blob: 51573858938d1435a5b74c2c36dbd833b5c27837 [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>
Hugh Dickins62b61f62009-12-14 17:59:33 -080032#include <linux/memory.h>
Izik Eidus31dbd012009-09-21 17:02:03 -070033#include <linux/mmu_notifier.h>
Izik Eidus2c6854f2009-09-23 15:56:04 -070034#include <linux/swap.h>
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070035#include <linux/ksm.h>
Lai Jiangshand9f89842010-08-09 17:20:02 -070036#include <linux/hash.h>
Andrea Arcangeli878aee72011-01-13 15:47:10 -080037#include <linux/freezer.h>
David Rientjes72788c32011-05-24 17:11:40 -070038#include <linux/oom.h>
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070039
Izik Eidus31dbd012009-09-21 17:02:03 -070040#include <asm/tlbflush.h>
Hugh Dickins73848b42009-12-14 17:59:22 -080041#include "internal.h"
Izik Eidus31dbd012009-09-21 17:02:03 -070042
43/*
44 * A few notes about the KSM scanning process,
45 * to make it easier to understand the data structures below:
46 *
47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
48 * contents into a data structure that holds pointers to the pages' locations.
49 *
50 * Since the contents of the pages may change at any moment, KSM cannot just
51 * insert the pages into a normal sorted tree and expect it to find anything.
52 * Therefore KSM uses two data structures - the stable and the unstable tree.
53 *
54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
55 * by their contents. Because each such page is write-protected, searching on
56 * this tree is fully assured to be working (except when pages are unmapped),
57 * and therefore this tree is called the stable tree.
58 *
59 * In addition to the stable tree, KSM uses a second data structure called the
60 * unstable tree: this tree holds pointers to pages which have been found to
61 * be "unchanged for a period of time". The unstable tree sorts these pages
62 * by their contents, but since they are not write-protected, KSM cannot rely
63 * upon the unstable tree to work correctly - the unstable tree is liable to
64 * be corrupted as its contents are modified, and so it is called unstable.
65 *
66 * KSM solves this problem by several techniques:
67 *
68 * 1) The unstable tree is flushed every time KSM completes scanning all
69 * memory areas, and then the tree is rebuilt again from the beginning.
70 * 2) KSM will only insert into the unstable tree, pages whose hash value
71 * has not changed since the previous scan of all memory areas.
72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
73 * colors of the nodes and not on their contents, assuring that even when
74 * the tree gets "corrupted" it won't get out of balance, so scanning time
75 * remains the same (also, searching and inserting nodes in an rbtree uses
76 * the same algorithm, so we have no overhead when we flush and rebuild).
77 * 4) KSM never flushes the stable tree, which means that even if it were to
78 * take 10 attempts to find a page in the unstable tree, once it is found,
79 * it is secured in the stable tree. (When we scan a new page, we first
80 * compare it against the stable tree, and then against the unstable tree.)
81 */
82
83/**
84 * struct mm_slot - ksm information per mm that is being scanned
85 * @link: link to the mm_slots hash list
86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
Hugh Dickins6514d512009-12-14 17:59:19 -080087 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
Izik Eidus31dbd012009-09-21 17:02:03 -070088 * @mm: the mm that this information is valid for
89 */
90struct mm_slot {
91 struct hlist_node link;
92 struct list_head mm_list;
Hugh Dickins6514d512009-12-14 17:59:19 -080093 struct rmap_item *rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -070094 struct mm_struct *mm;
95};
96
97/**
98 * struct ksm_scan - cursor for scanning
99 * @mm_slot: the current mm_slot we are scanning
100 * @address: the next address inside that to be scanned
Hugh Dickins6514d512009-12-14 17:59:19 -0800101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
Izik Eidus31dbd012009-09-21 17:02:03 -0700102 * @seqnr: count of completed full scans (needed when removing unstable node)
103 *
104 * There is only the one ksm_scan instance of this cursor structure.
105 */
106struct ksm_scan {
107 struct mm_slot *mm_slot;
108 unsigned long address;
Hugh Dickins6514d512009-12-14 17:59:19 -0800109 struct rmap_item **rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700110 unsigned long seqnr;
111};
112
113/**
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800114 * struct stable_node - node of the stable rbtree
115 * @node: rb node of this ksm page in the stable tree
116 * @hlist: hlist head of rmap_items using this ksm page
Hugh Dickins62b61f62009-12-14 17:59:33 -0800117 * @kpfn: page frame number of this ksm page
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800118 */
119struct stable_node {
120 struct rb_node node;
121 struct hlist_head hlist;
Hugh Dickins62b61f62009-12-14 17:59:33 -0800122 unsigned long kpfn;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800123};
124
125/**
Izik Eidus31dbd012009-09-21 17:02:03 -0700126 * struct rmap_item - reverse mapping item for virtual addresses
Hugh Dickins6514d512009-12-14 17:59:19 -0800127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
Izik Eidus31dbd012009-09-21 17:02:03 -0700129 * @mm: the memory structure this rmap_item is pointing into
130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
131 * @oldchecksum: previous checksum of the page at that virtual address
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800132 * @node: rb node of this rmap_item in the unstable tree
133 * @head: pointer to stable_node heading this list in the stable tree
134 * @hlist: link into hlist of rmap_items hanging off that stable_node
Izik Eidus31dbd012009-09-21 17:02:03 -0700135 */
136struct rmap_item {
Hugh Dickins6514d512009-12-14 17:59:19 -0800137 struct rmap_item *rmap_list;
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800138 struct anon_vma *anon_vma; /* when stable */
Izik Eidus31dbd012009-09-21 17:02:03 -0700139 struct mm_struct *mm;
140 unsigned long address; /* + low bits used for flags below */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800141 unsigned int oldchecksum; /* when unstable */
Izik Eidus31dbd012009-09-21 17:02:03 -0700142 union {
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800143 struct rb_node node; /* when node of unstable tree */
144 struct { /* when listed from stable tree */
145 struct stable_node *head;
146 struct hlist_node hlist;
147 };
Izik Eidus31dbd012009-09-21 17:02:03 -0700148 };
149};
150
151#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800152#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
153#define STABLE_FLAG 0x200 /* is listed from the stable tree */
Izik Eidus31dbd012009-09-21 17:02:03 -0700154
155/* The stable and unstable tree heads */
156static struct rb_root root_stable_tree = RB_ROOT;
157static struct rb_root root_unstable_tree = RB_ROOT;
158
Lai Jiangshand9f89842010-08-09 17:20:02 -0700159#define MM_SLOTS_HASH_SHIFT 10
160#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
161static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
Izik Eidus31dbd012009-09-21 17:02:03 -0700162
163static struct mm_slot ksm_mm_head = {
164 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
165};
166static struct ksm_scan ksm_scan = {
167 .mm_slot = &ksm_mm_head,
168};
169
170static struct kmem_cache *rmap_item_cache;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800171static struct kmem_cache *stable_node_cache;
Izik Eidus31dbd012009-09-21 17:02:03 -0700172static struct kmem_cache *mm_slot_cache;
173
174/* The number of nodes in the stable tree */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700175static unsigned long ksm_pages_shared;
Izik Eidus31dbd012009-09-21 17:02:03 -0700176
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700177/* The number of page slots additionally sharing those nodes */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700178static unsigned long ksm_pages_sharing;
Izik Eidus31dbd012009-09-21 17:02:03 -0700179
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700180/* The number of nodes in the unstable tree */
181static unsigned long ksm_pages_unshared;
182
183/* The number of rmap_items in use: to calculate pages_volatile */
184static unsigned long ksm_rmap_items;
185
Izik Eidus31dbd012009-09-21 17:02:03 -0700186/* Number of pages ksmd should scan in one batch */
Izik Eidus2c6854f2009-09-23 15:56:04 -0700187static unsigned int ksm_thread_pages_to_scan = 100;
Izik Eidus31dbd012009-09-21 17:02:03 -0700188
189/* Milliseconds ksmd should sleep between batches */
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700190static unsigned int ksm_thread_sleep_millisecs = 20;
Izik Eidus31dbd012009-09-21 17:02:03 -0700191
192#define KSM_RUN_STOP 0
193#define KSM_RUN_MERGE 1
194#define KSM_RUN_UNMERGE 2
Izik Eidus2c6854f2009-09-23 15:56:04 -0700195static unsigned int ksm_run = KSM_RUN_STOP;
Izik Eidus31dbd012009-09-21 17:02:03 -0700196
197static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
198static DEFINE_MUTEX(ksm_thread_mutex);
199static DEFINE_SPINLOCK(ksm_mmlist_lock);
200
201#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
202 sizeof(struct __struct), __alignof__(struct __struct),\
203 (__flags), NULL)
204
205static int __init ksm_slab_init(void)
206{
207 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
208 if (!rmap_item_cache)
209 goto out;
210
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800211 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
212 if (!stable_node_cache)
213 goto out_free1;
214
Izik Eidus31dbd012009-09-21 17:02:03 -0700215 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
216 if (!mm_slot_cache)
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800217 goto out_free2;
Izik Eidus31dbd012009-09-21 17:02:03 -0700218
219 return 0;
220
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800221out_free2:
222 kmem_cache_destroy(stable_node_cache);
223out_free1:
Izik Eidus31dbd012009-09-21 17:02:03 -0700224 kmem_cache_destroy(rmap_item_cache);
225out:
226 return -ENOMEM;
227}
228
229static void __init ksm_slab_free(void)
230{
231 kmem_cache_destroy(mm_slot_cache);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800232 kmem_cache_destroy(stable_node_cache);
Izik Eidus31dbd012009-09-21 17:02:03 -0700233 kmem_cache_destroy(rmap_item_cache);
234 mm_slot_cache = NULL;
235}
236
237static inline struct rmap_item *alloc_rmap_item(void)
238{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700239 struct rmap_item *rmap_item;
240
241 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
242 if (rmap_item)
243 ksm_rmap_items++;
244 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -0700245}
246
247static inline void free_rmap_item(struct rmap_item *rmap_item)
248{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700249 ksm_rmap_items--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700250 rmap_item->mm = NULL; /* debug safety */
251 kmem_cache_free(rmap_item_cache, rmap_item);
252}
253
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800254static inline struct stable_node *alloc_stable_node(void)
255{
256 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
257}
258
259static inline void free_stable_node(struct stable_node *stable_node)
260{
261 kmem_cache_free(stable_node_cache, stable_node);
262}
263
Izik Eidus31dbd012009-09-21 17:02:03 -0700264static inline struct mm_slot *alloc_mm_slot(void)
265{
266 if (!mm_slot_cache) /* initialization failed */
267 return NULL;
268 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
269}
270
271static inline void free_mm_slot(struct mm_slot *mm_slot)
272{
273 kmem_cache_free(mm_slot_cache, mm_slot);
274}
275
Izik Eidus31dbd012009-09-21 17:02:03 -0700276static struct mm_slot *get_mm_slot(struct mm_struct *mm)
277{
278 struct mm_slot *mm_slot;
279 struct hlist_head *bucket;
280 struct hlist_node *node;
281
Lai Jiangshand9f89842010-08-09 17:20:02 -0700282 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
Izik Eidus31dbd012009-09-21 17:02:03 -0700283 hlist_for_each_entry(mm_slot, node, bucket, link) {
284 if (mm == mm_slot->mm)
285 return mm_slot;
286 }
287 return NULL;
288}
289
290static void insert_to_mm_slots_hash(struct mm_struct *mm,
291 struct mm_slot *mm_slot)
292{
293 struct hlist_head *bucket;
294
Lai Jiangshand9f89842010-08-09 17:20:02 -0700295 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
Izik Eidus31dbd012009-09-21 17:02:03 -0700296 mm_slot->mm = mm;
Izik Eidus31dbd012009-09-21 17:02:03 -0700297 hlist_add_head(&mm_slot->link, bucket);
298}
299
300static inline int in_stable_tree(struct rmap_item *rmap_item)
301{
302 return rmap_item->address & STABLE_FLAG;
303}
304
305/*
Hugh Dickinsa913e182009-09-21 17:02:26 -0700306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
307 * page tables after it has passed through ksm_exit() - which, if necessary,
308 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
309 * a special flag: they can just back out as soon as mm_users goes to zero.
310 * ksm_test_exit() is used throughout to make this test for exit: in some
311 * places for correctness, in some places just to avoid unnecessary work.
312 */
313static inline bool ksm_test_exit(struct mm_struct *mm)
314{
315 return atomic_read(&mm->mm_users) == 0;
316}
317
318/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700319 * We use break_ksm to break COW on a ksm page: it's a stripped down
320 *
321 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
322 * put_page(page);
323 *
324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
325 * in case the application has unmapped and remapped mm,addr meanwhile.
326 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
328 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700329static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
Izik Eidus31dbd012009-09-21 17:02:03 -0700330{
331 struct page *page;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700332 int ret = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700333
334 do {
335 cond_resched();
336 page = follow_page(vma, addr, FOLL_GET);
Dan Carpenter22eccdd2010-04-23 13:18:10 -0400337 if (IS_ERR_OR_NULL(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700338 break;
339 if (PageKsm(page))
340 ret = handle_mm_fault(vma->vm_mm, vma, addr,
341 FAULT_FLAG_WRITE);
342 else
343 ret = VM_FAULT_WRITE;
344 put_page(page);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700345 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
346 /*
347 * We must loop because handle_mm_fault() may back out if there's
348 * any difficulty e.g. if pte accessed bit gets updated concurrently.
349 *
350 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
351 * COW has been broken, even if the vma does not permit VM_WRITE;
352 * but note that a concurrent fault might break PageKsm for us.
353 *
354 * VM_FAULT_SIGBUS could occur if we race with truncation of the
355 * backing file, which also invalidates anonymous pages: that's
356 * okay, that truncation will have unmapped the PageKsm for us.
357 *
358 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
359 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
360 * current task has TIF_MEMDIE set, and will be OOM killed on return
361 * to user; and ksmd, having no mm, would never be chosen for that.
362 *
363 * But if the mm is in a limited mem_cgroup, then the fault may fail
364 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
365 * even ksmd can fail in this way - though it's usually breaking ksm
366 * just to undo a merge it made a moment before, so unlikely to oom.
367 *
368 * That's a pity: we might therefore have more kernel pages allocated
369 * than we're counting as nodes in the stable tree; but ksm_do_scan
370 * will retry to break_cow on each pass, so should recover the page
371 * in due course. The important thing is to not let VM_MERGEABLE
372 * be cleared while any such pages might remain in the area.
373 */
374 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700375}
376
Bob Liuef694222012-03-21 16:34:11 -0700377static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
378 unsigned long addr)
379{
380 struct vm_area_struct *vma;
381 if (ksm_test_exit(mm))
382 return NULL;
383 vma = find_vma(mm, addr);
384 if (!vma || vma->vm_start > addr)
385 return NULL;
386 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
387 return NULL;
388 return vma;
389}
390
Hugh Dickins8dd35572009-12-14 17:59:18 -0800391static void break_cow(struct rmap_item *rmap_item)
Izik Eidus31dbd012009-09-21 17:02:03 -0700392{
Hugh Dickins8dd35572009-12-14 17:59:18 -0800393 struct mm_struct *mm = rmap_item->mm;
394 unsigned long addr = rmap_item->address;
Izik Eidus31dbd012009-09-21 17:02:03 -0700395 struct vm_area_struct *vma;
396
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800397 /*
398 * It is not an accident that whenever we want to break COW
399 * to undo, we also need to drop a reference to the anon_vma.
400 */
Peter Zijlstra9e601092011-03-22 16:32:46 -0700401 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800402
Hugh Dickins81464e302009-09-21 17:02:15 -0700403 down_read(&mm->mmap_sem);
Bob Liuef694222012-03-21 16:34:11 -0700404 vma = find_mergeable_vma(mm, addr);
405 if (vma)
406 break_ksm(vma, addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700407 up_read(&mm->mmap_sem);
408}
409
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800410static struct page *page_trans_compound_anon(struct page *page)
411{
412 if (PageTransCompound(page)) {
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800413 struct page *head = compound_trans_head(page);
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800414 /*
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800415 * head may actually be splitted and freed from under
416 * us but it's ok here.
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800417 */
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800418 if (PageAnon(head))
419 return head;
420 }
421 return NULL;
422}
423
Izik Eidus31dbd012009-09-21 17:02:03 -0700424static struct page *get_mergeable_page(struct rmap_item *rmap_item)
425{
426 struct mm_struct *mm = rmap_item->mm;
427 unsigned long addr = rmap_item->address;
428 struct vm_area_struct *vma;
429 struct page *page;
430
431 down_read(&mm->mmap_sem);
Bob Liuef694222012-03-21 16:34:11 -0700432 vma = find_mergeable_vma(mm, addr);
433 if (!vma)
Izik Eidus31dbd012009-09-21 17:02:03 -0700434 goto out;
435
436 page = follow_page(vma, addr, FOLL_GET);
Dan Carpenter22eccdd2010-04-23 13:18:10 -0400437 if (IS_ERR_OR_NULL(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700438 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800439 if (PageAnon(page) || page_trans_compound_anon(page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700440 flush_anon_page(vma, page, addr);
441 flush_dcache_page(page);
442 } else {
443 put_page(page);
444out: page = NULL;
445 }
446 up_read(&mm->mmap_sem);
447 return page;
448}
449
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800450static void remove_node_from_stable_tree(struct stable_node *stable_node)
451{
452 struct rmap_item *rmap_item;
453 struct hlist_node *hlist;
454
455 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
456 if (rmap_item->hlist.next)
457 ksm_pages_sharing--;
458 else
459 ksm_pages_shared--;
Peter Zijlstra9e601092011-03-22 16:32:46 -0700460 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800461 rmap_item->address &= PAGE_MASK;
462 cond_resched();
463 }
464
465 rb_erase(&stable_node->node, &root_stable_tree);
466 free_stable_node(stable_node);
467}
468
469/*
470 * get_ksm_page: checks if the page indicated by the stable node
471 * is still its ksm page, despite having held no reference to it.
472 * In which case we can trust the content of the page, and it
473 * returns the gotten page; but if the page has now been zapped,
474 * remove the stale node from the stable tree and return NULL.
475 *
476 * You would expect the stable_node to hold a reference to the ksm page.
477 * But if it increments the page's count, swapping out has to wait for
478 * ksmd to come around again before it can free the page, which may take
479 * seconds or even minutes: much too unresponsive. So instead we use a
480 * "keyhole reference": access to the ksm page from the stable node peeps
481 * out through its keyhole to see if that page still holds the right key,
482 * pointing back to this stable node. This relies on freeing a PageAnon
483 * page to reset its page->mapping to NULL, and relies on no other use of
484 * a page to put something that might look like our key in page->mapping.
485 *
486 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
487 * but this is different - made simpler by ksm_thread_mutex being held, but
488 * interesting for assuming that no other use of the struct page could ever
489 * put our expected_mapping into page->mapping (or a field of the union which
490 * coincides with page->mapping). The RCU calls are not for KSM at all, but
491 * to keep the page_count protocol described with page_cache_get_speculative.
492 *
493 * Note: it is possible that get_ksm_page() will return NULL one moment,
494 * then page the next, if the page is in between page_freeze_refs() and
495 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
496 * is on its way to being freed; but it is an anomaly to bear in mind.
497 */
498static struct page *get_ksm_page(struct stable_node *stable_node)
499{
500 struct page *page;
501 void *expected_mapping;
502
Hugh Dickins62b61f62009-12-14 17:59:33 -0800503 page = pfn_to_page(stable_node->kpfn);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800504 expected_mapping = (void *)stable_node +
505 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
506 rcu_read_lock();
507 if (page->mapping != expected_mapping)
508 goto stale;
509 if (!get_page_unless_zero(page))
510 goto stale;
511 if (page->mapping != expected_mapping) {
512 put_page(page);
513 goto stale;
514 }
515 rcu_read_unlock();
516 return page;
517stale:
518 rcu_read_unlock();
519 remove_node_from_stable_tree(stable_node);
520 return NULL;
521}
522
Izik Eidus31dbd012009-09-21 17:02:03 -0700523/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700524 * Removing rmap_item from stable or unstable tree.
525 * This function will clean the information from the stable/unstable tree.
526 */
527static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
528{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800529 if (rmap_item->address & STABLE_FLAG) {
530 struct stable_node *stable_node;
Hugh Dickins5ad64682009-12-14 17:59:24 -0800531 struct page *page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700532
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800533 stable_node = rmap_item->head;
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800534 page = get_ksm_page(stable_node);
535 if (!page)
536 goto out;
537
Hugh Dickins5ad64682009-12-14 17:59:24 -0800538 lock_page(page);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800539 hlist_del(&rmap_item->hlist);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800540 unlock_page(page);
541 put_page(page);
Hugh Dickins08beca42009-12-14 17:59:21 -0800542
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800543 if (stable_node->hlist.first)
544 ksm_pages_sharing--;
545 else
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800546 ksm_pages_shared--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700547
Peter Zijlstra9e601092011-03-22 16:32:46 -0700548 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins93d17712009-12-14 17:59:16 -0800549 rmap_item->address &= PAGE_MASK;
Izik Eidus31dbd012009-09-21 17:02:03 -0700550
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800551 } else if (rmap_item->address & UNSTABLE_FLAG) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700552 unsigned char age;
553 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -0700554 * Usually ksmd can and must skip the rb_erase, because
Izik Eidus31dbd012009-09-21 17:02:03 -0700555 * root_unstable_tree was already reset to RB_ROOT.
Hugh Dickins9ba69292009-09-21 17:02:20 -0700556 * But be careful when an mm is exiting: do the rb_erase
557 * if this rmap_item was inserted by this scan, rather
558 * than left over from before.
Izik Eidus31dbd012009-09-21 17:02:03 -0700559 */
560 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
Hugh Dickinscd551f92009-09-21 17:02:17 -0700561 BUG_ON(age > 1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700562 if (!age)
563 rb_erase(&rmap_item->node, &root_unstable_tree);
Izik Eidus31dbd012009-09-21 17:02:03 -0700564
Hugh Dickins93d17712009-12-14 17:59:16 -0800565 ksm_pages_unshared--;
566 rmap_item->address &= PAGE_MASK;
567 }
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800568out:
Izik Eidus31dbd012009-09-21 17:02:03 -0700569 cond_resched(); /* we're called from many long loops */
570}
571
Izik Eidus31dbd012009-09-21 17:02:03 -0700572static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -0800573 struct rmap_item **rmap_list)
Izik Eidus31dbd012009-09-21 17:02:03 -0700574{
Hugh Dickins6514d512009-12-14 17:59:19 -0800575 while (*rmap_list) {
576 struct rmap_item *rmap_item = *rmap_list;
577 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700578 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -0700579 free_rmap_item(rmap_item);
580 }
581}
582
583/*
584 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
585 * than check every pte of a given vma, the locking doesn't quite work for
586 * that - an rmap_item is assigned to the stable tree after inserting ksm
587 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
588 * rmap_items from parent to child at fork time (so as not to waste time
589 * if exit comes before the next scan reaches it).
Hugh Dickins81464e302009-09-21 17:02:15 -0700590 *
591 * Similarly, although we'd like to remove rmap_items (so updating counts
592 * and freeing memory) when unmerging an area, it's easier to leave that
593 * to the next pass of ksmd - consider, for example, how ksmd might be
594 * in cmp_and_merge_page on one of the rmap_items we would be removing.
Izik Eidus31dbd012009-09-21 17:02:03 -0700595 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700596static int unmerge_ksm_pages(struct vm_area_struct *vma,
597 unsigned long start, unsigned long end)
Izik Eidus31dbd012009-09-21 17:02:03 -0700598{
599 unsigned long addr;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700600 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700601
Hugh Dickinsd952b792009-09-21 17:02:16 -0700602 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700603 if (ksm_test_exit(vma->vm_mm))
604 break;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700605 if (signal_pending(current))
606 err = -ERESTARTSYS;
607 else
608 err = break_ksm(vma, addr);
609 }
610 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700611}
612
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700613#ifdef CONFIG_SYSFS
614/*
615 * Only called through the sysfs control interface:
616 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700617static int unmerge_and_remove_all_rmap_items(void)
Izik Eidus31dbd012009-09-21 17:02:03 -0700618{
619 struct mm_slot *mm_slot;
620 struct mm_struct *mm;
621 struct vm_area_struct *vma;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700622 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700623
Hugh Dickinsd952b792009-09-21 17:02:16 -0700624 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700625 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700626 struct mm_slot, mm_list);
627 spin_unlock(&ksm_mmlist_lock);
628
Hugh Dickins9ba69292009-09-21 17:02:20 -0700629 for (mm_slot = ksm_scan.mm_slot;
630 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700631 mm = mm_slot->mm;
632 down_read(&mm->mmap_sem);
633 for (vma = mm->mmap; vma; vma = vma->vm_next) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700634 if (ksm_test_exit(mm))
635 break;
Izik Eidus31dbd012009-09-21 17:02:03 -0700636 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
637 continue;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700638 err = unmerge_ksm_pages(vma,
639 vma->vm_start, vma->vm_end);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700640 if (err)
641 goto error;
Izik Eidus31dbd012009-09-21 17:02:03 -0700642 }
Hugh Dickins9ba69292009-09-21 17:02:20 -0700643
Hugh Dickins6514d512009-12-14 17:59:19 -0800644 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700645
646 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700647 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700648 struct mm_slot, mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700649 if (ksm_test_exit(mm)) {
650 hlist_del(&mm_slot->link);
651 list_del(&mm_slot->mm_list);
652 spin_unlock(&ksm_mmlist_lock);
653
654 free_mm_slot(mm_slot);
655 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
656 up_read(&mm->mmap_sem);
657 mmdrop(mm);
658 } else {
659 spin_unlock(&ksm_mmlist_lock);
660 up_read(&mm->mmap_sem);
661 }
Izik Eidus31dbd012009-09-21 17:02:03 -0700662 }
663
Hugh Dickinsd952b792009-09-21 17:02:16 -0700664 ksm_scan.seqnr = 0;
Hugh Dickins9ba69292009-09-21 17:02:20 -0700665 return 0;
666
667error:
668 up_read(&mm->mmap_sem);
Izik Eidus31dbd012009-09-21 17:02:03 -0700669 spin_lock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700670 ksm_scan.mm_slot = &ksm_mm_head;
Izik Eidus31dbd012009-09-21 17:02:03 -0700671 spin_unlock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700672 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700673}
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700674#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -0700675
Izik Eidus31dbd012009-09-21 17:02:03 -0700676static u32 calc_checksum(struct page *page)
677{
678 u32 checksum;
Cong Wang9b04c5f2011-11-25 23:14:39 +0800679 void *addr = kmap_atomic(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700680 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
Cong Wang9b04c5f2011-11-25 23:14:39 +0800681 kunmap_atomic(addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700682 return checksum;
683}
684
685static int memcmp_pages(struct page *page1, struct page *page2)
686{
687 char *addr1, *addr2;
688 int ret;
689
Cong Wang9b04c5f2011-11-25 23:14:39 +0800690 addr1 = kmap_atomic(page1);
691 addr2 = kmap_atomic(page2);
Izik Eidus31dbd012009-09-21 17:02:03 -0700692 ret = memcmp(addr1, addr2, PAGE_SIZE);
Cong Wang9b04c5f2011-11-25 23:14:39 +0800693 kunmap_atomic(addr2);
694 kunmap_atomic(addr1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700695 return ret;
696}
697
698static inline int pages_identical(struct page *page1, struct page *page2)
699{
700 return !memcmp_pages(page1, page2);
701}
702
703static int write_protect_page(struct vm_area_struct *vma, struct page *page,
704 pte_t *orig_pte)
705{
706 struct mm_struct *mm = vma->vm_mm;
707 unsigned long addr;
708 pte_t *ptep;
709 spinlock_t *ptl;
710 int swapped;
711 int err = -EFAULT;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700712 unsigned long mmun_start; /* For mmu_notifiers */
713 unsigned long mmun_end; /* For mmu_notifiers */
Izik Eidus31dbd012009-09-21 17:02:03 -0700714
715 addr = page_address_in_vma(page, vma);
716 if (addr == -EFAULT)
717 goto out;
718
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800719 BUG_ON(PageTransCompound(page));
Haggai Eran6bdb9132012-10-08 16:33:35 -0700720
721 mmun_start = addr;
722 mmun_end = addr + PAGE_SIZE;
723 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
724
Izik Eidus31dbd012009-09-21 17:02:03 -0700725 ptep = page_check_address(page, mm, addr, &ptl, 0);
726 if (!ptep)
Haggai Eran6bdb9132012-10-08 16:33:35 -0700727 goto out_mn;
Izik Eidus31dbd012009-09-21 17:02:03 -0700728
Hugh Dickins4e316352010-10-02 17:49:08 -0700729 if (pte_write(*ptep) || pte_dirty(*ptep)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700730 pte_t entry;
731
732 swapped = PageSwapCache(page);
733 flush_cache_page(vma, addr, page_to_pfn(page));
734 /*
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300735 * Ok this is tricky, when get_user_pages_fast() run it doesn't
Izik Eidus31dbd012009-09-21 17:02:03 -0700736 * take any lock, therefore the check that we are going to make
737 * with the pagecount against the mapcount is racey and
738 * O_DIRECT can happen right after the check.
739 * So we clear the pte and flush the tlb before the check
740 * this assure us that no O_DIRECT can happen after the check
741 * or in the middle of the check.
742 */
743 entry = ptep_clear_flush(vma, addr, ptep);
744 /*
745 * Check that no O_DIRECT or similar I/O is in progress on the
746 * page
747 */
Hugh Dickins31e855e2009-12-14 17:59:17 -0800748 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
Robin Holtcb532372010-03-23 13:35:26 -0700749 set_pte_at(mm, addr, ptep, entry);
Izik Eidus31dbd012009-09-21 17:02:03 -0700750 goto out_unlock;
751 }
Hugh Dickins4e316352010-10-02 17:49:08 -0700752 if (pte_dirty(entry))
753 set_page_dirty(page);
754 entry = pte_mkclean(pte_wrprotect(entry));
Izik Eidus31dbd012009-09-21 17:02:03 -0700755 set_pte_at_notify(mm, addr, ptep, entry);
756 }
757 *orig_pte = *ptep;
758 err = 0;
759
760out_unlock:
761 pte_unmap_unlock(ptep, ptl);
Haggai Eran6bdb9132012-10-08 16:33:35 -0700762out_mn:
763 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
Izik Eidus31dbd012009-09-21 17:02:03 -0700764out:
765 return err;
766}
767
768/**
769 * replace_page - replace page in vma by new ksm page
Hugh Dickins8dd35572009-12-14 17:59:18 -0800770 * @vma: vma that holds the pte pointing to page
771 * @page: the page we are replacing by kpage
772 * @kpage: the ksm page we replace page by
Izik Eidus31dbd012009-09-21 17:02:03 -0700773 * @orig_pte: the original value of the pte
774 *
775 * Returns 0 on success, -EFAULT on failure.
776 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800777static int replace_page(struct vm_area_struct *vma, struct page *page,
778 struct page *kpage, pte_t orig_pte)
Izik Eidus31dbd012009-09-21 17:02:03 -0700779{
780 struct mm_struct *mm = vma->vm_mm;
Izik Eidus31dbd012009-09-21 17:02:03 -0700781 pmd_t *pmd;
782 pte_t *ptep;
783 spinlock_t *ptl;
784 unsigned long addr;
Izik Eidus31dbd012009-09-21 17:02:03 -0700785 int err = -EFAULT;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700786 unsigned long mmun_start; /* For mmu_notifiers */
787 unsigned long mmun_end; /* For mmu_notifiers */
Izik Eidus31dbd012009-09-21 17:02:03 -0700788
Hugh Dickins8dd35572009-12-14 17:59:18 -0800789 addr = page_address_in_vma(page, vma);
Izik Eidus31dbd012009-09-21 17:02:03 -0700790 if (addr == -EFAULT)
791 goto out;
792
Bob Liu62190492012-12-11 16:00:37 -0800793 pmd = mm_find_pmd(mm, addr);
794 if (!pmd)
Izik Eidus31dbd012009-09-21 17:02:03 -0700795 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800796 BUG_ON(pmd_trans_huge(*pmd));
Izik Eidus31dbd012009-09-21 17:02:03 -0700797
Haggai Eran6bdb9132012-10-08 16:33:35 -0700798 mmun_start = addr;
799 mmun_end = addr + PAGE_SIZE;
800 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
801
Izik Eidus31dbd012009-09-21 17:02:03 -0700802 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
803 if (!pte_same(*ptep, orig_pte)) {
804 pte_unmap_unlock(ptep, ptl);
Haggai Eran6bdb9132012-10-08 16:33:35 -0700805 goto out_mn;
Izik Eidus31dbd012009-09-21 17:02:03 -0700806 }
807
Hugh Dickins8dd35572009-12-14 17:59:18 -0800808 get_page(kpage);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800809 page_add_anon_rmap(kpage, vma, addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700810
811 flush_cache_page(vma, addr, pte_pfn(*ptep));
812 ptep_clear_flush(vma, addr, ptep);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800813 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
Izik Eidus31dbd012009-09-21 17:02:03 -0700814
Hugh Dickins8dd35572009-12-14 17:59:18 -0800815 page_remove_rmap(page);
Hugh Dickinsae52a2a2011-01-13 15:46:28 -0800816 if (!page_mapped(page))
817 try_to_free_swap(page);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800818 put_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700819
820 pte_unmap_unlock(ptep, ptl);
821 err = 0;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700822out_mn:
823 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
Izik Eidus31dbd012009-09-21 17:02:03 -0700824out:
825 return err;
826}
827
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800828static int page_trans_compound_anon_split(struct page *page)
829{
830 int ret = 0;
831 struct page *transhuge_head = page_trans_compound_anon(page);
832 if (transhuge_head) {
833 /* Get the reference on the head to split it. */
834 if (get_page_unless_zero(transhuge_head)) {
835 /*
836 * Recheck we got the reference while the head
837 * was still anonymous.
838 */
839 if (PageAnon(transhuge_head))
840 ret = split_huge_page(transhuge_head);
841 else
842 /*
843 * Retry later if split_huge_page run
844 * from under us.
845 */
846 ret = 1;
847 put_page(transhuge_head);
848 } else
849 /* Retry later if split_huge_page run from under us. */
850 ret = 1;
851 }
852 return ret;
853}
854
Izik Eidus31dbd012009-09-21 17:02:03 -0700855/*
856 * try_to_merge_one_page - take two pages and merge them into one
Hugh Dickins8dd35572009-12-14 17:59:18 -0800857 * @vma: the vma that holds the pte pointing to page
858 * @page: the PageAnon page that we want to replace with kpage
Hugh Dickins80e148222009-12-14 17:59:29 -0800859 * @kpage: the PageKsm page that we want to map instead of page,
860 * or NULL the first time when we want to use page as kpage.
Izik Eidus31dbd012009-09-21 17:02:03 -0700861 *
862 * This function returns 0 if the pages were merged, -EFAULT otherwise.
863 */
864static int try_to_merge_one_page(struct vm_area_struct *vma,
Hugh Dickins8dd35572009-12-14 17:59:18 -0800865 struct page *page, struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -0700866{
867 pte_t orig_pte = __pte(0);
868 int err = -EFAULT;
869
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800870 if (page == kpage) /* ksm page forked */
871 return 0;
872
Izik Eidus31dbd012009-09-21 17:02:03 -0700873 if (!(vma->vm_flags & VM_MERGEABLE))
874 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800875 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
876 goto out;
877 BUG_ON(PageTransCompound(page));
Hugh Dickins8dd35572009-12-14 17:59:18 -0800878 if (!PageAnon(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700879 goto out;
880
Izik Eidus31dbd012009-09-21 17:02:03 -0700881 /*
882 * We need the page lock to read a stable PageSwapCache in
883 * write_protect_page(). We use trylock_page() instead of
884 * lock_page() because we don't want to wait here - we
885 * prefer to continue scanning and merging different pages,
886 * then come back to this page when it is unlocked.
887 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800888 if (!trylock_page(page))
Hugh Dickins31e855e2009-12-14 17:59:17 -0800889 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700890 /*
891 * If this anonymous page is mapped only here, its pte may need
892 * to be write-protected. If it's mapped elsewhere, all of its
893 * ptes are necessarily already write-protected. But in either
894 * case, we need to lock and check page_count is not raised.
895 */
Hugh Dickins80e148222009-12-14 17:59:29 -0800896 if (write_protect_page(vma, page, &orig_pte) == 0) {
897 if (!kpage) {
898 /*
899 * While we hold page lock, upgrade page from
900 * PageAnon+anon_vma to PageKsm+NULL stable_node:
901 * stable_tree_insert() will update stable_node.
902 */
903 set_page_stable_node(page, NULL);
904 mark_page_accessed(page);
905 err = 0;
906 } else if (pages_identical(page, kpage))
907 err = replace_page(vma, page, kpage, orig_pte);
908 }
Izik Eidus31dbd012009-09-21 17:02:03 -0700909
Hugh Dickins80e148222009-12-14 17:59:29 -0800910 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
Hugh Dickins73848b42009-12-14 17:59:22 -0800911 munlock_vma_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800912 if (!PageMlocked(kpage)) {
913 unlock_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800914 lock_page(kpage);
915 mlock_vma_page(kpage);
916 page = kpage; /* for final unlock */
917 }
918 }
Hugh Dickins73848b42009-12-14 17:59:22 -0800919
Hugh Dickins8dd35572009-12-14 17:59:18 -0800920 unlock_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700921out:
922 return err;
923}
924
925/*
Hugh Dickins81464e302009-09-21 17:02:15 -0700926 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
927 * but no new kernel page is allocated: kpage must already be a ksm page.
Hugh Dickins8dd35572009-12-14 17:59:18 -0800928 *
929 * This function returns 0 if the pages were merged, -EFAULT otherwise.
Hugh Dickins81464e302009-09-21 17:02:15 -0700930 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800931static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
932 struct page *page, struct page *kpage)
Hugh Dickins81464e302009-09-21 17:02:15 -0700933{
Hugh Dickins8dd35572009-12-14 17:59:18 -0800934 struct mm_struct *mm = rmap_item->mm;
Hugh Dickins81464e302009-09-21 17:02:15 -0700935 struct vm_area_struct *vma;
936 int err = -EFAULT;
937
Hugh Dickins8dd35572009-12-14 17:59:18 -0800938 down_read(&mm->mmap_sem);
939 if (ksm_test_exit(mm))
940 goto out;
941 vma = find_vma(mm, rmap_item->address);
942 if (!vma || vma->vm_start > rmap_item->address)
Hugh Dickins9ba69292009-09-21 17:02:20 -0700943 goto out;
944
Hugh Dickins8dd35572009-12-14 17:59:18 -0800945 err = try_to_merge_one_page(vma, page, kpage);
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800946 if (err)
947 goto out;
948
949 /* Must get reference to anon_vma while still holding mmap_sem */
Peter Zijlstra9e601092011-03-22 16:32:46 -0700950 rmap_item->anon_vma = vma->anon_vma;
951 get_anon_vma(vma->anon_vma);
Hugh Dickins81464e302009-09-21 17:02:15 -0700952out:
Hugh Dickins8dd35572009-12-14 17:59:18 -0800953 up_read(&mm->mmap_sem);
Hugh Dickins81464e302009-09-21 17:02:15 -0700954 return err;
955}
956
957/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700958 * try_to_merge_two_pages - take two identical pages and prepare them
959 * to be merged into one page.
960 *
Hugh Dickins8dd35572009-12-14 17:59:18 -0800961 * This function returns the kpage if we successfully merged two identical
962 * pages into one ksm page, NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -0700963 *
Hugh Dickins80e148222009-12-14 17:59:29 -0800964 * Note that this function upgrades page to ksm page: if one of the pages
Izik Eidus31dbd012009-09-21 17:02:03 -0700965 * is already a ksm page, try_to_merge_with_ksm_page should be used.
966 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800967static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
968 struct page *page,
969 struct rmap_item *tree_rmap_item,
970 struct page *tree_page)
Izik Eidus31dbd012009-09-21 17:02:03 -0700971{
Hugh Dickins80e148222009-12-14 17:59:29 -0800972 int err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700973
Hugh Dickins80e148222009-12-14 17:59:29 -0800974 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
Izik Eidus31dbd012009-09-21 17:02:03 -0700975 if (!err) {
Hugh Dickins8dd35572009-12-14 17:59:18 -0800976 err = try_to_merge_with_ksm_page(tree_rmap_item,
Hugh Dickins80e148222009-12-14 17:59:29 -0800977 tree_page, page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700978 /*
Hugh Dickins81464e302009-09-21 17:02:15 -0700979 * If that fails, we have a ksm page with only one pte
980 * pointing to it: so break it.
Izik Eidus31dbd012009-09-21 17:02:03 -0700981 */
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800982 if (err)
Hugh Dickins8dd35572009-12-14 17:59:18 -0800983 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -0700984 }
Hugh Dickins80e148222009-12-14 17:59:29 -0800985 return err ? NULL : page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700986}
987
988/*
Hugh Dickins8dd35572009-12-14 17:59:18 -0800989 * stable_tree_search - search for page inside the stable tree
Izik Eidus31dbd012009-09-21 17:02:03 -0700990 *
991 * This function checks if there is a page inside the stable tree
992 * with identical content to the page that we are scanning right now.
993 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800994 * This function returns the stable tree node of identical content if found,
Izik Eidus31dbd012009-09-21 17:02:03 -0700995 * NULL otherwise.
996 */
Hugh Dickins62b61f62009-12-14 17:59:33 -0800997static struct page *stable_tree_search(struct page *page)
Izik Eidus31dbd012009-09-21 17:02:03 -0700998{
999 struct rb_node *node = root_stable_tree.rb_node;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001000 struct stable_node *stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001001
Hugh Dickins08beca42009-12-14 17:59:21 -08001002 stable_node = page_stable_node(page);
1003 if (stable_node) { /* ksm page forked */
1004 get_page(page);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001005 return page;
Hugh Dickins08beca42009-12-14 17:59:21 -08001006 }
1007
Izik Eidus31dbd012009-09-21 17:02:03 -07001008 while (node) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001009 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001010 int ret;
1011
Hugh Dickins08beca42009-12-14 17:59:21 -08001012 cond_resched();
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001013 stable_node = rb_entry(node, struct stable_node, node);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001014 tree_page = get_ksm_page(stable_node);
1015 if (!tree_page)
1016 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001017
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001018 ret = memcmp_pages(page, tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001019
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001020 if (ret < 0) {
1021 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001022 node = node->rb_left;
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001023 } else if (ret > 0) {
1024 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001025 node = node->rb_right;
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001026 } else
Hugh Dickins62b61f62009-12-14 17:59:33 -08001027 return tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001028 }
1029
1030 return NULL;
1031}
1032
1033/*
1034 * stable_tree_insert - insert rmap_item pointing to new ksm page
1035 * into the stable tree.
1036 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001037 * This function returns the stable tree node just allocated on success,
1038 * NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -07001039 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001040static struct stable_node *stable_tree_insert(struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -07001041{
1042 struct rb_node **new = &root_stable_tree.rb_node;
1043 struct rb_node *parent = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001044 struct stable_node *stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001045
1046 while (*new) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001047 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001048 int ret;
1049
Hugh Dickins08beca42009-12-14 17:59:21 -08001050 cond_resched();
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001051 stable_node = rb_entry(*new, struct stable_node, node);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001052 tree_page = get_ksm_page(stable_node);
1053 if (!tree_page)
1054 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001055
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001056 ret = memcmp_pages(kpage, tree_page);
1057 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001058
1059 parent = *new;
1060 if (ret < 0)
1061 new = &parent->rb_left;
1062 else if (ret > 0)
1063 new = &parent->rb_right;
1064 else {
1065 /*
1066 * It is not a bug that stable_tree_search() didn't
1067 * find this node: because at that time our page was
1068 * not yet write-protected, so may have changed since.
1069 */
1070 return NULL;
1071 }
1072 }
1073
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001074 stable_node = alloc_stable_node();
1075 if (!stable_node)
1076 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001077
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001078 rb_link_node(&stable_node->node, parent, new);
1079 rb_insert_color(&stable_node->node, &root_stable_tree);
1080
1081 INIT_HLIST_HEAD(&stable_node->hlist);
1082
Hugh Dickins62b61f62009-12-14 17:59:33 -08001083 stable_node->kpfn = page_to_pfn(kpage);
Hugh Dickins08beca42009-12-14 17:59:21 -08001084 set_page_stable_node(kpage, stable_node);
1085
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001086 return stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001087}
1088
1089/*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001090 * unstable_tree_search_insert - search for identical page,
1091 * else insert rmap_item into the unstable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001092 *
1093 * This function searches for a page in the unstable tree identical to the
1094 * page currently being scanned; and if no identical page is found in the
1095 * tree, we insert rmap_item as a new object into the unstable tree.
1096 *
1097 * This function returns pointer to rmap_item found to be identical
1098 * to the currently scanned page, NULL otherwise.
1099 *
1100 * This function does both searching and inserting, because they share
1101 * the same walking algorithm in an rbtree.
1102 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001103static
1104struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1105 struct page *page,
1106 struct page **tree_pagep)
1107
Izik Eidus31dbd012009-09-21 17:02:03 -07001108{
1109 struct rb_node **new = &root_unstable_tree.rb_node;
1110 struct rb_node *parent = NULL;
1111
1112 while (*new) {
1113 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001114 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001115 int ret;
1116
Hugh Dickinsd178f272009-11-09 15:58:23 +00001117 cond_resched();
Izik Eidus31dbd012009-09-21 17:02:03 -07001118 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
Hugh Dickins8dd35572009-12-14 17:59:18 -08001119 tree_page = get_mergeable_page(tree_rmap_item);
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001120 if (IS_ERR_OR_NULL(tree_page))
Izik Eidus31dbd012009-09-21 17:02:03 -07001121 return NULL;
1122
1123 /*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001124 * Don't substitute a ksm page for a forked page.
Izik Eidus31dbd012009-09-21 17:02:03 -07001125 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001126 if (page == tree_page) {
1127 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001128 return NULL;
1129 }
1130
Hugh Dickins8dd35572009-12-14 17:59:18 -08001131 ret = memcmp_pages(page, tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001132
1133 parent = *new;
1134 if (ret < 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001135 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001136 new = &parent->rb_left;
1137 } else if (ret > 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001138 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001139 new = &parent->rb_right;
1140 } else {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001141 *tree_pagep = tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001142 return tree_rmap_item;
1143 }
1144 }
1145
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001146 rmap_item->address |= UNSTABLE_FLAG;
Izik Eidus31dbd012009-09-21 17:02:03 -07001147 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1148 rb_link_node(&rmap_item->node, parent, new);
1149 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1150
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001151 ksm_pages_unshared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001152 return NULL;
1153}
1154
1155/*
1156 * stable_tree_append - add another rmap_item to the linked list of
1157 * rmap_items hanging off a given node of the stable tree, all sharing
1158 * the same ksm page.
1159 */
1160static void stable_tree_append(struct rmap_item *rmap_item,
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001161 struct stable_node *stable_node)
Izik Eidus31dbd012009-09-21 17:02:03 -07001162{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001163 rmap_item->head = stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001164 rmap_item->address |= STABLE_FLAG;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001165 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001166
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001167 if (rmap_item->hlist.next)
1168 ksm_pages_sharing++;
1169 else
1170 ksm_pages_shared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001171}
1172
1173/*
Hugh Dickins81464e302009-09-21 17:02:15 -07001174 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1175 * if not, compare checksum to previous and if it's the same, see if page can
1176 * be inserted into the unstable tree, or merged with a page already there and
1177 * both transferred to the stable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001178 *
1179 * @page: the page that we are searching identical page to.
1180 * @rmap_item: the reverse mapping into the virtual address of this page
1181 */
1182static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1183{
Izik Eidus31dbd012009-09-21 17:02:03 -07001184 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001185 struct page *tree_page = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001186 struct stable_node *stable_node;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001187 struct page *kpage;
Izik Eidus31dbd012009-09-21 17:02:03 -07001188 unsigned int checksum;
1189 int err;
1190
Hugh Dickins93d17712009-12-14 17:59:16 -08001191 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001192
1193 /* We first start with searching the page inside the stable tree */
Hugh Dickins62b61f62009-12-14 17:59:33 -08001194 kpage = stable_tree_search(page);
1195 if (kpage) {
Hugh Dickins08beca42009-12-14 17:59:21 -08001196 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001197 if (!err) {
1198 /*
1199 * The page was successfully merged:
1200 * add its rmap_item to the stable tree.
1201 */
Hugh Dickins5ad64682009-12-14 17:59:24 -08001202 lock_page(kpage);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001203 stable_tree_append(rmap_item, page_stable_node(kpage));
Hugh Dickins5ad64682009-12-14 17:59:24 -08001204 unlock_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001205 }
Hugh Dickins8dd35572009-12-14 17:59:18 -08001206 put_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001207 return;
1208 }
1209
1210 /*
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001211 * If the hash value of the page has changed from the last time
1212 * we calculated it, this page is changing frequently: therefore we
1213 * don't want to insert it in the unstable tree, and we don't want
1214 * to waste our time searching for something identical to it there.
Izik Eidus31dbd012009-09-21 17:02:03 -07001215 */
1216 checksum = calc_checksum(page);
1217 if (rmap_item->oldchecksum != checksum) {
1218 rmap_item->oldchecksum = checksum;
1219 return;
1220 }
1221
Hugh Dickins8dd35572009-12-14 17:59:18 -08001222 tree_rmap_item =
1223 unstable_tree_search_insert(rmap_item, page, &tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001224 if (tree_rmap_item) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001225 kpage = try_to_merge_two_pages(rmap_item, page,
1226 tree_rmap_item, tree_page);
1227 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001228 /*
1229 * As soon as we merge this page, we want to remove the
1230 * rmap_item of the page we have merged with from the unstable
1231 * tree, and insert it instead as new node in the stable tree.
1232 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001233 if (kpage) {
Hugh Dickins93d17712009-12-14 17:59:16 -08001234 remove_rmap_item_from_tree(tree_rmap_item);
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001235
Hugh Dickins5ad64682009-12-14 17:59:24 -08001236 lock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001237 stable_node = stable_tree_insert(kpage);
1238 if (stable_node) {
1239 stable_tree_append(tree_rmap_item, stable_node);
1240 stable_tree_append(rmap_item, stable_node);
1241 }
Hugh Dickins5ad64682009-12-14 17:59:24 -08001242 unlock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001243
Izik Eidus31dbd012009-09-21 17:02:03 -07001244 /*
1245 * If we fail to insert the page into the stable tree,
1246 * we will have 2 virtual addresses that are pointing
1247 * to a ksm page left outside the stable tree,
1248 * in which case we need to break_cow on both.
1249 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001250 if (!stable_node) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001251 break_cow(tree_rmap_item);
1252 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001253 }
1254 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001255 }
1256}
1257
1258static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001259 struct rmap_item **rmap_list,
Izik Eidus31dbd012009-09-21 17:02:03 -07001260 unsigned long addr)
1261{
1262 struct rmap_item *rmap_item;
1263
Hugh Dickins6514d512009-12-14 17:59:19 -08001264 while (*rmap_list) {
1265 rmap_item = *rmap_list;
Hugh Dickins93d17712009-12-14 17:59:16 -08001266 if ((rmap_item->address & PAGE_MASK) == addr)
Izik Eidus31dbd012009-09-21 17:02:03 -07001267 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001268 if (rmap_item->address > addr)
1269 break;
Hugh Dickins6514d512009-12-14 17:59:19 -08001270 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001271 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001272 free_rmap_item(rmap_item);
1273 }
1274
1275 rmap_item = alloc_rmap_item();
1276 if (rmap_item) {
1277 /* It has already been zeroed */
1278 rmap_item->mm = mm_slot->mm;
1279 rmap_item->address = addr;
Hugh Dickins6514d512009-12-14 17:59:19 -08001280 rmap_item->rmap_list = *rmap_list;
1281 *rmap_list = rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001282 }
1283 return rmap_item;
1284}
1285
1286static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1287{
1288 struct mm_struct *mm;
1289 struct mm_slot *slot;
1290 struct vm_area_struct *vma;
1291 struct rmap_item *rmap_item;
1292
1293 if (list_empty(&ksm_mm_head.mm_list))
1294 return NULL;
1295
1296 slot = ksm_scan.mm_slot;
1297 if (slot == &ksm_mm_head) {
Hugh Dickins2919bfd2011-01-13 15:47:29 -08001298 /*
1299 * A number of pages can hang around indefinitely on per-cpu
1300 * pagevecs, raised page count preventing write_protect_page
1301 * from merging them. Though it doesn't really matter much,
1302 * it is puzzling to see some stuck in pages_volatile until
1303 * other activity jostles them out, and they also prevented
1304 * LTP's KSM test from succeeding deterministically; so drain
1305 * them here (here rather than on entry to ksm_do_scan(),
1306 * so we don't IPI too often when pages_to_scan is set low).
1307 */
1308 lru_add_drain_all();
1309
Izik Eidus31dbd012009-09-21 17:02:03 -07001310 root_unstable_tree = RB_ROOT;
1311
1312 spin_lock(&ksm_mmlist_lock);
1313 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1314 ksm_scan.mm_slot = slot;
1315 spin_unlock(&ksm_mmlist_lock);
Hugh Dickins2b472612011-06-15 15:08:58 -07001316 /*
1317 * Although we tested list_empty() above, a racing __ksm_exit
1318 * of the last mm on the list may have removed it since then.
1319 */
1320 if (slot == &ksm_mm_head)
1321 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001322next_mm:
1323 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001324 ksm_scan.rmap_list = &slot->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001325 }
1326
1327 mm = slot->mm;
1328 down_read(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001329 if (ksm_test_exit(mm))
1330 vma = NULL;
1331 else
1332 vma = find_vma(mm, ksm_scan.address);
1333
1334 for (; vma; vma = vma->vm_next) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001335 if (!(vma->vm_flags & VM_MERGEABLE))
1336 continue;
1337 if (ksm_scan.address < vma->vm_start)
1338 ksm_scan.address = vma->vm_start;
1339 if (!vma->anon_vma)
1340 ksm_scan.address = vma->vm_end;
1341
1342 while (ksm_scan.address < vma->vm_end) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001343 if (ksm_test_exit(mm))
1344 break;
Izik Eidus31dbd012009-09-21 17:02:03 -07001345 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001346 if (IS_ERR_OR_NULL(*page)) {
1347 ksm_scan.address += PAGE_SIZE;
1348 cond_resched();
1349 continue;
1350 }
Andrea Arcangeli29ad7682011-01-13 15:47:19 -08001351 if (PageAnon(*page) ||
1352 page_trans_compound_anon(*page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001353 flush_anon_page(vma, *page, ksm_scan.address);
1354 flush_dcache_page(*page);
1355 rmap_item = get_next_rmap_item(slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001356 ksm_scan.rmap_list, ksm_scan.address);
Izik Eidus31dbd012009-09-21 17:02:03 -07001357 if (rmap_item) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001358 ksm_scan.rmap_list =
1359 &rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001360 ksm_scan.address += PAGE_SIZE;
1361 } else
1362 put_page(*page);
1363 up_read(&mm->mmap_sem);
1364 return rmap_item;
1365 }
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001366 put_page(*page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001367 ksm_scan.address += PAGE_SIZE;
1368 cond_resched();
1369 }
1370 }
1371
Hugh Dickins9ba69292009-09-21 17:02:20 -07001372 if (ksm_test_exit(mm)) {
1373 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001374 ksm_scan.rmap_list = &slot->rmap_list;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001375 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001376 /*
1377 * Nuke all the rmap_items that are above this current rmap:
1378 * because there were no VM_MERGEABLE vmas with such addresses.
1379 */
Hugh Dickins6514d512009-12-14 17:59:19 -08001380 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
Izik Eidus31dbd012009-09-21 17:02:03 -07001381
1382 spin_lock(&ksm_mmlist_lock);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001383 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1384 struct mm_slot, mm_list);
1385 if (ksm_scan.address == 0) {
1386 /*
1387 * We've completed a full scan of all vmas, holding mmap_sem
1388 * throughout, and found no VM_MERGEABLE: so do the same as
1389 * __ksm_exit does to remove this mm from all our lists now.
Hugh Dickins9ba69292009-09-21 17:02:20 -07001390 * This applies either when cleaning up after __ksm_exit
1391 * (but beware: we can reach here even before __ksm_exit),
1392 * or when all VM_MERGEABLE areas have been unmapped (and
1393 * mmap_sem then protects against race with MADV_MERGEABLE).
Hugh Dickinscd551f92009-09-21 17:02:17 -07001394 */
1395 hlist_del(&slot->link);
1396 list_del(&slot->mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001397 spin_unlock(&ksm_mmlist_lock);
1398
Hugh Dickinscd551f92009-09-21 17:02:17 -07001399 free_mm_slot(slot);
1400 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001401 up_read(&mm->mmap_sem);
1402 mmdrop(mm);
1403 } else {
1404 spin_unlock(&ksm_mmlist_lock);
1405 up_read(&mm->mmap_sem);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001406 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001407
1408 /* Repeat until we've completed scanning the whole list */
Hugh Dickinscd551f92009-09-21 17:02:17 -07001409 slot = ksm_scan.mm_slot;
Izik Eidus31dbd012009-09-21 17:02:03 -07001410 if (slot != &ksm_mm_head)
1411 goto next_mm;
1412
Izik Eidus31dbd012009-09-21 17:02:03 -07001413 ksm_scan.seqnr++;
1414 return NULL;
1415}
1416
1417/**
1418 * ksm_do_scan - the ksm scanner main worker function.
1419 * @scan_npages - number of pages we want to scan before we return.
1420 */
1421static void ksm_do_scan(unsigned int scan_npages)
1422{
1423 struct rmap_item *rmap_item;
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001424 struct page *uninitialized_var(page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001425
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001426 while (scan_npages-- && likely(!freezing(current))) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001427 cond_resched();
1428 rmap_item = scan_get_next_rmap_item(&page);
1429 if (!rmap_item)
1430 return;
1431 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1432 cmp_and_merge_page(page, rmap_item);
1433 put_page(page);
1434 }
1435}
1436
Hugh Dickins6e1583842009-09-21 17:02:14 -07001437static int ksmd_should_run(void)
1438{
1439 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1440}
1441
Izik Eidus31dbd012009-09-21 17:02:03 -07001442static int ksm_scan_thread(void *nothing)
1443{
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001444 set_freezable();
Izik Eidus339aa622009-09-21 17:02:07 -07001445 set_user_nice(current, 5);
Izik Eidus31dbd012009-09-21 17:02:03 -07001446
1447 while (!kthread_should_stop()) {
Hugh Dickins6e1583842009-09-21 17:02:14 -07001448 mutex_lock(&ksm_thread_mutex);
1449 if (ksmd_should_run())
Izik Eidus31dbd012009-09-21 17:02:03 -07001450 ksm_do_scan(ksm_thread_pages_to_scan);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001451 mutex_unlock(&ksm_thread_mutex);
1452
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001453 try_to_freeze();
1454
Hugh Dickins6e1583842009-09-21 17:02:14 -07001455 if (ksmd_should_run()) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001456 schedule_timeout_interruptible(
1457 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1458 } else {
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001459 wait_event_freezable(ksm_thread_wait,
Hugh Dickins6e1583842009-09-21 17:02:14 -07001460 ksmd_should_run() || kthread_should_stop());
Izik Eidus31dbd012009-09-21 17:02:03 -07001461 }
1462 }
1463 return 0;
1464}
1465
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001466int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1467 unsigned long end, int advice, unsigned long *vm_flags)
1468{
1469 struct mm_struct *mm = vma->vm_mm;
Hugh Dickinsd952b792009-09-21 17:02:16 -07001470 int err;
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001471
1472 switch (advice) {
1473 case MADV_MERGEABLE:
1474 /*
1475 * Be somewhat over-protective for now!
1476 */
1477 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1478 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
Konstantin Khlebnikov314e51b2012-10-08 16:29:02 -07001479 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001480 return 0; /* just ignore the advice */
1481
Konstantin Khlebnikovcc2383e2012-10-08 16:28:37 -07001482#ifdef VM_SAO
1483 if (*vm_flags & VM_SAO)
1484 return 0;
1485#endif
1486
Hugh Dickinsd952b792009-09-21 17:02:16 -07001487 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1488 err = __ksm_enter(mm);
1489 if (err)
1490 return err;
1491 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001492
1493 *vm_flags |= VM_MERGEABLE;
1494 break;
1495
1496 case MADV_UNMERGEABLE:
1497 if (!(*vm_flags & VM_MERGEABLE))
1498 return 0; /* just ignore the advice */
1499
Hugh Dickinsd952b792009-09-21 17:02:16 -07001500 if (vma->anon_vma) {
1501 err = unmerge_ksm_pages(vma, start, end);
1502 if (err)
1503 return err;
1504 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001505
1506 *vm_flags &= ~VM_MERGEABLE;
1507 break;
1508 }
1509
1510 return 0;
1511}
1512
1513int __ksm_enter(struct mm_struct *mm)
1514{
Hugh Dickins6e1583842009-09-21 17:02:14 -07001515 struct mm_slot *mm_slot;
1516 int needs_wakeup;
1517
1518 mm_slot = alloc_mm_slot();
Izik Eidus31dbd012009-09-21 17:02:03 -07001519 if (!mm_slot)
1520 return -ENOMEM;
1521
Hugh Dickins6e1583842009-09-21 17:02:14 -07001522 /* Check ksm_run too? Would need tighter locking */
1523 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1524
Izik Eidus31dbd012009-09-21 17:02:03 -07001525 spin_lock(&ksm_mmlist_lock);
1526 insert_to_mm_slots_hash(mm, mm_slot);
1527 /*
1528 * Insert just behind the scanning cursor, to let the area settle
1529 * down a little; when fork is followed by immediate exec, we don't
1530 * want ksmd to waste time setting up and tearing down an rmap_list.
1531 */
1532 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1533 spin_unlock(&ksm_mmlist_lock);
1534
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001535 set_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001536 atomic_inc(&mm->mm_count);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001537
1538 if (needs_wakeup)
1539 wake_up_interruptible(&ksm_thread_wait);
1540
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001541 return 0;
1542}
1543
Andrea Arcangeli1c2fb7a2009-09-21 17:02:22 -07001544void __ksm_exit(struct mm_struct *mm)
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001545{
Hugh Dickinscd551f92009-09-21 17:02:17 -07001546 struct mm_slot *mm_slot;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001547 int easy_to_free = 0;
Hugh Dickinscd551f92009-09-21 17:02:17 -07001548
Izik Eidus31dbd012009-09-21 17:02:03 -07001549 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -07001550 * This process is exiting: if it's straightforward (as is the
1551 * case when ksmd was never running), free mm_slot immediately.
1552 * But if it's at the cursor or has rmap_items linked to it, use
1553 * mmap_sem to synchronize with any break_cows before pagetables
1554 * are freed, and leave the mm_slot on the list for ksmd to free.
1555 * Beware: ksm may already have noticed it exiting and freed the slot.
Izik Eidus31dbd012009-09-21 17:02:03 -07001556 */
Hugh Dickins9ba69292009-09-21 17:02:20 -07001557
Hugh Dickinscd551f92009-09-21 17:02:17 -07001558 spin_lock(&ksm_mmlist_lock);
1559 mm_slot = get_mm_slot(mm);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001560 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001561 if (!mm_slot->rmap_list) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001562 hlist_del(&mm_slot->link);
1563 list_del(&mm_slot->mm_list);
1564 easy_to_free = 1;
1565 } else {
1566 list_move(&mm_slot->mm_list,
1567 &ksm_scan.mm_slot->mm_list);
1568 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001569 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001570 spin_unlock(&ksm_mmlist_lock);
1571
Hugh Dickins9ba69292009-09-21 17:02:20 -07001572 if (easy_to_free) {
1573 free_mm_slot(mm_slot);
1574 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1575 mmdrop(mm);
1576 } else if (mm_slot) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001577 down_write(&mm->mmap_sem);
1578 up_write(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001579 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001580}
Izik Eidus31dbd012009-09-21 17:02:03 -07001581
Hugh Dickins5ad64682009-12-14 17:59:24 -08001582struct page *ksm_does_need_to_copy(struct page *page,
1583 struct vm_area_struct *vma, unsigned long address)
1584{
1585 struct page *new_page;
1586
Hugh Dickins5ad64682009-12-14 17:59:24 -08001587 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1588 if (new_page) {
1589 copy_user_highpage(new_page, page, address, vma);
1590
1591 SetPageDirty(new_page);
1592 __SetPageUptodate(new_page);
1593 SetPageSwapBacked(new_page);
1594 __set_page_locked(new_page);
1595
Hugh Dickins39b5f292012-10-08 16:33:18 -07001596 if (!mlocked_vma_newpage(vma, new_page))
Hugh Dickins5ad64682009-12-14 17:59:24 -08001597 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1598 else
1599 add_page_to_unevictable_list(new_page);
1600 }
1601
Hugh Dickins5ad64682009-12-14 17:59:24 -08001602 return new_page;
1603}
1604
1605int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1606 unsigned long *vm_flags)
1607{
1608 struct stable_node *stable_node;
1609 struct rmap_item *rmap_item;
1610 struct hlist_node *hlist;
1611 unsigned int mapcount = page_mapcount(page);
1612 int referenced = 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001613 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001614
1615 VM_BUG_ON(!PageKsm(page));
1616 VM_BUG_ON(!PageLocked(page));
1617
1618 stable_node = page_stable_node(page);
1619 if (!stable_node)
1620 return 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001621again:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001622 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001623 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001624 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001625 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001626
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001627 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07001628 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1629 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08001630 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001631 if (rmap_item->address < vma->vm_start ||
1632 rmap_item->address >= vma->vm_end)
1633 continue;
1634 /*
1635 * Initially we examine only the vma which covers this
1636 * rmap_item; but later, if there is still work to do,
1637 * we examine covering vmas in other mms: in case they
1638 * were forked from the original since ksmd passed.
1639 */
1640 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1641 continue;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001642
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001643 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1644 continue;
1645
1646 referenced += page_referenced_one(page, vma,
Hugh Dickins5ad64682009-12-14 17:59:24 -08001647 rmap_item->address, &mapcount, vm_flags);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001648 if (!search_new_forks || !mapcount)
1649 break;
1650 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001651 anon_vma_unlock_read(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001652 if (!mapcount)
1653 goto out;
1654 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001655 if (!search_new_forks++)
1656 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001657out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001658 return referenced;
1659}
1660
1661int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1662{
1663 struct stable_node *stable_node;
1664 struct hlist_node *hlist;
1665 struct rmap_item *rmap_item;
1666 int ret = SWAP_AGAIN;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001667 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001668
1669 VM_BUG_ON(!PageKsm(page));
1670 VM_BUG_ON(!PageLocked(page));
1671
1672 stable_node = page_stable_node(page);
1673 if (!stable_node)
1674 return SWAP_FAIL;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001675again:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001676 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001677 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001678 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001679 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001680
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001681 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07001682 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1683 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08001684 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001685 if (rmap_item->address < vma->vm_start ||
1686 rmap_item->address >= vma->vm_end)
1687 continue;
1688 /*
1689 * Initially we examine only the vma which covers this
1690 * rmap_item; but later, if there is still work to do,
1691 * we examine covering vmas in other mms: in case they
1692 * were forked from the original since ksmd passed.
1693 */
1694 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1695 continue;
1696
1697 ret = try_to_unmap_one(page, vma,
1698 rmap_item->address, flags);
1699 if (ret != SWAP_AGAIN || !page_mapped(page)) {
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001700 anon_vma_unlock_read(anon_vma);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001701 goto out;
1702 }
1703 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001704 anon_vma_unlock_read(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001705 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001706 if (!search_new_forks++)
1707 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001708out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001709 return ret;
1710}
1711
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001712#ifdef CONFIG_MIGRATION
1713int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1714 struct vm_area_struct *, unsigned long, void *), void *arg)
1715{
1716 struct stable_node *stable_node;
1717 struct hlist_node *hlist;
1718 struct rmap_item *rmap_item;
1719 int ret = SWAP_AGAIN;
1720 int search_new_forks = 0;
1721
1722 VM_BUG_ON(!PageKsm(page));
1723 VM_BUG_ON(!PageLocked(page));
1724
1725 stable_node = page_stable_node(page);
1726 if (!stable_node)
1727 return ret;
1728again:
1729 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1730 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001731 struct anon_vma_chain *vmac;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001732 struct vm_area_struct *vma;
1733
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001734 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07001735 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1736 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08001737 vma = vmac->vma;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001738 if (rmap_item->address < vma->vm_start ||
1739 rmap_item->address >= vma->vm_end)
1740 continue;
1741 /*
1742 * Initially we examine only the vma which covers this
1743 * rmap_item; but later, if there is still work to do,
1744 * we examine covering vmas in other mms: in case they
1745 * were forked from the original since ksmd passed.
1746 */
1747 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1748 continue;
1749
1750 ret = rmap_one(page, vma, rmap_item->address, arg);
1751 if (ret != SWAP_AGAIN) {
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001752 anon_vma_unlock_read(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001753 goto out;
1754 }
1755 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001756 anon_vma_unlock_read(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001757 }
1758 if (!search_new_forks++)
1759 goto again;
1760out:
1761 return ret;
1762}
1763
1764void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1765{
1766 struct stable_node *stable_node;
1767
1768 VM_BUG_ON(!PageLocked(oldpage));
1769 VM_BUG_ON(!PageLocked(newpage));
1770 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1771
1772 stable_node = page_stable_node(newpage);
1773 if (stable_node) {
Hugh Dickins62b61f62009-12-14 17:59:33 -08001774 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1775 stable_node->kpfn = page_to_pfn(newpage);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001776 }
1777}
1778#endif /* CONFIG_MIGRATION */
1779
Hugh Dickins62b61f62009-12-14 17:59:33 -08001780#ifdef CONFIG_MEMORY_HOTREMOVE
1781static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1782 unsigned long end_pfn)
1783{
1784 struct rb_node *node;
1785
1786 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1787 struct stable_node *stable_node;
1788
1789 stable_node = rb_entry(node, struct stable_node, node);
1790 if (stable_node->kpfn >= start_pfn &&
1791 stable_node->kpfn < end_pfn)
1792 return stable_node;
1793 }
1794 return NULL;
1795}
1796
1797static int ksm_memory_callback(struct notifier_block *self,
1798 unsigned long action, void *arg)
1799{
1800 struct memory_notify *mn = arg;
1801 struct stable_node *stable_node;
1802
1803 switch (action) {
1804 case MEM_GOING_OFFLINE:
1805 /*
1806 * Keep it very simple for now: just lock out ksmd and
1807 * MADV_UNMERGEABLE while any memory is going offline.
KOSAKI Motohiroa0b0f582010-12-02 14:31:20 -08001808 * mutex_lock_nested() is necessary because lockdep was alarmed
1809 * that here we take ksm_thread_mutex inside notifier chain
1810 * mutex, and later take notifier chain mutex inside
1811 * ksm_thread_mutex to unlock it. But that's safe because both
1812 * are inside mem_hotplug_mutex.
Hugh Dickins62b61f62009-12-14 17:59:33 -08001813 */
KOSAKI Motohiroa0b0f582010-12-02 14:31:20 -08001814 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001815 break;
1816
1817 case MEM_OFFLINE:
1818 /*
1819 * Most of the work is done by page migration; but there might
1820 * be a few stable_nodes left over, still pointing to struct
1821 * pages which have been offlined: prune those from the tree.
1822 */
1823 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1824 mn->start_pfn + mn->nr_pages)) != NULL)
1825 remove_node_from_stable_tree(stable_node);
1826 /* fallthrough */
1827
1828 case MEM_CANCEL_OFFLINE:
1829 mutex_unlock(&ksm_thread_mutex);
1830 break;
1831 }
1832 return NOTIFY_OK;
1833}
1834#endif /* CONFIG_MEMORY_HOTREMOVE */
1835
Hugh Dickins2ffd8672009-09-21 17:02:23 -07001836#ifdef CONFIG_SYSFS
1837/*
1838 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1839 */
1840
Izik Eidus31dbd012009-09-21 17:02:03 -07001841#define KSM_ATTR_RO(_name) \
1842 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1843#define KSM_ATTR(_name) \
1844 static struct kobj_attribute _name##_attr = \
1845 __ATTR(_name, 0644, _name##_show, _name##_store)
1846
1847static ssize_t sleep_millisecs_show(struct kobject *kobj,
1848 struct kobj_attribute *attr, char *buf)
1849{
1850 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1851}
1852
1853static ssize_t sleep_millisecs_store(struct kobject *kobj,
1854 struct kobj_attribute *attr,
1855 const char *buf, size_t count)
1856{
1857 unsigned long msecs;
1858 int err;
1859
1860 err = strict_strtoul(buf, 10, &msecs);
1861 if (err || msecs > UINT_MAX)
1862 return -EINVAL;
1863
1864 ksm_thread_sleep_millisecs = msecs;
1865
1866 return count;
1867}
1868KSM_ATTR(sleep_millisecs);
1869
1870static ssize_t pages_to_scan_show(struct kobject *kobj,
1871 struct kobj_attribute *attr, char *buf)
1872{
1873 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1874}
1875
1876static ssize_t pages_to_scan_store(struct kobject *kobj,
1877 struct kobj_attribute *attr,
1878 const char *buf, size_t count)
1879{
1880 int err;
1881 unsigned long nr_pages;
1882
1883 err = strict_strtoul(buf, 10, &nr_pages);
1884 if (err || nr_pages > UINT_MAX)
1885 return -EINVAL;
1886
1887 ksm_thread_pages_to_scan = nr_pages;
1888
1889 return count;
1890}
1891KSM_ATTR(pages_to_scan);
1892
1893static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1894 char *buf)
1895{
1896 return sprintf(buf, "%u\n", ksm_run);
1897}
1898
1899static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1900 const char *buf, size_t count)
1901{
1902 int err;
1903 unsigned long flags;
1904
1905 err = strict_strtoul(buf, 10, &flags);
1906 if (err || flags > UINT_MAX)
1907 return -EINVAL;
1908 if (flags > KSM_RUN_UNMERGE)
1909 return -EINVAL;
1910
1911 /*
1912 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1913 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
Hugh Dickinsd0f209f2009-12-14 17:59:34 -08001914 * breaking COW to free the pages_shared (but leaves mm_slots
1915 * on the list for when ksmd may be set running again).
Izik Eidus31dbd012009-09-21 17:02:03 -07001916 */
1917
1918 mutex_lock(&ksm_thread_mutex);
1919 if (ksm_run != flags) {
1920 ksm_run = flags;
Hugh Dickinsd952b792009-09-21 17:02:16 -07001921 if (flags & KSM_RUN_UNMERGE) {
David Rientjese1e12d22012-12-11 16:02:56 -08001922 set_current_oom_origin();
Hugh Dickinsd952b792009-09-21 17:02:16 -07001923 err = unmerge_and_remove_all_rmap_items();
David Rientjese1e12d22012-12-11 16:02:56 -08001924 clear_current_oom_origin();
Hugh Dickinsd952b792009-09-21 17:02:16 -07001925 if (err) {
1926 ksm_run = KSM_RUN_STOP;
1927 count = err;
1928 }
1929 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001930 }
1931 mutex_unlock(&ksm_thread_mutex);
1932
1933 if (flags & KSM_RUN_MERGE)
1934 wake_up_interruptible(&ksm_thread_wait);
1935
1936 return count;
1937}
1938KSM_ATTR(run);
1939
Hugh Dickinsb4028262009-09-21 17:02:09 -07001940static ssize_t pages_shared_show(struct kobject *kobj,
1941 struct kobj_attribute *attr, char *buf)
1942{
1943 return sprintf(buf, "%lu\n", ksm_pages_shared);
1944}
1945KSM_ATTR_RO(pages_shared);
1946
1947static ssize_t pages_sharing_show(struct kobject *kobj,
1948 struct kobj_attribute *attr, char *buf)
1949{
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001950 return sprintf(buf, "%lu\n", ksm_pages_sharing);
Hugh Dickinsb4028262009-09-21 17:02:09 -07001951}
1952KSM_ATTR_RO(pages_sharing);
1953
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001954static ssize_t pages_unshared_show(struct kobject *kobj,
1955 struct kobj_attribute *attr, char *buf)
1956{
1957 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1958}
1959KSM_ATTR_RO(pages_unshared);
1960
1961static ssize_t pages_volatile_show(struct kobject *kobj,
1962 struct kobj_attribute *attr, char *buf)
1963{
1964 long ksm_pages_volatile;
1965
1966 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1967 - ksm_pages_sharing - ksm_pages_unshared;
1968 /*
1969 * It was not worth any locking to calculate that statistic,
1970 * but it might therefore sometimes be negative: conceal that.
1971 */
1972 if (ksm_pages_volatile < 0)
1973 ksm_pages_volatile = 0;
1974 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1975}
1976KSM_ATTR_RO(pages_volatile);
1977
1978static ssize_t full_scans_show(struct kobject *kobj,
1979 struct kobj_attribute *attr, char *buf)
1980{
1981 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1982}
1983KSM_ATTR_RO(full_scans);
1984
Izik Eidus31dbd012009-09-21 17:02:03 -07001985static struct attribute *ksm_attrs[] = {
1986 &sleep_millisecs_attr.attr,
1987 &pages_to_scan_attr.attr,
1988 &run_attr.attr,
Hugh Dickinsb4028262009-09-21 17:02:09 -07001989 &pages_shared_attr.attr,
1990 &pages_sharing_attr.attr,
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001991 &pages_unshared_attr.attr,
1992 &pages_volatile_attr.attr,
1993 &full_scans_attr.attr,
Izik Eidus31dbd012009-09-21 17:02:03 -07001994 NULL,
1995};
1996
1997static struct attribute_group ksm_attr_group = {
1998 .attrs = ksm_attrs,
1999 .name = "ksm",
2000};
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002001#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07002002
2003static int __init ksm_init(void)
2004{
2005 struct task_struct *ksm_thread;
2006 int err;
2007
2008 err = ksm_slab_init();
2009 if (err)
2010 goto out;
2011
Izik Eidus31dbd012009-09-21 17:02:03 -07002012 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2013 if (IS_ERR(ksm_thread)) {
2014 printk(KERN_ERR "ksm: creating kthread failed\n");
2015 err = PTR_ERR(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07002016 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07002017 }
2018
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002019#ifdef CONFIG_SYSFS
Izik Eidus31dbd012009-09-21 17:02:03 -07002020 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2021 if (err) {
2022 printk(KERN_ERR "ksm: register sysfs failed\n");
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002023 kthread_stop(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07002024 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07002025 }
Hugh Dickinsc73602a2009-10-07 16:32:22 -07002026#else
2027 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2028
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002029#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07002030
Hugh Dickins62b61f62009-12-14 17:59:33 -08002031#ifdef CONFIG_MEMORY_HOTREMOVE
2032 /*
2033 * Choose a high priority since the callback takes ksm_thread_mutex:
2034 * later callbacks could only be taking locks which nest within that.
2035 */
2036 hotplug_memory_notifier(ksm_memory_callback, 100);
2037#endif
Izik Eidus31dbd012009-09-21 17:02:03 -07002038 return 0;
2039
Lai Jiangshand9f89842010-08-09 17:20:02 -07002040out_free:
Izik Eidus31dbd012009-09-21 17:02:03 -07002041 ksm_slab_free();
2042out:
2043 return err;
2044}
2045module_init(ksm_init)