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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 | * | |
7 | * Copyright (C) 2008 Red Hat, Inc. | |
8 | * Authors: | |
9 | * Izik Eidus | |
10 | * Andrea Arcangeli | |
11 | * Chris Wright | |
12 | * | |
13 | * This work is licensed under the terms of the GNU GPL, version 2. | |
f8af4da3 HD |
14 | */ |
15 | ||
16 | #include <linux/errno.h> | |
31dbd01f IE |
17 | #include <linux/mm.h> |
18 | #include <linux/fs.h> | |
f8af4da3 | 19 | #include <linux/mman.h> |
31dbd01f IE |
20 | #include <linux/sched.h> |
21 | #include <linux/rwsem.h> | |
22 | #include <linux/pagemap.h> | |
23 | #include <linux/rmap.h> | |
24 | #include <linux/spinlock.h> | |
25 | #include <linux/jhash.h> | |
26 | #include <linux/delay.h> | |
27 | #include <linux/kthread.h> | |
28 | #include <linux/wait.h> | |
29 | #include <linux/slab.h> | |
30 | #include <linux/rbtree.h> | |
31 | #include <linux/mmu_notifier.h> | |
f8af4da3 HD |
32 | #include <linux/ksm.h> |
33 | ||
31dbd01f IE |
34 | #include <asm/tlbflush.h> |
35 | ||
36 | /* | |
37 | * A few notes about the KSM scanning process, | |
38 | * to make it easier to understand the data structures below: | |
39 | * | |
40 | * In order to reduce excessive scanning, KSM sorts the memory pages by their | |
41 | * contents into a data structure that holds pointers to the pages' locations. | |
42 | * | |
43 | * Since the contents of the pages may change at any moment, KSM cannot just | |
44 | * insert the pages into a normal sorted tree and expect it to find anything. | |
45 | * Therefore KSM uses two data structures - the stable and the unstable tree. | |
46 | * | |
47 | * The stable tree holds pointers to all the merged pages (ksm pages), sorted | |
48 | * by their contents. Because each such page is write-protected, searching on | |
49 | * this tree is fully assured to be working (except when pages are unmapped), | |
50 | * and therefore this tree is called the stable tree. | |
51 | * | |
52 | * In addition to the stable tree, KSM uses a second data structure called the | |
53 | * unstable tree: this tree holds pointers to pages which have been found to | |
54 | * be "unchanged for a period of time". The unstable tree sorts these pages | |
55 | * by their contents, but since they are not write-protected, KSM cannot rely | |
56 | * upon the unstable tree to work correctly - the unstable tree is liable to | |
57 | * be corrupted as its contents are modified, and so it is called unstable. | |
58 | * | |
59 | * KSM solves this problem by several techniques: | |
60 | * | |
61 | * 1) The unstable tree is flushed every time KSM completes scanning all | |
62 | * memory areas, and then the tree is rebuilt again from the beginning. | |
63 | * 2) KSM will only insert into the unstable tree, pages whose hash value | |
64 | * has not changed since the previous scan of all memory areas. | |
65 | * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the | |
66 | * colors of the nodes and not on their contents, assuring that even when | |
67 | * the tree gets "corrupted" it won't get out of balance, so scanning time | |
68 | * remains the same (also, searching and inserting nodes in an rbtree uses | |
69 | * the same algorithm, so we have no overhead when we flush and rebuild). | |
70 | * 4) KSM never flushes the stable tree, which means that even if it were to | |
71 | * take 10 attempts to find a page in the unstable tree, once it is found, | |
72 | * it is secured in the stable tree. (When we scan a new page, we first | |
73 | * compare it against the stable tree, and then against the unstable tree.) | |
74 | */ | |
75 | ||
76 | /** | |
77 | * struct mm_slot - ksm information per mm that is being scanned | |
78 | * @link: link to the mm_slots hash list | |
79 | * @mm_list: link into the mm_slots list, rooted in ksm_mm_head | |
80 | * @rmap_list: head for this mm_slot's list of rmap_items | |
81 | * @mm: the mm that this information is valid for | |
82 | */ | |
83 | struct mm_slot { | |
84 | struct hlist_node link; | |
85 | struct list_head mm_list; | |
86 | struct list_head rmap_list; | |
87 | struct mm_struct *mm; | |
88 | }; | |
89 | ||
90 | /** | |
91 | * struct ksm_scan - cursor for scanning | |
92 | * @mm_slot: the current mm_slot we are scanning | |
93 | * @address: the next address inside that to be scanned | |
94 | * @rmap_item: the current rmap that we are scanning inside the rmap_list | |
95 | * @seqnr: count of completed full scans (needed when removing unstable node) | |
96 | * | |
97 | * There is only the one ksm_scan instance of this cursor structure. | |
98 | */ | |
99 | struct ksm_scan { | |
100 | struct mm_slot *mm_slot; | |
101 | unsigned long address; | |
102 | struct rmap_item *rmap_item; | |
103 | unsigned long seqnr; | |
104 | }; | |
105 | ||
106 | /** | |
107 | * struct rmap_item - reverse mapping item for virtual addresses | |
108 | * @link: link into mm_slot's rmap_list (rmap_list is per mm) | |
109 | * @mm: the memory structure this rmap_item is pointing into | |
110 | * @address: the virtual address this rmap_item tracks (+ flags in low bits) | |
111 | * @oldchecksum: previous checksum of the page at that virtual address | |
112 | * @node: rb_node of this rmap_item in either unstable or stable tree | |
113 | * @next: next rmap_item hanging off the same node of the stable tree | |
114 | * @prev: previous rmap_item hanging off the same node of the stable tree | |
115 | */ | |
116 | struct rmap_item { | |
117 | struct list_head link; | |
118 | struct mm_struct *mm; | |
119 | unsigned long address; /* + low bits used for flags below */ | |
120 | union { | |
121 | unsigned int oldchecksum; /* when unstable */ | |
122 | struct rmap_item *next; /* when stable */ | |
123 | }; | |
124 | union { | |
125 | struct rb_node node; /* when tree node */ | |
126 | struct rmap_item *prev; /* in stable list */ | |
127 | }; | |
128 | }; | |
129 | ||
130 | #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ | |
131 | #define NODE_FLAG 0x100 /* is a node of unstable or stable tree */ | |
132 | #define STABLE_FLAG 0x200 /* is a node or list item of stable tree */ | |
133 | ||
134 | /* The stable and unstable tree heads */ | |
135 | static struct rb_root root_stable_tree = RB_ROOT; | |
136 | static struct rb_root root_unstable_tree = RB_ROOT; | |
137 | ||
138 | #define MM_SLOTS_HASH_HEADS 1024 | |
139 | static struct hlist_head *mm_slots_hash; | |
140 | ||
141 | static struct mm_slot ksm_mm_head = { | |
142 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), | |
143 | }; | |
144 | static struct ksm_scan ksm_scan = { | |
145 | .mm_slot = &ksm_mm_head, | |
146 | }; | |
147 | ||
148 | static struct kmem_cache *rmap_item_cache; | |
149 | static struct kmem_cache *mm_slot_cache; | |
150 | ||
151 | /* The number of nodes in the stable tree */ | |
152 | static unsigned long ksm_kernel_pages_allocated; | |
153 | ||
154 | /* The number of page slots sharing those nodes */ | |
155 | static unsigned long ksm_pages_shared; | |
156 | ||
157 | /* Limit on the number of unswappable pages used */ | |
158 | static unsigned long ksm_max_kernel_pages; | |
159 | ||
160 | /* Number of pages ksmd should scan in one batch */ | |
161 | static unsigned int ksm_thread_pages_to_scan; | |
162 | ||
163 | /* Milliseconds ksmd should sleep between batches */ | |
164 | static unsigned int ksm_thread_sleep_millisecs; | |
165 | ||
166 | #define KSM_RUN_STOP 0 | |
167 | #define KSM_RUN_MERGE 1 | |
168 | #define KSM_RUN_UNMERGE 2 | |
169 | static unsigned int ksm_run; | |
170 | ||
171 | static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); | |
172 | static DEFINE_MUTEX(ksm_thread_mutex); | |
173 | static DEFINE_SPINLOCK(ksm_mmlist_lock); | |
174 | ||
175 | #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ | |
176 | sizeof(struct __struct), __alignof__(struct __struct),\ | |
177 | (__flags), NULL) | |
178 | ||
179 | static int __init ksm_slab_init(void) | |
180 | { | |
181 | rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); | |
182 | if (!rmap_item_cache) | |
183 | goto out; | |
184 | ||
185 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); | |
186 | if (!mm_slot_cache) | |
187 | goto out_free; | |
188 | ||
189 | return 0; | |
190 | ||
191 | out_free: | |
192 | kmem_cache_destroy(rmap_item_cache); | |
193 | out: | |
194 | return -ENOMEM; | |
195 | } | |
196 | ||
197 | static void __init ksm_slab_free(void) | |
198 | { | |
199 | kmem_cache_destroy(mm_slot_cache); | |
200 | kmem_cache_destroy(rmap_item_cache); | |
201 | mm_slot_cache = NULL; | |
202 | } | |
203 | ||
204 | static inline struct rmap_item *alloc_rmap_item(void) | |
205 | { | |
206 | return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); | |
207 | } | |
208 | ||
209 | static inline void free_rmap_item(struct rmap_item *rmap_item) | |
210 | { | |
211 | rmap_item->mm = NULL; /* debug safety */ | |
212 | kmem_cache_free(rmap_item_cache, rmap_item); | |
213 | } | |
214 | ||
215 | static inline struct mm_slot *alloc_mm_slot(void) | |
216 | { | |
217 | if (!mm_slot_cache) /* initialization failed */ | |
218 | return NULL; | |
219 | return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); | |
220 | } | |
221 | ||
222 | static inline void free_mm_slot(struct mm_slot *mm_slot) | |
223 | { | |
224 | kmem_cache_free(mm_slot_cache, mm_slot); | |
225 | } | |
226 | ||
227 | static int __init mm_slots_hash_init(void) | |
228 | { | |
229 | mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head), | |
230 | GFP_KERNEL); | |
231 | if (!mm_slots_hash) | |
232 | return -ENOMEM; | |
233 | return 0; | |
234 | } | |
235 | ||
236 | static void __init mm_slots_hash_free(void) | |
237 | { | |
238 | kfree(mm_slots_hash); | |
239 | } | |
240 | ||
241 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) | |
242 | { | |
243 | struct mm_slot *mm_slot; | |
244 | struct hlist_head *bucket; | |
245 | struct hlist_node *node; | |
246 | ||
247 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
248 | % MM_SLOTS_HASH_HEADS]; | |
249 | hlist_for_each_entry(mm_slot, node, bucket, link) { | |
250 | if (mm == mm_slot->mm) | |
251 | return mm_slot; | |
252 | } | |
253 | return NULL; | |
254 | } | |
255 | ||
256 | static void insert_to_mm_slots_hash(struct mm_struct *mm, | |
257 | struct mm_slot *mm_slot) | |
258 | { | |
259 | struct hlist_head *bucket; | |
260 | ||
261 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
262 | % MM_SLOTS_HASH_HEADS]; | |
263 | mm_slot->mm = mm; | |
264 | INIT_LIST_HEAD(&mm_slot->rmap_list); | |
265 | hlist_add_head(&mm_slot->link, bucket); | |
266 | } | |
267 | ||
268 | static inline int in_stable_tree(struct rmap_item *rmap_item) | |
269 | { | |
270 | return rmap_item->address & STABLE_FLAG; | |
271 | } | |
272 | ||
273 | /* | |
274 | * We use break_ksm to break COW on a ksm page: it's a stripped down | |
275 | * | |
276 | * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) | |
277 | * put_page(page); | |
278 | * | |
279 | * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, | |
280 | * in case the application has unmapped and remapped mm,addr meanwhile. | |
281 | * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP | |
282 | * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. | |
283 | */ | |
284 | static void break_ksm(struct vm_area_struct *vma, unsigned long addr) | |
285 | { | |
286 | struct page *page; | |
287 | int ret; | |
288 | ||
289 | do { | |
290 | cond_resched(); | |
291 | page = follow_page(vma, addr, FOLL_GET); | |
292 | if (!page) | |
293 | break; | |
294 | if (PageKsm(page)) | |
295 | ret = handle_mm_fault(vma->vm_mm, vma, addr, | |
296 | FAULT_FLAG_WRITE); | |
297 | else | |
298 | ret = VM_FAULT_WRITE; | |
299 | put_page(page); | |
300 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS))); | |
301 | ||
302 | /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */ | |
303 | } | |
304 | ||
305 | static void __break_cow(struct mm_struct *mm, unsigned long addr) | |
306 | { | |
307 | struct vm_area_struct *vma; | |
308 | ||
309 | vma = find_vma(mm, addr); | |
310 | if (!vma || vma->vm_start > addr) | |
311 | return; | |
312 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
313 | return; | |
314 | break_ksm(vma, addr); | |
315 | } | |
316 | ||
317 | static void break_cow(struct mm_struct *mm, unsigned long addr) | |
318 | { | |
319 | down_read(&mm->mmap_sem); | |
320 | __break_cow(mm, addr); | |
321 | up_read(&mm->mmap_sem); | |
322 | } | |
323 | ||
324 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) | |
325 | { | |
326 | struct mm_struct *mm = rmap_item->mm; | |
327 | unsigned long addr = rmap_item->address; | |
328 | struct vm_area_struct *vma; | |
329 | struct page *page; | |
330 | ||
331 | down_read(&mm->mmap_sem); | |
332 | vma = find_vma(mm, addr); | |
333 | if (!vma || vma->vm_start > addr) | |
334 | goto out; | |
335 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
336 | goto out; | |
337 | ||
338 | page = follow_page(vma, addr, FOLL_GET); | |
339 | if (!page) | |
340 | goto out; | |
341 | if (PageAnon(page)) { | |
342 | flush_anon_page(vma, page, addr); | |
343 | flush_dcache_page(page); | |
344 | } else { | |
345 | put_page(page); | |
346 | out: page = NULL; | |
347 | } | |
348 | up_read(&mm->mmap_sem); | |
349 | return page; | |
350 | } | |
351 | ||
352 | /* | |
353 | * get_ksm_page: checks if the page at the virtual address in rmap_item | |
354 | * is still PageKsm, in which case we can trust the content of the page, | |
355 | * and it returns the gotten page; but NULL if the page has been zapped. | |
356 | */ | |
357 | static struct page *get_ksm_page(struct rmap_item *rmap_item) | |
358 | { | |
359 | struct page *page; | |
360 | ||
361 | page = get_mergeable_page(rmap_item); | |
362 | if (page && !PageKsm(page)) { | |
363 | put_page(page); | |
364 | page = NULL; | |
365 | } | |
366 | return page; | |
367 | } | |
368 | ||
369 | /* | |
370 | * Removing rmap_item from stable or unstable tree. | |
371 | * This function will clean the information from the stable/unstable tree. | |
372 | */ | |
373 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) | |
374 | { | |
375 | if (in_stable_tree(rmap_item)) { | |
376 | struct rmap_item *next_item = rmap_item->next; | |
377 | ||
378 | if (rmap_item->address & NODE_FLAG) { | |
379 | if (next_item) { | |
380 | rb_replace_node(&rmap_item->node, | |
381 | &next_item->node, | |
382 | &root_stable_tree); | |
383 | next_item->address |= NODE_FLAG; | |
384 | } else { | |
385 | rb_erase(&rmap_item->node, &root_stable_tree); | |
386 | ksm_kernel_pages_allocated--; | |
387 | } | |
388 | } else { | |
389 | struct rmap_item *prev_item = rmap_item->prev; | |
390 | ||
391 | BUG_ON(prev_item->next != rmap_item); | |
392 | prev_item->next = next_item; | |
393 | if (next_item) { | |
394 | BUG_ON(next_item->prev != rmap_item); | |
395 | next_item->prev = rmap_item->prev; | |
396 | } | |
397 | } | |
398 | ||
399 | rmap_item->next = NULL; | |
400 | ksm_pages_shared--; | |
401 | ||
402 | } else if (rmap_item->address & NODE_FLAG) { | |
403 | unsigned char age; | |
404 | /* | |
405 | * ksm_thread can and must skip the rb_erase, because | |
406 | * root_unstable_tree was already reset to RB_ROOT. | |
407 | * But __ksm_exit has to be careful: do the rb_erase | |
408 | * if it's interrupting a scan, and this rmap_item was | |
409 | * inserted by this scan rather than left from before. | |
410 | * | |
411 | * Because of the case in which remove_mm_from_lists | |
412 | * increments seqnr before removing rmaps, unstable_nr | |
413 | * may even be 2 behind seqnr, but should never be | |
414 | * further behind. Yes, I did have trouble with this! | |
415 | */ | |
416 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); | |
417 | BUG_ON(age > 2); | |
418 | if (!age) | |
419 | rb_erase(&rmap_item->node, &root_unstable_tree); | |
420 | } | |
421 | ||
422 | rmap_item->address &= PAGE_MASK; | |
423 | ||
424 | cond_resched(); /* we're called from many long loops */ | |
425 | } | |
426 | ||
427 | static void remove_all_slot_rmap_items(struct mm_slot *mm_slot) | |
428 | { | |
429 | struct rmap_item *rmap_item, *node; | |
430 | ||
431 | list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) { | |
432 | remove_rmap_item_from_tree(rmap_item); | |
433 | list_del(&rmap_item->link); | |
434 | free_rmap_item(rmap_item); | |
435 | } | |
436 | } | |
437 | ||
438 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, | |
439 | struct list_head *cur) | |
440 | { | |
441 | struct rmap_item *rmap_item; | |
442 | ||
443 | while (cur != &mm_slot->rmap_list) { | |
444 | rmap_item = list_entry(cur, struct rmap_item, link); | |
445 | cur = cur->next; | |
446 | remove_rmap_item_from_tree(rmap_item); | |
447 | list_del(&rmap_item->link); | |
448 | free_rmap_item(rmap_item); | |
449 | } | |
450 | } | |
451 | ||
452 | /* | |
453 | * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather | |
454 | * than check every pte of a given vma, the locking doesn't quite work for | |
455 | * that - an rmap_item is assigned to the stable tree after inserting ksm | |
456 | * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing | |
457 | * rmap_items from parent to child at fork time (so as not to waste time | |
458 | * if exit comes before the next scan reaches it). | |
459 | */ | |
460 | static void unmerge_ksm_pages(struct vm_area_struct *vma, | |
461 | unsigned long start, unsigned long end) | |
462 | { | |
463 | unsigned long addr; | |
464 | ||
465 | for (addr = start; addr < end; addr += PAGE_SIZE) | |
466 | break_ksm(vma, addr); | |
467 | } | |
468 | ||
469 | static void unmerge_and_remove_all_rmap_items(void) | |
470 | { | |
471 | struct mm_slot *mm_slot; | |
472 | struct mm_struct *mm; | |
473 | struct vm_area_struct *vma; | |
474 | ||
475 | list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) { | |
476 | mm = mm_slot->mm; | |
477 | down_read(&mm->mmap_sem); | |
478 | for (vma = mm->mmap; vma; vma = vma->vm_next) { | |
479 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
480 | continue; | |
481 | unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end); | |
482 | } | |
483 | remove_all_slot_rmap_items(mm_slot); | |
484 | up_read(&mm->mmap_sem); | |
485 | } | |
486 | ||
487 | spin_lock(&ksm_mmlist_lock); | |
488 | if (ksm_scan.mm_slot != &ksm_mm_head) { | |
489 | ksm_scan.mm_slot = &ksm_mm_head; | |
490 | ksm_scan.seqnr++; | |
491 | } | |
492 | spin_unlock(&ksm_mmlist_lock); | |
493 | } | |
494 | ||
495 | static void remove_mm_from_lists(struct mm_struct *mm) | |
496 | { | |
497 | struct mm_slot *mm_slot; | |
498 | ||
499 | spin_lock(&ksm_mmlist_lock); | |
500 | mm_slot = get_mm_slot(mm); | |
501 | ||
502 | /* | |
503 | * This mm_slot is always at the scanning cursor when we're | |
504 | * called from scan_get_next_rmap_item; but it's a special | |
505 | * case when we're called from __ksm_exit. | |
506 | */ | |
507 | if (ksm_scan.mm_slot == mm_slot) { | |
508 | ksm_scan.mm_slot = list_entry( | |
509 | mm_slot->mm_list.next, struct mm_slot, mm_list); | |
510 | ksm_scan.address = 0; | |
511 | ksm_scan.rmap_item = list_entry( | |
512 | &ksm_scan.mm_slot->rmap_list, struct rmap_item, link); | |
513 | if (ksm_scan.mm_slot == &ksm_mm_head) | |
514 | ksm_scan.seqnr++; | |
515 | } | |
516 | ||
517 | hlist_del(&mm_slot->link); | |
518 | list_del(&mm_slot->mm_list); | |
519 | spin_unlock(&ksm_mmlist_lock); | |
520 | ||
521 | remove_all_slot_rmap_items(mm_slot); | |
522 | free_mm_slot(mm_slot); | |
523 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
524 | } | |
525 | ||
526 | static u32 calc_checksum(struct page *page) | |
527 | { | |
528 | u32 checksum; | |
529 | void *addr = kmap_atomic(page, KM_USER0); | |
530 | checksum = jhash2(addr, PAGE_SIZE / 4, 17); | |
531 | kunmap_atomic(addr, KM_USER0); | |
532 | return checksum; | |
533 | } | |
534 | ||
535 | static int memcmp_pages(struct page *page1, struct page *page2) | |
536 | { | |
537 | char *addr1, *addr2; | |
538 | int ret; | |
539 | ||
540 | addr1 = kmap_atomic(page1, KM_USER0); | |
541 | addr2 = kmap_atomic(page2, KM_USER1); | |
542 | ret = memcmp(addr1, addr2, PAGE_SIZE); | |
543 | kunmap_atomic(addr2, KM_USER1); | |
544 | kunmap_atomic(addr1, KM_USER0); | |
545 | return ret; | |
546 | } | |
547 | ||
548 | static inline int pages_identical(struct page *page1, struct page *page2) | |
549 | { | |
550 | return !memcmp_pages(page1, page2); | |
551 | } | |
552 | ||
553 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, | |
554 | pte_t *orig_pte) | |
555 | { | |
556 | struct mm_struct *mm = vma->vm_mm; | |
557 | unsigned long addr; | |
558 | pte_t *ptep; | |
559 | spinlock_t *ptl; | |
560 | int swapped; | |
561 | int err = -EFAULT; | |
562 | ||
563 | addr = page_address_in_vma(page, vma); | |
564 | if (addr == -EFAULT) | |
565 | goto out; | |
566 | ||
567 | ptep = page_check_address(page, mm, addr, &ptl, 0); | |
568 | if (!ptep) | |
569 | goto out; | |
570 | ||
571 | if (pte_write(*ptep)) { | |
572 | pte_t entry; | |
573 | ||
574 | swapped = PageSwapCache(page); | |
575 | flush_cache_page(vma, addr, page_to_pfn(page)); | |
576 | /* | |
577 | * Ok this is tricky, when get_user_pages_fast() run it doesnt | |
578 | * take any lock, therefore the check that we are going to make | |
579 | * with the pagecount against the mapcount is racey and | |
580 | * O_DIRECT can happen right after the check. | |
581 | * So we clear the pte and flush the tlb before the check | |
582 | * this assure us that no O_DIRECT can happen after the check | |
583 | * or in the middle of the check. | |
584 | */ | |
585 | entry = ptep_clear_flush(vma, addr, ptep); | |
586 | /* | |
587 | * Check that no O_DIRECT or similar I/O is in progress on the | |
588 | * page | |
589 | */ | |
590 | if ((page_mapcount(page) + 2 + swapped) != page_count(page)) { | |
591 | set_pte_at_notify(mm, addr, ptep, entry); | |
592 | goto out_unlock; | |
593 | } | |
594 | entry = pte_wrprotect(entry); | |
595 | set_pte_at_notify(mm, addr, ptep, entry); | |
596 | } | |
597 | *orig_pte = *ptep; | |
598 | err = 0; | |
599 | ||
600 | out_unlock: | |
601 | pte_unmap_unlock(ptep, ptl); | |
602 | out: | |
603 | return err; | |
604 | } | |
605 | ||
606 | /** | |
607 | * replace_page - replace page in vma by new ksm page | |
608 | * @vma: vma that holds the pte pointing to oldpage | |
609 | * @oldpage: the page we are replacing by newpage | |
610 | * @newpage: the ksm page we replace oldpage by | |
611 | * @orig_pte: the original value of the pte | |
612 | * | |
613 | * Returns 0 on success, -EFAULT on failure. | |
614 | */ | |
615 | static int replace_page(struct vm_area_struct *vma, struct page *oldpage, | |
616 | struct page *newpage, pte_t orig_pte) | |
617 | { | |
618 | struct mm_struct *mm = vma->vm_mm; | |
619 | pgd_t *pgd; | |
620 | pud_t *pud; | |
621 | pmd_t *pmd; | |
622 | pte_t *ptep; | |
623 | spinlock_t *ptl; | |
624 | unsigned long addr; | |
625 | pgprot_t prot; | |
626 | int err = -EFAULT; | |
627 | ||
628 | prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE); | |
629 | ||
630 | addr = page_address_in_vma(oldpage, vma); | |
631 | if (addr == -EFAULT) | |
632 | goto out; | |
633 | ||
634 | pgd = pgd_offset(mm, addr); | |
635 | if (!pgd_present(*pgd)) | |
636 | goto out; | |
637 | ||
638 | pud = pud_offset(pgd, addr); | |
639 | if (!pud_present(*pud)) | |
640 | goto out; | |
641 | ||
642 | pmd = pmd_offset(pud, addr); | |
643 | if (!pmd_present(*pmd)) | |
644 | goto out; | |
645 | ||
646 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); | |
647 | if (!pte_same(*ptep, orig_pte)) { | |
648 | pte_unmap_unlock(ptep, ptl); | |
649 | goto out; | |
650 | } | |
651 | ||
652 | get_page(newpage); | |
653 | page_add_ksm_rmap(newpage); | |
654 | ||
655 | flush_cache_page(vma, addr, pte_pfn(*ptep)); | |
656 | ptep_clear_flush(vma, addr, ptep); | |
657 | set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot)); | |
658 | ||
659 | page_remove_rmap(oldpage); | |
660 | put_page(oldpage); | |
661 | ||
662 | pte_unmap_unlock(ptep, ptl); | |
663 | err = 0; | |
664 | out: | |
665 | return err; | |
666 | } | |
667 | ||
668 | /* | |
669 | * try_to_merge_one_page - take two pages and merge them into one | |
670 | * @vma: the vma that hold the pte pointing into oldpage | |
671 | * @oldpage: the page that we want to replace with newpage | |
672 | * @newpage: the page that we want to map instead of oldpage | |
673 | * | |
674 | * Note: | |
675 | * oldpage should be a PageAnon page, while newpage should be a PageKsm page, | |
676 | * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm. | |
677 | * | |
678 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
679 | */ | |
680 | static int try_to_merge_one_page(struct vm_area_struct *vma, | |
681 | struct page *oldpage, | |
682 | struct page *newpage) | |
683 | { | |
684 | pte_t orig_pte = __pte(0); | |
685 | int err = -EFAULT; | |
686 | ||
687 | if (!(vma->vm_flags & VM_MERGEABLE)) | |
688 | goto out; | |
689 | ||
690 | if (!PageAnon(oldpage)) | |
691 | goto out; | |
692 | ||
693 | get_page(newpage); | |
694 | get_page(oldpage); | |
695 | ||
696 | /* | |
697 | * We need the page lock to read a stable PageSwapCache in | |
698 | * write_protect_page(). We use trylock_page() instead of | |
699 | * lock_page() because we don't want to wait here - we | |
700 | * prefer to continue scanning and merging different pages, | |
701 | * then come back to this page when it is unlocked. | |
702 | */ | |
703 | if (!trylock_page(oldpage)) | |
704 | goto out_putpage; | |
705 | /* | |
706 | * If this anonymous page is mapped only here, its pte may need | |
707 | * to be write-protected. If it's mapped elsewhere, all of its | |
708 | * ptes are necessarily already write-protected. But in either | |
709 | * case, we need to lock and check page_count is not raised. | |
710 | */ | |
711 | if (write_protect_page(vma, oldpage, &orig_pte)) { | |
712 | unlock_page(oldpage); | |
713 | goto out_putpage; | |
714 | } | |
715 | unlock_page(oldpage); | |
716 | ||
717 | if (pages_identical(oldpage, newpage)) | |
718 | err = replace_page(vma, oldpage, newpage, orig_pte); | |
719 | ||
720 | out_putpage: | |
721 | put_page(oldpage); | |
722 | put_page(newpage); | |
723 | out: | |
724 | return err; | |
725 | } | |
726 | ||
727 | /* | |
728 | * try_to_merge_two_pages - take two identical pages and prepare them | |
729 | * to be merged into one page. | |
730 | * | |
731 | * This function returns 0 if we successfully mapped two identical pages | |
732 | * into one page, -EFAULT otherwise. | |
733 | * | |
734 | * Note that this function allocates a new kernel page: if one of the pages | |
735 | * is already a ksm page, try_to_merge_with_ksm_page should be used. | |
736 | */ | |
737 | static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1, | |
738 | struct page *page1, struct mm_struct *mm2, | |
739 | unsigned long addr2, struct page *page2) | |
740 | { | |
741 | struct vm_area_struct *vma; | |
742 | struct page *kpage; | |
743 | int err = -EFAULT; | |
744 | ||
745 | /* | |
746 | * The number of nodes in the stable tree | |
747 | * is the number of kernel pages that we hold. | |
748 | */ | |
749 | if (ksm_max_kernel_pages && | |
750 | ksm_max_kernel_pages <= ksm_kernel_pages_allocated) | |
751 | return err; | |
752 | ||
753 | kpage = alloc_page(GFP_HIGHUSER); | |
754 | if (!kpage) | |
755 | return err; | |
756 | ||
757 | down_read(&mm1->mmap_sem); | |
758 | vma = find_vma(mm1, addr1); | |
759 | if (!vma || vma->vm_start > addr1) { | |
760 | put_page(kpage); | |
761 | up_read(&mm1->mmap_sem); | |
762 | return err; | |
763 | } | |
764 | ||
765 | copy_user_highpage(kpage, page1, addr1, vma); | |
766 | err = try_to_merge_one_page(vma, page1, kpage); | |
767 | up_read(&mm1->mmap_sem); | |
768 | ||
769 | if (!err) { | |
770 | down_read(&mm2->mmap_sem); | |
771 | vma = find_vma(mm2, addr2); | |
772 | if (!vma || vma->vm_start > addr2) { | |
773 | put_page(kpage); | |
774 | up_read(&mm2->mmap_sem); | |
775 | break_cow(mm1, addr1); | |
776 | return -EFAULT; | |
777 | } | |
778 | ||
779 | err = try_to_merge_one_page(vma, page2, kpage); | |
780 | up_read(&mm2->mmap_sem); | |
781 | ||
782 | /* | |
783 | * If the second try_to_merge_one_page failed, we have a | |
784 | * ksm page with just one pte pointing to it, so break it. | |
785 | */ | |
786 | if (err) | |
787 | break_cow(mm1, addr1); | |
788 | else | |
789 | ksm_pages_shared += 2; | |
790 | } | |
791 | ||
792 | put_page(kpage); | |
793 | return err; | |
794 | } | |
795 | ||
796 | /* | |
797 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, | |
798 | * but no new kernel page is allocated: kpage must already be a ksm page. | |
799 | */ | |
800 | static int try_to_merge_with_ksm_page(struct mm_struct *mm1, | |
801 | unsigned long addr1, | |
802 | struct page *page1, | |
803 | struct page *kpage) | |
804 | { | |
805 | struct vm_area_struct *vma; | |
806 | int err = -EFAULT; | |
807 | ||
808 | down_read(&mm1->mmap_sem); | |
809 | vma = find_vma(mm1, addr1); | |
810 | if (!vma || vma->vm_start > addr1) { | |
811 | up_read(&mm1->mmap_sem); | |
812 | return err; | |
813 | } | |
814 | ||
815 | err = try_to_merge_one_page(vma, page1, kpage); | |
816 | up_read(&mm1->mmap_sem); | |
817 | ||
818 | if (!err) | |
819 | ksm_pages_shared++; | |
820 | ||
821 | return err; | |
822 | } | |
823 | ||
824 | /* | |
825 | * stable_tree_search - search page inside the stable tree | |
826 | * @page: the page that we are searching identical pages to. | |
827 | * @page2: pointer into identical page that we are holding inside the stable | |
828 | * tree that we have found. | |
829 | * @rmap_item: the reverse mapping item | |
830 | * | |
831 | * This function checks if there is a page inside the stable tree | |
832 | * with identical content to the page that we are scanning right now. | |
833 | * | |
834 | * This function return rmap_item pointer to the identical item if found, | |
835 | * NULL otherwise. | |
836 | */ | |
837 | static struct rmap_item *stable_tree_search(struct page *page, | |
838 | struct page **page2, | |
839 | struct rmap_item *rmap_item) | |
840 | { | |
841 | struct rb_node *node = root_stable_tree.rb_node; | |
842 | ||
843 | while (node) { | |
844 | struct rmap_item *tree_rmap_item, *next_rmap_item; | |
845 | int ret; | |
846 | ||
847 | tree_rmap_item = rb_entry(node, struct rmap_item, node); | |
848 | while (tree_rmap_item) { | |
849 | BUG_ON(!in_stable_tree(tree_rmap_item)); | |
850 | cond_resched(); | |
851 | page2[0] = get_ksm_page(tree_rmap_item); | |
852 | if (page2[0]) | |
853 | break; | |
854 | next_rmap_item = tree_rmap_item->next; | |
855 | remove_rmap_item_from_tree(tree_rmap_item); | |
856 | tree_rmap_item = next_rmap_item; | |
857 | } | |
858 | if (!tree_rmap_item) | |
859 | return NULL; | |
860 | ||
861 | ret = memcmp_pages(page, page2[0]); | |
862 | ||
863 | if (ret < 0) { | |
864 | put_page(page2[0]); | |
865 | node = node->rb_left; | |
866 | } else if (ret > 0) { | |
867 | put_page(page2[0]); | |
868 | node = node->rb_right; | |
869 | } else { | |
870 | return tree_rmap_item; | |
871 | } | |
872 | } | |
873 | ||
874 | return NULL; | |
875 | } | |
876 | ||
877 | /* | |
878 | * stable_tree_insert - insert rmap_item pointing to new ksm page | |
879 | * into the stable tree. | |
880 | * | |
881 | * @page: the page that we are searching identical page to inside the stable | |
882 | * tree. | |
883 | * @rmap_item: pointer to the reverse mapping item. | |
884 | * | |
885 | * This function returns rmap_item if success, NULL otherwise. | |
886 | */ | |
887 | static struct rmap_item *stable_tree_insert(struct page *page, | |
888 | struct rmap_item *rmap_item) | |
889 | { | |
890 | struct rb_node **new = &root_stable_tree.rb_node; | |
891 | struct rb_node *parent = NULL; | |
892 | ||
893 | while (*new) { | |
894 | struct rmap_item *tree_rmap_item, *next_rmap_item; | |
895 | struct page *tree_page; | |
896 | int ret; | |
897 | ||
898 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); | |
899 | while (tree_rmap_item) { | |
900 | BUG_ON(!in_stable_tree(tree_rmap_item)); | |
901 | cond_resched(); | |
902 | tree_page = get_ksm_page(tree_rmap_item); | |
903 | if (tree_page) | |
904 | break; | |
905 | next_rmap_item = tree_rmap_item->next; | |
906 | remove_rmap_item_from_tree(tree_rmap_item); | |
907 | tree_rmap_item = next_rmap_item; | |
908 | } | |
909 | if (!tree_rmap_item) | |
910 | return NULL; | |
911 | ||
912 | ret = memcmp_pages(page, tree_page); | |
913 | put_page(tree_page); | |
914 | ||
915 | parent = *new; | |
916 | if (ret < 0) | |
917 | new = &parent->rb_left; | |
918 | else if (ret > 0) | |
919 | new = &parent->rb_right; | |
920 | else { | |
921 | /* | |
922 | * It is not a bug that stable_tree_search() didn't | |
923 | * find this node: because at that time our page was | |
924 | * not yet write-protected, so may have changed since. | |
925 | */ | |
926 | return NULL; | |
927 | } | |
928 | } | |
929 | ||
930 | ksm_kernel_pages_allocated++; | |
931 | ||
932 | rmap_item->address |= NODE_FLAG | STABLE_FLAG; | |
933 | rmap_item->next = NULL; | |
934 | rb_link_node(&rmap_item->node, parent, new); | |
935 | rb_insert_color(&rmap_item->node, &root_stable_tree); | |
936 | ||
937 | return rmap_item; | |
938 | } | |
939 | ||
940 | /* | |
941 | * unstable_tree_search_insert - search and insert items into the unstable tree. | |
942 | * | |
943 | * @page: the page that we are going to search for identical page or to insert | |
944 | * into the unstable tree | |
945 | * @page2: pointer into identical page that was found inside the unstable tree | |
946 | * @rmap_item: the reverse mapping item of page | |
947 | * | |
948 | * This function searches for a page in the unstable tree identical to the | |
949 | * page currently being scanned; and if no identical page is found in the | |
950 | * tree, we insert rmap_item as a new object into the unstable tree. | |
951 | * | |
952 | * This function returns pointer to rmap_item found to be identical | |
953 | * to the currently scanned page, NULL otherwise. | |
954 | * | |
955 | * This function does both searching and inserting, because they share | |
956 | * the same walking algorithm in an rbtree. | |
957 | */ | |
958 | static struct rmap_item *unstable_tree_search_insert(struct page *page, | |
959 | struct page **page2, | |
960 | struct rmap_item *rmap_item) | |
961 | { | |
962 | struct rb_node **new = &root_unstable_tree.rb_node; | |
963 | struct rb_node *parent = NULL; | |
964 | ||
965 | while (*new) { | |
966 | struct rmap_item *tree_rmap_item; | |
967 | int ret; | |
968 | ||
969 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); | |
970 | page2[0] = get_mergeable_page(tree_rmap_item); | |
971 | if (!page2[0]) | |
972 | return NULL; | |
973 | ||
974 | /* | |
975 | * Don't substitute an unswappable ksm page | |
976 | * just for one good swappable forked page. | |
977 | */ | |
978 | if (page == page2[0]) { | |
979 | put_page(page2[0]); | |
980 | return NULL; | |
981 | } | |
982 | ||
983 | ret = memcmp_pages(page, page2[0]); | |
984 | ||
985 | parent = *new; | |
986 | if (ret < 0) { | |
987 | put_page(page2[0]); | |
988 | new = &parent->rb_left; | |
989 | } else if (ret > 0) { | |
990 | put_page(page2[0]); | |
991 | new = &parent->rb_right; | |
992 | } else { | |
993 | return tree_rmap_item; | |
994 | } | |
995 | } | |
996 | ||
997 | rmap_item->address |= NODE_FLAG; | |
998 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); | |
999 | rb_link_node(&rmap_item->node, parent, new); | |
1000 | rb_insert_color(&rmap_item->node, &root_unstable_tree); | |
1001 | ||
1002 | return NULL; | |
1003 | } | |
1004 | ||
1005 | /* | |
1006 | * stable_tree_append - add another rmap_item to the linked list of | |
1007 | * rmap_items hanging off a given node of the stable tree, all sharing | |
1008 | * the same ksm page. | |
1009 | */ | |
1010 | static void stable_tree_append(struct rmap_item *rmap_item, | |
1011 | struct rmap_item *tree_rmap_item) | |
1012 | { | |
1013 | rmap_item->next = tree_rmap_item->next; | |
1014 | rmap_item->prev = tree_rmap_item; | |
1015 | ||
1016 | if (tree_rmap_item->next) | |
1017 | tree_rmap_item->next->prev = rmap_item; | |
1018 | ||
1019 | tree_rmap_item->next = rmap_item; | |
1020 | rmap_item->address |= STABLE_FLAG; | |
1021 | } | |
1022 | ||
1023 | /* | |
1024 | * cmp_and_merge_page - take a page computes its hash value and check if there | |
1025 | * is similar hash value to different page, | |
1026 | * in case we find that there is similar hash to different page we call to | |
1027 | * try_to_merge_two_pages(). | |
1028 | * | |
1029 | * @page: the page that we are searching identical page to. | |
1030 | * @rmap_item: the reverse mapping into the virtual address of this page | |
1031 | */ | |
1032 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) | |
1033 | { | |
1034 | struct page *page2[1]; | |
1035 | struct rmap_item *tree_rmap_item; | |
1036 | unsigned int checksum; | |
1037 | int err; | |
1038 | ||
1039 | if (in_stable_tree(rmap_item)) | |
1040 | remove_rmap_item_from_tree(rmap_item); | |
1041 | ||
1042 | /* We first start with searching the page inside the stable tree */ | |
1043 | tree_rmap_item = stable_tree_search(page, page2, rmap_item); | |
1044 | if (tree_rmap_item) { | |
1045 | if (page == page2[0]) { /* forked */ | |
1046 | ksm_pages_shared++; | |
1047 | err = 0; | |
1048 | } else | |
1049 | err = try_to_merge_with_ksm_page(rmap_item->mm, | |
1050 | rmap_item->address, | |
1051 | page, page2[0]); | |
1052 | put_page(page2[0]); | |
1053 | ||
1054 | if (!err) { | |
1055 | /* | |
1056 | * The page was successfully merged: | |
1057 | * add its rmap_item to the stable tree. | |
1058 | */ | |
1059 | stable_tree_append(rmap_item, tree_rmap_item); | |
1060 | } | |
1061 | return; | |
1062 | } | |
1063 | ||
1064 | /* | |
1065 | * A ksm page might have got here by fork, but its other | |
1066 | * references have already been removed from the stable tree. | |
1067 | */ | |
1068 | if (PageKsm(page)) | |
1069 | break_cow(rmap_item->mm, rmap_item->address); | |
1070 | ||
1071 | /* | |
1072 | * In case the hash value of the page was changed from the last time we | |
1073 | * have calculated it, this page to be changed frequely, therefore we | |
1074 | * don't want to insert it to the unstable tree, and we don't want to | |
1075 | * waste our time to search if there is something identical to it there. | |
1076 | */ | |
1077 | checksum = calc_checksum(page); | |
1078 | if (rmap_item->oldchecksum != checksum) { | |
1079 | rmap_item->oldchecksum = checksum; | |
1080 | return; | |
1081 | } | |
1082 | ||
1083 | tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item); | |
1084 | if (tree_rmap_item) { | |
1085 | err = try_to_merge_two_pages(rmap_item->mm, | |
1086 | rmap_item->address, page, | |
1087 | tree_rmap_item->mm, | |
1088 | tree_rmap_item->address, page2[0]); | |
1089 | /* | |
1090 | * As soon as we merge this page, we want to remove the | |
1091 | * rmap_item of the page we have merged with from the unstable | |
1092 | * tree, and insert it instead as new node in the stable tree. | |
1093 | */ | |
1094 | if (!err) { | |
1095 | rb_erase(&tree_rmap_item->node, &root_unstable_tree); | |
1096 | tree_rmap_item->address &= ~NODE_FLAG; | |
1097 | /* | |
1098 | * If we fail to insert the page into the stable tree, | |
1099 | * we will have 2 virtual addresses that are pointing | |
1100 | * to a ksm page left outside the stable tree, | |
1101 | * in which case we need to break_cow on both. | |
1102 | */ | |
1103 | if (stable_tree_insert(page2[0], tree_rmap_item)) | |
1104 | stable_tree_append(rmap_item, tree_rmap_item); | |
1105 | else { | |
1106 | break_cow(tree_rmap_item->mm, | |
1107 | tree_rmap_item->address); | |
1108 | break_cow(rmap_item->mm, rmap_item->address); | |
1109 | ksm_pages_shared -= 2; | |
1110 | } | |
1111 | } | |
1112 | ||
1113 | put_page(page2[0]); | |
1114 | } | |
1115 | } | |
1116 | ||
1117 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, | |
1118 | struct list_head *cur, | |
1119 | unsigned long addr) | |
1120 | { | |
1121 | struct rmap_item *rmap_item; | |
1122 | ||
1123 | while (cur != &mm_slot->rmap_list) { | |
1124 | rmap_item = list_entry(cur, struct rmap_item, link); | |
1125 | if ((rmap_item->address & PAGE_MASK) == addr) { | |
1126 | if (!in_stable_tree(rmap_item)) | |
1127 | remove_rmap_item_from_tree(rmap_item); | |
1128 | return rmap_item; | |
1129 | } | |
1130 | if (rmap_item->address > addr) | |
1131 | break; | |
1132 | cur = cur->next; | |
1133 | remove_rmap_item_from_tree(rmap_item); | |
1134 | list_del(&rmap_item->link); | |
1135 | free_rmap_item(rmap_item); | |
1136 | } | |
1137 | ||
1138 | rmap_item = alloc_rmap_item(); | |
1139 | if (rmap_item) { | |
1140 | /* It has already been zeroed */ | |
1141 | rmap_item->mm = mm_slot->mm; | |
1142 | rmap_item->address = addr; | |
1143 | list_add_tail(&rmap_item->link, cur); | |
1144 | } | |
1145 | return rmap_item; | |
1146 | } | |
1147 | ||
1148 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) | |
1149 | { | |
1150 | struct mm_struct *mm; | |
1151 | struct mm_slot *slot; | |
1152 | struct vm_area_struct *vma; | |
1153 | struct rmap_item *rmap_item; | |
1154 | ||
1155 | if (list_empty(&ksm_mm_head.mm_list)) | |
1156 | return NULL; | |
1157 | ||
1158 | slot = ksm_scan.mm_slot; | |
1159 | if (slot == &ksm_mm_head) { | |
1160 | root_unstable_tree = RB_ROOT; | |
1161 | ||
1162 | spin_lock(&ksm_mmlist_lock); | |
1163 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); | |
1164 | ksm_scan.mm_slot = slot; | |
1165 | spin_unlock(&ksm_mmlist_lock); | |
1166 | next_mm: | |
1167 | ksm_scan.address = 0; | |
1168 | ksm_scan.rmap_item = list_entry(&slot->rmap_list, | |
1169 | struct rmap_item, link); | |
1170 | } | |
1171 | ||
1172 | mm = slot->mm; | |
1173 | down_read(&mm->mmap_sem); | |
1174 | for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) { | |
1175 | if (!(vma->vm_flags & VM_MERGEABLE)) | |
1176 | continue; | |
1177 | if (ksm_scan.address < vma->vm_start) | |
1178 | ksm_scan.address = vma->vm_start; | |
1179 | if (!vma->anon_vma) | |
1180 | ksm_scan.address = vma->vm_end; | |
1181 | ||
1182 | while (ksm_scan.address < vma->vm_end) { | |
1183 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); | |
1184 | if (*page && PageAnon(*page)) { | |
1185 | flush_anon_page(vma, *page, ksm_scan.address); | |
1186 | flush_dcache_page(*page); | |
1187 | rmap_item = get_next_rmap_item(slot, | |
1188 | ksm_scan.rmap_item->link.next, | |
1189 | ksm_scan.address); | |
1190 | if (rmap_item) { | |
1191 | ksm_scan.rmap_item = rmap_item; | |
1192 | ksm_scan.address += PAGE_SIZE; | |
1193 | } else | |
1194 | put_page(*page); | |
1195 | up_read(&mm->mmap_sem); | |
1196 | return rmap_item; | |
1197 | } | |
1198 | if (*page) | |
1199 | put_page(*page); | |
1200 | ksm_scan.address += PAGE_SIZE; | |
1201 | cond_resched(); | |
1202 | } | |
1203 | } | |
1204 | ||
1205 | if (!ksm_scan.address) { | |
1206 | /* | |
1207 | * We've completed a full scan of all vmas, holding mmap_sem | |
1208 | * throughout, and found no VM_MERGEABLE: so do the same as | |
1209 | * __ksm_exit does to remove this mm from all our lists now. | |
1210 | */ | |
1211 | remove_mm_from_lists(mm); | |
1212 | up_read(&mm->mmap_sem); | |
1213 | slot = ksm_scan.mm_slot; | |
1214 | if (slot != &ksm_mm_head) | |
1215 | goto next_mm; | |
1216 | return NULL; | |
1217 | } | |
1218 | ||
1219 | /* | |
1220 | * Nuke all the rmap_items that are above this current rmap: | |
1221 | * because there were no VM_MERGEABLE vmas with such addresses. | |
1222 | */ | |
1223 | remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next); | |
1224 | up_read(&mm->mmap_sem); | |
1225 | ||
1226 | spin_lock(&ksm_mmlist_lock); | |
1227 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); | |
1228 | ksm_scan.mm_slot = slot; | |
1229 | spin_unlock(&ksm_mmlist_lock); | |
1230 | ||
1231 | /* Repeat until we've completed scanning the whole list */ | |
1232 | if (slot != &ksm_mm_head) | |
1233 | goto next_mm; | |
1234 | ||
1235 | /* | |
1236 | * Bump seqnr here rather than at top, so that __ksm_exit | |
1237 | * can skip rb_erase on unstable tree until we run again. | |
1238 | */ | |
1239 | ksm_scan.seqnr++; | |
1240 | return NULL; | |
1241 | } | |
1242 | ||
1243 | /** | |
1244 | * ksm_do_scan - the ksm scanner main worker function. | |
1245 | * @scan_npages - number of pages we want to scan before we return. | |
1246 | */ | |
1247 | static void ksm_do_scan(unsigned int scan_npages) | |
1248 | { | |
1249 | struct rmap_item *rmap_item; | |
1250 | struct page *page; | |
1251 | ||
1252 | while (scan_npages--) { | |
1253 | cond_resched(); | |
1254 | rmap_item = scan_get_next_rmap_item(&page); | |
1255 | if (!rmap_item) | |
1256 | return; | |
1257 | if (!PageKsm(page) || !in_stable_tree(rmap_item)) | |
1258 | cmp_and_merge_page(page, rmap_item); | |
1259 | put_page(page); | |
1260 | } | |
1261 | } | |
1262 | ||
1263 | static int ksm_scan_thread(void *nothing) | |
1264 | { | |
1265 | set_user_nice(current, 0); | |
1266 | ||
1267 | while (!kthread_should_stop()) { | |
1268 | if (ksm_run & KSM_RUN_MERGE) { | |
1269 | mutex_lock(&ksm_thread_mutex); | |
1270 | ksm_do_scan(ksm_thread_pages_to_scan); | |
1271 | mutex_unlock(&ksm_thread_mutex); | |
1272 | schedule_timeout_interruptible( | |
1273 | msecs_to_jiffies(ksm_thread_sleep_millisecs)); | |
1274 | } else { | |
1275 | wait_event_interruptible(ksm_thread_wait, | |
1276 | (ksm_run & KSM_RUN_MERGE) || | |
1277 | kthread_should_stop()); | |
1278 | } | |
1279 | } | |
1280 | return 0; | |
1281 | } | |
1282 | ||
f8af4da3 HD |
1283 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
1284 | unsigned long end, int advice, unsigned long *vm_flags) | |
1285 | { | |
1286 | struct mm_struct *mm = vma->vm_mm; | |
1287 | ||
1288 | switch (advice) { | |
1289 | case MADV_MERGEABLE: | |
1290 | /* | |
1291 | * Be somewhat over-protective for now! | |
1292 | */ | |
1293 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | | |
1294 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | | |
1295 | VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | | |
1296 | VM_MIXEDMAP | VM_SAO)) | |
1297 | return 0; /* just ignore the advice */ | |
1298 | ||
1299 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) | |
1300 | if (__ksm_enter(mm) < 0) | |
1301 | return -EAGAIN; | |
1302 | ||
1303 | *vm_flags |= VM_MERGEABLE; | |
1304 | break; | |
1305 | ||
1306 | case MADV_UNMERGEABLE: | |
1307 | if (!(*vm_flags & VM_MERGEABLE)) | |
1308 | return 0; /* just ignore the advice */ | |
1309 | ||
31dbd01f IE |
1310 | if (vma->anon_vma) |
1311 | unmerge_ksm_pages(vma, start, end); | |
f8af4da3 HD |
1312 | |
1313 | *vm_flags &= ~VM_MERGEABLE; | |
1314 | break; | |
1315 | } | |
1316 | ||
1317 | return 0; | |
1318 | } | |
1319 | ||
1320 | int __ksm_enter(struct mm_struct *mm) | |
1321 | { | |
31dbd01f IE |
1322 | struct mm_slot *mm_slot = alloc_mm_slot(); |
1323 | if (!mm_slot) | |
1324 | return -ENOMEM; | |
1325 | ||
1326 | spin_lock(&ksm_mmlist_lock); | |
1327 | insert_to_mm_slots_hash(mm, mm_slot); | |
1328 | /* | |
1329 | * Insert just behind the scanning cursor, to let the area settle | |
1330 | * down a little; when fork is followed by immediate exec, we don't | |
1331 | * want ksmd to waste time setting up and tearing down an rmap_list. | |
1332 | */ | |
1333 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); | |
1334 | spin_unlock(&ksm_mmlist_lock); | |
1335 | ||
f8af4da3 HD |
1336 | set_bit(MMF_VM_MERGEABLE, &mm->flags); |
1337 | return 0; | |
1338 | } | |
1339 | ||
1340 | void __ksm_exit(struct mm_struct *mm) | |
1341 | { | |
31dbd01f IE |
1342 | /* |
1343 | * This process is exiting: doesn't hold and doesn't need mmap_sem; | |
1344 | * but we do need to exclude ksmd and other exiters while we modify | |
1345 | * the various lists and trees. | |
1346 | */ | |
1347 | mutex_lock(&ksm_thread_mutex); | |
1348 | remove_mm_from_lists(mm); | |
1349 | mutex_unlock(&ksm_thread_mutex); | |
1350 | } | |
1351 | ||
1352 | #define KSM_ATTR_RO(_name) \ | |
1353 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) | |
1354 | #define KSM_ATTR(_name) \ | |
1355 | static struct kobj_attribute _name##_attr = \ | |
1356 | __ATTR(_name, 0644, _name##_show, _name##_store) | |
1357 | ||
1358 | static ssize_t sleep_millisecs_show(struct kobject *kobj, | |
1359 | struct kobj_attribute *attr, char *buf) | |
1360 | { | |
1361 | return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); | |
1362 | } | |
1363 | ||
1364 | static ssize_t sleep_millisecs_store(struct kobject *kobj, | |
1365 | struct kobj_attribute *attr, | |
1366 | const char *buf, size_t count) | |
1367 | { | |
1368 | unsigned long msecs; | |
1369 | int err; | |
1370 | ||
1371 | err = strict_strtoul(buf, 10, &msecs); | |
1372 | if (err || msecs > UINT_MAX) | |
1373 | return -EINVAL; | |
1374 | ||
1375 | ksm_thread_sleep_millisecs = msecs; | |
1376 | ||
1377 | return count; | |
1378 | } | |
1379 | KSM_ATTR(sleep_millisecs); | |
1380 | ||
1381 | static ssize_t pages_to_scan_show(struct kobject *kobj, | |
1382 | struct kobj_attribute *attr, char *buf) | |
1383 | { | |
1384 | return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); | |
1385 | } | |
1386 | ||
1387 | static ssize_t pages_to_scan_store(struct kobject *kobj, | |
1388 | struct kobj_attribute *attr, | |
1389 | const char *buf, size_t count) | |
1390 | { | |
1391 | int err; | |
1392 | unsigned long nr_pages; | |
1393 | ||
1394 | err = strict_strtoul(buf, 10, &nr_pages); | |
1395 | if (err || nr_pages > UINT_MAX) | |
1396 | return -EINVAL; | |
1397 | ||
1398 | ksm_thread_pages_to_scan = nr_pages; | |
1399 | ||
1400 | return count; | |
1401 | } | |
1402 | KSM_ATTR(pages_to_scan); | |
1403 | ||
1404 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, | |
1405 | char *buf) | |
1406 | { | |
1407 | return sprintf(buf, "%u\n", ksm_run); | |
1408 | } | |
1409 | ||
1410 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, | |
1411 | const char *buf, size_t count) | |
1412 | { | |
1413 | int err; | |
1414 | unsigned long flags; | |
1415 | ||
1416 | err = strict_strtoul(buf, 10, &flags); | |
1417 | if (err || flags > UINT_MAX) | |
1418 | return -EINVAL; | |
1419 | if (flags > KSM_RUN_UNMERGE) | |
1420 | return -EINVAL; | |
1421 | ||
1422 | /* | |
1423 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. | |
1424 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, | |
1425 | * breaking COW to free the kernel_pages_allocated (but leaves | |
1426 | * mm_slots on the list for when ksmd may be set running again). | |
1427 | */ | |
1428 | ||
1429 | mutex_lock(&ksm_thread_mutex); | |
1430 | if (ksm_run != flags) { | |
1431 | ksm_run = flags; | |
1432 | if (flags & KSM_RUN_UNMERGE) | |
1433 | unmerge_and_remove_all_rmap_items(); | |
1434 | } | |
1435 | mutex_unlock(&ksm_thread_mutex); | |
1436 | ||
1437 | if (flags & KSM_RUN_MERGE) | |
1438 | wake_up_interruptible(&ksm_thread_wait); | |
1439 | ||
1440 | return count; | |
1441 | } | |
1442 | KSM_ATTR(run); | |
1443 | ||
1444 | static ssize_t pages_shared_show(struct kobject *kobj, | |
1445 | struct kobj_attribute *attr, char *buf) | |
1446 | { | |
1447 | return sprintf(buf, "%lu\n", | |
1448 | ksm_pages_shared - ksm_kernel_pages_allocated); | |
1449 | } | |
1450 | KSM_ATTR_RO(pages_shared); | |
1451 | ||
1452 | static ssize_t kernel_pages_allocated_show(struct kobject *kobj, | |
1453 | struct kobj_attribute *attr, | |
1454 | char *buf) | |
1455 | { | |
1456 | return sprintf(buf, "%lu\n", ksm_kernel_pages_allocated); | |
1457 | } | |
1458 | KSM_ATTR_RO(kernel_pages_allocated); | |
1459 | ||
1460 | static ssize_t max_kernel_pages_store(struct kobject *kobj, | |
1461 | struct kobj_attribute *attr, | |
1462 | const char *buf, size_t count) | |
1463 | { | |
1464 | int err; | |
1465 | unsigned long nr_pages; | |
1466 | ||
1467 | err = strict_strtoul(buf, 10, &nr_pages); | |
1468 | if (err) | |
1469 | return -EINVAL; | |
1470 | ||
1471 | ksm_max_kernel_pages = nr_pages; | |
1472 | ||
1473 | return count; | |
1474 | } | |
1475 | ||
1476 | static ssize_t max_kernel_pages_show(struct kobject *kobj, | |
1477 | struct kobj_attribute *attr, char *buf) | |
1478 | { | |
1479 | return sprintf(buf, "%lu\n", ksm_max_kernel_pages); | |
1480 | } | |
1481 | KSM_ATTR(max_kernel_pages); | |
1482 | ||
1483 | static struct attribute *ksm_attrs[] = { | |
1484 | &sleep_millisecs_attr.attr, | |
1485 | &pages_to_scan_attr.attr, | |
1486 | &run_attr.attr, | |
1487 | &pages_shared_attr.attr, | |
1488 | &kernel_pages_allocated_attr.attr, | |
1489 | &max_kernel_pages_attr.attr, | |
1490 | NULL, | |
1491 | }; | |
1492 | ||
1493 | static struct attribute_group ksm_attr_group = { | |
1494 | .attrs = ksm_attrs, | |
1495 | .name = "ksm", | |
1496 | }; | |
1497 | ||
1498 | static int __init ksm_init(void) | |
1499 | { | |
1500 | struct task_struct *ksm_thread; | |
1501 | int err; | |
1502 | ||
1503 | err = ksm_slab_init(); | |
1504 | if (err) | |
1505 | goto out; | |
1506 | ||
1507 | err = mm_slots_hash_init(); | |
1508 | if (err) | |
1509 | goto out_free1; | |
1510 | ||
1511 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); | |
1512 | if (IS_ERR(ksm_thread)) { | |
1513 | printk(KERN_ERR "ksm: creating kthread failed\n"); | |
1514 | err = PTR_ERR(ksm_thread); | |
1515 | goto out_free2; | |
1516 | } | |
1517 | ||
1518 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); | |
1519 | if (err) { | |
1520 | printk(KERN_ERR "ksm: register sysfs failed\n"); | |
1521 | goto out_free3; | |
1522 | } | |
1523 | ||
1524 | return 0; | |
1525 | ||
1526 | out_free3: | |
1527 | kthread_stop(ksm_thread); | |
1528 | out_free2: | |
1529 | mm_slots_hash_free(); | |
1530 | out_free1: | |
1531 | ksm_slab_free(); | |
1532 | out: | |
1533 | return err; | |
f8af4da3 | 1534 | } |
31dbd01f | 1535 | module_init(ksm_init) |