
2c6854fd | 182 | static unsigned long ksm_max_kernel_pages; |
31dbd01f IE |
183 | |
184 | /* Number of pages ksmd should scan in one batch */ | |
2c6854fd | 185 | static unsigned int ksm_thread_pages_to_scan = 100; |
31dbd01f IE |
186 | |
187 | /* Milliseconds ksmd should sleep between batches */ | |
2ffd8679 | 188 | static unsigned int ksm_thread_sleep_millisecs = 20; |
31dbd01f IE |
189 | |
190 | #define KSM_RUN_STOP 0 | |
191 | #define KSM_RUN_MERGE 1 | |
192 | #define KSM_RUN_UNMERGE 2 | |
2c6854fd | 193 | static unsigned int ksm_run = KSM_RUN_STOP; |
31dbd01f IE |
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 | ||
7b6ba2c7 HD |
209 | stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); |
210 | if (!stable_node_cache) | |
211 | goto out_free1; | |
212 | ||
31dbd01f IE |
213 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); |
214 | if (!mm_slot_cache) | |
7b6ba2c7 | 215 | goto out_free2; |
31dbd01f IE |
216 | |
217 | return 0; | |
218 | ||
7b6ba2c7 HD |
219 | out_free2: |
220 | kmem_cache_destroy(stable_node_cache); | |
221 | out_free1: | |
31dbd01f IE |
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); | |
7b6ba2c7 | 230 | kmem_cache_destroy(stable_node_cache); |
31dbd01f IE |
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 | { | |
473b0ce4 HD |
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; | |
31dbd01f IE |
243 | } |
244 | ||
245 | static inline void free_rmap_item(struct rmap_item *rmap_item) | |
246 | { | |
473b0ce4 | 247 | ksm_rmap_items--; |
31dbd01f IE |
248 | rmap_item->mm = NULL; /* debug safety */ |
249 | kmem_cache_free(rmap_item_cache, rmap_item); | |
250 | } | |
251 | ||
7b6ba2c7 HD |
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 | ||
31dbd01f IE |
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 int __init mm_slots_hash_init(void) | |
275 | { | |
276 | mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head), | |
277 | GFP_KERNEL); | |
278 | if (!mm_slots_hash) | |
279 | return -ENOMEM; | |
280 | return 0; | |
281 | } | |
282 | ||
283 | static void __init mm_slots_hash_free(void) | |
284 | { | |
285 | kfree(mm_slots_hash); | |
286 | } | |
287 | ||
288 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) | |
289 | { | |
290 | struct mm_slot *mm_slot; | |
291 | struct hlist_head *bucket; | |
292 | struct hlist_node *node; | |
293 | ||
294 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
295 | % MM_SLOTS_HASH_HEADS]; | |
296 | hlist_for_each_entry(mm_slot, node, bucket, link) { | |
297 | if (mm == mm_slot->mm) | |
298 | return mm_slot; | |
299 | } | |
300 | return NULL; | |
301 | } | |
302 | ||
303 | static void insert_to_mm_slots_hash(struct mm_struct *mm, | |
304 | struct mm_slot *mm_slot) | |
305 | { | |
306 | struct hlist_head *bucket; | |
307 | ||
308 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
309 | % MM_SLOTS_HASH_HEADS]; | |
310 | mm_slot->mm = mm; | |
31dbd01f IE |
311 | hlist_add_head(&mm_slot->link, bucket); |
312 | } | |
313 | ||
314 | static inline int in_stable_tree(struct rmap_item *rmap_item) | |
315 | { | |
316 | return rmap_item->address & STABLE_FLAG; | |
317 | } | |
318 | ||
db114b83 HD |
319 | static void hold_anon_vma(struct rmap_item *rmap_item, |
320 | struct anon_vma *anon_vma) | |
321 | { | |
322 | rmap_item->anon_vma = anon_vma; | |
323 | atomic_inc(&anon_vma->ksm_refcount); | |
324 | } | |
325 | ||
326 | static void drop_anon_vma(struct rmap_item *rmap_item) | |
327 | { | |
328 | struct anon_vma *anon_vma = rmap_item->anon_vma; | |
329 | ||
330 | if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) { | |
331 | int empty = list_empty(&anon_vma->head); | |
332 | spin_unlock(&anon_vma->lock); | |
333 | if (empty) | |
334 | anon_vma_free(anon_vma); | |
335 | } | |
336 | } | |
337 | ||
a913e182 HD |
338 | /* |
339 | * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's | |
340 | * page tables after it has passed through ksm_exit() - which, if necessary, | |
341 | * takes mmap_sem briefly to serialize against them. ksm_exit() does not set | |
342 | * a special flag: they can just back out as soon as mm_users goes to zero. | |
343 | * ksm_test_exit() is used throughout to make this test for exit: in some | |
344 | * places for correctness, in some places just to avoid unnecessary work. | |
345 | */ | |
346 | static inline bool ksm_test_exit(struct mm_struct *mm) | |
347 | { | |
348 | return atomic_read(&mm->mm_users) == 0; | |
349 | } | |
350 | ||
31dbd01f IE |
351 | /* |
352 | * We use break_ksm to break COW on a ksm page: it's a stripped down | |
353 | * | |
354 | * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) | |
355 | * put_page(page); | |
356 | * | |
357 | * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, | |
358 | * in case the application has unmapped and remapped mm,addr meanwhile. | |
359 | * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP | |
360 | * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. | |
361 | */ | |
d952b791 | 362 | static int break_ksm(struct vm_area_struct *vma, unsigned long addr) |
31dbd01f IE |
363 | { |
364 | struct page *page; | |
d952b791 | 365 | int ret = 0; |
31dbd01f IE |
366 | |
367 | do { | |
368 | cond_resched(); | |
369 | page = follow_page(vma, addr, FOLL_GET); | |
370 | if (!page) | |
371 | break; | |
372 | if (PageKsm(page)) | |
373 | ret = handle_mm_fault(vma->vm_mm, vma, addr, | |
374 | FAULT_FLAG_WRITE); | |
375 | else | |
376 | ret = VM_FAULT_WRITE; | |
377 | put_page(page); | |
d952b791 HD |
378 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM))); |
379 | /* | |
380 | * We must loop because handle_mm_fault() may back out if there's | |
381 | * any difficulty e.g. if pte accessed bit gets updated concurrently. | |
382 | * | |
383 | * VM_FAULT_WRITE is what we have been hoping for: it indicates that | |
384 | * COW has been broken, even if the vma does not permit VM_WRITE; | |
385 | * but note that a concurrent fault might break PageKsm for us. | |
386 | * | |
387 | * VM_FAULT_SIGBUS could occur if we race with truncation of the | |
388 | * backing file, which also invalidates anonymous pages: that's | |
389 | * okay, that truncation will have unmapped the PageKsm for us. | |
390 | * | |
391 | * VM_FAULT_OOM: at the time of writing (late July 2009), setting | |
392 | * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the | |
393 | * current task has TIF_MEMDIE set, and will be OOM killed on return | |
394 | * to user; and ksmd, having no mm, would never be chosen for that. | |
395 | * | |
396 | * But if the mm is in a limited mem_cgroup, then the fault may fail | |
397 | * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and | |
398 | * even ksmd can fail in this way - though it's usually breaking ksm | |
399 | * just to undo a merge it made a moment before, so unlikely to oom. | |
400 | * | |
401 | * That's a pity: we might therefore have more kernel pages allocated | |
402 | * than we're counting as nodes in the stable tree; but ksm_do_scan | |
403 | * will retry to break_cow on each pass, so should recover the page | |
404 | * in due course. The important thing is to not let VM_MERGEABLE | |
405 | * be cleared while any such pages might remain in the area. | |
406 | */ | |
407 | return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; | |
31dbd01f IE |
408 | } |
409 | ||
8dd3557a | 410 | static void break_cow(struct rmap_item *rmap_item) |
31dbd01f | 411 | { |
8dd3557a HD |
412 | struct mm_struct *mm = rmap_item->mm; |
413 | unsigned long addr = rmap_item->address; | |
31dbd01f IE |
414 | struct vm_area_struct *vma; |
415 | ||
4035c07a HD |
416 | /* |
417 | * It is not an accident that whenever we want to break COW | |
418 | * to undo, we also need to drop a reference to the anon_vma. | |
419 | */ | |
420 | drop_anon_vma(rmap_item); | |
421 | ||
81464e30 | 422 | down_read(&mm->mmap_sem); |
9ba69294 HD |
423 | if (ksm_test_exit(mm)) |
424 | goto out; | |
31dbd01f IE |
425 | vma = find_vma(mm, addr); |
426 | if (!vma || vma->vm_start > addr) | |
81464e30 | 427 | goto out; |
31dbd01f | 428 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
81464e30 | 429 | goto out; |
31dbd01f | 430 | break_ksm(vma, addr); |
81464e30 | 431 | out: |
31dbd01f IE |
432 | up_read(&mm->mmap_sem); |
433 | } | |
434 | ||
435 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) | |
436 | { | |
437 | struct mm_struct *mm = rmap_item->mm; | |
438 | unsigned long addr = rmap_item->address; | |
439 | struct vm_area_struct *vma; | |
440 | struct page *page; | |
441 | ||
442 | down_read(&mm->mmap_sem); | |
9ba69294 HD |
443 | if (ksm_test_exit(mm)) |
444 | goto out; | |
31dbd01f IE |
445 | vma = find_vma(mm, addr); |
446 | if (!vma || vma->vm_start > addr) | |
447 | goto out; | |
448 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
449 | goto out; | |
450 | ||
451 | page = follow_page(vma, addr, FOLL_GET); | |
452 | if (!page) | |
453 | goto out; | |
454 | if (PageAnon(page)) { | |
455 | flush_anon_page(vma, page, addr); | |
456 | flush_dcache_page(page); | |
457 | } else { | |
458 | put_page(page); | |
459 | out: page = NULL; | |
460 | } | |
461 | up_read(&mm->mmap_sem); | |
462 | return page; | |
463 | } | |
464 | ||
4035c07a HD |
465 | static void remove_node_from_stable_tree(struct stable_node *stable_node) |
466 | { | |
467 | struct rmap_item *rmap_item; | |
468 | struct hlist_node *hlist; | |
469 | ||
470 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { | |
471 | if (rmap_item->hlist.next) | |
472 | ksm_pages_sharing--; | |
473 | else | |
474 | ksm_pages_shared--; | |
475 | drop_anon_vma(rmap_item); | |
476 | rmap_item->address &= PAGE_MASK; | |
477 | cond_resched(); | |
478 | } | |
479 | ||
480 | rb_erase(&stable_node->node, &root_stable_tree); | |
481 | free_stable_node(stable_node); | |
482 | } | |
483 | ||
484 | /* | |
485 | * get_ksm_page: checks if the page indicated by the stable node | |
486 | * is still its ksm page, despite having held no reference to it. | |
487 | * In which case we can trust the content of the page, and it | |
488 | * returns the gotten page; but if the page has now been zapped, | |
489 | * remove the stale node from the stable tree and return NULL. | |
490 | * | |
491 | * You would expect the stable_node to hold a reference to the ksm page. | |
492 | * But if it increments the page's count, swapping out has to wait for | |
493 | * ksmd to come around again before it can free the page, which may take | |
494 | * seconds or even minutes: much too unresponsive. So instead we use a | |
495 | * "keyhole reference": access to the ksm page from the stable node peeps | |
496 | * out through its keyhole to see if that page still holds the right key, | |
497 | * pointing back to this stable node. This relies on freeing a PageAnon | |
498 | * page to reset its page->mapping to NULL, and relies on no other use of | |
499 | * a page to put something that might look like our key in page->mapping. | |
500 | * | |
501 | * include/linux/pagemap.h page_cache_get_speculative() is a good reference, | |
502 | * but this is different - made simpler by ksm_thread_mutex being held, but | |
503 | * interesting for assuming that no other use of the struct page could ever | |
504 | * put our expected_mapping into page->mapping (or a field of the union which | |
505 | * coincides with page->mapping). The RCU calls are not for KSM at all, but | |
506 | * to keep the page_count protocol described with page_cache_get_speculative. | |
507 | * | |
508 | * Note: it is possible that get_ksm_page() will return NULL one moment, | |
509 | * then page the next, if the page is in between page_freeze_refs() and | |
510 | * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page | |
511 | * is on its way to being freed; but it is an anomaly to bear in mind. | |
512 | */ | |
513 | static struct page *get_ksm_page(struct stable_node *stable_node) | |
514 | { | |
515 | struct page *page; | |
516 | void *expected_mapping; | |
517 | ||
518 | page = stable_node->page; | |
519 | expected_mapping = (void *)stable_node + | |
520 | (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM); | |
521 | rcu_read_lock(); | |
522 | if (page->mapping != expected_mapping) | |
523 | goto stale; | |
524 | if (!get_page_unless_zero(page)) | |
525 | goto stale; | |
526 | if (page->mapping != expected_mapping) { | |
527 | put_page(page); | |
528 | goto stale; | |
529 | } | |
530 | rcu_read_unlock(); | |
531 | return page; | |
532 | stale: | |
533 | rcu_read_unlock(); | |
534 | remove_node_from_stable_tree(stable_node); | |
535 | return NULL; | |
536 | } | |
537 | ||
31dbd01f IE |
538 | /* |
539 | * Removing rmap_item from stable or unstable tree. | |
540 | * This function will clean the information from the stable/unstable tree. | |
541 | */ | |
542 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) | |
543 | { | |
7b6ba2c7 HD |
544 | if (rmap_item->address & STABLE_FLAG) { |
545 | struct stable_node *stable_node; | |
5ad64688 | 546 | struct page *page; |
31dbd01f | 547 | |
7b6ba2c7 | 548 | stable_node = rmap_item->head; |
4035c07a HD |
549 | page = get_ksm_page(stable_node); |
550 | if (!page) | |
551 | goto out; | |
5ad64688 | 552 | |
4035c07a | 553 | lock_page(page); |
7b6ba2c7 | 554 | hlist_del(&rmap_item->hlist); |
4035c07a HD |
555 | unlock_page(page); |
556 | put_page(page); | |
08beca44 | 557 | |
4035c07a HD |
558 | if (stable_node->hlist.first) |
559 | ksm_pages_sharing--; | |
560 | else | |
7b6ba2c7 | 561 | ksm_pages_shared--; |
31dbd01f | 562 | |
db114b83 | 563 | drop_anon_vma(rmap_item); |
93d17715 | 564 | rmap_item->address &= PAGE_MASK; |
31dbd01f | 565 | |
7b6ba2c7 | 566 | } else if (rmap_item->address & UNSTABLE_FLAG) { |
31dbd01f IE |
567 | unsigned char age; |
568 | /* | |
9ba69294 | 569 | * Usually ksmd can and must skip the rb_erase, because |
31dbd01f | 570 | * root_unstable_tree was already reset to RB_ROOT. |
9ba69294 HD |
571 | * But be careful when an mm is exiting: do the rb_erase |
572 | * if this rmap_item was inserted by this scan, rather | |
573 | * than left over from before. | |
31dbd01f IE |
574 | */ |
575 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); | |
cd551f97 | 576 | BUG_ON(age > 1); |
31dbd01f IE |
577 | if (!age) |
578 | rb_erase(&rmap_item->node, &root_unstable_tree); | |
93d17715 | 579 | |
473b0ce4 | 580 | ksm_pages_unshared--; |
93d17715 | 581 | rmap_item->address &= PAGE_MASK; |
31dbd01f | 582 | } |
4035c07a | 583 | out: |
31dbd01f IE |
584 | cond_resched(); /* we're called from many long loops */ |
585 | } | |
586 | ||
31dbd01f | 587 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, |
6514d511 | 588 | struct rmap_item **rmap_list) |
31dbd01f | 589 | { |
6514d511 HD |
590 | while (*rmap_list) { |
591 | struct rmap_item *rmap_item = *rmap_list; | |
592 | *rmap_list = rmap_item->rmap_list; | |
31dbd01f | 593 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
594 | free_rmap_item(rmap_item); |
595 | } | |
596 | } | |
597 | ||
598 | /* | |
599 | * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather | |
600 | * than check every pte of a given vma, the locking doesn't quite work for | |
601 | * that - an rmap_item is assigned to the stable tree after inserting ksm | |
602 | * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing | |
603 | * rmap_items from parent to child at fork time (so as not to waste time | |
604 | * if exit comes before the next scan reaches it). | |
81464e30 HD |
605 | * |
606 | * Similarly, although we'd like to remove rmap_items (so updating counts | |
607 | * and freeing memory) when unmerging an area, it's easier to leave that | |
608 | * to the next pass of ksmd - consider, for example, how ksmd might be | |
609 | * in cmp_and_merge_page on one of the rmap_items we would be removing. | |
31dbd01f | 610 | */ |
d952b791 HD |
611 | static int unmerge_ksm_pages(struct vm_area_struct *vma, |
612 | unsigned long start, unsigned long end) | |
31dbd01f IE |
613 | { |
614 | unsigned long addr; | |
d952b791 | 615 | int err = 0; |
31dbd01f | 616 | |
d952b791 | 617 | for (addr = start; addr < end && !err; addr += PAGE_SIZE) { |
9ba69294 HD |
618 | if (ksm_test_exit(vma->vm_mm)) |
619 | break; | |
d952b791 HD |
620 | if (signal_pending(current)) |
621 | err = -ERESTARTSYS; | |
622 | else | |
623 | err = break_ksm(vma, addr); | |
624 | } | |
625 | return err; | |
31dbd01f IE |
626 | } |
627 | ||
2ffd8679 HD |
628 | #ifdef CONFIG_SYSFS |
629 | /* | |
630 | * Only called through the sysfs control interface: | |
631 | */ | |
d952b791 | 632 | static int unmerge_and_remove_all_rmap_items(void) |
31dbd01f IE |
633 | { |
634 | struct mm_slot *mm_slot; | |
635 | struct mm_struct *mm; | |
636 | struct vm_area_struct *vma; | |
d952b791 HD |
637 | int err = 0; |
638 | ||
639 | spin_lock(&ksm_mmlist_lock); | |
9ba69294 | 640 | ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, |
d952b791 HD |
641 | struct mm_slot, mm_list); |
642 | spin_unlock(&ksm_mmlist_lock); | |
31dbd01f | 643 | |
9ba69294 HD |
644 | for (mm_slot = ksm_scan.mm_slot; |
645 | mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { | |
31dbd01f IE |
646 | mm = mm_slot->mm; |
647 | down_read(&mm->mmap_sem); | |
648 | for (vma = mm->mmap; vma; vma = vma->vm_next) { | |
9ba69294 HD |
649 | if (ksm_test_exit(mm)) |
650 | break; | |
31dbd01f IE |
651 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
652 | continue; | |
d952b791 HD |
653 | err = unmerge_ksm_pages(vma, |
654 | vma->vm_start, vma->vm_end); | |
9ba69294 HD |
655 | if (err) |
656 | goto error; | |
31dbd01f | 657 | } |
9ba69294 | 658 | |
6514d511 | 659 | remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); |
d952b791 HD |
660 | |
661 | spin_lock(&ksm_mmlist_lock); | |
9ba69294 | 662 | ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, |
d952b791 | 663 | struct mm_slot, mm_list); |
9ba69294 HD |
664 | if (ksm_test_exit(mm)) { |
665 | hlist_del(&mm_slot->link); | |
666 | list_del(&mm_slot->mm_list); | |
667 | spin_unlock(&ksm_mmlist_lock); | |
668 | ||
669 | free_mm_slot(mm_slot); | |
670 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
671 | up_read(&mm->mmap_sem); | |
672 | mmdrop(mm); | |
673 | } else { | |
674 | spin_unlock(&ksm_mmlist_lock); | |
675 | up_read(&mm->mmap_sem); | |
676 | } | |
31dbd01f IE |
677 | } |
678 | ||
d952b791 | 679 | ksm_scan.seqnr = 0; |
9ba69294 HD |
680 | return 0; |
681 | ||
682 | error: | |
683 | up_read(&mm->mmap_sem); | |
31dbd01f | 684 | spin_lock(&ksm_mmlist_lock); |
d952b791 | 685 | ksm_scan.mm_slot = &ksm_mm_head; |
31dbd01f | 686 | spin_unlock(&ksm_mmlist_lock); |
d952b791 | 687 | return err; |
31dbd01f | 688 | } |
2ffd8679 | 689 | #endif /* CONFIG_SYSFS */ |
31dbd01f | 690 | |
31dbd01f IE |
691 | static u32 calc_checksum(struct page *page) |
692 | { | |
693 | u32 checksum; | |
694 | void *addr = kmap_atomic(page, KM_USER0); | |
695 | checksum = jhash2(addr, PAGE_SIZE / 4, 17); | |
696 | kunmap_atomic(addr, KM_USER0); | |
697 | return checksum; | |
698 | } | |
699 | ||
700 | static int memcmp_pages(struct page *page1, struct page *page2) | |
701 | { | |
702 | char *addr1, *addr2; | |
703 | int ret; | |
704 | ||
705 | addr1 = kmap_atomic(page1, KM_USER0); | |
706 | addr2 = kmap_atomic(page2, KM_USER1); | |
707 | ret = memcmp(addr1, addr2, PAGE_SIZE); | |
708 | kunmap_atomic(addr2, KM_USER1); | |
709 | kunmap_atomic(addr1, KM_USER0); | |
710 | return ret; | |
711 | } | |
712 | ||
713 | static inline int pages_identical(struct page *page1, struct page *page2) | |
714 | { | |
715 | return !memcmp_pages(page1, page2); | |
716 | } | |
717 | ||
718 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, | |
719 | pte_t *orig_pte) | |
720 | { | |
721 | struct mm_struct *mm = vma->vm_mm; | |
722 | unsigned long addr; | |
723 | pte_t *ptep; | |
724 | spinlock_t *ptl; | |
725 | int swapped; | |
726 | int err = -EFAULT; | |
727 | ||
728 | addr = page_address_in_vma(page, vma); | |
729 | if (addr == -EFAULT) | |
730 | goto out; | |
731 | ||
732 | ptep = page_check_address(page, mm, addr, &ptl, 0); | |
733 | if (!ptep) | |
734 | goto out; | |
735 | ||
736 | if (pte_write(*ptep)) { | |
737 | pte_t entry; | |
738 | ||
739 | swapped = PageSwapCache(page); | |
740 | flush_cache_page(vma, addr, page_to_pfn(page)); | |
741 | /* | |
742 | * Ok this is tricky, when get_user_pages_fast() run it doesnt | |
743 | * take any lock, therefore the check that we are going to make | |
744 | * with the pagecount against the mapcount is racey and | |
745 | * O_DIRECT can happen right after the check. | |
746 | * So we clear the pte and flush the tlb before the check | |
747 | * this assure us that no O_DIRECT can happen after the check | |
748 | * or in the middle of the check. | |
749 | */ | |
750 | entry = ptep_clear_flush(vma, addr, ptep); | |
751 | /* | |
752 | * Check that no O_DIRECT or similar I/O is in progress on the | |
753 | * page | |
754 | */ | |
31e855ea | 755 | if (page_mapcount(page) + 1 + swapped != page_count(page)) { |
31dbd01f IE |
756 | set_pte_at_notify(mm, addr, ptep, entry); |
757 | goto out_unlock; | |
758 | } | |
759 | entry = pte_wrprotect(entry); | |
760 | set_pte_at_notify(mm, addr, ptep, entry); | |
761 | } | |
762 | *orig_pte = *ptep; | |
763 | err = 0; | |
764 | ||
765 | out_unlock: | |
766 | pte_unmap_unlock(ptep, ptl); | |
767 | out: | |
768 | return err; | |
769 | } | |
770 | ||
771 | /** | |
772 | * replace_page - replace page in vma by new ksm page | |
8dd3557a HD |
773 | * @vma: vma that holds the pte pointing to page |
774 | * @page: the page we are replacing by kpage | |
775 | * @kpage: the ksm page we replace page by | |
31dbd01f IE |
776 | * @orig_pte: the original value of the pte |
777 | * | |
778 | * Returns 0 on success, -EFAULT on failure. | |
779 | */ | |
8dd3557a HD |
780 | static int replace_page(struct vm_area_struct *vma, struct page *page, |
781 | struct page *kpage, pte_t orig_pte) | |
31dbd01f IE |
782 | { |
783 | struct mm_struct *mm = vma->vm_mm; | |
784 | pgd_t *pgd; | |
785 | pud_t *pud; | |
786 | pmd_t *pmd; | |
787 | pte_t *ptep; | |
788 | spinlock_t *ptl; | |
789 | unsigned long addr; | |
31dbd01f IE |
790 | int err = -EFAULT; |
791 | ||
8dd3557a | 792 | addr = page_address_in_vma(page, vma); |
31dbd01f IE |
793 | if (addr == -EFAULT) |
794 | goto out; | |
795 | ||
796 | pgd = pgd_offset(mm, addr); | |
797 | if (!pgd_present(*pgd)) | |
798 | goto out; | |
799 | ||
800 | pud = pud_offset(pgd, addr); | |
801 | if (!pud_present(*pud)) | |
802 | goto out; | |
803 | ||
804 | pmd = pmd_offset(pud, addr); | |
805 | if (!pmd_present(*pmd)) | |
806 | goto out; | |
807 | ||
808 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); | |
809 | if (!pte_same(*ptep, orig_pte)) { | |
810 | pte_unmap_unlock(ptep, ptl); | |
811 | goto out; | |
812 | } | |
813 | ||
8dd3557a | 814 | get_page(kpage); |
5ad64688 | 815 | page_add_anon_rmap(kpage, vma, addr); |
31dbd01f IE |
816 | |
817 | flush_cache_page(vma, addr, pte_pfn(*ptep)); | |
818 | ptep_clear_flush(vma, addr, ptep); | |
8dd3557a | 819 | set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot)); |
31dbd01f | 820 | |
8dd3557a HD |
821 | page_remove_rmap(page); |
822 | put_page(page); | |
31dbd01f IE |
823 | |
824 | pte_unmap_unlock(ptep, ptl); | |
825 | err = 0; | |
826 | out: | |
827 | return err; | |
828 | } | |
829 | ||
830 | /* | |
831 | * try_to_merge_one_page - take two pages and merge them into one | |
8dd3557a HD |
832 | * @vma: the vma that holds the pte pointing to page |
833 | * @page: the PageAnon page that we want to replace with kpage | |
80e14822 HD |
834 | * @kpage: the PageKsm page that we want to map instead of page, |
835 | * or NULL the first time when we want to use page as kpage. | |
31dbd01f IE |
836 | * |
837 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
838 | */ | |
839 | static int try_to_merge_one_page(struct vm_area_struct *vma, | |
8dd3557a | 840 | struct page *page, struct page *kpage) |
31dbd01f IE |
841 | { |
842 | pte_t orig_pte = __pte(0); | |
843 | int err = -EFAULT; | |
844 | ||
db114b83 HD |
845 | if (page == kpage) /* ksm page forked */ |
846 | return 0; | |
847 | ||
31dbd01f IE |
848 | if (!(vma->vm_flags & VM_MERGEABLE)) |
849 | goto out; | |
8dd3557a | 850 | if (!PageAnon(page)) |
31dbd01f IE |
851 | goto out; |
852 | ||
31dbd01f IE |
853 | /* |
854 | * We need the page lock to read a stable PageSwapCache in | |
855 | * write_protect_page(). We use trylock_page() instead of | |
856 | * lock_page() because we don't want to wait here - we | |
857 | * prefer to continue scanning and merging different pages, | |
858 | * then come back to this page when it is unlocked. | |
859 | */ | |
8dd3557a | 860 | if (!trylock_page(page)) |
31e855ea | 861 | goto out; |
31dbd01f IE |
862 | /* |
863 | * If this anonymous page is mapped only here, its pte may need | |
864 | * to be write-protected. If it's mapped elsewhere, all of its | |
865 | * ptes are necessarily already write-protected. But in either | |
866 | * case, we need to lock and check page_count is not raised. | |
867 | */ | |
80e14822 HD |
868 | if (write_protect_page(vma, page, &orig_pte) == 0) { |
869 | if (!kpage) { | |
870 | /* | |
871 | * While we hold page lock, upgrade page from | |
872 | * PageAnon+anon_vma to PageKsm+NULL stable_node: | |
873 | * stable_tree_insert() will update stable_node. | |
874 | */ | |
875 | set_page_stable_node(page, NULL); | |
876 | mark_page_accessed(page); | |
877 | err = 0; | |
878 | } else if (pages_identical(page, kpage)) | |
879 | err = replace_page(vma, page, kpage, orig_pte); | |
880 | } | |
31dbd01f | 881 | |
80e14822 | 882 | if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { |
73848b46 | 883 | munlock_vma_page(page); |
5ad64688 HD |
884 | if (!PageMlocked(kpage)) { |
885 | unlock_page(page); | |
5ad64688 HD |
886 | lock_page(kpage); |
887 | mlock_vma_page(kpage); | |
888 | page = kpage; /* for final unlock */ | |
889 | } | |
890 | } | |
73848b46 | 891 | |
8dd3557a | 892 | unlock_page(page); |
31dbd01f IE |
893 | out: |
894 | return err; | |
895 | } | |
896 | ||
81464e30 HD |
897 | /* |
898 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, | |
899 | * but no new kernel page is allocated: kpage must already be a ksm page. | |
8dd3557a HD |
900 | * |
901 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
81464e30 | 902 | */ |
8dd3557a HD |
903 | static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, |
904 | struct page *page, struct page *kpage) | |
81464e30 | 905 | { |
8dd3557a | 906 | struct mm_struct *mm = rmap_item->mm; |
81464e30 HD |
907 | struct vm_area_struct *vma; |
908 | int err = -EFAULT; | |
909 | ||
8dd3557a HD |
910 | down_read(&mm->mmap_sem); |
911 | if (ksm_test_exit(mm)) | |
9ba69294 | 912 | goto out; |
8dd3557a HD |
913 | vma = find_vma(mm, rmap_item->address); |
914 | if (!vma || vma->vm_start > rmap_item->address) | |
81464e30 HD |
915 | goto out; |
916 | ||
8dd3557a | 917 | err = try_to_merge_one_page(vma, page, kpage); |
db114b83 HD |
918 | if (err) |
919 | goto out; | |
920 | ||
921 | /* Must get reference to anon_vma while still holding mmap_sem */ | |
922 | hold_anon_vma(rmap_item, vma->anon_vma); | |
81464e30 | 923 | out: |
8dd3557a | 924 | up_read(&mm->mmap_sem); |
81464e30 HD |
925 | return err; |
926 | } | |
927 | ||
31dbd01f IE |
928 | /* |
929 | * try_to_merge_two_pages - take two identical pages and prepare them | |
930 | * to be merged into one page. | |
931 | * | |
8dd3557a HD |
932 | * This function returns the kpage if we successfully merged two identical |
933 | * pages into one ksm page, NULL otherwise. | |
31dbd01f | 934 | * |
80e14822 | 935 | * Note that this function upgrades page to ksm page: if one of the pages |
31dbd01f IE |
936 | * is already a ksm page, try_to_merge_with_ksm_page should be used. |
937 | */ | |
8dd3557a HD |
938 | static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, |
939 | struct page *page, | |
940 | struct rmap_item *tree_rmap_item, | |
941 | struct page *tree_page) | |
31dbd01f | 942 | { |
80e14822 | 943 | int err; |
31dbd01f IE |
944 | |
945 | /* | |
946 | * The number of nodes in the stable tree | |
947 | * is the number of kernel pages that we hold. | |
948 | */ | |
949 | if (ksm_max_kernel_pages && | |
b4028260 | 950 | ksm_max_kernel_pages <= ksm_pages_shared) |
8dd3557a | 951 | return NULL; |
31dbd01f | 952 | |
80e14822 | 953 | err = try_to_merge_with_ksm_page(rmap_item, page, NULL); |
31dbd01f | 954 | if (!err) { |
8dd3557a | 955 | err = try_to_merge_with_ksm_page(tree_rmap_item, |
80e14822 | 956 | tree_page, page); |
31dbd01f | 957 | /* |
81464e30 HD |
958 | * If that fails, we have a ksm page with only one pte |
959 | * pointing to it: so break it. | |
31dbd01f | 960 | */ |
4035c07a | 961 | if (err) |
8dd3557a | 962 | break_cow(rmap_item); |
31dbd01f | 963 | } |
80e14822 | 964 | return err ? NULL : page; |
31dbd01f IE |
965 | } |
966 | ||
31dbd01f | 967 | /* |
8dd3557a | 968 | * stable_tree_search - search for page inside the stable tree |
31dbd01f IE |
969 | * |
970 | * This function checks if there is a page inside the stable tree | |
971 | * with identical content to the page that we are scanning right now. | |
972 | * | |
7b6ba2c7 | 973 | * This function returns the stable tree node of identical content if found, |
31dbd01f IE |
974 | * NULL otherwise. |
975 | */ | |
08beca44 | 976 | static struct stable_node *stable_tree_search(struct page *page) |
31dbd01f IE |
977 | { |
978 | struct rb_node *node = root_stable_tree.rb_node; | |
7b6ba2c7 | 979 | struct stable_node *stable_node; |
31dbd01f | 980 | |
08beca44 HD |
981 | stable_node = page_stable_node(page); |
982 | if (stable_node) { /* ksm page forked */ | |
983 | get_page(page); | |
984 | return stable_node; | |
985 | } | |
986 | ||
31dbd01f | 987 | while (node) { |
4035c07a | 988 | struct page *tree_page; |
31dbd01f IE |
989 | int ret; |
990 | ||
08beca44 | 991 | cond_resched(); |
7b6ba2c7 | 992 | stable_node = rb_entry(node, struct stable_node, node); |
4035c07a HD |
993 | tree_page = get_ksm_page(stable_node); |
994 | if (!tree_page) | |
995 | return NULL; | |
31dbd01f | 996 | |
4035c07a | 997 | ret = memcmp_pages(page, tree_page); |
31dbd01f | 998 | |
4035c07a HD |
999 | if (ret < 0) { |
1000 | put_page(tree_page); | |
31dbd01f | 1001 | node = node->rb_left; |
4035c07a HD |
1002 | } else if (ret > 0) { |
1003 | put_page(tree_page); | |
31dbd01f | 1004 | node = node->rb_right; |
4035c07a | 1005 | } else |
7b6ba2c7 | 1006 | return stable_node; |
31dbd01f IE |
1007 | } |
1008 | ||
1009 | return NULL; | |
1010 | } | |
1011 | ||
1012 | /* | |
1013 | * stable_tree_insert - insert rmap_item pointing to new ksm page | |
1014 | * into the stable tree. | |
1015 | * | |
7b6ba2c7 HD |
1016 | * This function returns the stable tree node just allocated on success, |
1017 | * NULL otherwise. | |
31dbd01f | 1018 | */ |
7b6ba2c7 | 1019 | static struct stable_node *stable_tree_insert(struct page *kpage) |
31dbd01f IE |
1020 | { |
1021 | struct rb_node **new = &root_stable_tree.rb_node; | |
1022 | struct rb_node *parent = NULL; | |
7b6ba2c7 | 1023 | struct stable_node *stable_node; |
31dbd01f IE |
1024 | |
1025 | while (*new) { | |
4035c07a | 1026 | struct page *tree_page; |
31dbd01f IE |
1027 | int ret; |
1028 | ||
08beca44 | 1029 | cond_resched(); |
7b6ba2c7 | 1030 | stable_node = rb_entry(*new, struct stable_node, node); |
4035c07a HD |
1031 | tree_page = get_ksm_page(stable_node); |
1032 | if (!tree_page) | |
1033 | return NULL; | |
31dbd01f | 1034 | |
4035c07a HD |
1035 | ret = memcmp_pages(kpage, tree_page); |
1036 | put_page(tree_page); | |
31dbd01f IE |
1037 | |
1038 | parent = *new; | |
1039 | if (ret < 0) | |
1040 | new = &parent->rb_left; | |
1041 | else if (ret > 0) | |
1042 | new = &parent->rb_right; | |
1043 | else { | |
1044 | /* | |
1045 | * It is not a bug that stable_tree_search() didn't | |
1046 | * find this node: because at that time our page was | |
1047 | * not yet write-protected, so may have changed since. | |
1048 | */ | |
1049 | return NULL; | |
1050 | } | |
1051 | } | |
1052 | ||
7b6ba2c7 HD |
1053 | stable_node = alloc_stable_node(); |
1054 | if (!stable_node) | |
1055 | return NULL; | |
31dbd01f | 1056 | |
7b6ba2c7 HD |
1057 | rb_link_node(&stable_node->node, parent, new); |
1058 | rb_insert_color(&stable_node->node, &root_stable_tree); | |
1059 | ||
1060 | INIT_HLIST_HEAD(&stable_node->hlist); | |
1061 | ||
08beca44 HD |
1062 | stable_node->page = kpage; |
1063 | set_page_stable_node(kpage, stable_node); | |
1064 | ||
7b6ba2c7 | 1065 | return stable_node; |
31dbd01f IE |
1066 | } |
1067 | ||
1068 | /* | |
8dd3557a HD |
1069 | * unstable_tree_search_insert - search for identical page, |
1070 | * else insert rmap_item into the unstable tree. | |
31dbd01f IE |
1071 | * |
1072 | * This function searches for a page in the unstable tree identical to the | |
1073 | * page currently being scanned; and if no identical page is found in the | |
1074 | * tree, we insert rmap_item as a new object into the unstable tree. | |
1075 | * | |
1076 | * This function returns pointer to rmap_item found to be identical | |
1077 | * to the currently scanned page, NULL otherwise. | |
1078 | * | |
1079 | * This function does both searching and inserting, because they share | |
1080 | * the same walking algorithm in an rbtree. | |
1081 | */ | |
8dd3557a HD |
1082 | static |
1083 | struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, | |
1084 | struct page *page, | |
1085 | struct page **tree_pagep) | |
1086 | ||
31dbd01f IE |
1087 | { |
1088 | struct rb_node **new = &root_unstable_tree.rb_node; | |
1089 | struct rb_node *parent = NULL; | |
1090 | ||
1091 | while (*new) { | |
1092 | struct rmap_item *tree_rmap_item; | |
8dd3557a | 1093 | struct page *tree_page; |
31dbd01f IE |
1094 | int ret; |
1095 | ||
d178f27f | 1096 | cond_resched(); |
31dbd01f | 1097 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
8dd3557a HD |
1098 | tree_page = get_mergeable_page(tree_rmap_item); |
1099 | if (!tree_page) | |
31dbd01f IE |
1100 | return NULL; |
1101 | ||
1102 | /* | |
8dd3557a | 1103 | * Don't substitute a ksm page for a forked page. |
31dbd01f | 1104 | */ |
8dd3557a HD |
1105 | if (page == tree_page) { |
1106 | put_page(tree_page); | |
31dbd01f IE |
1107 | return NULL; |
1108 | } | |
1109 | ||
8dd3557a | 1110 | ret = memcmp_pages(page, tree_page); |
31dbd01f IE |
1111 | |
1112 | parent = *new; | |
1113 | if (ret < 0) { | |
8dd3557a | 1114 | put_page(tree_page); |
31dbd01f IE |
1115 | new = &parent->rb_left; |
1116 | } else if (ret > 0) { | |
8dd3557a | 1117 | put_page(tree_page); |
31dbd01f IE |
1118 | new = &parent->rb_right; |
1119 | } else { | |
8dd3557a | 1120 | *tree_pagep = tree_page; |
31dbd01f IE |
1121 | return tree_rmap_item; |
1122 | } | |
1123 | } | |
1124 | ||
7b6ba2c7 | 1125 | rmap_item->address |= UNSTABLE_FLAG; |
31dbd01f IE |
1126 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); |
1127 | rb_link_node(&rmap_item->node, parent, new); | |
1128 | rb_insert_color(&rmap_item->node, &root_unstable_tree); | |
1129 | ||
473b0ce4 | 1130 | ksm_pages_unshared++; |
31dbd01f IE |
1131 | return NULL; |
1132 | } | |
1133 | ||
1134 | /* | |
1135 | * stable_tree_append - add another rmap_item to the linked list of | |
1136 | * rmap_items hanging off a given node of the stable tree, all sharing | |
1137 | * the same ksm page. | |
1138 | */ | |
1139 | static void stable_tree_append(struct rmap_item *rmap_item, | |
7b6ba2c7 | 1140 | struct stable_node *stable_node) |
31dbd01f | 1141 | { |
7b6ba2c7 | 1142 | rmap_item->head = stable_node; |
31dbd01f | 1143 | rmap_item->address |= STABLE_FLAG; |
7b6ba2c7 | 1144 | hlist_add_head(&rmap_item->hlist, &stable_node->hlist); |
e178dfde | 1145 | |
7b6ba2c7 HD |
1146 | if (rmap_item->hlist.next) |
1147 | ksm_pages_sharing++; | |
1148 | else | |
1149 | ksm_pages_shared++; | |
31dbd01f IE |
1150 | } |
1151 | ||
1152 | /* | |
81464e30 HD |
1153 | * cmp_and_merge_page - first see if page can be merged into the stable tree; |
1154 | * if not, compare checksum to previous and if it's the same, see if page can | |
1155 | * be inserted into the unstable tree, or merged with a page already there and | |
1156 | * both transferred to the stable tree. | |
31dbd01f IE |
1157 | * |
1158 | * @page: the page that we are searching identical page to. | |
1159 | * @rmap_item: the reverse mapping into the virtual address of this page | |
1160 | */ | |
1161 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) | |
1162 | { | |
31dbd01f | 1163 | struct rmap_item *tree_rmap_item; |
8dd3557a | 1164 | struct page *tree_page = NULL; |
7b6ba2c7 | 1165 | struct stable_node *stable_node; |
8dd3557a | 1166 | struct page *kpage; |
31dbd01f IE |
1167 | unsigned int checksum; |
1168 | int err; | |
1169 | ||
93d17715 | 1170 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
1171 | |
1172 | /* We first start with searching the page inside the stable tree */ | |
08beca44 | 1173 | stable_node = stable_tree_search(page); |
7b6ba2c7 | 1174 | if (stable_node) { |
08beca44 HD |
1175 | kpage = stable_node->page; |
1176 | err = try_to_merge_with_ksm_page(rmap_item, page, kpage); | |
31dbd01f IE |
1177 | if (!err) { |
1178 | /* | |
1179 | * The page was successfully merged: | |
1180 | * add its rmap_item to the stable tree. | |
1181 | */ | |
5ad64688 | 1182 | lock_page(kpage); |
7b6ba2c7 | 1183 | stable_tree_append(rmap_item, stable_node); |
5ad64688 | 1184 | unlock_page(kpage); |
31dbd01f | 1185 | } |
8dd3557a | 1186 | put_page(kpage); |
31dbd01f IE |
1187 | return; |
1188 | } | |
1189 | ||
1190 | /* | |
4035c07a HD |
1191 | * If the hash value of the page has changed from the last time |
1192 | * we calculated it, this page is changing frequently: therefore we | |
1193 | * don't want to insert it in the unstable tree, and we don't want | |
1194 | * to waste our time searching for something identical to it there. | |
31dbd01f IE |
1195 | */ |
1196 | checksum = calc_checksum(page); | |
1197 | if (rmap_item->oldchecksum != checksum) { | |
1198 | rmap_item->oldchecksum = checksum; | |
1199 | return; | |
1200 | } | |
1201 | ||
8dd3557a HD |
1202 | tree_rmap_item = |
1203 | unstable_tree_search_insert(rmap_item, page, &tree_page); | |
31dbd01f | 1204 | if (tree_rmap_item) { |
8dd3557a HD |
1205 | kpage = try_to_merge_two_pages(rmap_item, page, |
1206 | tree_rmap_item, tree_page); | |
1207 | put_page(tree_page); | |
31dbd01f IE |
1208 | /* |
1209 | * As soon as we merge this page, we want to remove the | |
1210 | * rmap_item of the page we have merged with from the unstable | |
1211 | * tree, and insert it instead as new node in the stable tree. | |
1212 | */ | |
8dd3557a | 1213 | if (kpage) { |
93d17715 | 1214 | remove_rmap_item_from_tree(tree_rmap_item); |
473b0ce4 | 1215 | |
5ad64688 | 1216 | lock_page(kpage); |
7b6ba2c7 HD |
1217 | stable_node = stable_tree_insert(kpage); |
1218 | if (stable_node) { | |
1219 | stable_tree_append(tree_rmap_item, stable_node); | |
1220 | stable_tree_append(rmap_item, stable_node); | |
1221 | } | |
5ad64688 | 1222 | unlock_page(kpage); |
7b6ba2c7 | 1223 | |
31dbd01f IE |
1224 | /* |
1225 | * If we fail to insert the page into the stable tree, | |
1226 | * we will have 2 virtual addresses that are pointing | |
1227 | * to a ksm page left outside the stable tree, | |
1228 | * in which case we need to break_cow on both. | |
1229 | */ | |
7b6ba2c7 | 1230 | if (!stable_node) { |
8dd3557a HD |
1231 | break_cow(tree_rmap_item); |
1232 | break_cow(rmap_item); | |
31dbd01f IE |
1233 | } |
1234 | } | |
31dbd01f IE |
1235 | } |
1236 | } | |
1237 | ||
1238 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, | |
6514d511 | 1239 | struct rmap_item **rmap_list, |
31dbd01f IE |
1240 | unsigned long addr) |
1241 | { | |
1242 | struct rmap_item *rmap_item; | |
1243 | ||
6514d511 HD |
1244 | while (*rmap_list) { |
1245 | rmap_item = *rmap_list; | |
93d17715 | 1246 | if ((rmap_item->address & PAGE_MASK) == addr) |
31dbd01f | 1247 | return rmap_item; |
31dbd01f IE |
1248 | if (rmap_item->address > addr) |
1249 | break; | |
6514d511 | 1250 | *rmap_list = rmap_item->rmap_list; |
31dbd01f | 1251 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
1252 | free_rmap_item(rmap_item); |
1253 | } | |
1254 | ||
1255 | rmap_item = alloc_rmap_item(); | |
1256 | if (rmap_item) { | |
1257 | /* It has already been zeroed */ | |
1258 | rmap_item->mm = mm_slot->mm; | |
1259 | rmap_item->address = addr; | |
6514d511 HD |
1260 | rmap_item->rmap_list = *rmap_list; |
1261 | *rmap_list = rmap_item; | |
31dbd01f IE |
1262 | } |
1263 | return rmap_item; | |
1264 | } | |
1265 | ||
1266 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) | |
1267 | { | |
1268 | struct mm_struct *mm; | |
1269 | struct mm_slot *slot; | |
1270 | struct vm_area_struct *vma; | |
1271 | struct rmap_item *rmap_item; | |
1272 | ||
1273 | if (list_empty(&ksm_mm_head.mm_list)) | |
1274 | return NULL; | |
1275 | ||
1276 | slot = ksm_scan.mm_slot; | |
1277 | if (slot == &ksm_mm_head) { | |
1278 | root_unstable_tree = RB_ROOT; | |
1279 | ||
1280 | spin_lock(&ksm_mmlist_lock); | |
1281 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); | |
1282 | ksm_scan.mm_slot = slot; | |
1283 | spin_unlock(&ksm_mmlist_lock); | |
1284 | next_mm: | |
1285 | ksm_scan.address = 0; | |
6514d511 | 1286 | ksm_scan.rmap_list = &slot->rmap_list; |
31dbd01f IE |
1287 | } |
1288 | ||
1289 | mm = slot->mm; | |
1290 | down_read(&mm->mmap_sem); | |
9ba69294 HD |
1291 | if (ksm_test_exit(mm)) |
1292 | vma = NULL; | |
1293 | else | |
1294 | vma = find_vma(mm, ksm_scan.address); | |
1295 | ||
1296 | for (; vma; vma = vma->vm_next) { | |
31dbd01f IE |
1297 | if (!(vma->vm_flags & VM_MERGEABLE)) |
1298 | continue; | |
1299 | if (ksm_scan.address < vma->vm_start) | |
1300 | ksm_scan.address = vma->vm_start; | |
1301 | if (!vma->anon_vma) | |
1302 | ksm_scan.address = vma->vm_end; | |
1303 | ||
1304 | while (ksm_scan.address < vma->vm_end) { | |
9ba69294 HD |
1305 | if (ksm_test_exit(mm)) |
1306 | break; | |
31dbd01f IE |
1307 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); |
1308 | if (*page && PageAnon(*page)) { | |
1309 | flush_anon_page(vma, *page, ksm_scan.address); | |
1310 | flush_dcache_page(*page); | |
1311 | rmap_item = get_next_rmap_item(slot, | |
6514d511 | 1312 | ksm_scan.rmap_list, ksm_scan.address); |
31dbd01f | 1313 | if (rmap_item) { |
6514d511 HD |
1314 | ksm_scan.rmap_list = |
1315 | &rmap_item->rmap_list; | |
31dbd01f IE |
1316 | ksm_scan.address += PAGE_SIZE; |
1317 | } else | |
1318 | put_page(*page); | |
1319 | up_read(&mm->mmap_sem); | |
1320 | return rmap_item; | |
1321 | } | |
1322 | if (*page) | |
1323 | put_page(*page); | |
1324 | ksm_scan.address += PAGE_SIZE; | |
1325 | cond_resched(); | |
1326 | } | |
1327 | } | |
1328 | ||
9ba69294 HD |
1329 | if (ksm_test_exit(mm)) { |
1330 | ksm_scan.address = 0; | |
6514d511 | 1331 | ksm_scan.rmap_list = &slot->rmap_list; |
9ba69294 | 1332 | } |
31dbd01f IE |
1333 | /* |
1334 | * Nuke all the rmap_items that are above this current rmap: | |
1335 | * because there were no VM_MERGEABLE vmas with such addresses. | |
1336 | */ | |
6514d511 | 1337 | remove_trailing_rmap_items(slot, ksm_scan.rmap_list); |
31dbd01f IE |
1338 | |
1339 | spin_lock(&ksm_mmlist_lock); | |
cd551f97 HD |
1340 | ksm_scan.mm_slot = list_entry(slot->mm_list.next, |
1341 | struct mm_slot, mm_list); | |
1342 | if (ksm_scan.address == 0) { | |
1343 | /* | |
1344 | * We've completed a full scan of all vmas, holding mmap_sem | |
1345 | * throughout, and found no VM_MERGEABLE: so do the same as | |
1346 | * __ksm_exit does to remove this mm from all our lists now. | |
9ba69294 HD |
1347 | * This applies either when cleaning up after __ksm_exit |
1348 | * (but beware: we can reach here even before __ksm_exit), | |
1349 | * or when all VM_MERGEABLE areas have been unmapped (and | |
1350 | * mmap_sem then protects against race with MADV_MERGEABLE). | |
cd551f97 HD |
1351 | */ |
1352 | hlist_del(&slot->link); | |
1353 | list_del(&slot->mm_list); | |
9ba69294 HD |
1354 | spin_unlock(&ksm_mmlist_lock); |
1355 | ||
cd551f97 HD |
1356 | free_mm_slot(slot); |
1357 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
9ba69294 HD |
1358 | up_read(&mm->mmap_sem); |
1359 | mmdrop(mm); | |
1360 | } else { | |
1361 | spin_unlock(&ksm_mmlist_lock); | |
1362 | up_read(&mm->mmap_sem); | |
cd551f97 | 1363 | } |
31dbd01f IE |
1364 | |
1365 | /* Repeat until we've completed scanning the whole list */ | |
cd551f97 | 1366 | slot = ksm_scan.mm_slot; |
31dbd01f IE |
1367 | if (slot != &ksm_mm_head) |
1368 | goto next_mm; | |
1369 | ||
31dbd01f IE |
1370 | ksm_scan.seqnr++; |
1371 | return NULL; | |
1372 | } | |
1373 | ||
1374 | /** | |
1375 | * ksm_do_scan - the ksm scanner main worker function. | |
1376 | * @scan_npages - number of pages we want to scan before we return. | |
1377 | */ | |
1378 | static void ksm_do_scan(unsigned int scan_npages) | |
1379 | { | |
1380 | struct rmap_item *rmap_item; | |
1381 | struct page *page; | |
1382 | ||
1383 | while (scan_npages--) { | |
1384 | cond_resched(); | |
1385 | rmap_item = scan_get_next_rmap_item(&page); | |
1386 | if (!rmap_item) | |
1387 | return; | |
1388 | if (!PageKsm(page) || !in_stable_tree(rmap_item)) | |
1389 | cmp_and_merge_page(page, rmap_item); | |
1390 | put_page(page); | |
1391 | } | |
1392 | } | |
1393 | ||
6e158384 HD |
1394 | static int ksmd_should_run(void) |
1395 | { | |
1396 | return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); | |
1397 | } | |
1398 | ||
31dbd01f IE |
1399 | static int ksm_scan_thread(void *nothing) |
1400 | { | |
339aa624 | 1401 | set_user_nice(current, 5); |
31dbd01f IE |
1402 | |
1403 | while (!kthread_should_stop()) { | |
6e158384 HD |
1404 | mutex_lock(&ksm_thread_mutex); |
1405 | if (ksmd_should_run()) | |
31dbd01f | 1406 | ksm_do_scan(ksm_thread_pages_to_scan); |
6e158384 HD |
1407 | mutex_unlock(&ksm_thread_mutex); |
1408 | ||
1409 | if (ksmd_should_run()) { | |
31dbd01f IE |
1410 | schedule_timeout_interruptible( |
1411 | msecs_to_jiffies(ksm_thread_sleep_millisecs)); | |
1412 | } else { | |
1413 | wait_event_interruptible(ksm_thread_wait, | |
6e158384 | 1414 | ksmd_should_run() || kthread_should_stop()); |
31dbd01f IE |
1415 | } |
1416 | } | |
1417 | return 0; | |
1418 | } | |
1419 | ||
f8af4da3 HD |
1420 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
1421 | unsigned long end, int advice, unsigned long *vm_flags) | |
1422 | { | |
1423 | struct mm_struct *mm = vma->vm_mm; | |
d952b791 | 1424 | int err; |
f8af4da3 HD |
1425 | |
1426 | switch (advice) { | |
1427 | case MADV_MERGEABLE: | |
1428 | /* | |
1429 | * Be somewhat over-protective for now! | |
1430 | */ | |
1431 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | | |
1432 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | | |
1433 | VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | | |
5ad64688 | 1434 | VM_NONLINEAR | VM_MIXEDMAP | VM_SAO)) |
f8af4da3 HD |
1435 | return 0; /* just ignore the advice */ |
1436 | ||
d952b791 HD |
1437 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
1438 | err = __ksm_enter(mm); | |
1439 | if (err) | |
1440 | return err; | |
1441 | } | |
f8af4da3 HD |
1442 | |
1443 | *vm_flags |= VM_MERGEABLE; | |
1444 | break; | |
1445 | ||
1446 | case MADV_UNMERGEABLE: | |
1447 | if (!(*vm_flags & VM_MERGEABLE)) | |
1448 | return 0; /* just ignore the advice */ | |
1449 | ||
d952b791 HD |
1450 | if (vma->anon_vma) { |
1451 | err = unmerge_ksm_pages(vma, start, end); | |
1452 | if (err) | |
1453 | return err; | |
1454 | } | |
f8af4da3 HD |
1455 | |
1456 | *vm_flags &= ~VM_MERGEABLE; | |
1457 | break; | |
1458 | } | |
1459 | ||
1460 | return 0; | |
1461 | } | |
1462 | ||
1463 | int __ksm_enter(struct mm_struct *mm) | |
1464 | { | |
6e158384 HD |
1465 | struct mm_slot *mm_slot; |
1466 | int needs_wakeup; | |
1467 | ||
1468 | mm_slot = alloc_mm_slot(); | |
31dbd01f IE |
1469 | if (!mm_slot) |
1470 | return -ENOMEM; | |
1471 | ||
6e158384 HD |
1472 | /* Check ksm_run too? Would need tighter locking */ |
1473 | needs_wakeup = list_empty(&ksm_mm_head.mm_list); | |
1474 | ||
31dbd01f IE |
1475 | spin_lock(&ksm_mmlist_lock); |
1476 | insert_to_mm_slots_hash(mm, mm_slot); | |
1477 | /* | |
1478 | * Insert just behind the scanning cursor, to let the area settle | |
1479 | * down a little; when fork is followed by immediate exec, we don't | |
1480 | * want ksmd to waste time setting up and tearing down an rmap_list. | |
1481 | */ | |
1482 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); | |
1483 | spin_unlock(&ksm_mmlist_lock); | |
1484 | ||
f8af4da3 | 1485 | set_bit(MMF_VM_MERGEABLE, &mm->flags); |
9ba69294 | 1486 | atomic_inc(&mm->mm_count); |
6e158384 HD |
1487 | |
1488 | if (needs_wakeup) | |
1489 | wake_up_interruptible(&ksm_thread_wait); | |
1490 | ||
f8af4da3 HD |
1491 | return 0; |
1492 | } | |
1493 | ||
1c2fb7a4 | 1494 | void __ksm_exit(struct mm_struct *mm) |
f8af4da3 | 1495 | { |
cd551f97 | 1496 | struct mm_slot *mm_slot; |
9ba69294 | 1497 | int easy_to_free = 0; |
cd551f97 | 1498 | |
31dbd01f | 1499 | /* |
9ba69294 HD |
1500 | * This process is exiting: if it's straightforward (as is the |
1501 | * case when ksmd was never running), free mm_slot immediately. | |
1502 | * But if it's at the cursor or has rmap_items linked to it, use | |
1503 | * mmap_sem to synchronize with any break_cows before pagetables | |
1504 | * are freed, and leave the mm_slot on the list for ksmd to free. | |
1505 | * Beware: ksm may already have noticed it exiting and freed the slot. | |
31dbd01f | 1506 | */ |
9ba69294 | 1507 | |
cd551f97 HD |
1508 | spin_lock(&ksm_mmlist_lock); |
1509 | mm_slot = get_mm_slot(mm); | |
9ba69294 | 1510 | if (mm_slot && ksm_scan.mm_slot != mm_slot) { |
6514d511 | 1511 | if (!mm_slot->rmap_list) { |
9ba69294 HD |
1512 | hlist_del(&mm_slot->link); |
1513 | list_del(&mm_slot->mm_list); | |
1514 | easy_to_free = 1; | |
1515 | } else { | |
1516 | list_move(&mm_slot->mm_list, | |
1517 | &ksm_scan.mm_slot->mm_list); | |
1518 | } | |
cd551f97 | 1519 | } |
cd551f97 HD |
1520 | spin_unlock(&ksm_mmlist_lock); |
1521 | ||
9ba69294 HD |
1522 | if (easy_to_free) { |
1523 | free_mm_slot(mm_slot); | |
1524 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
1525 | mmdrop(mm); | |
1526 | } else if (mm_slot) { | |
9ba69294 HD |
1527 | down_write(&mm->mmap_sem); |
1528 | up_write(&mm->mmap_sem); | |
9ba69294 | 1529 | } |
31dbd01f IE |
1530 | } |
1531 | ||
5ad64688 HD |
1532 | struct page *ksm_does_need_to_copy(struct page *page, |
1533 | struct vm_area_struct *vma, unsigned long address) | |
1534 | { | |
1535 | struct page *new_page; | |
1536 | ||
1537 | unlock_page(page); /* any racers will COW it, not modify it */ | |
1538 | ||
1539 | new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); | |
1540 | if (new_page) { | |
1541 | copy_user_highpage(new_page, page, address, vma); | |
1542 | ||
1543 | SetPageDirty(new_page); | |
1544 | __SetPageUptodate(new_page); | |
1545 | SetPageSwapBacked(new_page); | |
1546 | __set_page_locked(new_page); | |
1547 | ||
1548 | if (page_evictable(new_page, vma)) | |
1549 | lru_cache_add_lru(new_page, LRU_ACTIVE_ANON); | |
1550 | else | |
1551 | add_page_to_unevictable_list(new_page); | |
1552 | } | |
1553 | ||
1554 | page_cache_release(page); | |
1555 | return new_page; | |
1556 | } | |
1557 | ||
1558 | int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg, | |
1559 | unsigned long *vm_flags) | |
1560 | { | |
1561 | struct stable_node *stable_node; | |
1562 | struct rmap_item *rmap_item; | |
1563 | struct hlist_node *hlist; | |
1564 | unsigned int mapcount = page_mapcount(page); | |
1565 | int referenced = 0; | |
db114b83 | 1566 | int search_new_forks = 0; |
5ad64688 HD |
1567 | |
1568 | VM_BUG_ON(!PageKsm(page)); | |
1569 | VM_BUG_ON(!PageLocked(page)); | |
1570 | ||
1571 | stable_node = page_stable_node(page); | |
1572 | if (!stable_node) | |
1573 | return 0; | |
db114b83 | 1574 | again: |
5ad64688 | 1575 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
db114b83 HD |
1576 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1577 | struct vm_area_struct *vma; | |
5ad64688 | 1578 | |
db114b83 HD |
1579 | spin_lock(&anon_vma->lock); |
1580 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1581 | if (rmap_item->address < vma->vm_start || | |
1582 | rmap_item->address >= vma->vm_end) | |
1583 | continue; | |
1584 | /* | |
1585 | * Initially we examine only the vma which covers this | |
1586 | * rmap_item; but later, if there is still work to do, | |
1587 | * we examine covering vmas in other mms: in case they | |
1588 | * were forked from the original since ksmd passed. | |
1589 | */ | |
1590 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1591 | continue; | |
1592 | ||
1593 | if (memcg && !mm_match_cgroup(vma->vm_mm, memcg)) | |
1594 | continue; | |
5ad64688 | 1595 | |
db114b83 | 1596 | referenced += page_referenced_one(page, vma, |
5ad64688 | 1597 | rmap_item->address, &mapcount, vm_flags); |
db114b83 HD |
1598 | if (!search_new_forks || !mapcount) |
1599 | break; | |
1600 | } | |
1601 | spin_unlock(&anon_vma->lock); | |
5ad64688 HD |
1602 | if (!mapcount) |
1603 | goto out; | |
1604 | } | |
db114b83 HD |
1605 | if (!search_new_forks++) |
1606 | goto again; | |
5ad64688 | 1607 | out: |
5ad64688 HD |
1608 | return referenced; |
1609 | } | |
1610 | ||
1611 | int try_to_unmap_ksm(struct page *page, enum ttu_flags flags) | |
1612 | { | |
1613 | struct stable_node *stable_node; | |
1614 | struct hlist_node *hlist; | |
1615 | struct rmap_item *rmap_item; | |
1616 | int ret = SWAP_AGAIN; | |
db114b83 | 1617 | int search_new_forks = 0; |
5ad64688 HD |
1618 | |
1619 | VM_BUG_ON(!PageKsm(page)); | |
1620 | VM_BUG_ON(!PageLocked(page)); | |
1621 | ||
1622 | stable_node = page_stable_node(page); | |
1623 | if (!stable_node) | |
1624 | return SWAP_FAIL; | |
db114b83 | 1625 | again: |
5ad64688 | 1626 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
db114b83 HD |
1627 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1628 | struct vm_area_struct *vma; | |
5ad64688 | 1629 | |
db114b83 HD |
1630 | spin_lock(&anon_vma->lock); |
1631 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1632 | if (rmap_item->address < vma->vm_start || | |
1633 | rmap_item->address >= vma->vm_end) | |
1634 | continue; | |
1635 | /* | |
1636 | * Initially we examine only the vma which covers this | |
1637 | * rmap_item; but later, if there is still work to do, | |
1638 | * we examine covering vmas in other mms: in case they | |
1639 | * were forked from the original since ksmd passed. | |
1640 | */ | |
1641 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1642 | continue; | |
1643 | ||
1644 | ret = try_to_unmap_one(page, vma, | |
1645 | rmap_item->address, flags); | |
1646 | if (ret != SWAP_AGAIN || !page_mapped(page)) { | |
1647 | spin_unlock(&anon_vma->lock); | |
1648 | goto out; | |
1649 | } | |
1650 | } | |
1651 | spin_unlock(&anon_vma->lock); | |
5ad64688 | 1652 | } |
db114b83 HD |
1653 | if (!search_new_forks++) |
1654 | goto again; | |
5ad64688 | 1655 | out: |
5ad64688 HD |
1656 | return ret; |
1657 | } | |
1658 | ||
e9995ef9 HD |
1659 | #ifdef CONFIG_MIGRATION |
1660 | int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *, | |
1661 | struct vm_area_struct *, unsigned long, void *), void *arg) | |
1662 | { | |
1663 | struct stable_node *stable_node; | |
1664 | struct hlist_node *hlist; | |
1665 | struct rmap_item *rmap_item; | |
1666 | int ret = SWAP_AGAIN; | |
1667 | int search_new_forks = 0; | |
1668 | ||
1669 | VM_BUG_ON(!PageKsm(page)); | |
1670 | VM_BUG_ON(!PageLocked(page)); | |
1671 | ||
1672 | stable_node = page_stable_node(page); | |
1673 | if (!stable_node) | |
1674 | return ret; | |
1675 | again: | |
1676 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { | |
1677 | struct anon_vma *anon_vma = rmap_item->anon_vma; | |
1678 | struct vm_area_struct *vma; | |
1679 | ||
1680 | spin_lock(&anon_vma->lock); | |
1681 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1682 | if (rmap_item->address < vma->vm_start || | |
1683 | rmap_item->address >= vma->vm_end) | |
1684 | continue; | |
1685 | /* | |
1686 | * Initially we examine only the vma which covers this | |
1687 | * rmap_item; but later, if there is still work to do, | |
1688 | * we examine covering vmas in other mms: in case they | |
1689 | * were forked from the original since ksmd passed. | |
1690 | */ | |
1691 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1692 | continue; | |
1693 | ||
1694 | ret = rmap_one(page, vma, rmap_item->address, arg); | |
1695 | if (ret != SWAP_AGAIN) { | |
1696 | spin_unlock(&anon_vma->lock); | |
1697 | goto out; | |
1698 | } | |
1699 | } | |
1700 | spin_unlock(&anon_vma->lock); | |
1701 | } | |
1702 | if (!search_new_forks++) | |
1703 | goto again; | |
1704 | out: | |
1705 | return ret; | |
1706 | } | |
1707 | ||
1708 | void ksm_migrate_page(struct page *newpage, struct page *oldpage) | |
1709 | { | |
1710 | struct stable_node *stable_node; | |
1711 | ||
1712 | VM_BUG_ON(!PageLocked(oldpage)); | |
1713 | VM_BUG_ON(!PageLocked(newpage)); | |
1714 | VM_BUG_ON(newpage->mapping != oldpage->mapping); | |
1715 | ||
1716 | stable_node = page_stable_node(newpage); | |
1717 | if (stable_node) { | |
1718 | VM_BUG_ON(stable_node->page != oldpage); | |
1719 | stable_node->page = newpage; | |
1720 | } | |
1721 | } | |
1722 | #endif /* CONFIG_MIGRATION */ | |
1723 | ||
2ffd8679 HD |
1724 | #ifdef CONFIG_SYSFS |
1725 | /* | |
1726 | * This all compiles without CONFIG_SYSFS, but is a waste of space. | |
1727 | */ | |
1728 | ||
31dbd01f IE |
1729 | #define KSM_ATTR_RO(_name) \ |
1730 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) | |
1731 | #define KSM_ATTR(_name) \ | |
1732 | static struct kobj_attribute _name##_attr = \ | |
1733 | __ATTR(_name, 0644, _name##_show, _name##_store) | |
1734 | ||
1735 | static ssize_t sleep_millisecs_show(struct kobject *kobj, | |
1736 | struct kobj_attribute *attr, char *buf) | |
1737 | { | |
1738 | return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); | |
1739 | } | |
1740 | ||
1741 | static ssize_t sleep_millisecs_store(struct kobject *kobj, | |
1742 | struct kobj_attribute *attr, | |
1743 | const char *buf, size_t count) | |
1744 | { | |
1745 | unsigned long msecs; | |
1746 | int err; | |
1747 | ||
1748 | err = strict_strtoul(buf, 10, &msecs); | |
1749 | if (err || msecs > UINT_MAX) | |
1750 | return -EINVAL; | |
1751 | ||
1752 | ksm_thread_sleep_millisecs = msecs; | |
1753 | ||
1754 | return count; | |
1755 | } | |
1756 | KSM_ATTR(sleep_millisecs); | |
1757 | ||
1758 | static ssize_t pages_to_scan_show(struct kobject *kobj, | |
1759 | struct kobj_attribute *attr, char *buf) | |
1760 | { | |
1761 | return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); | |
1762 | } | |
1763 | ||
1764 | static ssize_t pages_to_scan_store(struct kobject *kobj, | |
1765 | struct kobj_attribute *attr, | |
1766 | const char *buf, size_t count) | |
1767 | { | |
1768 | int err; | |
1769 | unsigned long nr_pages; | |
1770 | ||
1771 | err = strict_strtoul(buf, 10, &nr_pages); | |
1772 | if (err || nr_pages > UINT_MAX) | |
1773 | return -EINVAL; | |
1774 | ||
1775 | ksm_thread_pages_to_scan = nr_pages; | |
1776 | ||
1777 | return count; | |
1778 | } | |
1779 | KSM_ATTR(pages_to_scan); | |
1780 | ||
1781 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, | |
1782 | char *buf) | |
1783 | { | |
1784 | return sprintf(buf, "%u\n", ksm_run); | |
1785 | } | |
1786 | ||
1787 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, | |
1788 | const char *buf, size_t count) | |
1789 | { | |
1790 | int err; | |
1791 | unsigned long flags; | |
1792 | ||
1793 | err = strict_strtoul(buf, 10, &flags); | |
1794 | if (err || flags > UINT_MAX) | |
1795 | return -EINVAL; | |
1796 | if (flags > KSM_RUN_UNMERGE) | |
1797 | return -EINVAL; | |
1798 | ||
1799 | /* | |
1800 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. | |
1801 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, | |
b4028260 | 1802 | * breaking COW to free the unswappable pages_shared (but leaves |
31dbd01f IE |
1803 | * mm_slots on the list for when ksmd may be set running again). |
1804 | */ | |
1805 | ||
1806 | mutex_lock(&ksm_thread_mutex); | |
1807 | if (ksm_run != flags) { | |
1808 | ksm_run = flags; | |
d952b791 | 1809 | if (flags & KSM_RUN_UNMERGE) { |
35451bee | 1810 | current->flags |= PF_OOM_ORIGIN; |
d952b791 | 1811 | err = unmerge_and_remove_all_rmap_items(); |
35451bee | 1812 | current->flags &= ~PF_OOM_ORIGIN; |
d952b791 HD |
1813 | if (err) { |
1814 | ksm_run = KSM_RUN_STOP; | |
1815 | count = err; | |
1816 | } | |
1817 | } | |
31dbd01f IE |
1818 | } |
1819 | mutex_unlock(&ksm_thread_mutex); | |
1820 | ||
1821 | if (flags & KSM_RUN_MERGE) | |
1822 | wake_up_interruptible(&ksm_thread_wait); | |
1823 | ||
1824 | return count; | |
1825 | } | |
1826 | KSM_ATTR(run); | |
1827 | ||
31dbd01f IE |
1828 | static ssize_t max_kernel_pages_store(struct kobject *kobj, |
1829 | struct kobj_attribute *attr, | |
1830 | const char *buf, size_t count) | |
1831 | { | |
1832 | int err; | |
1833 | unsigned long nr_pages; | |
1834 | ||
1835 | err = strict_strtoul(buf, 10, &nr_pages); | |
1836 | if (err) | |
1837 | return -EINVAL; | |
1838 | ||
1839 | ksm_max_kernel_pages = nr_pages; | |
1840 | ||
1841 | return count; | |
1842 | } | |
1843 | ||
1844 | static ssize_t max_kernel_pages_show(struct kobject *kobj, | |
1845 | struct kobj_attribute *attr, char *buf) | |
1846 | { | |
1847 | return sprintf(buf, "%lu\n", ksm_max_kernel_pages); | |
1848 | } | |
1849 | KSM_ATTR(max_kernel_pages); | |
1850 | ||
b4028260 HD |
1851 | static ssize_t pages_shared_show(struct kobject *kobj, |
1852 | struct kobj_attribute *attr, char *buf) | |
1853 | { | |
1854 | return sprintf(buf, "%lu\n", ksm_pages_shared); | |
1855 | } | |
1856 | KSM_ATTR_RO(pages_shared); | |
1857 | ||
1858 | static ssize_t pages_sharing_show(struct kobject *kobj, | |
1859 | struct kobj_attribute *attr, char *buf) | |
1860 | { | |
e178dfde | 1861 | return sprintf(buf, "%lu\n", ksm_pages_sharing); |
b4028260 HD |
1862 | } |
1863 | KSM_ATTR_RO(pages_sharing); | |
1864 | ||
473b0ce4 HD |
1865 | static ssize_t pages_unshared_show(struct kobject *kobj, |
1866 | struct kobj_attribute *attr, char *buf) | |
1867 | { | |
1868 | return sprintf(buf, "%lu\n", ksm_pages_unshared); | |
1869 | } | |
1870 | KSM_ATTR_RO(pages_unshared); | |
1871 | ||
1872 | static ssize_t pages_volatile_show(struct kobject *kobj, | |
1873 | struct kobj_attribute *attr, char *buf) | |
1874 | { | |
1875 | long ksm_pages_volatile; | |
1876 | ||
1877 | ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared | |
1878 | - ksm_pages_sharing - ksm_pages_unshared; | |
1879 | /* | |
1880 | * It was not worth any locking to calculate that statistic, | |
1881 | * but it might therefore sometimes be negative: conceal that. | |
1882 | */ | |
1883 | if (ksm_pages_volatile < 0) | |
1884 | ksm_pages_volatile = 0; | |
1885 | return sprintf(buf, "%ld\n", ksm_pages_volatile); | |
1886 | } | |
1887 | KSM_ATTR_RO(pages_volatile); | |
1888 | ||
1889 | static ssize_t full_scans_show(struct kobject *kobj, | |
1890 | struct kobj_attribute *attr, char *buf) | |
1891 | { | |
1892 | return sprintf(buf, "%lu\n", ksm_scan.seqnr); | |
1893 | } | |
1894 | KSM_ATTR_RO(full_scans); | |
1895 | ||
31dbd01f IE |
1896 | static struct attribute *ksm_attrs[] = { |
1897 | &sleep_millisecs_attr.attr, | |
1898 | &pages_to_scan_attr.attr, | |
1899 | &run_attr.attr, | |
31dbd01f | 1900 | &max_kernel_pages_attr.attr, |
b4028260 HD |
1901 | &pages_shared_attr.attr, |
1902 | &pages_sharing_attr.attr, | |
473b0ce4 HD |
1903 | &pages_unshared_attr.attr, |
1904 | &pages_volatile_attr.attr, | |
1905 | &full_scans_attr.attr, | |
31dbd01f IE |
1906 | NULL, |
1907 | }; | |
1908 | ||
1909 | static struct attribute_group ksm_attr_group = { | |
1910 | .attrs = ksm_attrs, | |
1911 | .name = "ksm", | |
1912 | }; | |
2ffd8679 | 1913 | #endif /* CONFIG_SYSFS */ |
31dbd01f IE |
1914 | |
1915 | static int __init ksm_init(void) | |
1916 | { | |
1917 | struct task_struct *ksm_thread; | |
1918 | int err; | |
1919 | ||
c73602ad | 1920 | ksm_max_kernel_pages = totalram_pages / 4; |
2c6854fd | 1921 | |
31dbd01f IE |
1922 | err = ksm_slab_init(); |
1923 | if (err) | |
1924 | goto out; | |
1925 | ||
1926 | err = mm_slots_hash_init(); | |
1927 | if (err) | |
1928 | goto out_free1; | |
1929 | ||
1930 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); | |
1931 | if (IS_ERR(ksm_thread)) { | |
1932 | printk(KERN_ERR "ksm: creating kthread failed\n"); | |
1933 | err = PTR_ERR(ksm_thread); | |
1934 | goto out_free2; | |
1935 | } | |
1936 | ||
2ffd8679 | 1937 | #ifdef CONFIG_SYSFS |
31dbd01f IE |
1938 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); |
1939 | if (err) { | |
1940 | printk(KERN_ERR "ksm: register sysfs failed\n"); | |
2ffd8679 HD |
1941 | kthread_stop(ksm_thread); |
1942 | goto out_free2; | |
31dbd01f | 1943 | } |
c73602ad HD |
1944 | #else |
1945 | ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ | |
1946 | ||
2ffd8679 | 1947 | #endif /* CONFIG_SYSFS */ |
31dbd01f IE |
1948 | |
1949 | return 0; | |
1950 | ||
31dbd01f IE |
1951 | out_free2: |
1952 | mm_slots_hash_free(); | |
1953 | out_free1: | |
1954 | ksm_slab_free(); | |
1955 | out: | |
1956 | return err; | |
f8af4da3 | 1957 | } |
31dbd01f | 1958 | module_init(ksm_init) |