blob: d708b3ef2260282a3d6e5784a60c1fb003339f8e [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
Hugh Dickins8dd35572009-12-14 17:59:18 -0800377static void break_cow(struct rmap_item *rmap_item)
Izik Eidus31dbd012009-09-21 17:02:03 -0700378{
Hugh Dickins8dd35572009-12-14 17:59:18 -0800379 struct mm_struct *mm = rmap_item->mm;
380 unsigned long addr = rmap_item->address;
Izik Eidus31dbd012009-09-21 17:02:03 -0700381 struct vm_area_struct *vma;
382
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800383 /*
384 * It is not an accident that whenever we want to break COW
385 * to undo, we also need to drop a reference to the anon_vma.
386 */
Peter Zijlstra9e601092011-03-22 16:32:46 -0700387 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800388
Hugh Dickins81464e302009-09-21 17:02:15 -0700389 down_read(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700390 if (ksm_test_exit(mm))
391 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700392 vma = find_vma(mm, addr);
393 if (!vma || vma->vm_start > addr)
Hugh Dickins81464e302009-09-21 17:02:15 -0700394 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700395 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
Hugh Dickins81464e302009-09-21 17:02:15 -0700396 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700397 break_ksm(vma, addr);
Hugh Dickins81464e302009-09-21 17:02:15 -0700398out:
Izik Eidus31dbd012009-09-21 17:02:03 -0700399 up_read(&mm->mmap_sem);
400}
401
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800402static struct page *page_trans_compound_anon(struct page *page)
403{
404 if (PageTransCompound(page)) {
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800405 struct page *head = compound_trans_head(page);
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800406 /*
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800407 * head may actually be splitted and freed from under
408 * us but it's ok here.
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800409 */
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800410 if (PageAnon(head))
411 return head;
412 }
413 return NULL;
414}
415
Izik Eidus31dbd012009-09-21 17:02:03 -0700416static struct page *get_mergeable_page(struct rmap_item *rmap_item)
417{
418 struct mm_struct *mm = rmap_item->mm;
419 unsigned long addr = rmap_item->address;
420 struct vm_area_struct *vma;
421 struct page *page;
422
423 down_read(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700424 if (ksm_test_exit(mm))
425 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700426 vma = find_vma(mm, addr);
427 if (!vma || vma->vm_start > addr)
428 goto out;
429 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
430 goto out;
431
432 page = follow_page(vma, addr, FOLL_GET);
Dan Carpenter22eccdd2010-04-23 13:18:10 -0400433 if (IS_ERR_OR_NULL(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700434 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800435 if (PageAnon(page) || page_trans_compound_anon(page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700436 flush_anon_page(vma, page, addr);
437 flush_dcache_page(page);
438 } else {
439 put_page(page);
440out: page = NULL;
441 }
442 up_read(&mm->mmap_sem);
443 return page;
444}
445
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800446static void remove_node_from_stable_tree(struct stable_node *stable_node)
447{
448 struct rmap_item *rmap_item;
449 struct hlist_node *hlist;
450
451 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
452 if (rmap_item->hlist.next)
453 ksm_pages_sharing--;
454 else
455 ksm_pages_shared--;
Peter Zijlstra9e601092011-03-22 16:32:46 -0700456 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800457 rmap_item->address &= PAGE_MASK;
458 cond_resched();
459 }
460
461 rb_erase(&stable_node->node, &root_stable_tree);
462 free_stable_node(stable_node);
463}
464
465/*
466 * get_ksm_page: checks if the page indicated by the stable node
467 * is still its ksm page, despite having held no reference to it.
468 * In which case we can trust the content of the page, and it
469 * returns the gotten page; but if the page has now been zapped,
470 * remove the stale node from the stable tree and return NULL.
471 *
472 * You would expect the stable_node to hold a reference to the ksm page.
473 * But if it increments the page's count, swapping out has to wait for
474 * ksmd to come around again before it can free the page, which may take
475 * seconds or even minutes: much too unresponsive. So instead we use a
476 * "keyhole reference": access to the ksm page from the stable node peeps
477 * out through its keyhole to see if that page still holds the right key,
478 * pointing back to this stable node. This relies on freeing a PageAnon
479 * page to reset its page->mapping to NULL, and relies on no other use of
480 * a page to put something that might look like our key in page->mapping.
481 *
482 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
483 * but this is different - made simpler by ksm_thread_mutex being held, but
484 * interesting for assuming that no other use of the struct page could ever
485 * put our expected_mapping into page->mapping (or a field of the union which
486 * coincides with page->mapping). The RCU calls are not for KSM at all, but
487 * to keep the page_count protocol described with page_cache_get_speculative.
488 *
489 * Note: it is possible that get_ksm_page() will return NULL one moment,
490 * then page the next, if the page is in between page_freeze_refs() and
491 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
492 * is on its way to being freed; but it is an anomaly to bear in mind.
493 */
494static struct page *get_ksm_page(struct stable_node *stable_node)
495{
496 struct page *page;
497 void *expected_mapping;
498
Hugh Dickins62b61f62009-12-14 17:59:33 -0800499 page = pfn_to_page(stable_node->kpfn);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800500 expected_mapping = (void *)stable_node +
501 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
502 rcu_read_lock();
503 if (page->mapping != expected_mapping)
504 goto stale;
505 if (!get_page_unless_zero(page))
506 goto stale;
507 if (page->mapping != expected_mapping) {
508 put_page(page);
509 goto stale;
510 }
511 rcu_read_unlock();
512 return page;
513stale:
514 rcu_read_unlock();
515 remove_node_from_stable_tree(stable_node);
516 return NULL;
517}
518
Izik Eidus31dbd012009-09-21 17:02:03 -0700519/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700520 * Removing rmap_item from stable or unstable tree.
521 * This function will clean the information from the stable/unstable tree.
522 */
523static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
524{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800525 if (rmap_item->address & STABLE_FLAG) {
526 struct stable_node *stable_node;
Hugh Dickins5ad64682009-12-14 17:59:24 -0800527 struct page *page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700528
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800529 stable_node = rmap_item->head;
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800530 page = get_ksm_page(stable_node);
531 if (!page)
532 goto out;
533
Hugh Dickins5ad64682009-12-14 17:59:24 -0800534 lock_page(page);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800535 hlist_del(&rmap_item->hlist);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800536 unlock_page(page);
537 put_page(page);
Hugh Dickins08beca42009-12-14 17:59:21 -0800538
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800539 if (stable_node->hlist.first)
540 ksm_pages_sharing--;
541 else
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800542 ksm_pages_shared--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700543
Peter Zijlstra9e601092011-03-22 16:32:46 -0700544 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins93d17712009-12-14 17:59:16 -0800545 rmap_item->address &= PAGE_MASK;
Izik Eidus31dbd012009-09-21 17:02:03 -0700546
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800547 } else if (rmap_item->address & UNSTABLE_FLAG) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700548 unsigned char age;
549 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -0700550 * Usually ksmd can and must skip the rb_erase, because
Izik Eidus31dbd012009-09-21 17:02:03 -0700551 * root_unstable_tree was already reset to RB_ROOT.
Hugh Dickins9ba69292009-09-21 17:02:20 -0700552 * But be careful when an mm is exiting: do the rb_erase
553 * if this rmap_item was inserted by this scan, rather
554 * than left over from before.
Izik Eidus31dbd012009-09-21 17:02:03 -0700555 */
556 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
Hugh Dickinscd551f92009-09-21 17:02:17 -0700557 BUG_ON(age > 1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700558 if (!age)
559 rb_erase(&rmap_item->node, &root_unstable_tree);
Izik Eidus31dbd012009-09-21 17:02:03 -0700560
Hugh Dickins93d17712009-12-14 17:59:16 -0800561 ksm_pages_unshared--;
562 rmap_item->address &= PAGE_MASK;
563 }
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800564out:
Izik Eidus31dbd012009-09-21 17:02:03 -0700565 cond_resched(); /* we're called from many long loops */
566}
567
Izik Eidus31dbd012009-09-21 17:02:03 -0700568static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -0800569 struct rmap_item **rmap_list)
Izik Eidus31dbd012009-09-21 17:02:03 -0700570{
Hugh Dickins6514d512009-12-14 17:59:19 -0800571 while (*rmap_list) {
572 struct rmap_item *rmap_item = *rmap_list;
573 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700574 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -0700575 free_rmap_item(rmap_item);
576 }
577}
578
579/*
580 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
581 * than check every pte of a given vma, the locking doesn't quite work for
582 * that - an rmap_item is assigned to the stable tree after inserting ksm
583 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
584 * rmap_items from parent to child at fork time (so as not to waste time
585 * if exit comes before the next scan reaches it).
Hugh Dickins81464e302009-09-21 17:02:15 -0700586 *
587 * Similarly, although we'd like to remove rmap_items (so updating counts
588 * and freeing memory) when unmerging an area, it's easier to leave that
589 * to the next pass of ksmd - consider, for example, how ksmd might be
590 * in cmp_and_merge_page on one of the rmap_items we would be removing.
Izik Eidus31dbd012009-09-21 17:02:03 -0700591 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700592static int unmerge_ksm_pages(struct vm_area_struct *vma,
593 unsigned long start, unsigned long end)
Izik Eidus31dbd012009-09-21 17:02:03 -0700594{
595 unsigned long addr;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700596 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700597
Hugh Dickinsd952b792009-09-21 17:02:16 -0700598 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700599 if (ksm_test_exit(vma->vm_mm))
600 break;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700601 if (signal_pending(current))
602 err = -ERESTARTSYS;
603 else
604 err = break_ksm(vma, addr);
605 }
606 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700607}
608
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700609#ifdef CONFIG_SYSFS
610/*
611 * Only called through the sysfs control interface:
612 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700613static int unmerge_and_remove_all_rmap_items(void)
Izik Eidus31dbd012009-09-21 17:02:03 -0700614{
615 struct mm_slot *mm_slot;
616 struct mm_struct *mm;
617 struct vm_area_struct *vma;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700618 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700619
Hugh Dickinsd952b792009-09-21 17:02:16 -0700620 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700621 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700622 struct mm_slot, mm_list);
623 spin_unlock(&ksm_mmlist_lock);
624
Hugh Dickins9ba69292009-09-21 17:02:20 -0700625 for (mm_slot = ksm_scan.mm_slot;
626 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700627 mm = mm_slot->mm;
628 down_read(&mm->mmap_sem);
629 for (vma = mm->mmap; vma; vma = vma->vm_next) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700630 if (ksm_test_exit(mm))
631 break;
Izik Eidus31dbd012009-09-21 17:02:03 -0700632 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
633 continue;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700634 err = unmerge_ksm_pages(vma,
635 vma->vm_start, vma->vm_end);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700636 if (err)
637 goto error;
Izik Eidus31dbd012009-09-21 17:02:03 -0700638 }
Hugh Dickins9ba69292009-09-21 17:02:20 -0700639
Hugh Dickins6514d512009-12-14 17:59:19 -0800640 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700641
642 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700643 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700644 struct mm_slot, mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700645 if (ksm_test_exit(mm)) {
646 hlist_del(&mm_slot->link);
647 list_del(&mm_slot->mm_list);
648 spin_unlock(&ksm_mmlist_lock);
649
650 free_mm_slot(mm_slot);
651 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
652 up_read(&mm->mmap_sem);
653 mmdrop(mm);
654 } else {
655 spin_unlock(&ksm_mmlist_lock);
656 up_read(&mm->mmap_sem);
657 }
Izik Eidus31dbd012009-09-21 17:02:03 -0700658 }
659
Hugh Dickinsd952b792009-09-21 17:02:16 -0700660 ksm_scan.seqnr = 0;
Hugh Dickins9ba69292009-09-21 17:02:20 -0700661 return 0;
662
663error:
664 up_read(&mm->mmap_sem);
Izik Eidus31dbd012009-09-21 17:02:03 -0700665 spin_lock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700666 ksm_scan.mm_slot = &ksm_mm_head;
Izik Eidus31dbd012009-09-21 17:02:03 -0700667 spin_unlock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700668 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700669}
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700670#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -0700671
Izik Eidus31dbd012009-09-21 17:02:03 -0700672static u32 calc_checksum(struct page *page)
673{
674 u32 checksum;
675 void *addr = kmap_atomic(page, KM_USER0);
676 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
677 kunmap_atomic(addr, KM_USER0);
678 return checksum;
679}
680
681static int memcmp_pages(struct page *page1, struct page *page2)
682{
683 char *addr1, *addr2;
684 int ret;
685
686 addr1 = kmap_atomic(page1, KM_USER0);
687 addr2 = kmap_atomic(page2, KM_USER1);
688 ret = memcmp(addr1, addr2, PAGE_SIZE);
689 kunmap_atomic(addr2, KM_USER1);
690 kunmap_atomic(addr1, KM_USER0);
691 return ret;
692}
693
694static inline int pages_identical(struct page *page1, struct page *page2)
695{
696 return !memcmp_pages(page1, page2);
697}
698
699static int write_protect_page(struct vm_area_struct *vma, struct page *page,
700 pte_t *orig_pte)
701{
702 struct mm_struct *mm = vma->vm_mm;
703 unsigned long addr;
704 pte_t *ptep;
705 spinlock_t *ptl;
706 int swapped;
707 int err = -EFAULT;
708
709 addr = page_address_in_vma(page, vma);
710 if (addr == -EFAULT)
711 goto out;
712
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800713 BUG_ON(PageTransCompound(page));
Izik Eidus31dbd012009-09-21 17:02:03 -0700714 ptep = page_check_address(page, mm, addr, &ptl, 0);
715 if (!ptep)
716 goto out;
717
Hugh Dickins4e316352010-10-02 17:49:08 -0700718 if (pte_write(*ptep) || pte_dirty(*ptep)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700719 pte_t entry;
720
721 swapped = PageSwapCache(page);
722 flush_cache_page(vma, addr, page_to_pfn(page));
723 /*
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300724 * Ok this is tricky, when get_user_pages_fast() run it doesn't
Izik Eidus31dbd012009-09-21 17:02:03 -0700725 * take any lock, therefore the check that we are going to make
726 * with the pagecount against the mapcount is racey and
727 * O_DIRECT can happen right after the check.
728 * So we clear the pte and flush the tlb before the check
729 * this assure us that no O_DIRECT can happen after the check
730 * or in the middle of the check.
731 */
732 entry = ptep_clear_flush(vma, addr, ptep);
733 /*
734 * Check that no O_DIRECT or similar I/O is in progress on the
735 * page
736 */
Hugh Dickins31e855e2009-12-14 17:59:17 -0800737 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
Robin Holtcb532372010-03-23 13:35:26 -0700738 set_pte_at(mm, addr, ptep, entry);
Izik Eidus31dbd012009-09-21 17:02:03 -0700739 goto out_unlock;
740 }
Hugh Dickins4e316352010-10-02 17:49:08 -0700741 if (pte_dirty(entry))
742 set_page_dirty(page);
743 entry = pte_mkclean(pte_wrprotect(entry));
Izik Eidus31dbd012009-09-21 17:02:03 -0700744 set_pte_at_notify(mm, addr, ptep, entry);
745 }
746 *orig_pte = *ptep;
747 err = 0;
748
749out_unlock:
750 pte_unmap_unlock(ptep, ptl);
751out:
752 return err;
753}
754
755/**
756 * replace_page - replace page in vma by new ksm page
Hugh Dickins8dd35572009-12-14 17:59:18 -0800757 * @vma: vma that holds the pte pointing to page
758 * @page: the page we are replacing by kpage
759 * @kpage: the ksm page we replace page by
Izik Eidus31dbd012009-09-21 17:02:03 -0700760 * @orig_pte: the original value of the pte
761 *
762 * Returns 0 on success, -EFAULT on failure.
763 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800764static int replace_page(struct vm_area_struct *vma, struct page *page,
765 struct page *kpage, pte_t orig_pte)
Izik Eidus31dbd012009-09-21 17:02:03 -0700766{
767 struct mm_struct *mm = vma->vm_mm;
768 pgd_t *pgd;
769 pud_t *pud;
770 pmd_t *pmd;
771 pte_t *ptep;
772 spinlock_t *ptl;
773 unsigned long addr;
Izik Eidus31dbd012009-09-21 17:02:03 -0700774 int err = -EFAULT;
775
Hugh Dickins8dd35572009-12-14 17:59:18 -0800776 addr = page_address_in_vma(page, vma);
Izik Eidus31dbd012009-09-21 17:02:03 -0700777 if (addr == -EFAULT)
778 goto out;
779
780 pgd = pgd_offset(mm, addr);
781 if (!pgd_present(*pgd))
782 goto out;
783
784 pud = pud_offset(pgd, addr);
785 if (!pud_present(*pud))
786 goto out;
787
788 pmd = pmd_offset(pud, addr);
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800789 BUG_ON(pmd_trans_huge(*pmd));
Izik Eidus31dbd012009-09-21 17:02:03 -0700790 if (!pmd_present(*pmd))
791 goto out;
792
793 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
794 if (!pte_same(*ptep, orig_pte)) {
795 pte_unmap_unlock(ptep, ptl);
796 goto out;
797 }
798
Hugh Dickins8dd35572009-12-14 17:59:18 -0800799 get_page(kpage);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800800 page_add_anon_rmap(kpage, vma, addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700801
802 flush_cache_page(vma, addr, pte_pfn(*ptep));
803 ptep_clear_flush(vma, addr, ptep);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800804 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
Izik Eidus31dbd012009-09-21 17:02:03 -0700805
Hugh Dickins8dd35572009-12-14 17:59:18 -0800806 page_remove_rmap(page);
Hugh Dickinsae52a2a2011-01-13 15:46:28 -0800807 if (!page_mapped(page))
808 try_to_free_swap(page);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800809 put_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700810
811 pte_unmap_unlock(ptep, ptl);
812 err = 0;
813out:
814 return err;
815}
816
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800817static int page_trans_compound_anon_split(struct page *page)
818{
819 int ret = 0;
820 struct page *transhuge_head = page_trans_compound_anon(page);
821 if (transhuge_head) {
822 /* Get the reference on the head to split it. */
823 if (get_page_unless_zero(transhuge_head)) {
824 /*
825 * Recheck we got the reference while the head
826 * was still anonymous.
827 */
828 if (PageAnon(transhuge_head))
829 ret = split_huge_page(transhuge_head);
830 else
831 /*
832 * Retry later if split_huge_page run
833 * from under us.
834 */
835 ret = 1;
836 put_page(transhuge_head);
837 } else
838 /* Retry later if split_huge_page run from under us. */
839 ret = 1;
840 }
841 return ret;
842}
843
Izik Eidus31dbd012009-09-21 17:02:03 -0700844/*
845 * try_to_merge_one_page - take two pages and merge them into one
Hugh Dickins8dd35572009-12-14 17:59:18 -0800846 * @vma: the vma that holds the pte pointing to page
847 * @page: the PageAnon page that we want to replace with kpage
Hugh Dickins80e148222009-12-14 17:59:29 -0800848 * @kpage: the PageKsm page that we want to map instead of page,
849 * or NULL the first time when we want to use page as kpage.
Izik Eidus31dbd012009-09-21 17:02:03 -0700850 *
851 * This function returns 0 if the pages were merged, -EFAULT otherwise.
852 */
853static int try_to_merge_one_page(struct vm_area_struct *vma,
Hugh Dickins8dd35572009-12-14 17:59:18 -0800854 struct page *page, struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -0700855{
856 pte_t orig_pte = __pte(0);
857 int err = -EFAULT;
858
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800859 if (page == kpage) /* ksm page forked */
860 return 0;
861
Izik Eidus31dbd012009-09-21 17:02:03 -0700862 if (!(vma->vm_flags & VM_MERGEABLE))
863 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800864 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
865 goto out;
866 BUG_ON(PageTransCompound(page));
Hugh Dickins8dd35572009-12-14 17:59:18 -0800867 if (!PageAnon(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700868 goto out;
869
Izik Eidus31dbd012009-09-21 17:02:03 -0700870 /*
871 * We need the page lock to read a stable PageSwapCache in
872 * write_protect_page(). We use trylock_page() instead of
873 * lock_page() because we don't want to wait here - we
874 * prefer to continue scanning and merging different pages,
875 * then come back to this page when it is unlocked.
876 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800877 if (!trylock_page(page))
Hugh Dickins31e855e2009-12-14 17:59:17 -0800878 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -0700879 /*
880 * If this anonymous page is mapped only here, its pte may need
881 * to be write-protected. If it's mapped elsewhere, all of its
882 * ptes are necessarily already write-protected. But in either
883 * case, we need to lock and check page_count is not raised.
884 */
Hugh Dickins80e148222009-12-14 17:59:29 -0800885 if (write_protect_page(vma, page, &orig_pte) == 0) {
886 if (!kpage) {
887 /*
888 * While we hold page lock, upgrade page from
889 * PageAnon+anon_vma to PageKsm+NULL stable_node:
890 * stable_tree_insert() will update stable_node.
891 */
892 set_page_stable_node(page, NULL);
893 mark_page_accessed(page);
894 err = 0;
895 } else if (pages_identical(page, kpage))
896 err = replace_page(vma, page, kpage, orig_pte);
897 }
Izik Eidus31dbd012009-09-21 17:02:03 -0700898
Hugh Dickins80e148222009-12-14 17:59:29 -0800899 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
Hugh Dickins73848b42009-12-14 17:59:22 -0800900 munlock_vma_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800901 if (!PageMlocked(kpage)) {
902 unlock_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800903 lock_page(kpage);
904 mlock_vma_page(kpage);
905 page = kpage; /* for final unlock */
906 }
907 }
Hugh Dickins73848b42009-12-14 17:59:22 -0800908
Hugh Dickins8dd35572009-12-14 17:59:18 -0800909 unlock_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700910out:
911 return err;
912}
913
914/*
Hugh Dickins81464e302009-09-21 17:02:15 -0700915 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
916 * but no new kernel page is allocated: kpage must already be a ksm page.
Hugh Dickins8dd35572009-12-14 17:59:18 -0800917 *
918 * This function returns 0 if the pages were merged, -EFAULT otherwise.
Hugh Dickins81464e302009-09-21 17:02:15 -0700919 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800920static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
921 struct page *page, struct page *kpage)
Hugh Dickins81464e302009-09-21 17:02:15 -0700922{
Hugh Dickins8dd35572009-12-14 17:59:18 -0800923 struct mm_struct *mm = rmap_item->mm;
Hugh Dickins81464e302009-09-21 17:02:15 -0700924 struct vm_area_struct *vma;
925 int err = -EFAULT;
926
Hugh Dickins8dd35572009-12-14 17:59:18 -0800927 down_read(&mm->mmap_sem);
928 if (ksm_test_exit(mm))
929 goto out;
930 vma = find_vma(mm, rmap_item->address);
931 if (!vma || vma->vm_start > rmap_item->address)
Hugh Dickins9ba69292009-09-21 17:02:20 -0700932 goto out;
933
Hugh Dickins8dd35572009-12-14 17:59:18 -0800934 err = try_to_merge_one_page(vma, page, kpage);
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800935 if (err)
936 goto out;
937
938 /* Must get reference to anon_vma while still holding mmap_sem */
Peter Zijlstra9e601092011-03-22 16:32:46 -0700939 rmap_item->anon_vma = vma->anon_vma;
940 get_anon_vma(vma->anon_vma);
Hugh Dickins81464e302009-09-21 17:02:15 -0700941out:
Hugh Dickins8dd35572009-12-14 17:59:18 -0800942 up_read(&mm->mmap_sem);
Hugh Dickins81464e302009-09-21 17:02:15 -0700943 return err;
944}
945
946/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700947 * try_to_merge_two_pages - take two identical pages and prepare them
948 * to be merged into one page.
949 *
Hugh Dickins8dd35572009-12-14 17:59:18 -0800950 * This function returns the kpage if we successfully merged two identical
951 * pages into one ksm page, NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -0700952 *
Hugh Dickins80e148222009-12-14 17:59:29 -0800953 * Note that this function upgrades page to ksm page: if one of the pages
Izik Eidus31dbd012009-09-21 17:02:03 -0700954 * is already a ksm page, try_to_merge_with_ksm_page should be used.
955 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800956static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
957 struct page *page,
958 struct rmap_item *tree_rmap_item,
959 struct page *tree_page)
Izik Eidus31dbd012009-09-21 17:02:03 -0700960{
Hugh Dickins80e148222009-12-14 17:59:29 -0800961 int err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700962
Hugh Dickins80e148222009-12-14 17:59:29 -0800963 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
Izik Eidus31dbd012009-09-21 17:02:03 -0700964 if (!err) {
Hugh Dickins8dd35572009-12-14 17:59:18 -0800965 err = try_to_merge_with_ksm_page(tree_rmap_item,
Hugh Dickins80e148222009-12-14 17:59:29 -0800966 tree_page, page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700967 /*
Hugh Dickins81464e302009-09-21 17:02:15 -0700968 * If that fails, we have a ksm page with only one pte
969 * pointing to it: so break it.
Izik Eidus31dbd012009-09-21 17:02:03 -0700970 */
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800971 if (err)
Hugh Dickins8dd35572009-12-14 17:59:18 -0800972 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -0700973 }
Hugh Dickins80e148222009-12-14 17:59:29 -0800974 return err ? NULL : page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700975}
976
977/*
Hugh Dickins8dd35572009-12-14 17:59:18 -0800978 * stable_tree_search - search for page inside the stable tree
Izik Eidus31dbd012009-09-21 17:02:03 -0700979 *
980 * This function checks if there is a page inside the stable tree
981 * with identical content to the page that we are scanning right now.
982 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800983 * This function returns the stable tree node of identical content if found,
Izik Eidus31dbd012009-09-21 17:02:03 -0700984 * NULL otherwise.
985 */
Hugh Dickins62b61f62009-12-14 17:59:33 -0800986static struct page *stable_tree_search(struct page *page)
Izik Eidus31dbd012009-09-21 17:02:03 -0700987{
988 struct rb_node *node = root_stable_tree.rb_node;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800989 struct stable_node *stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -0700990
Hugh Dickins08beca42009-12-14 17:59:21 -0800991 stable_node = page_stable_node(page);
992 if (stable_node) { /* ksm page forked */
993 get_page(page);
Hugh Dickins62b61f62009-12-14 17:59:33 -0800994 return page;
Hugh Dickins08beca42009-12-14 17:59:21 -0800995 }
996
Izik Eidus31dbd012009-09-21 17:02:03 -0700997 while (node) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800998 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700999 int ret;
1000
Hugh Dickins08beca42009-12-14 17:59:21 -08001001 cond_resched();
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001002 stable_node = rb_entry(node, struct stable_node, node);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001003 tree_page = get_ksm_page(stable_node);
1004 if (!tree_page)
1005 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001006
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001007 ret = memcmp_pages(page, tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001008
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001009 if (ret < 0) {
1010 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001011 node = node->rb_left;
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001012 } else if (ret > 0) {
1013 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001014 node = node->rb_right;
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001015 } else
Hugh Dickins62b61f62009-12-14 17:59:33 -08001016 return tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001017 }
1018
1019 return NULL;
1020}
1021
1022/*
1023 * stable_tree_insert - insert rmap_item pointing to new ksm page
1024 * into the stable tree.
1025 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001026 * This function returns the stable tree node just allocated on success,
1027 * NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -07001028 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001029static struct stable_node *stable_tree_insert(struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -07001030{
1031 struct rb_node **new = &root_stable_tree.rb_node;
1032 struct rb_node *parent = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001033 struct stable_node *stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001034
1035 while (*new) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001036 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001037 int ret;
1038
Hugh Dickins08beca42009-12-14 17:59:21 -08001039 cond_resched();
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001040 stable_node = rb_entry(*new, struct stable_node, node);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001041 tree_page = get_ksm_page(stable_node);
1042 if (!tree_page)
1043 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001044
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001045 ret = memcmp_pages(kpage, tree_page);
1046 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001047
1048 parent = *new;
1049 if (ret < 0)
1050 new = &parent->rb_left;
1051 else if (ret > 0)
1052 new = &parent->rb_right;
1053 else {
1054 /*
1055 * It is not a bug that stable_tree_search() didn't
1056 * find this node: because at that time our page was
1057 * not yet write-protected, so may have changed since.
1058 */
1059 return NULL;
1060 }
1061 }
1062
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001063 stable_node = alloc_stable_node();
1064 if (!stable_node)
1065 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001066
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001067 rb_link_node(&stable_node->node, parent, new);
1068 rb_insert_color(&stable_node->node, &root_stable_tree);
1069
1070 INIT_HLIST_HEAD(&stable_node->hlist);
1071
Hugh Dickins62b61f62009-12-14 17:59:33 -08001072 stable_node->kpfn = page_to_pfn(kpage);
Hugh Dickins08beca42009-12-14 17:59:21 -08001073 set_page_stable_node(kpage, stable_node);
1074
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001075 return stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001076}
1077
1078/*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001079 * unstable_tree_search_insert - search for identical page,
1080 * else insert rmap_item into the unstable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001081 *
1082 * This function searches for a page in the unstable tree identical to the
1083 * page currently being scanned; and if no identical page is found in the
1084 * tree, we insert rmap_item as a new object into the unstable tree.
1085 *
1086 * This function returns pointer to rmap_item found to be identical
1087 * to the currently scanned page, NULL otherwise.
1088 *
1089 * This function does both searching and inserting, because they share
1090 * the same walking algorithm in an rbtree.
1091 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001092static
1093struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1094 struct page *page,
1095 struct page **tree_pagep)
1096
Izik Eidus31dbd012009-09-21 17:02:03 -07001097{
1098 struct rb_node **new = &root_unstable_tree.rb_node;
1099 struct rb_node *parent = NULL;
1100
1101 while (*new) {
1102 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001103 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001104 int ret;
1105
Hugh Dickinsd178f272009-11-09 15:58:23 +00001106 cond_resched();
Izik Eidus31dbd012009-09-21 17:02:03 -07001107 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
Hugh Dickins8dd35572009-12-14 17:59:18 -08001108 tree_page = get_mergeable_page(tree_rmap_item);
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001109 if (IS_ERR_OR_NULL(tree_page))
Izik Eidus31dbd012009-09-21 17:02:03 -07001110 return NULL;
1111
1112 /*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001113 * Don't substitute a ksm page for a forked page.
Izik Eidus31dbd012009-09-21 17:02:03 -07001114 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001115 if (page == tree_page) {
1116 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001117 return NULL;
1118 }
1119
Hugh Dickins8dd35572009-12-14 17:59:18 -08001120 ret = memcmp_pages(page, tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001121
1122 parent = *new;
1123 if (ret < 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001124 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001125 new = &parent->rb_left;
1126 } else if (ret > 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001127 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001128 new = &parent->rb_right;
1129 } else {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001130 *tree_pagep = tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001131 return tree_rmap_item;
1132 }
1133 }
1134
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001135 rmap_item->address |= UNSTABLE_FLAG;
Izik Eidus31dbd012009-09-21 17:02:03 -07001136 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1137 rb_link_node(&rmap_item->node, parent, new);
1138 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1139
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001140 ksm_pages_unshared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001141 return NULL;
1142}
1143
1144/*
1145 * stable_tree_append - add another rmap_item to the linked list of
1146 * rmap_items hanging off a given node of the stable tree, all sharing
1147 * the same ksm page.
1148 */
1149static void stable_tree_append(struct rmap_item *rmap_item,
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001150 struct stable_node *stable_node)
Izik Eidus31dbd012009-09-21 17:02:03 -07001151{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001152 rmap_item->head = stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001153 rmap_item->address |= STABLE_FLAG;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001154 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001155
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001156 if (rmap_item->hlist.next)
1157 ksm_pages_sharing++;
1158 else
1159 ksm_pages_shared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001160}
1161
1162/*
Hugh Dickins81464e302009-09-21 17:02:15 -07001163 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1164 * if not, compare checksum to previous and if it's the same, see if page can
1165 * be inserted into the unstable tree, or merged with a page already there and
1166 * both transferred to the stable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001167 *
1168 * @page: the page that we are searching identical page to.
1169 * @rmap_item: the reverse mapping into the virtual address of this page
1170 */
1171static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1172{
Izik Eidus31dbd012009-09-21 17:02:03 -07001173 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001174 struct page *tree_page = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001175 struct stable_node *stable_node;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001176 struct page *kpage;
Izik Eidus31dbd012009-09-21 17:02:03 -07001177 unsigned int checksum;
1178 int err;
1179
Hugh Dickins93d17712009-12-14 17:59:16 -08001180 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001181
1182 /* We first start with searching the page inside the stable tree */
Hugh Dickins62b61f62009-12-14 17:59:33 -08001183 kpage = stable_tree_search(page);
1184 if (kpage) {
Hugh Dickins08beca42009-12-14 17:59:21 -08001185 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001186 if (!err) {
1187 /*
1188 * The page was successfully merged:
1189 * add its rmap_item to the stable tree.
1190 */
Hugh Dickins5ad64682009-12-14 17:59:24 -08001191 lock_page(kpage);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001192 stable_tree_append(rmap_item, page_stable_node(kpage));
Hugh Dickins5ad64682009-12-14 17:59:24 -08001193 unlock_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001194 }
Hugh Dickins8dd35572009-12-14 17:59:18 -08001195 put_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001196 return;
1197 }
1198
1199 /*
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001200 * If the hash value of the page has changed from the last time
1201 * we calculated it, this page is changing frequently: therefore we
1202 * don't want to insert it in the unstable tree, and we don't want
1203 * to waste our time searching for something identical to it there.
Izik Eidus31dbd012009-09-21 17:02:03 -07001204 */
1205 checksum = calc_checksum(page);
1206 if (rmap_item->oldchecksum != checksum) {
1207 rmap_item->oldchecksum = checksum;
1208 return;
1209 }
1210
Hugh Dickins8dd35572009-12-14 17:59:18 -08001211 tree_rmap_item =
1212 unstable_tree_search_insert(rmap_item, page, &tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001213 if (tree_rmap_item) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001214 kpage = try_to_merge_two_pages(rmap_item, page,
1215 tree_rmap_item, tree_page);
1216 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001217 /*
1218 * As soon as we merge this page, we want to remove the
1219 * rmap_item of the page we have merged with from the unstable
1220 * tree, and insert it instead as new node in the stable tree.
1221 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001222 if (kpage) {
Hugh Dickins93d17712009-12-14 17:59:16 -08001223 remove_rmap_item_from_tree(tree_rmap_item);
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001224
Hugh Dickins5ad64682009-12-14 17:59:24 -08001225 lock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001226 stable_node = stable_tree_insert(kpage);
1227 if (stable_node) {
1228 stable_tree_append(tree_rmap_item, stable_node);
1229 stable_tree_append(rmap_item, stable_node);
1230 }
Hugh Dickins5ad64682009-12-14 17:59:24 -08001231 unlock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001232
Izik Eidus31dbd012009-09-21 17:02:03 -07001233 /*
1234 * If we fail to insert the page into the stable tree,
1235 * we will have 2 virtual addresses that are pointing
1236 * to a ksm page left outside the stable tree,
1237 * in which case we need to break_cow on both.
1238 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001239 if (!stable_node) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001240 break_cow(tree_rmap_item);
1241 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001242 }
1243 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001244 }
1245}
1246
1247static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001248 struct rmap_item **rmap_list,
Izik Eidus31dbd012009-09-21 17:02:03 -07001249 unsigned long addr)
1250{
1251 struct rmap_item *rmap_item;
1252
Hugh Dickins6514d512009-12-14 17:59:19 -08001253 while (*rmap_list) {
1254 rmap_item = *rmap_list;
Hugh Dickins93d17712009-12-14 17:59:16 -08001255 if ((rmap_item->address & PAGE_MASK) == addr)
Izik Eidus31dbd012009-09-21 17:02:03 -07001256 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001257 if (rmap_item->address > addr)
1258 break;
Hugh Dickins6514d512009-12-14 17:59:19 -08001259 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001260 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001261 free_rmap_item(rmap_item);
1262 }
1263
1264 rmap_item = alloc_rmap_item();
1265 if (rmap_item) {
1266 /* It has already been zeroed */
1267 rmap_item->mm = mm_slot->mm;
1268 rmap_item->address = addr;
Hugh Dickins6514d512009-12-14 17:59:19 -08001269 rmap_item->rmap_list = *rmap_list;
1270 *rmap_list = rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001271 }
1272 return rmap_item;
1273}
1274
1275static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1276{
1277 struct mm_struct *mm;
1278 struct mm_slot *slot;
1279 struct vm_area_struct *vma;
1280 struct rmap_item *rmap_item;
1281
1282 if (list_empty(&ksm_mm_head.mm_list))
1283 return NULL;
1284
1285 slot = ksm_scan.mm_slot;
1286 if (slot == &ksm_mm_head) {
Hugh Dickins2919bfd2011-01-13 15:47:29 -08001287 /*
1288 * A number of pages can hang around indefinitely on per-cpu
1289 * pagevecs, raised page count preventing write_protect_page
1290 * from merging them. Though it doesn't really matter much,
1291 * it is puzzling to see some stuck in pages_volatile until
1292 * other activity jostles them out, and they also prevented
1293 * LTP's KSM test from succeeding deterministically; so drain
1294 * them here (here rather than on entry to ksm_do_scan(),
1295 * so we don't IPI too often when pages_to_scan is set low).
1296 */
1297 lru_add_drain_all();
1298
Izik Eidus31dbd012009-09-21 17:02:03 -07001299 root_unstable_tree = RB_ROOT;
1300
1301 spin_lock(&ksm_mmlist_lock);
1302 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1303 ksm_scan.mm_slot = slot;
1304 spin_unlock(&ksm_mmlist_lock);
1305next_mm:
1306 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001307 ksm_scan.rmap_list = &slot->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001308 }
1309
1310 mm = slot->mm;
1311 down_read(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001312 if (ksm_test_exit(mm))
1313 vma = NULL;
1314 else
1315 vma = find_vma(mm, ksm_scan.address);
1316
1317 for (; vma; vma = vma->vm_next) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001318 if (!(vma->vm_flags & VM_MERGEABLE))
1319 continue;
1320 if (ksm_scan.address < vma->vm_start)
1321 ksm_scan.address = vma->vm_start;
1322 if (!vma->anon_vma)
1323 ksm_scan.address = vma->vm_end;
1324
1325 while (ksm_scan.address < vma->vm_end) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001326 if (ksm_test_exit(mm))
1327 break;
Izik Eidus31dbd012009-09-21 17:02:03 -07001328 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001329 if (IS_ERR_OR_NULL(*page)) {
1330 ksm_scan.address += PAGE_SIZE;
1331 cond_resched();
1332 continue;
1333 }
Andrea Arcangeli29ad7682011-01-13 15:47:19 -08001334 if (PageAnon(*page) ||
1335 page_trans_compound_anon(*page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001336 flush_anon_page(vma, *page, ksm_scan.address);
1337 flush_dcache_page(*page);
1338 rmap_item = get_next_rmap_item(slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001339 ksm_scan.rmap_list, ksm_scan.address);
Izik Eidus31dbd012009-09-21 17:02:03 -07001340 if (rmap_item) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001341 ksm_scan.rmap_list =
1342 &rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001343 ksm_scan.address += PAGE_SIZE;
1344 } else
1345 put_page(*page);
1346 up_read(&mm->mmap_sem);
1347 return rmap_item;
1348 }
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001349 put_page(*page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001350 ksm_scan.address += PAGE_SIZE;
1351 cond_resched();
1352 }
1353 }
1354
Hugh Dickins9ba69292009-09-21 17:02:20 -07001355 if (ksm_test_exit(mm)) {
1356 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001357 ksm_scan.rmap_list = &slot->rmap_list;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001358 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001359 /*
1360 * Nuke all the rmap_items that are above this current rmap:
1361 * because there were no VM_MERGEABLE vmas with such addresses.
1362 */
Hugh Dickins6514d512009-12-14 17:59:19 -08001363 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
Izik Eidus31dbd012009-09-21 17:02:03 -07001364
1365 spin_lock(&ksm_mmlist_lock);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001366 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1367 struct mm_slot, mm_list);
1368 if (ksm_scan.address == 0) {
1369 /*
1370 * We've completed a full scan of all vmas, holding mmap_sem
1371 * throughout, and found no VM_MERGEABLE: so do the same as
1372 * __ksm_exit does to remove this mm from all our lists now.
Hugh Dickins9ba69292009-09-21 17:02:20 -07001373 * This applies either when cleaning up after __ksm_exit
1374 * (but beware: we can reach here even before __ksm_exit),
1375 * or when all VM_MERGEABLE areas have been unmapped (and
1376 * mmap_sem then protects against race with MADV_MERGEABLE).
Hugh Dickinscd551f92009-09-21 17:02:17 -07001377 */
1378 hlist_del(&slot->link);
1379 list_del(&slot->mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001380 spin_unlock(&ksm_mmlist_lock);
1381
Hugh Dickinscd551f92009-09-21 17:02:17 -07001382 free_mm_slot(slot);
1383 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001384 up_read(&mm->mmap_sem);
1385 mmdrop(mm);
1386 } else {
1387 spin_unlock(&ksm_mmlist_lock);
1388 up_read(&mm->mmap_sem);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001389 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001390
1391 /* Repeat until we've completed scanning the whole list */
Hugh Dickinscd551f92009-09-21 17:02:17 -07001392 slot = ksm_scan.mm_slot;
Izik Eidus31dbd012009-09-21 17:02:03 -07001393 if (slot != &ksm_mm_head)
1394 goto next_mm;
1395
Izik Eidus31dbd012009-09-21 17:02:03 -07001396 ksm_scan.seqnr++;
1397 return NULL;
1398}
1399
1400/**
1401 * ksm_do_scan - the ksm scanner main worker function.
1402 * @scan_npages - number of pages we want to scan before we return.
1403 */
1404static void ksm_do_scan(unsigned int scan_npages)
1405{
1406 struct rmap_item *rmap_item;
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001407 struct page *uninitialized_var(page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001408
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001409 while (scan_npages-- && likely(!freezing(current))) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001410 cond_resched();
1411 rmap_item = scan_get_next_rmap_item(&page);
1412 if (!rmap_item)
1413 return;
1414 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1415 cmp_and_merge_page(page, rmap_item);
1416 put_page(page);
1417 }
1418}
1419
Hugh Dickins6e1583842009-09-21 17:02:14 -07001420static int ksmd_should_run(void)
1421{
1422 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1423}
1424
Izik Eidus31dbd012009-09-21 17:02:03 -07001425static int ksm_scan_thread(void *nothing)
1426{
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001427 set_freezable();
Izik Eidus339aa622009-09-21 17:02:07 -07001428 set_user_nice(current, 5);
Izik Eidus31dbd012009-09-21 17:02:03 -07001429
1430 while (!kthread_should_stop()) {
Hugh Dickins6e1583842009-09-21 17:02:14 -07001431 mutex_lock(&ksm_thread_mutex);
1432 if (ksmd_should_run())
Izik Eidus31dbd012009-09-21 17:02:03 -07001433 ksm_do_scan(ksm_thread_pages_to_scan);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001434 mutex_unlock(&ksm_thread_mutex);
1435
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001436 try_to_freeze();
1437
Hugh Dickins6e1583842009-09-21 17:02:14 -07001438 if (ksmd_should_run()) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001439 schedule_timeout_interruptible(
1440 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1441 } else {
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001442 wait_event_freezable(ksm_thread_wait,
Hugh Dickins6e1583842009-09-21 17:02:14 -07001443 ksmd_should_run() || kthread_should_stop());
Izik Eidus31dbd012009-09-21 17:02:03 -07001444 }
1445 }
1446 return 0;
1447}
1448
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001449int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1450 unsigned long end, int advice, unsigned long *vm_flags)
1451{
1452 struct mm_struct *mm = vma->vm_mm;
Hugh Dickinsd952b792009-09-21 17:02:16 -07001453 int err;
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001454
1455 switch (advice) {
1456 case MADV_MERGEABLE:
1457 /*
1458 * Be somewhat over-protective for now!
1459 */
1460 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1461 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1462 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
Hugh Dickins5ad64682009-12-14 17:59:24 -08001463 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001464 return 0; /* just ignore the advice */
1465
Hugh Dickinsd952b792009-09-21 17:02:16 -07001466 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1467 err = __ksm_enter(mm);
1468 if (err)
1469 return err;
1470 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001471
1472 *vm_flags |= VM_MERGEABLE;
1473 break;
1474
1475 case MADV_UNMERGEABLE:
1476 if (!(*vm_flags & VM_MERGEABLE))
1477 return 0; /* just ignore the advice */
1478
Hugh Dickinsd952b792009-09-21 17:02:16 -07001479 if (vma->anon_vma) {
1480 err = unmerge_ksm_pages(vma, start, end);
1481 if (err)
1482 return err;
1483 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001484
1485 *vm_flags &= ~VM_MERGEABLE;
1486 break;
1487 }
1488
1489 return 0;
1490}
1491
1492int __ksm_enter(struct mm_struct *mm)
1493{
Hugh Dickins6e1583842009-09-21 17:02:14 -07001494 struct mm_slot *mm_slot;
1495 int needs_wakeup;
1496
1497 mm_slot = alloc_mm_slot();
Izik Eidus31dbd012009-09-21 17:02:03 -07001498 if (!mm_slot)
1499 return -ENOMEM;
1500
Hugh Dickins6e1583842009-09-21 17:02:14 -07001501 /* Check ksm_run too? Would need tighter locking */
1502 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1503
Izik Eidus31dbd012009-09-21 17:02:03 -07001504 spin_lock(&ksm_mmlist_lock);
1505 insert_to_mm_slots_hash(mm, mm_slot);
1506 /*
1507 * Insert just behind the scanning cursor, to let the area settle
1508 * down a little; when fork is followed by immediate exec, we don't
1509 * want ksmd to waste time setting up and tearing down an rmap_list.
1510 */
1511 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1512 spin_unlock(&ksm_mmlist_lock);
1513
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001514 set_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001515 atomic_inc(&mm->mm_count);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001516
1517 if (needs_wakeup)
1518 wake_up_interruptible(&ksm_thread_wait);
1519
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001520 return 0;
1521}
1522
Andrea Arcangeli1c2fb7a2009-09-21 17:02:22 -07001523void __ksm_exit(struct mm_struct *mm)
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001524{
Hugh Dickinscd551f92009-09-21 17:02:17 -07001525 struct mm_slot *mm_slot;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001526 int easy_to_free = 0;
Hugh Dickinscd551f92009-09-21 17:02:17 -07001527
Izik Eidus31dbd012009-09-21 17:02:03 -07001528 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -07001529 * This process is exiting: if it's straightforward (as is the
1530 * case when ksmd was never running), free mm_slot immediately.
1531 * But if it's at the cursor or has rmap_items linked to it, use
1532 * mmap_sem to synchronize with any break_cows before pagetables
1533 * are freed, and leave the mm_slot on the list for ksmd to free.
1534 * Beware: ksm may already have noticed it exiting and freed the slot.
Izik Eidus31dbd012009-09-21 17:02:03 -07001535 */
Hugh Dickins9ba69292009-09-21 17:02:20 -07001536
Hugh Dickinscd551f92009-09-21 17:02:17 -07001537 spin_lock(&ksm_mmlist_lock);
1538 mm_slot = get_mm_slot(mm);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001539 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001540 if (!mm_slot->rmap_list) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001541 hlist_del(&mm_slot->link);
1542 list_del(&mm_slot->mm_list);
1543 easy_to_free = 1;
1544 } else {
1545 list_move(&mm_slot->mm_list,
1546 &ksm_scan.mm_slot->mm_list);
1547 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001548 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001549 spin_unlock(&ksm_mmlist_lock);
1550
Hugh Dickins9ba69292009-09-21 17:02:20 -07001551 if (easy_to_free) {
1552 free_mm_slot(mm_slot);
1553 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1554 mmdrop(mm);
1555 } else if (mm_slot) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001556 down_write(&mm->mmap_sem);
1557 up_write(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001558 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001559}
Izik Eidus31dbd012009-09-21 17:02:03 -07001560
Hugh Dickins5ad64682009-12-14 17:59:24 -08001561struct page *ksm_does_need_to_copy(struct page *page,
1562 struct vm_area_struct *vma, unsigned long address)
1563{
1564 struct page *new_page;
1565
Hugh Dickins5ad64682009-12-14 17:59:24 -08001566 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1567 if (new_page) {
1568 copy_user_highpage(new_page, page, address, vma);
1569
1570 SetPageDirty(new_page);
1571 __SetPageUptodate(new_page);
1572 SetPageSwapBacked(new_page);
1573 __set_page_locked(new_page);
1574
1575 if (page_evictable(new_page, vma))
1576 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1577 else
1578 add_page_to_unevictable_list(new_page);
1579 }
1580
Hugh Dickins5ad64682009-12-14 17:59:24 -08001581 return new_page;
1582}
1583
1584int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1585 unsigned long *vm_flags)
1586{
1587 struct stable_node *stable_node;
1588 struct rmap_item *rmap_item;
1589 struct hlist_node *hlist;
1590 unsigned int mapcount = page_mapcount(page);
1591 int referenced = 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001592 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001593
1594 VM_BUG_ON(!PageKsm(page));
1595 VM_BUG_ON(!PageLocked(page));
1596
1597 stable_node = page_stable_node(page);
1598 if (!stable_node)
1599 return 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001600again:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001601 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001602 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001603 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001604 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001605
Rik van Rielcba48b92010-08-09 17:18:38 -07001606 anon_vma_lock(anon_vma);
Rik van Riel5beb4932010-03-05 13:42:07 -08001607 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1608 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001609 if (rmap_item->address < vma->vm_start ||
1610 rmap_item->address >= vma->vm_end)
1611 continue;
1612 /*
1613 * Initially we examine only the vma which covers this
1614 * rmap_item; but later, if there is still work to do,
1615 * we examine covering vmas in other mms: in case they
1616 * were forked from the original since ksmd passed.
1617 */
1618 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1619 continue;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001620
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001621 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1622 continue;
1623
1624 referenced += page_referenced_one(page, vma,
Hugh Dickins5ad64682009-12-14 17:59:24 -08001625 rmap_item->address, &mapcount, vm_flags);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001626 if (!search_new_forks || !mapcount)
1627 break;
1628 }
Rik van Rielcba48b92010-08-09 17:18:38 -07001629 anon_vma_unlock(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001630 if (!mapcount)
1631 goto out;
1632 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001633 if (!search_new_forks++)
1634 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001635out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001636 return referenced;
1637}
1638
1639int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1640{
1641 struct stable_node *stable_node;
1642 struct hlist_node *hlist;
1643 struct rmap_item *rmap_item;
1644 int ret = SWAP_AGAIN;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001645 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001646
1647 VM_BUG_ON(!PageKsm(page));
1648 VM_BUG_ON(!PageLocked(page));
1649
1650 stable_node = page_stable_node(page);
1651 if (!stable_node)
1652 return SWAP_FAIL;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001653again:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001654 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001655 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001656 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001657 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001658
Rik van Rielcba48b92010-08-09 17:18:38 -07001659 anon_vma_lock(anon_vma);
Rik van Riel5beb4932010-03-05 13:42:07 -08001660 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1661 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001662 if (rmap_item->address < vma->vm_start ||
1663 rmap_item->address >= vma->vm_end)
1664 continue;
1665 /*
1666 * Initially we examine only the vma which covers this
1667 * rmap_item; but later, if there is still work to do,
1668 * we examine covering vmas in other mms: in case they
1669 * were forked from the original since ksmd passed.
1670 */
1671 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1672 continue;
1673
1674 ret = try_to_unmap_one(page, vma,
1675 rmap_item->address, flags);
1676 if (ret != SWAP_AGAIN || !page_mapped(page)) {
Rik van Rielcba48b92010-08-09 17:18:38 -07001677 anon_vma_unlock(anon_vma);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001678 goto out;
1679 }
1680 }
Rik van Rielcba48b92010-08-09 17:18:38 -07001681 anon_vma_unlock(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001682 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001683 if (!search_new_forks++)
1684 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001685out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001686 return ret;
1687}
1688
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001689#ifdef CONFIG_MIGRATION
1690int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1691 struct vm_area_struct *, unsigned long, void *), void *arg)
1692{
1693 struct stable_node *stable_node;
1694 struct hlist_node *hlist;
1695 struct rmap_item *rmap_item;
1696 int ret = SWAP_AGAIN;
1697 int search_new_forks = 0;
1698
1699 VM_BUG_ON(!PageKsm(page));
1700 VM_BUG_ON(!PageLocked(page));
1701
1702 stable_node = page_stable_node(page);
1703 if (!stable_node)
1704 return ret;
1705again:
1706 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1707 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001708 struct anon_vma_chain *vmac;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001709 struct vm_area_struct *vma;
1710
Rik van Rielcba48b92010-08-09 17:18:38 -07001711 anon_vma_lock(anon_vma);
Rik van Riel5beb4932010-03-05 13:42:07 -08001712 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1713 vma = vmac->vma;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001714 if (rmap_item->address < vma->vm_start ||
1715 rmap_item->address >= vma->vm_end)
1716 continue;
1717 /*
1718 * Initially we examine only the vma which covers this
1719 * rmap_item; but later, if there is still work to do,
1720 * we examine covering vmas in other mms: in case they
1721 * were forked from the original since ksmd passed.
1722 */
1723 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1724 continue;
1725
1726 ret = rmap_one(page, vma, rmap_item->address, arg);
1727 if (ret != SWAP_AGAIN) {
Rik van Rielcba48b92010-08-09 17:18:38 -07001728 anon_vma_unlock(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001729 goto out;
1730 }
1731 }
Rik van Rielcba48b92010-08-09 17:18:38 -07001732 anon_vma_unlock(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001733 }
1734 if (!search_new_forks++)
1735 goto again;
1736out:
1737 return ret;
1738}
1739
1740void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1741{
1742 struct stable_node *stable_node;
1743
1744 VM_BUG_ON(!PageLocked(oldpage));
1745 VM_BUG_ON(!PageLocked(newpage));
1746 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1747
1748 stable_node = page_stable_node(newpage);
1749 if (stable_node) {
Hugh Dickins62b61f62009-12-14 17:59:33 -08001750 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1751 stable_node->kpfn = page_to_pfn(newpage);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001752 }
1753}
1754#endif /* CONFIG_MIGRATION */
1755
Hugh Dickins62b61f62009-12-14 17:59:33 -08001756#ifdef CONFIG_MEMORY_HOTREMOVE
1757static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1758 unsigned long end_pfn)
1759{
1760 struct rb_node *node;
1761
1762 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1763 struct stable_node *stable_node;
1764
1765 stable_node = rb_entry(node, struct stable_node, node);
1766 if (stable_node->kpfn >= start_pfn &&
1767 stable_node->kpfn < end_pfn)
1768 return stable_node;
1769 }
1770 return NULL;
1771}
1772
1773static int ksm_memory_callback(struct notifier_block *self,
1774 unsigned long action, void *arg)
1775{
1776 struct memory_notify *mn = arg;
1777 struct stable_node *stable_node;
1778
1779 switch (action) {
1780 case MEM_GOING_OFFLINE:
1781 /*
1782 * Keep it very simple for now: just lock out ksmd and
1783 * MADV_UNMERGEABLE while any memory is going offline.
KOSAKI Motohiroa0b0f582010-12-02 14:31:20 -08001784 * mutex_lock_nested() is necessary because lockdep was alarmed
1785 * that here we take ksm_thread_mutex inside notifier chain
1786 * mutex, and later take notifier chain mutex inside
1787 * ksm_thread_mutex to unlock it. But that's safe because both
1788 * are inside mem_hotplug_mutex.
Hugh Dickins62b61f62009-12-14 17:59:33 -08001789 */
KOSAKI Motohiroa0b0f582010-12-02 14:31:20 -08001790 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001791 break;
1792
1793 case MEM_OFFLINE:
1794 /*
1795 * Most of the work is done by page migration; but there might
1796 * be a few stable_nodes left over, still pointing to struct
1797 * pages which have been offlined: prune those from the tree.
1798 */
1799 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1800 mn->start_pfn + mn->nr_pages)) != NULL)
1801 remove_node_from_stable_tree(stable_node);
1802 /* fallthrough */
1803
1804 case MEM_CANCEL_OFFLINE:
1805 mutex_unlock(&ksm_thread_mutex);
1806 break;
1807 }
1808 return NOTIFY_OK;
1809}
1810#endif /* CONFIG_MEMORY_HOTREMOVE */
1811
Hugh Dickins2ffd8672009-09-21 17:02:23 -07001812#ifdef CONFIG_SYSFS
1813/*
1814 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1815 */
1816
Izik Eidus31dbd012009-09-21 17:02:03 -07001817#define KSM_ATTR_RO(_name) \
1818 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1819#define KSM_ATTR(_name) \
1820 static struct kobj_attribute _name##_attr = \
1821 __ATTR(_name, 0644, _name##_show, _name##_store)
1822
1823static ssize_t sleep_millisecs_show(struct kobject *kobj,
1824 struct kobj_attribute *attr, char *buf)
1825{
1826 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1827}
1828
1829static ssize_t sleep_millisecs_store(struct kobject *kobj,
1830 struct kobj_attribute *attr,
1831 const char *buf, size_t count)
1832{
1833 unsigned long msecs;
1834 int err;
1835
1836 err = strict_strtoul(buf, 10, &msecs);
1837 if (err || msecs > UINT_MAX)
1838 return -EINVAL;
1839
1840 ksm_thread_sleep_millisecs = msecs;
1841
1842 return count;
1843}
1844KSM_ATTR(sleep_millisecs);
1845
1846static ssize_t pages_to_scan_show(struct kobject *kobj,
1847 struct kobj_attribute *attr, char *buf)
1848{
1849 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1850}
1851
1852static ssize_t pages_to_scan_store(struct kobject *kobj,
1853 struct kobj_attribute *attr,
1854 const char *buf, size_t count)
1855{
1856 int err;
1857 unsigned long nr_pages;
1858
1859 err = strict_strtoul(buf, 10, &nr_pages);
1860 if (err || nr_pages > UINT_MAX)
1861 return -EINVAL;
1862
1863 ksm_thread_pages_to_scan = nr_pages;
1864
1865 return count;
1866}
1867KSM_ATTR(pages_to_scan);
1868
1869static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1870 char *buf)
1871{
1872 return sprintf(buf, "%u\n", ksm_run);
1873}
1874
1875static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1876 const char *buf, size_t count)
1877{
1878 int err;
1879 unsigned long flags;
1880
1881 err = strict_strtoul(buf, 10, &flags);
1882 if (err || flags > UINT_MAX)
1883 return -EINVAL;
1884 if (flags > KSM_RUN_UNMERGE)
1885 return -EINVAL;
1886
1887 /*
1888 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1889 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
Hugh Dickinsd0f209f2009-12-14 17:59:34 -08001890 * breaking COW to free the pages_shared (but leaves mm_slots
1891 * on the list for when ksmd may be set running again).
Izik Eidus31dbd012009-09-21 17:02:03 -07001892 */
1893
1894 mutex_lock(&ksm_thread_mutex);
1895 if (ksm_run != flags) {
1896 ksm_run = flags;
Hugh Dickinsd952b792009-09-21 17:02:16 -07001897 if (flags & KSM_RUN_UNMERGE) {
David Rientjes72788c32011-05-24 17:11:40 -07001898 int oom_score_adj;
1899
1900 oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
Hugh Dickinsd952b792009-09-21 17:02:16 -07001901 err = unmerge_and_remove_all_rmap_items();
David Rientjes72788c32011-05-24 17:11:40 -07001902 test_set_oom_score_adj(oom_score_adj);
Hugh Dickinsd952b792009-09-21 17:02:16 -07001903 if (err) {
1904 ksm_run = KSM_RUN_STOP;
1905 count = err;
1906 }
1907 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001908 }
1909 mutex_unlock(&ksm_thread_mutex);
1910
1911 if (flags & KSM_RUN_MERGE)
1912 wake_up_interruptible(&ksm_thread_wait);
1913
1914 return count;
1915}
1916KSM_ATTR(run);
1917
Hugh Dickinsb4028262009-09-21 17:02:09 -07001918static ssize_t pages_shared_show(struct kobject *kobj,
1919 struct kobj_attribute *attr, char *buf)
1920{
1921 return sprintf(buf, "%lu\n", ksm_pages_shared);
1922}
1923KSM_ATTR_RO(pages_shared);
1924
1925static ssize_t pages_sharing_show(struct kobject *kobj,
1926 struct kobj_attribute *attr, char *buf)
1927{
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001928 return sprintf(buf, "%lu\n", ksm_pages_sharing);
Hugh Dickinsb4028262009-09-21 17:02:09 -07001929}
1930KSM_ATTR_RO(pages_sharing);
1931
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001932static ssize_t pages_unshared_show(struct kobject *kobj,
1933 struct kobj_attribute *attr, char *buf)
1934{
1935 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1936}
1937KSM_ATTR_RO(pages_unshared);
1938
1939static ssize_t pages_volatile_show(struct kobject *kobj,
1940 struct kobj_attribute *attr, char *buf)
1941{
1942 long ksm_pages_volatile;
1943
1944 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1945 - ksm_pages_sharing - ksm_pages_unshared;
1946 /*
1947 * It was not worth any locking to calculate that statistic,
1948 * but it might therefore sometimes be negative: conceal that.
1949 */
1950 if (ksm_pages_volatile < 0)
1951 ksm_pages_volatile = 0;
1952 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1953}
1954KSM_ATTR_RO(pages_volatile);
1955
1956static ssize_t full_scans_show(struct kobject *kobj,
1957 struct kobj_attribute *attr, char *buf)
1958{
1959 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1960}
1961KSM_ATTR_RO(full_scans);
1962
Izik Eidus31dbd012009-09-21 17:02:03 -07001963static struct attribute *ksm_attrs[] = {
1964 &sleep_millisecs_attr.attr,
1965 &pages_to_scan_attr.attr,
1966 &run_attr.attr,
Hugh Dickinsb4028262009-09-21 17:02:09 -07001967 &pages_shared_attr.attr,
1968 &pages_sharing_attr.attr,
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001969 &pages_unshared_attr.attr,
1970 &pages_volatile_attr.attr,
1971 &full_scans_attr.attr,
Izik Eidus31dbd012009-09-21 17:02:03 -07001972 NULL,
1973};
1974
1975static struct attribute_group ksm_attr_group = {
1976 .attrs = ksm_attrs,
1977 .name = "ksm",
1978};
Hugh Dickins2ffd8672009-09-21 17:02:23 -07001979#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07001980
1981static int __init ksm_init(void)
1982{
1983 struct task_struct *ksm_thread;
1984 int err;
1985
1986 err = ksm_slab_init();
1987 if (err)
1988 goto out;
1989
Izik Eidus31dbd012009-09-21 17:02:03 -07001990 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1991 if (IS_ERR(ksm_thread)) {
1992 printk(KERN_ERR "ksm: creating kthread failed\n");
1993 err = PTR_ERR(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07001994 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07001995 }
1996
Hugh Dickins2ffd8672009-09-21 17:02:23 -07001997#ifdef CONFIG_SYSFS
Izik Eidus31dbd012009-09-21 17:02:03 -07001998 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1999 if (err) {
2000 printk(KERN_ERR "ksm: register sysfs failed\n");
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002001 kthread_stop(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07002002 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07002003 }
Hugh Dickinsc73602a2009-10-07 16:32:22 -07002004#else
2005 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2006
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002007#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07002008
Hugh Dickins62b61f62009-12-14 17:59:33 -08002009#ifdef CONFIG_MEMORY_HOTREMOVE
2010 /*
2011 * Choose a high priority since the callback takes ksm_thread_mutex:
2012 * later callbacks could only be taking locks which nest within that.
2013 */
2014 hotplug_memory_notifier(ksm_memory_callback, 100);
2015#endif
Izik Eidus31dbd012009-09-21 17:02:03 -07002016 return 0;
2017
Lai Jiangshand9f89842010-08-09 17:20:02 -07002018out_free:
Izik Eidus31dbd012009-09-21 17:02:03 -07002019 ksm_slab_free();
2020out:
2021 return err;
2022}
2023module_init(ksm_init)