blob: 9f8f0523562baee9d2b42641969d29bf3f2ac61b [file] [log] [blame]
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001/*
Izik Eidus31dbd012009-09-21 17:02:03 -07002 * 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 *
Izik Eidus36b25282009-09-21 17:02:06 -07007 * Copyright (C) 2008-2009 Red Hat, Inc.
Izik Eidus31dbd012009-09-21 17:02:03 -07008 * Authors:
9 * Izik Eidus
10 * Andrea Arcangeli
11 * Chris Wright
Izik Eidus36b25282009-09-21 17:02:06 -070012 * Hugh Dickins
Izik Eidus31dbd012009-09-21 17:02:03 -070013 *
14 * This work is licensed under the terms of the GNU GPL, version 2.
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070015 */
16
17#include <linux/errno.h>
Izik Eidus31dbd012009-09-21 17:02:03 -070018#include <linux/mm.h>
19#include <linux/fs.h>
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070020#include <linux/mman.h>
Izik Eidus31dbd012009-09-21 17:02:03 -070021#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>
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070033#include <linux/ksm.h>
34
Izik Eidus31dbd012009-09-21 17:02:03 -070035#include <asm/tlbflush.h>
36
37/*
38 * A few notes about the KSM scanning process,
39 * to make it easier to understand the data structures below:
40 *
41 * In order to reduce excessive scanning, KSM sorts the memory pages by their
42 * contents into a data structure that holds pointers to the pages' locations.
43 *
44 * Since the contents of the pages may change at any moment, KSM cannot just
45 * insert the pages into a normal sorted tree and expect it to find anything.
46 * Therefore KSM uses two data structures - the stable and the unstable tree.
47 *
48 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
49 * by their contents. Because each such page is write-protected, searching on
50 * this tree is fully assured to be working (except when pages are unmapped),
51 * and therefore this tree is called the stable tree.
52 *
53 * In addition to the stable tree, KSM uses a second data structure called the
54 * unstable tree: this tree holds pointers to pages which have been found to
55 * be "unchanged for a period of time". The unstable tree sorts these pages
56 * by their contents, but since they are not write-protected, KSM cannot rely
57 * upon the unstable tree to work correctly - the unstable tree is liable to
58 * be corrupted as its contents are modified, and so it is called unstable.
59 *
60 * KSM solves this problem by several techniques:
61 *
62 * 1) The unstable tree is flushed every time KSM completes scanning all
63 * memory areas, and then the tree is rebuilt again from the beginning.
64 * 2) KSM will only insert into the unstable tree, pages whose hash value
65 * has not changed since the previous scan of all memory areas.
66 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
67 * colors of the nodes and not on their contents, assuring that even when
68 * the tree gets "corrupted" it won't get out of balance, so scanning time
69 * remains the same (also, searching and inserting nodes in an rbtree uses
70 * the same algorithm, so we have no overhead when we flush and rebuild).
71 * 4) KSM never flushes the stable tree, which means that even if it were to
72 * take 10 attempts to find a page in the unstable tree, once it is found,
73 * it is secured in the stable tree. (When we scan a new page, we first
74 * compare it against the stable tree, and then against the unstable tree.)
75 */
76
77/**
78 * struct mm_slot - ksm information per mm that is being scanned
79 * @link: link to the mm_slots hash list
80 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
81 * @rmap_list: head for this mm_slot's list of rmap_items
82 * @mm: the mm that this information is valid for
83 */
84struct mm_slot {
85 struct hlist_node link;
86 struct list_head mm_list;
87 struct list_head rmap_list;
88 struct mm_struct *mm;
89};
90
91/**
92 * struct ksm_scan - cursor for scanning
93 * @mm_slot: the current mm_slot we are scanning
94 * @address: the next address inside that to be scanned
95 * @rmap_item: the current rmap that we are scanning inside the rmap_list
96 * @seqnr: count of completed full scans (needed when removing unstable node)
97 *
98 * There is only the one ksm_scan instance of this cursor structure.
99 */
100struct ksm_scan {
101 struct mm_slot *mm_slot;
102 unsigned long address;
103 struct rmap_item *rmap_item;
104 unsigned long seqnr;
105};
106
107/**
108 * struct rmap_item - reverse mapping item for virtual addresses
109 * @link: link into mm_slot's rmap_list (rmap_list is per mm)
110 * @mm: the memory structure this rmap_item is pointing into
111 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
112 * @oldchecksum: previous checksum of the page at that virtual address
113 * @node: rb_node of this rmap_item in either unstable or stable tree
114 * @next: next rmap_item hanging off the same node of the stable tree
115 * @prev: previous rmap_item hanging off the same node of the stable tree
116 */
117struct rmap_item {
118 struct list_head link;
119 struct mm_struct *mm;
120 unsigned long address; /* + low bits used for flags below */
121 union {
122 unsigned int oldchecksum; /* when unstable */
123 struct rmap_item *next; /* when stable */
124 };
125 union {
126 struct rb_node node; /* when tree node */
127 struct rmap_item *prev; /* in stable list */
128 };
129};
130
131#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
132#define NODE_FLAG 0x100 /* is a node of unstable or stable tree */
133#define STABLE_FLAG 0x200 /* is a node or list item of stable tree */
134
135/* The stable and unstable tree heads */
136static struct rb_root root_stable_tree = RB_ROOT;
137static struct rb_root root_unstable_tree = RB_ROOT;
138
139#define MM_SLOTS_HASH_HEADS 1024
140static struct hlist_head *mm_slots_hash;
141
142static struct mm_slot ksm_mm_head = {
143 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
144};
145static struct ksm_scan ksm_scan = {
146 .mm_slot = &ksm_mm_head,
147};
148
149static struct kmem_cache *rmap_item_cache;
150static struct kmem_cache *mm_slot_cache;
151
152/* The number of nodes in the stable tree */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700153static unsigned long ksm_pages_shared;
Izik Eidus31dbd012009-09-21 17:02:03 -0700154
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700155/* The number of page slots additionally sharing those nodes */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700156static unsigned long ksm_pages_sharing;
Izik Eidus31dbd012009-09-21 17:02:03 -0700157
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700158/* The number of nodes in the unstable tree */
159static unsigned long ksm_pages_unshared;
160
161/* The number of rmap_items in use: to calculate pages_volatile */
162static unsigned long ksm_rmap_items;
163
Izik Eidus31dbd012009-09-21 17:02:03 -0700164/* Limit on the number of unswappable pages used */
165static unsigned long ksm_max_kernel_pages;
166
167/* Number of pages ksmd should scan in one batch */
168static unsigned int ksm_thread_pages_to_scan;
169
170/* Milliseconds ksmd should sleep between batches */
171static unsigned int ksm_thread_sleep_millisecs;
172
173#define KSM_RUN_STOP 0
174#define KSM_RUN_MERGE 1
175#define KSM_RUN_UNMERGE 2
176static unsigned int ksm_run;
177
178static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
179static DEFINE_MUTEX(ksm_thread_mutex);
180static DEFINE_SPINLOCK(ksm_mmlist_lock);
181
182#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
183 sizeof(struct __struct), __alignof__(struct __struct),\
184 (__flags), NULL)
185
186static int __init ksm_slab_init(void)
187{
188 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
189 if (!rmap_item_cache)
190 goto out;
191
192 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
193 if (!mm_slot_cache)
194 goto out_free;
195
196 return 0;
197
198out_free:
199 kmem_cache_destroy(rmap_item_cache);
200out:
201 return -ENOMEM;
202}
203
204static void __init ksm_slab_free(void)
205{
206 kmem_cache_destroy(mm_slot_cache);
207 kmem_cache_destroy(rmap_item_cache);
208 mm_slot_cache = NULL;
209}
210
211static inline struct rmap_item *alloc_rmap_item(void)
212{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700213 struct rmap_item *rmap_item;
214
215 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
216 if (rmap_item)
217 ksm_rmap_items++;
218 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -0700219}
220
221static inline void free_rmap_item(struct rmap_item *rmap_item)
222{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700223 ksm_rmap_items--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700224 rmap_item->mm = NULL; /* debug safety */
225 kmem_cache_free(rmap_item_cache, rmap_item);
226}
227
228static inline struct mm_slot *alloc_mm_slot(void)
229{
230 if (!mm_slot_cache) /* initialization failed */
231 return NULL;
232 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
233}
234
235static inline void free_mm_slot(struct mm_slot *mm_slot)
236{
237 kmem_cache_free(mm_slot_cache, mm_slot);
238}
239
240static int __init mm_slots_hash_init(void)
241{
242 mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
243 GFP_KERNEL);
244 if (!mm_slots_hash)
245 return -ENOMEM;
246 return 0;
247}
248
249static void __init mm_slots_hash_free(void)
250{
251 kfree(mm_slots_hash);
252}
253
254static struct mm_slot *get_mm_slot(struct mm_struct *mm)
255{
256 struct mm_slot *mm_slot;
257 struct hlist_head *bucket;
258 struct hlist_node *node;
259
260 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
261 % MM_SLOTS_HASH_HEADS];
262 hlist_for_each_entry(mm_slot, node, bucket, link) {
263 if (mm == mm_slot->mm)
264 return mm_slot;
265 }
266 return NULL;
267}
268
269static void insert_to_mm_slots_hash(struct mm_struct *mm,
270 struct mm_slot *mm_slot)
271{
272 struct hlist_head *bucket;
273
274 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
275 % MM_SLOTS_HASH_HEADS];
276 mm_slot->mm = mm;
277 INIT_LIST_HEAD(&mm_slot->rmap_list);
278 hlist_add_head(&mm_slot->link, bucket);
279}
280
281static inline int in_stable_tree(struct rmap_item *rmap_item)
282{
283 return rmap_item->address & STABLE_FLAG;
284}
285
286/*
287 * We use break_ksm to break COW on a ksm page: it's a stripped down
288 *
289 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
290 * put_page(page);
291 *
292 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
293 * in case the application has unmapped and remapped mm,addr meanwhile.
294 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
295 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
296 */
297static void break_ksm(struct vm_area_struct *vma, unsigned long addr)
298{
299 struct page *page;
300 int ret;
301
302 do {
303 cond_resched();
304 page = follow_page(vma, addr, FOLL_GET);
305 if (!page)
306 break;
307 if (PageKsm(page))
308 ret = handle_mm_fault(vma->vm_mm, vma, addr,
309 FAULT_FLAG_WRITE);
310 else
311 ret = VM_FAULT_WRITE;
312 put_page(page);
313 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS)));
314
315 /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */
316}
317
318static void __break_cow(struct mm_struct *mm, unsigned long addr)
319{
320 struct vm_area_struct *vma;
321
322 vma = find_vma(mm, addr);
323 if (!vma || vma->vm_start > addr)
324 return;
325 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
326 return;
327 break_ksm(vma, addr);
328}
329
330static void break_cow(struct mm_struct *mm, unsigned long addr)
331{
332 down_read(&mm->mmap_sem);
333 __break_cow(mm, addr);
334 up_read(&mm->mmap_sem);
335}
336
337static struct page *get_mergeable_page(struct rmap_item *rmap_item)
338{
339 struct mm_struct *mm = rmap_item->mm;
340 unsigned long addr = rmap_item->address;
341 struct vm_area_struct *vma;
342 struct page *page;
343
344 down_read(&mm->mmap_sem);
345 vma = find_vma(mm, addr);
346 if (!vma || vma->vm_start > addr)
347 goto out;
348 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
349 goto out;
350
351 page = follow_page(vma, addr, FOLL_GET);
352 if (!page)
353 goto out;
354 if (PageAnon(page)) {
355 flush_anon_page(vma, page, addr);
356 flush_dcache_page(page);
357 } else {
358 put_page(page);
359out: page = NULL;
360 }
361 up_read(&mm->mmap_sem);
362 return page;
363}
364
365/*
366 * get_ksm_page: checks if the page at the virtual address in rmap_item
367 * is still PageKsm, in which case we can trust the content of the page,
368 * and it returns the gotten page; but NULL if the page has been zapped.
369 */
370static struct page *get_ksm_page(struct rmap_item *rmap_item)
371{
372 struct page *page;
373
374 page = get_mergeable_page(rmap_item);
375 if (page && !PageKsm(page)) {
376 put_page(page);
377 page = NULL;
378 }
379 return page;
380}
381
382/*
383 * Removing rmap_item from stable or unstable tree.
384 * This function will clean the information from the stable/unstable tree.
385 */
386static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
387{
388 if (in_stable_tree(rmap_item)) {
389 struct rmap_item *next_item = rmap_item->next;
390
391 if (rmap_item->address & NODE_FLAG) {
392 if (next_item) {
393 rb_replace_node(&rmap_item->node,
394 &next_item->node,
395 &root_stable_tree);
396 next_item->address |= NODE_FLAG;
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700397 ksm_pages_sharing--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700398 } else {
399 rb_erase(&rmap_item->node, &root_stable_tree);
Hugh Dickinsb4028262009-09-21 17:02:09 -0700400 ksm_pages_shared--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700401 }
402 } else {
403 struct rmap_item *prev_item = rmap_item->prev;
404
405 BUG_ON(prev_item->next != rmap_item);
406 prev_item->next = next_item;
407 if (next_item) {
408 BUG_ON(next_item->prev != rmap_item);
409 next_item->prev = rmap_item->prev;
410 }
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700411 ksm_pages_sharing--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700412 }
413
414 rmap_item->next = NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -0700415
416 } else if (rmap_item->address & NODE_FLAG) {
417 unsigned char age;
418 /*
419 * ksm_thread can and must skip the rb_erase, because
420 * root_unstable_tree was already reset to RB_ROOT.
421 * But __ksm_exit has to be careful: do the rb_erase
422 * if it's interrupting a scan, and this rmap_item was
423 * inserted by this scan rather than left from before.
424 *
425 * Because of the case in which remove_mm_from_lists
426 * increments seqnr before removing rmaps, unstable_nr
427 * may even be 2 behind seqnr, but should never be
428 * further behind. Yes, I did have trouble with this!
429 */
430 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
431 BUG_ON(age > 2);
432 if (!age)
433 rb_erase(&rmap_item->node, &root_unstable_tree);
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700434 ksm_pages_unshared--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700435 }
436
437 rmap_item->address &= PAGE_MASK;
438
439 cond_resched(); /* we're called from many long loops */
440}
441
442static void remove_all_slot_rmap_items(struct mm_slot *mm_slot)
443{
444 struct rmap_item *rmap_item, *node;
445
446 list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) {
447 remove_rmap_item_from_tree(rmap_item);
448 list_del(&rmap_item->link);
449 free_rmap_item(rmap_item);
450 }
451}
452
453static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
454 struct list_head *cur)
455{
456 struct rmap_item *rmap_item;
457
458 while (cur != &mm_slot->rmap_list) {
459 rmap_item = list_entry(cur, struct rmap_item, link);
460 cur = cur->next;
461 remove_rmap_item_from_tree(rmap_item);
462 list_del(&rmap_item->link);
463 free_rmap_item(rmap_item);
464 }
465}
466
467/*
468 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
469 * than check every pte of a given vma, the locking doesn't quite work for
470 * that - an rmap_item is assigned to the stable tree after inserting ksm
471 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
472 * rmap_items from parent to child at fork time (so as not to waste time
473 * if exit comes before the next scan reaches it).
474 */
475static void unmerge_ksm_pages(struct vm_area_struct *vma,
476 unsigned long start, unsigned long end)
477{
478 unsigned long addr;
479
480 for (addr = start; addr < end; addr += PAGE_SIZE)
481 break_ksm(vma, addr);
482}
483
484static void unmerge_and_remove_all_rmap_items(void)
485{
486 struct mm_slot *mm_slot;
487 struct mm_struct *mm;
488 struct vm_area_struct *vma;
489
490 list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) {
491 mm = mm_slot->mm;
492 down_read(&mm->mmap_sem);
493 for (vma = mm->mmap; vma; vma = vma->vm_next) {
494 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
495 continue;
496 unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
497 }
498 remove_all_slot_rmap_items(mm_slot);
499 up_read(&mm->mmap_sem);
500 }
501
502 spin_lock(&ksm_mmlist_lock);
503 if (ksm_scan.mm_slot != &ksm_mm_head) {
504 ksm_scan.mm_slot = &ksm_mm_head;
505 ksm_scan.seqnr++;
506 }
507 spin_unlock(&ksm_mmlist_lock);
508}
509
510static void remove_mm_from_lists(struct mm_struct *mm)
511{
512 struct mm_slot *mm_slot;
513
514 spin_lock(&ksm_mmlist_lock);
515 mm_slot = get_mm_slot(mm);
516
517 /*
518 * This mm_slot is always at the scanning cursor when we're
519 * called from scan_get_next_rmap_item; but it's a special
520 * case when we're called from __ksm_exit.
521 */
522 if (ksm_scan.mm_slot == mm_slot) {
523 ksm_scan.mm_slot = list_entry(
524 mm_slot->mm_list.next, struct mm_slot, mm_list);
525 ksm_scan.address = 0;
526 ksm_scan.rmap_item = list_entry(
527 &ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
528 if (ksm_scan.mm_slot == &ksm_mm_head)
529 ksm_scan.seqnr++;
530 }
531
532 hlist_del(&mm_slot->link);
533 list_del(&mm_slot->mm_list);
534 spin_unlock(&ksm_mmlist_lock);
535
536 remove_all_slot_rmap_items(mm_slot);
537 free_mm_slot(mm_slot);
538 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
539}
540
541static u32 calc_checksum(struct page *page)
542{
543 u32 checksum;
544 void *addr = kmap_atomic(page, KM_USER0);
545 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
546 kunmap_atomic(addr, KM_USER0);
547 return checksum;
548}
549
550static int memcmp_pages(struct page *page1, struct page *page2)
551{
552 char *addr1, *addr2;
553 int ret;
554
555 addr1 = kmap_atomic(page1, KM_USER0);
556 addr2 = kmap_atomic(page2, KM_USER1);
557 ret = memcmp(addr1, addr2, PAGE_SIZE);
558 kunmap_atomic(addr2, KM_USER1);
559 kunmap_atomic(addr1, KM_USER0);
560 return ret;
561}
562
563static inline int pages_identical(struct page *page1, struct page *page2)
564{
565 return !memcmp_pages(page1, page2);
566}
567
568static int write_protect_page(struct vm_area_struct *vma, struct page *page,
569 pte_t *orig_pte)
570{
571 struct mm_struct *mm = vma->vm_mm;
572 unsigned long addr;
573 pte_t *ptep;
574 spinlock_t *ptl;
575 int swapped;
576 int err = -EFAULT;
577
578 addr = page_address_in_vma(page, vma);
579 if (addr == -EFAULT)
580 goto out;
581
582 ptep = page_check_address(page, mm, addr, &ptl, 0);
583 if (!ptep)
584 goto out;
585
586 if (pte_write(*ptep)) {
587 pte_t entry;
588
589 swapped = PageSwapCache(page);
590 flush_cache_page(vma, addr, page_to_pfn(page));
591 /*
592 * Ok this is tricky, when get_user_pages_fast() run it doesnt
593 * take any lock, therefore the check that we are going to make
594 * with the pagecount against the mapcount is racey and
595 * O_DIRECT can happen right after the check.
596 * So we clear the pte and flush the tlb before the check
597 * this assure us that no O_DIRECT can happen after the check
598 * or in the middle of the check.
599 */
600 entry = ptep_clear_flush(vma, addr, ptep);
601 /*
602 * Check that no O_DIRECT or similar I/O is in progress on the
603 * page
604 */
605 if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
606 set_pte_at_notify(mm, addr, ptep, entry);
607 goto out_unlock;
608 }
609 entry = pte_wrprotect(entry);
610 set_pte_at_notify(mm, addr, ptep, entry);
611 }
612 *orig_pte = *ptep;
613 err = 0;
614
615out_unlock:
616 pte_unmap_unlock(ptep, ptl);
617out:
618 return err;
619}
620
621/**
622 * replace_page - replace page in vma by new ksm page
623 * @vma: vma that holds the pte pointing to oldpage
624 * @oldpage: the page we are replacing by newpage
625 * @newpage: the ksm page we replace oldpage by
626 * @orig_pte: the original value of the pte
627 *
628 * Returns 0 on success, -EFAULT on failure.
629 */
630static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
631 struct page *newpage, pte_t orig_pte)
632{
633 struct mm_struct *mm = vma->vm_mm;
634 pgd_t *pgd;
635 pud_t *pud;
636 pmd_t *pmd;
637 pte_t *ptep;
638 spinlock_t *ptl;
639 unsigned long addr;
640 pgprot_t prot;
641 int err = -EFAULT;
642
643 prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
644
645 addr = page_address_in_vma(oldpage, vma);
646 if (addr == -EFAULT)
647 goto out;
648
649 pgd = pgd_offset(mm, addr);
650 if (!pgd_present(*pgd))
651 goto out;
652
653 pud = pud_offset(pgd, addr);
654 if (!pud_present(*pud))
655 goto out;
656
657 pmd = pmd_offset(pud, addr);
658 if (!pmd_present(*pmd))
659 goto out;
660
661 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
662 if (!pte_same(*ptep, orig_pte)) {
663 pte_unmap_unlock(ptep, ptl);
664 goto out;
665 }
666
667 get_page(newpage);
668 page_add_ksm_rmap(newpage);
669
670 flush_cache_page(vma, addr, pte_pfn(*ptep));
671 ptep_clear_flush(vma, addr, ptep);
672 set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
673
674 page_remove_rmap(oldpage);
675 put_page(oldpage);
676
677 pte_unmap_unlock(ptep, ptl);
678 err = 0;
679out:
680 return err;
681}
682
683/*
684 * try_to_merge_one_page - take two pages and merge them into one
685 * @vma: the vma that hold the pte pointing into oldpage
686 * @oldpage: the page that we want to replace with newpage
687 * @newpage: the page that we want to map instead of oldpage
688 *
689 * Note:
690 * oldpage should be a PageAnon page, while newpage should be a PageKsm page,
691 * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
692 *
693 * This function returns 0 if the pages were merged, -EFAULT otherwise.
694 */
695static int try_to_merge_one_page(struct vm_area_struct *vma,
696 struct page *oldpage,
697 struct page *newpage)
698{
699 pte_t orig_pte = __pte(0);
700 int err = -EFAULT;
701
702 if (!(vma->vm_flags & VM_MERGEABLE))
703 goto out;
704
705 if (!PageAnon(oldpage))
706 goto out;
707
708 get_page(newpage);
709 get_page(oldpage);
710
711 /*
712 * We need the page lock to read a stable PageSwapCache in
713 * write_protect_page(). We use trylock_page() instead of
714 * lock_page() because we don't want to wait here - we
715 * prefer to continue scanning and merging different pages,
716 * then come back to this page when it is unlocked.
717 */
718 if (!trylock_page(oldpage))
719 goto out_putpage;
720 /*
721 * If this anonymous page is mapped only here, its pte may need
722 * to be write-protected. If it's mapped elsewhere, all of its
723 * ptes are necessarily already write-protected. But in either
724 * case, we need to lock and check page_count is not raised.
725 */
726 if (write_protect_page(vma, oldpage, &orig_pte)) {
727 unlock_page(oldpage);
728 goto out_putpage;
729 }
730 unlock_page(oldpage);
731
732 if (pages_identical(oldpage, newpage))
733 err = replace_page(vma, oldpage, newpage, orig_pte);
734
735out_putpage:
736 put_page(oldpage);
737 put_page(newpage);
738out:
739 return err;
740}
741
742/*
743 * try_to_merge_two_pages - take two identical pages and prepare them
744 * to be merged into one page.
745 *
746 * This function returns 0 if we successfully mapped two identical pages
747 * into one page, -EFAULT otherwise.
748 *
749 * Note that this function allocates a new kernel page: if one of the pages
750 * is already a ksm page, try_to_merge_with_ksm_page should be used.
751 */
752static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
753 struct page *page1, struct mm_struct *mm2,
754 unsigned long addr2, struct page *page2)
755{
756 struct vm_area_struct *vma;
757 struct page *kpage;
758 int err = -EFAULT;
759
760 /*
761 * The number of nodes in the stable tree
762 * is the number of kernel pages that we hold.
763 */
764 if (ksm_max_kernel_pages &&
Hugh Dickinsb4028262009-09-21 17:02:09 -0700765 ksm_max_kernel_pages <= ksm_pages_shared)
Izik Eidus31dbd012009-09-21 17:02:03 -0700766 return err;
767
768 kpage = alloc_page(GFP_HIGHUSER);
769 if (!kpage)
770 return err;
771
772 down_read(&mm1->mmap_sem);
773 vma = find_vma(mm1, addr1);
774 if (!vma || vma->vm_start > addr1) {
775 put_page(kpage);
776 up_read(&mm1->mmap_sem);
777 return err;
778 }
779
780 copy_user_highpage(kpage, page1, addr1, vma);
781 err = try_to_merge_one_page(vma, page1, kpage);
782 up_read(&mm1->mmap_sem);
783
784 if (!err) {
785 down_read(&mm2->mmap_sem);
786 vma = find_vma(mm2, addr2);
787 if (!vma || vma->vm_start > addr2) {
788 put_page(kpage);
789 up_read(&mm2->mmap_sem);
790 break_cow(mm1, addr1);
791 return -EFAULT;
792 }
793
794 err = try_to_merge_one_page(vma, page2, kpage);
795 up_read(&mm2->mmap_sem);
796
797 /*
798 * If the second try_to_merge_one_page failed, we have a
799 * ksm page with just one pte pointing to it, so break it.
800 */
801 if (err)
802 break_cow(mm1, addr1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700803 }
804
805 put_page(kpage);
806 return err;
807}
808
809/*
810 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
811 * but no new kernel page is allocated: kpage must already be a ksm page.
812 */
813static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
814 unsigned long addr1,
815 struct page *page1,
816 struct page *kpage)
817{
818 struct vm_area_struct *vma;
819 int err = -EFAULT;
820
821 down_read(&mm1->mmap_sem);
822 vma = find_vma(mm1, addr1);
823 if (!vma || vma->vm_start > addr1) {
824 up_read(&mm1->mmap_sem);
825 return err;
826 }
827
828 err = try_to_merge_one_page(vma, page1, kpage);
829 up_read(&mm1->mmap_sem);
830
Izik Eidus31dbd012009-09-21 17:02:03 -0700831 return err;
832}
833
834/*
835 * stable_tree_search - search page inside the stable tree
836 * @page: the page that we are searching identical pages to.
837 * @page2: pointer into identical page that we are holding inside the stable
838 * tree that we have found.
839 * @rmap_item: the reverse mapping item
840 *
841 * This function checks if there is a page inside the stable tree
842 * with identical content to the page that we are scanning right now.
843 *
844 * This function return rmap_item pointer to the identical item if found,
845 * NULL otherwise.
846 */
847static struct rmap_item *stable_tree_search(struct page *page,
848 struct page **page2,
849 struct rmap_item *rmap_item)
850{
851 struct rb_node *node = root_stable_tree.rb_node;
852
853 while (node) {
854 struct rmap_item *tree_rmap_item, *next_rmap_item;
855 int ret;
856
857 tree_rmap_item = rb_entry(node, struct rmap_item, node);
858 while (tree_rmap_item) {
859 BUG_ON(!in_stable_tree(tree_rmap_item));
860 cond_resched();
861 page2[0] = get_ksm_page(tree_rmap_item);
862 if (page2[0])
863 break;
864 next_rmap_item = tree_rmap_item->next;
865 remove_rmap_item_from_tree(tree_rmap_item);
866 tree_rmap_item = next_rmap_item;
867 }
868 if (!tree_rmap_item)
869 return NULL;
870
871 ret = memcmp_pages(page, page2[0]);
872
873 if (ret < 0) {
874 put_page(page2[0]);
875 node = node->rb_left;
876 } else if (ret > 0) {
877 put_page(page2[0]);
878 node = node->rb_right;
879 } else {
880 return tree_rmap_item;
881 }
882 }
883
884 return NULL;
885}
886
887/*
888 * stable_tree_insert - insert rmap_item pointing to new ksm page
889 * into the stable tree.
890 *
891 * @page: the page that we are searching identical page to inside the stable
892 * tree.
893 * @rmap_item: pointer to the reverse mapping item.
894 *
895 * This function returns rmap_item if success, NULL otherwise.
896 */
897static struct rmap_item *stable_tree_insert(struct page *page,
898 struct rmap_item *rmap_item)
899{
900 struct rb_node **new = &root_stable_tree.rb_node;
901 struct rb_node *parent = NULL;
902
903 while (*new) {
904 struct rmap_item *tree_rmap_item, *next_rmap_item;
905 struct page *tree_page;
906 int ret;
907
908 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
909 while (tree_rmap_item) {
910 BUG_ON(!in_stable_tree(tree_rmap_item));
911 cond_resched();
912 tree_page = get_ksm_page(tree_rmap_item);
913 if (tree_page)
914 break;
915 next_rmap_item = tree_rmap_item->next;
916 remove_rmap_item_from_tree(tree_rmap_item);
917 tree_rmap_item = next_rmap_item;
918 }
919 if (!tree_rmap_item)
920 return NULL;
921
922 ret = memcmp_pages(page, tree_page);
923 put_page(tree_page);
924
925 parent = *new;
926 if (ret < 0)
927 new = &parent->rb_left;
928 else if (ret > 0)
929 new = &parent->rb_right;
930 else {
931 /*
932 * It is not a bug that stable_tree_search() didn't
933 * find this node: because at that time our page was
934 * not yet write-protected, so may have changed since.
935 */
936 return NULL;
937 }
938 }
939
Izik Eidus31dbd012009-09-21 17:02:03 -0700940 rmap_item->address |= NODE_FLAG | STABLE_FLAG;
941 rmap_item->next = NULL;
942 rb_link_node(&rmap_item->node, parent, new);
943 rb_insert_color(&rmap_item->node, &root_stable_tree);
944
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700945 ksm_pages_shared++;
Izik Eidus31dbd012009-09-21 17:02:03 -0700946 return rmap_item;
947}
948
949/*
950 * unstable_tree_search_insert - search and insert items into the unstable tree.
951 *
952 * @page: the page that we are going to search for identical page or to insert
953 * into the unstable tree
954 * @page2: pointer into identical page that was found inside the unstable tree
955 * @rmap_item: the reverse mapping item of page
956 *
957 * This function searches for a page in the unstable tree identical to the
958 * page currently being scanned; and if no identical page is found in the
959 * tree, we insert rmap_item as a new object into the unstable tree.
960 *
961 * This function returns pointer to rmap_item found to be identical
962 * to the currently scanned page, NULL otherwise.
963 *
964 * This function does both searching and inserting, because they share
965 * the same walking algorithm in an rbtree.
966 */
967static struct rmap_item *unstable_tree_search_insert(struct page *page,
968 struct page **page2,
969 struct rmap_item *rmap_item)
970{
971 struct rb_node **new = &root_unstable_tree.rb_node;
972 struct rb_node *parent = NULL;
973
974 while (*new) {
975 struct rmap_item *tree_rmap_item;
976 int ret;
977
978 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
979 page2[0] = get_mergeable_page(tree_rmap_item);
980 if (!page2[0])
981 return NULL;
982
983 /*
984 * Don't substitute an unswappable ksm page
985 * just for one good swappable forked page.
986 */
987 if (page == page2[0]) {
988 put_page(page2[0]);
989 return NULL;
990 }
991
992 ret = memcmp_pages(page, page2[0]);
993
994 parent = *new;
995 if (ret < 0) {
996 put_page(page2[0]);
997 new = &parent->rb_left;
998 } else if (ret > 0) {
999 put_page(page2[0]);
1000 new = &parent->rb_right;
1001 } else {
1002 return tree_rmap_item;
1003 }
1004 }
1005
1006 rmap_item->address |= NODE_FLAG;
1007 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1008 rb_link_node(&rmap_item->node, parent, new);
1009 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1010
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001011 ksm_pages_unshared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001012 return NULL;
1013}
1014
1015/*
1016 * stable_tree_append - add another rmap_item to the linked list of
1017 * rmap_items hanging off a given node of the stable tree, all sharing
1018 * the same ksm page.
1019 */
1020static void stable_tree_append(struct rmap_item *rmap_item,
1021 struct rmap_item *tree_rmap_item)
1022{
1023 rmap_item->next = tree_rmap_item->next;
1024 rmap_item->prev = tree_rmap_item;
1025
1026 if (tree_rmap_item->next)
1027 tree_rmap_item->next->prev = rmap_item;
1028
1029 tree_rmap_item->next = rmap_item;
1030 rmap_item->address |= STABLE_FLAG;
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001031
1032 ksm_pages_sharing++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001033}
1034
1035/*
1036 * cmp_and_merge_page - take a page computes its hash value and check if there
1037 * is similar hash value to different page,
1038 * in case we find that there is similar hash to different page we call to
1039 * try_to_merge_two_pages().
1040 *
1041 * @page: the page that we are searching identical page to.
1042 * @rmap_item: the reverse mapping into the virtual address of this page
1043 */
1044static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1045{
1046 struct page *page2[1];
1047 struct rmap_item *tree_rmap_item;
1048 unsigned int checksum;
1049 int err;
1050
1051 if (in_stable_tree(rmap_item))
1052 remove_rmap_item_from_tree(rmap_item);
1053
1054 /* We first start with searching the page inside the stable tree */
1055 tree_rmap_item = stable_tree_search(page, page2, rmap_item);
1056 if (tree_rmap_item) {
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001057 if (page == page2[0]) /* forked */
Izik Eidus31dbd012009-09-21 17:02:03 -07001058 err = 0;
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001059 else
Izik Eidus31dbd012009-09-21 17:02:03 -07001060 err = try_to_merge_with_ksm_page(rmap_item->mm,
1061 rmap_item->address,
1062 page, page2[0]);
1063 put_page(page2[0]);
1064
1065 if (!err) {
1066 /*
1067 * The page was successfully merged:
1068 * add its rmap_item to the stable tree.
1069 */
1070 stable_tree_append(rmap_item, tree_rmap_item);
1071 }
1072 return;
1073 }
1074
1075 /*
1076 * A ksm page might have got here by fork, but its other
1077 * references have already been removed from the stable tree.
1078 */
1079 if (PageKsm(page))
1080 break_cow(rmap_item->mm, rmap_item->address);
1081
1082 /*
1083 * In case the hash value of the page was changed from the last time we
1084 * have calculated it, this page to be changed frequely, therefore we
1085 * don't want to insert it to the unstable tree, and we don't want to
1086 * waste our time to search if there is something identical to it there.
1087 */
1088 checksum = calc_checksum(page);
1089 if (rmap_item->oldchecksum != checksum) {
1090 rmap_item->oldchecksum = checksum;
1091 return;
1092 }
1093
1094 tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
1095 if (tree_rmap_item) {
1096 err = try_to_merge_two_pages(rmap_item->mm,
1097 rmap_item->address, page,
1098 tree_rmap_item->mm,
1099 tree_rmap_item->address, page2[0]);
1100 /*
1101 * As soon as we merge this page, we want to remove the
1102 * rmap_item of the page we have merged with from the unstable
1103 * tree, and insert it instead as new node in the stable tree.
1104 */
1105 if (!err) {
1106 rb_erase(&tree_rmap_item->node, &root_unstable_tree);
1107 tree_rmap_item->address &= ~NODE_FLAG;
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001108 ksm_pages_unshared--;
1109
Izik Eidus31dbd012009-09-21 17:02:03 -07001110 /*
1111 * If we fail to insert the page into the stable tree,
1112 * we will have 2 virtual addresses that are pointing
1113 * to a ksm page left outside the stable tree,
1114 * in which case we need to break_cow on both.
1115 */
1116 if (stable_tree_insert(page2[0], tree_rmap_item))
1117 stable_tree_append(rmap_item, tree_rmap_item);
1118 else {
1119 break_cow(tree_rmap_item->mm,
1120 tree_rmap_item->address);
1121 break_cow(rmap_item->mm, rmap_item->address);
Izik Eidus31dbd012009-09-21 17:02:03 -07001122 }
1123 }
1124
1125 put_page(page2[0]);
1126 }
1127}
1128
1129static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1130 struct list_head *cur,
1131 unsigned long addr)
1132{
1133 struct rmap_item *rmap_item;
1134
1135 while (cur != &mm_slot->rmap_list) {
1136 rmap_item = list_entry(cur, struct rmap_item, link);
1137 if ((rmap_item->address & PAGE_MASK) == addr) {
1138 if (!in_stable_tree(rmap_item))
1139 remove_rmap_item_from_tree(rmap_item);
1140 return rmap_item;
1141 }
1142 if (rmap_item->address > addr)
1143 break;
1144 cur = cur->next;
1145 remove_rmap_item_from_tree(rmap_item);
1146 list_del(&rmap_item->link);
1147 free_rmap_item(rmap_item);
1148 }
1149
1150 rmap_item = alloc_rmap_item();
1151 if (rmap_item) {
1152 /* It has already been zeroed */
1153 rmap_item->mm = mm_slot->mm;
1154 rmap_item->address = addr;
1155 list_add_tail(&rmap_item->link, cur);
1156 }
1157 return rmap_item;
1158}
1159
1160static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1161{
1162 struct mm_struct *mm;
1163 struct mm_slot *slot;
1164 struct vm_area_struct *vma;
1165 struct rmap_item *rmap_item;
1166
1167 if (list_empty(&ksm_mm_head.mm_list))
1168 return NULL;
1169
1170 slot = ksm_scan.mm_slot;
1171 if (slot == &ksm_mm_head) {
1172 root_unstable_tree = RB_ROOT;
1173
1174 spin_lock(&ksm_mmlist_lock);
1175 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1176 ksm_scan.mm_slot = slot;
1177 spin_unlock(&ksm_mmlist_lock);
1178next_mm:
1179 ksm_scan.address = 0;
1180 ksm_scan.rmap_item = list_entry(&slot->rmap_list,
1181 struct rmap_item, link);
1182 }
1183
1184 mm = slot->mm;
1185 down_read(&mm->mmap_sem);
1186 for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) {
1187 if (!(vma->vm_flags & VM_MERGEABLE))
1188 continue;
1189 if (ksm_scan.address < vma->vm_start)
1190 ksm_scan.address = vma->vm_start;
1191 if (!vma->anon_vma)
1192 ksm_scan.address = vma->vm_end;
1193
1194 while (ksm_scan.address < vma->vm_end) {
1195 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1196 if (*page && PageAnon(*page)) {
1197 flush_anon_page(vma, *page, ksm_scan.address);
1198 flush_dcache_page(*page);
1199 rmap_item = get_next_rmap_item(slot,
1200 ksm_scan.rmap_item->link.next,
1201 ksm_scan.address);
1202 if (rmap_item) {
1203 ksm_scan.rmap_item = rmap_item;
1204 ksm_scan.address += PAGE_SIZE;
1205 } else
1206 put_page(*page);
1207 up_read(&mm->mmap_sem);
1208 return rmap_item;
1209 }
1210 if (*page)
1211 put_page(*page);
1212 ksm_scan.address += PAGE_SIZE;
1213 cond_resched();
1214 }
1215 }
1216
1217 if (!ksm_scan.address) {
1218 /*
1219 * We've completed a full scan of all vmas, holding mmap_sem
1220 * throughout, and found no VM_MERGEABLE: so do the same as
1221 * __ksm_exit does to remove this mm from all our lists now.
1222 */
1223 remove_mm_from_lists(mm);
1224 up_read(&mm->mmap_sem);
1225 slot = ksm_scan.mm_slot;
1226 if (slot != &ksm_mm_head)
1227 goto next_mm;
1228 return NULL;
1229 }
1230
1231 /*
1232 * Nuke all the rmap_items that are above this current rmap:
1233 * because there were no VM_MERGEABLE vmas with such addresses.
1234 */
1235 remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
1236 up_read(&mm->mmap_sem);
1237
1238 spin_lock(&ksm_mmlist_lock);
1239 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1240 ksm_scan.mm_slot = slot;
1241 spin_unlock(&ksm_mmlist_lock);
1242
1243 /* Repeat until we've completed scanning the whole list */
1244 if (slot != &ksm_mm_head)
1245 goto next_mm;
1246
1247 /*
1248 * Bump seqnr here rather than at top, so that __ksm_exit
1249 * can skip rb_erase on unstable tree until we run again.
1250 */
1251 ksm_scan.seqnr++;
1252 return NULL;
1253}
1254
1255/**
1256 * ksm_do_scan - the ksm scanner main worker function.
1257 * @scan_npages - number of pages we want to scan before we return.
1258 */
1259static void ksm_do_scan(unsigned int scan_npages)
1260{
1261 struct rmap_item *rmap_item;
1262 struct page *page;
1263
1264 while (scan_npages--) {
1265 cond_resched();
1266 rmap_item = scan_get_next_rmap_item(&page);
1267 if (!rmap_item)
1268 return;
1269 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1270 cmp_and_merge_page(page, rmap_item);
1271 put_page(page);
1272 }
1273}
1274
1275static int ksm_scan_thread(void *nothing)
1276{
Izik Eidus339aa622009-09-21 17:02:07 -07001277 set_user_nice(current, 5);
Izik Eidus31dbd012009-09-21 17:02:03 -07001278
1279 while (!kthread_should_stop()) {
1280 if (ksm_run & KSM_RUN_MERGE) {
1281 mutex_lock(&ksm_thread_mutex);
1282 ksm_do_scan(ksm_thread_pages_to_scan);
1283 mutex_unlock(&ksm_thread_mutex);
1284 schedule_timeout_interruptible(
1285 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1286 } else {
1287 wait_event_interruptible(ksm_thread_wait,
1288 (ksm_run & KSM_RUN_MERGE) ||
1289 kthread_should_stop());
1290 }
1291 }
1292 return 0;
1293}
1294
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001295int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1296 unsigned long end, int advice, unsigned long *vm_flags)
1297{
1298 struct mm_struct *mm = vma->vm_mm;
1299
1300 switch (advice) {
1301 case MADV_MERGEABLE:
1302 /*
1303 * Be somewhat over-protective for now!
1304 */
1305 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1306 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1307 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1308 VM_MIXEDMAP | VM_SAO))
1309 return 0; /* just ignore the advice */
1310
1311 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
1312 if (__ksm_enter(mm) < 0)
1313 return -EAGAIN;
1314
1315 *vm_flags |= VM_MERGEABLE;
1316 break;
1317
1318 case MADV_UNMERGEABLE:
1319 if (!(*vm_flags & VM_MERGEABLE))
1320 return 0; /* just ignore the advice */
1321
Izik Eidus31dbd012009-09-21 17:02:03 -07001322 if (vma->anon_vma)
1323 unmerge_ksm_pages(vma, start, end);
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001324
1325 *vm_flags &= ~VM_MERGEABLE;
1326 break;
1327 }
1328
1329 return 0;
1330}
1331
1332int __ksm_enter(struct mm_struct *mm)
1333{
Izik Eidus31dbd012009-09-21 17:02:03 -07001334 struct mm_slot *mm_slot = alloc_mm_slot();
1335 if (!mm_slot)
1336 return -ENOMEM;
1337
1338 spin_lock(&ksm_mmlist_lock);
1339 insert_to_mm_slots_hash(mm, mm_slot);
1340 /*
1341 * Insert just behind the scanning cursor, to let the area settle
1342 * down a little; when fork is followed by immediate exec, we don't
1343 * want ksmd to waste time setting up and tearing down an rmap_list.
1344 */
1345 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1346 spin_unlock(&ksm_mmlist_lock);
1347
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001348 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1349 return 0;
1350}
1351
1352void __ksm_exit(struct mm_struct *mm)
1353{
Izik Eidus31dbd012009-09-21 17:02:03 -07001354 /*
1355 * This process is exiting: doesn't hold and doesn't need mmap_sem;
1356 * but we do need to exclude ksmd and other exiters while we modify
1357 * the various lists and trees.
1358 */
1359 mutex_lock(&ksm_thread_mutex);
1360 remove_mm_from_lists(mm);
1361 mutex_unlock(&ksm_thread_mutex);
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001362}
Izik Eidus31dbd012009-09-21 17:02:03 -07001363
1364#define KSM_ATTR_RO(_name) \
1365 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1366#define KSM_ATTR(_name) \
1367 static struct kobj_attribute _name##_attr = \
1368 __ATTR(_name, 0644, _name##_show, _name##_store)
1369
1370static ssize_t sleep_millisecs_show(struct kobject *kobj,
1371 struct kobj_attribute *attr, char *buf)
1372{
1373 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1374}
1375
1376static ssize_t sleep_millisecs_store(struct kobject *kobj,
1377 struct kobj_attribute *attr,
1378 const char *buf, size_t count)
1379{
1380 unsigned long msecs;
1381 int err;
1382
1383 err = strict_strtoul(buf, 10, &msecs);
1384 if (err || msecs > UINT_MAX)
1385 return -EINVAL;
1386
1387 ksm_thread_sleep_millisecs = msecs;
1388
1389 return count;
1390}
1391KSM_ATTR(sleep_millisecs);
1392
1393static ssize_t pages_to_scan_show(struct kobject *kobj,
1394 struct kobj_attribute *attr, char *buf)
1395{
1396 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1397}
1398
1399static ssize_t pages_to_scan_store(struct kobject *kobj,
1400 struct kobj_attribute *attr,
1401 const char *buf, size_t count)
1402{
1403 int err;
1404 unsigned long nr_pages;
1405
1406 err = strict_strtoul(buf, 10, &nr_pages);
1407 if (err || nr_pages > UINT_MAX)
1408 return -EINVAL;
1409
1410 ksm_thread_pages_to_scan = nr_pages;
1411
1412 return count;
1413}
1414KSM_ATTR(pages_to_scan);
1415
1416static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1417 char *buf)
1418{
1419 return sprintf(buf, "%u\n", ksm_run);
1420}
1421
1422static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1423 const char *buf, size_t count)
1424{
1425 int err;
1426 unsigned long flags;
1427
1428 err = strict_strtoul(buf, 10, &flags);
1429 if (err || flags > UINT_MAX)
1430 return -EINVAL;
1431 if (flags > KSM_RUN_UNMERGE)
1432 return -EINVAL;
1433
1434 /*
1435 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1436 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
Hugh Dickinsb4028262009-09-21 17:02:09 -07001437 * breaking COW to free the unswappable pages_shared (but leaves
Izik Eidus31dbd012009-09-21 17:02:03 -07001438 * mm_slots on the list for when ksmd may be set running again).
1439 */
1440
1441 mutex_lock(&ksm_thread_mutex);
1442 if (ksm_run != flags) {
1443 ksm_run = flags;
1444 if (flags & KSM_RUN_UNMERGE)
1445 unmerge_and_remove_all_rmap_items();
1446 }
1447 mutex_unlock(&ksm_thread_mutex);
1448
1449 if (flags & KSM_RUN_MERGE)
1450 wake_up_interruptible(&ksm_thread_wait);
1451
1452 return count;
1453}
1454KSM_ATTR(run);
1455
Izik Eidus31dbd012009-09-21 17:02:03 -07001456static ssize_t max_kernel_pages_store(struct kobject *kobj,
1457 struct kobj_attribute *attr,
1458 const char *buf, size_t count)
1459{
1460 int err;
1461 unsigned long nr_pages;
1462
1463 err = strict_strtoul(buf, 10, &nr_pages);
1464 if (err)
1465 return -EINVAL;
1466
1467 ksm_max_kernel_pages = nr_pages;
1468
1469 return count;
1470}
1471
1472static ssize_t max_kernel_pages_show(struct kobject *kobj,
1473 struct kobj_attribute *attr, char *buf)
1474{
1475 return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1476}
1477KSM_ATTR(max_kernel_pages);
1478
Hugh Dickinsb4028262009-09-21 17:02:09 -07001479static ssize_t pages_shared_show(struct kobject *kobj,
1480 struct kobj_attribute *attr, char *buf)
1481{
1482 return sprintf(buf, "%lu\n", ksm_pages_shared);
1483}
1484KSM_ATTR_RO(pages_shared);
1485
1486static ssize_t pages_sharing_show(struct kobject *kobj,
1487 struct kobj_attribute *attr, char *buf)
1488{
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001489 return sprintf(buf, "%lu\n", ksm_pages_sharing);
Hugh Dickinsb4028262009-09-21 17:02:09 -07001490}
1491KSM_ATTR_RO(pages_sharing);
1492
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001493static ssize_t pages_unshared_show(struct kobject *kobj,
1494 struct kobj_attribute *attr, char *buf)
1495{
1496 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1497}
1498KSM_ATTR_RO(pages_unshared);
1499
1500static ssize_t pages_volatile_show(struct kobject *kobj,
1501 struct kobj_attribute *attr, char *buf)
1502{
1503 long ksm_pages_volatile;
1504
1505 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1506 - ksm_pages_sharing - ksm_pages_unshared;
1507 /*
1508 * It was not worth any locking to calculate that statistic,
1509 * but it might therefore sometimes be negative: conceal that.
1510 */
1511 if (ksm_pages_volatile < 0)
1512 ksm_pages_volatile = 0;
1513 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1514}
1515KSM_ATTR_RO(pages_volatile);
1516
1517static ssize_t full_scans_show(struct kobject *kobj,
1518 struct kobj_attribute *attr, char *buf)
1519{
1520 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1521}
1522KSM_ATTR_RO(full_scans);
1523
Izik Eidus31dbd012009-09-21 17:02:03 -07001524static struct attribute *ksm_attrs[] = {
1525 &sleep_millisecs_attr.attr,
1526 &pages_to_scan_attr.attr,
1527 &run_attr.attr,
Izik Eidus31dbd012009-09-21 17:02:03 -07001528 &max_kernel_pages_attr.attr,
Hugh Dickinsb4028262009-09-21 17:02:09 -07001529 &pages_shared_attr.attr,
1530 &pages_sharing_attr.attr,
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001531 &pages_unshared_attr.attr,
1532 &pages_volatile_attr.attr,
1533 &full_scans_attr.attr,
Izik Eidus31dbd012009-09-21 17:02:03 -07001534 NULL,
1535};
1536
1537static struct attribute_group ksm_attr_group = {
1538 .attrs = ksm_attrs,
1539 .name = "ksm",
1540};
1541
1542static int __init ksm_init(void)
1543{
1544 struct task_struct *ksm_thread;
1545 int err;
1546
1547 err = ksm_slab_init();
1548 if (err)
1549 goto out;
1550
1551 err = mm_slots_hash_init();
1552 if (err)
1553 goto out_free1;
1554
1555 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1556 if (IS_ERR(ksm_thread)) {
1557 printk(KERN_ERR "ksm: creating kthread failed\n");
1558 err = PTR_ERR(ksm_thread);
1559 goto out_free2;
1560 }
1561
1562 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1563 if (err) {
1564 printk(KERN_ERR "ksm: register sysfs failed\n");
1565 goto out_free3;
1566 }
1567
1568 return 0;
1569
1570out_free3:
1571 kthread_stop(ksm_thread);
1572out_free2:
1573 mm_slots_hash_free();
1574out_free1:
1575 ksm_slab_free();
1576out:
1577 return err;
1578}
1579module_init(ksm_init)