blob: b6afe0c440d8b3e500f4a09e2875491c7d70199a [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>
Sasha Levin4ca3a692013-02-22 16:32:28 -080036#include <linux/hashtable.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>
Petr Holasek90bd6fd2013-02-22 16:35:00 -080039#include <linux/numa.h>
Hugh Dickinsf8af4da2009-09-21 17:01:57 -070040
Izik Eidus31dbd012009-09-21 17:02:03 -070041#include <asm/tlbflush.h>
Hugh Dickins73848b42009-12-14 17:59:22 -080042#include "internal.h"
Izik Eidus31dbd012009-09-21 17:02:03 -070043
Hugh Dickinse850dcf2013-02-22 16:35:03 -080044#ifdef CONFIG_NUMA
45#define NUMA(x) (x)
46#define DO_NUMA(x) do { (x); } while (0)
47#else
48#define NUMA(x) (0)
49#define DO_NUMA(x) do { } while (0)
50#endif
51
Izik Eidus31dbd012009-09-21 17:02:03 -070052/*
53 * A few notes about the KSM scanning process,
54 * to make it easier to understand the data structures below:
55 *
56 * In order to reduce excessive scanning, KSM sorts the memory pages by their
57 * contents into a data structure that holds pointers to the pages' locations.
58 *
59 * Since the contents of the pages may change at any moment, KSM cannot just
60 * insert the pages into a normal sorted tree and expect it to find anything.
61 * Therefore KSM uses two data structures - the stable and the unstable tree.
62 *
63 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
64 * by their contents. Because each such page is write-protected, searching on
65 * this tree is fully assured to be working (except when pages are unmapped),
66 * and therefore this tree is called the stable tree.
67 *
68 * In addition to the stable tree, KSM uses a second data structure called the
69 * unstable tree: this tree holds pointers to pages which have been found to
70 * be "unchanged for a period of time". The unstable tree sorts these pages
71 * by their contents, but since they are not write-protected, KSM cannot rely
72 * upon the unstable tree to work correctly - the unstable tree is liable to
73 * be corrupted as its contents are modified, and so it is called unstable.
74 *
75 * KSM solves this problem by several techniques:
76 *
77 * 1) The unstable tree is flushed every time KSM completes scanning all
78 * memory areas, and then the tree is rebuilt again from the beginning.
79 * 2) KSM will only insert into the unstable tree, pages whose hash value
80 * has not changed since the previous scan of all memory areas.
81 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
82 * colors of the nodes and not on their contents, assuring that even when
83 * the tree gets "corrupted" it won't get out of balance, so scanning time
84 * remains the same (also, searching and inserting nodes in an rbtree uses
85 * the same algorithm, so we have no overhead when we flush and rebuild).
86 * 4) KSM never flushes the stable tree, which means that even if it were to
87 * take 10 attempts to find a page in the unstable tree, once it is found,
88 * it is secured in the stable tree. (When we scan a new page, we first
89 * compare it against the stable tree, and then against the unstable tree.)
Hugh Dickins8fdb3db2013-02-22 16:36:03 -080090 *
91 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
92 * stable trees and multiple unstable trees: one of each for each NUMA node.
Izik Eidus31dbd012009-09-21 17:02:03 -070093 */
94
95/**
96 * struct mm_slot - ksm information per mm that is being scanned
97 * @link: link to the mm_slots hash list
98 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
Hugh Dickins6514d512009-12-14 17:59:19 -080099 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
Izik Eidus31dbd012009-09-21 17:02:03 -0700100 * @mm: the mm that this information is valid for
101 */
102struct mm_slot {
103 struct hlist_node link;
104 struct list_head mm_list;
Hugh Dickins6514d512009-12-14 17:59:19 -0800105 struct rmap_item *rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700106 struct mm_struct *mm;
107};
108
109/**
110 * struct ksm_scan - cursor for scanning
111 * @mm_slot: the current mm_slot we are scanning
112 * @address: the next address inside that to be scanned
Hugh Dickins6514d512009-12-14 17:59:19 -0800113 * @rmap_list: link to the next rmap to be scanned in the rmap_list
Izik Eidus31dbd012009-09-21 17:02:03 -0700114 * @seqnr: count of completed full scans (needed when removing unstable node)
115 *
116 * There is only the one ksm_scan instance of this cursor structure.
117 */
118struct ksm_scan {
119 struct mm_slot *mm_slot;
120 unsigned long address;
Hugh Dickins6514d512009-12-14 17:59:19 -0800121 struct rmap_item **rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700122 unsigned long seqnr;
123};
124
125/**
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800126 * struct stable_node - node of the stable rbtree
127 * @node: rb node of this ksm page in the stable tree
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800128 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129 * @list: linked into migrate_nodes, pending placement in the proper node tree
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800130 * @hlist: hlist head of rmap_items using this ksm page
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800131 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
132 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800133 */
134struct stable_node {
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800135 union {
136 struct rb_node node; /* when node of stable tree */
137 struct { /* when listed for migration */
138 struct list_head *head;
139 struct list_head list;
140 };
141 };
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800142 struct hlist_head hlist;
Hugh Dickins62b61f62009-12-14 17:59:33 -0800143 unsigned long kpfn;
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800144#ifdef CONFIG_NUMA
145 int nid;
146#endif
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800147};
148
149/**
Izik Eidus31dbd012009-09-21 17:02:03 -0700150 * struct rmap_item - reverse mapping item for virtual addresses
Hugh Dickins6514d512009-12-14 17:59:19 -0800151 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
Hugh Dickinsdb114b82009-12-14 17:59:25 -0800152 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
Hugh Dickinsbc566202013-02-22 16:36:06 -0800153 * @nid: NUMA node id of unstable tree in which linked (may not match page)
Izik Eidus31dbd012009-09-21 17:02:03 -0700154 * @mm: the memory structure this rmap_item is pointing into
155 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
156 * @oldchecksum: previous checksum of the page at that virtual address
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800157 * @node: rb node of this rmap_item in the unstable tree
158 * @head: pointer to stable_node heading this list in the stable tree
159 * @hlist: link into hlist of rmap_items hanging off that stable_node
Izik Eidus31dbd012009-09-21 17:02:03 -0700160 */
161struct rmap_item {
Hugh Dickins6514d512009-12-14 17:59:19 -0800162 struct rmap_item *rmap_list;
Hugh Dickinsbc566202013-02-22 16:36:06 -0800163 union {
164 struct anon_vma *anon_vma; /* when stable */
165#ifdef CONFIG_NUMA
166 int nid; /* when node of unstable tree */
167#endif
168 };
Izik Eidus31dbd012009-09-21 17:02:03 -0700169 struct mm_struct *mm;
170 unsigned long address; /* + low bits used for flags below */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800171 unsigned int oldchecksum; /* when unstable */
Izik Eidus31dbd012009-09-21 17:02:03 -0700172 union {
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800173 struct rb_node node; /* when node of unstable tree */
174 struct { /* when listed from stable tree */
175 struct stable_node *head;
176 struct hlist_node hlist;
177 };
Izik Eidus31dbd012009-09-21 17:02:03 -0700178 };
179};
180
181#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800182#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
183#define STABLE_FLAG 0x200 /* is listed from the stable tree */
Izik Eidus31dbd012009-09-21 17:02:03 -0700184
185/* The stable and unstable tree heads */
Hugh Dickinsef53d162013-02-22 16:36:12 -0800186static struct rb_root one_stable_tree[1] = { RB_ROOT };
187static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188static struct rb_root *root_stable_tree = one_stable_tree;
189static struct rb_root *root_unstable_tree = one_unstable_tree;
Izik Eidus31dbd012009-09-21 17:02:03 -0700190
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800191/* Recently migrated nodes of stable tree, pending proper placement */
192static LIST_HEAD(migrate_nodes);
193
Sasha Levin4ca3a692013-02-22 16:32:28 -0800194#define MM_SLOTS_HASH_BITS 10
195static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
Izik Eidus31dbd012009-09-21 17:02:03 -0700196
197static struct mm_slot ksm_mm_head = {
198 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
199};
200static struct ksm_scan ksm_scan = {
201 .mm_slot = &ksm_mm_head,
202};
203
204static struct kmem_cache *rmap_item_cache;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800205static struct kmem_cache *stable_node_cache;
Izik Eidus31dbd012009-09-21 17:02:03 -0700206static struct kmem_cache *mm_slot_cache;
207
208/* The number of nodes in the stable tree */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700209static unsigned long ksm_pages_shared;
Izik Eidus31dbd012009-09-21 17:02:03 -0700210
Hugh Dickinse178dfd2009-09-21 17:02:10 -0700211/* The number of page slots additionally sharing those nodes */
Hugh Dickinsb4028262009-09-21 17:02:09 -0700212static unsigned long ksm_pages_sharing;
Izik Eidus31dbd012009-09-21 17:02:03 -0700213
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700214/* The number of nodes in the unstable tree */
215static unsigned long ksm_pages_unshared;
216
217/* The number of rmap_items in use: to calculate pages_volatile */
218static unsigned long ksm_rmap_items;
219
Izik Eidus31dbd012009-09-21 17:02:03 -0700220/* Number of pages ksmd should scan in one batch */
Izik Eidus2c6854f2009-09-23 15:56:04 -0700221static unsigned int ksm_thread_pages_to_scan = 100;
Izik Eidus31dbd012009-09-21 17:02:03 -0700222
223/* Milliseconds ksmd should sleep between batches */
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700224static unsigned int ksm_thread_sleep_millisecs = 20;
Izik Eidus31dbd012009-09-21 17:02:03 -0700225
Hugh Dickinse850dcf2013-02-22 16:35:03 -0800226#ifdef CONFIG_NUMA
Petr Holasek90bd6fd2013-02-22 16:35:00 -0800227/* Zeroed when merging across nodes is not allowed */
228static unsigned int ksm_merge_across_nodes = 1;
Hugh Dickinsef53d162013-02-22 16:36:12 -0800229static int ksm_nr_node_ids = 1;
Hugh Dickinse850dcf2013-02-22 16:35:03 -0800230#else
231#define ksm_merge_across_nodes 1U
Hugh Dickinsef53d162013-02-22 16:36:12 -0800232#define ksm_nr_node_ids 1
Hugh Dickinse850dcf2013-02-22 16:35:03 -0800233#endif
Petr Holasek90bd6fd2013-02-22 16:35:00 -0800234
Izik Eidus31dbd012009-09-21 17:02:03 -0700235#define KSM_RUN_STOP 0
236#define KSM_RUN_MERGE 1
237#define KSM_RUN_UNMERGE 2
Hugh Dickinsef4d43a2013-02-22 16:35:16 -0800238#define KSM_RUN_OFFLINE 4
239static unsigned long ksm_run = KSM_RUN_STOP;
240static void wait_while_offlining(void);
Izik Eidus31dbd012009-09-21 17:02:03 -0700241
242static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243static DEFINE_MUTEX(ksm_thread_mutex);
244static DEFINE_SPINLOCK(ksm_mmlist_lock);
245
246#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247 sizeof(struct __struct), __alignof__(struct __struct),\
248 (__flags), NULL)
249
250static int __init ksm_slab_init(void)
251{
252 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
253 if (!rmap_item_cache)
254 goto out;
255
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800256 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257 if (!stable_node_cache)
258 goto out_free1;
259
Izik Eidus31dbd012009-09-21 17:02:03 -0700260 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261 if (!mm_slot_cache)
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800262 goto out_free2;
Izik Eidus31dbd012009-09-21 17:02:03 -0700263
264 return 0;
265
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800266out_free2:
267 kmem_cache_destroy(stable_node_cache);
268out_free1:
Izik Eidus31dbd012009-09-21 17:02:03 -0700269 kmem_cache_destroy(rmap_item_cache);
270out:
271 return -ENOMEM;
272}
273
274static void __init ksm_slab_free(void)
275{
276 kmem_cache_destroy(mm_slot_cache);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800277 kmem_cache_destroy(stable_node_cache);
Izik Eidus31dbd012009-09-21 17:02:03 -0700278 kmem_cache_destroy(rmap_item_cache);
279 mm_slot_cache = NULL;
280}
281
282static inline struct rmap_item *alloc_rmap_item(void)
283{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700284 struct rmap_item *rmap_item;
285
286 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
287 if (rmap_item)
288 ksm_rmap_items++;
289 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -0700290}
291
292static inline void free_rmap_item(struct rmap_item *rmap_item)
293{
Hugh Dickins473b0ce2009-09-21 17:02:11 -0700294 ksm_rmap_items--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700295 rmap_item->mm = NULL; /* debug safety */
296 kmem_cache_free(rmap_item_cache, rmap_item);
297}
298
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800299static inline struct stable_node *alloc_stable_node(void)
300{
301 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
302}
303
304static inline void free_stable_node(struct stable_node *stable_node)
305{
306 kmem_cache_free(stable_node_cache, stable_node);
307}
308
Izik Eidus31dbd012009-09-21 17:02:03 -0700309static inline struct mm_slot *alloc_mm_slot(void)
310{
311 if (!mm_slot_cache) /* initialization failed */
312 return NULL;
313 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
314}
315
316static inline void free_mm_slot(struct mm_slot *mm_slot)
317{
318 kmem_cache_free(mm_slot_cache, mm_slot);
319}
320
Izik Eidus31dbd012009-09-21 17:02:03 -0700321static struct mm_slot *get_mm_slot(struct mm_struct *mm)
322{
Sasha Levin4ca3a692013-02-22 16:32:28 -0800323 struct mm_slot *slot;
Izik Eidus31dbd012009-09-21 17:02:03 -0700324
Sasha Levinb67bfe02013-02-27 17:06:00 -0800325 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
Sasha Levin4ca3a692013-02-22 16:32:28 -0800326 if (slot->mm == mm)
327 return slot;
328
Izik Eidus31dbd012009-09-21 17:02:03 -0700329 return NULL;
330}
331
332static void insert_to_mm_slots_hash(struct mm_struct *mm,
333 struct mm_slot *mm_slot)
334{
Izik Eidus31dbd012009-09-21 17:02:03 -0700335 mm_slot->mm = mm;
Sasha Levin4ca3a692013-02-22 16:32:28 -0800336 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
Izik Eidus31dbd012009-09-21 17:02:03 -0700337}
338
Izik Eidus31dbd012009-09-21 17:02:03 -0700339/*
Hugh Dickinsa913e182009-09-21 17:02:26 -0700340 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
341 * page tables after it has passed through ksm_exit() - which, if necessary,
342 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
343 * a special flag: they can just back out as soon as mm_users goes to zero.
344 * ksm_test_exit() is used throughout to make this test for exit: in some
345 * places for correctness, in some places just to avoid unnecessary work.
346 */
347static inline bool ksm_test_exit(struct mm_struct *mm)
348{
349 return atomic_read(&mm->mm_users) == 0;
350}
351
352/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700353 * We use break_ksm to break COW on a ksm page: it's a stripped down
354 *
355 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
356 * put_page(page);
357 *
358 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
359 * in case the application has unmapped and remapped mm,addr meanwhile.
360 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
361 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
362 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700363static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
Izik Eidus31dbd012009-09-21 17:02:03 -0700364{
365 struct page *page;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700366 int ret = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700367
368 do {
369 cond_resched();
Hugh Dickins5117b3b2013-02-22 16:36:07 -0800370 page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
Dan Carpenter22eccdd2010-04-23 13:18:10 -0400371 if (IS_ERR_OR_NULL(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700372 break;
373 if (PageKsm(page))
374 ret = handle_mm_fault(vma->vm_mm, vma, addr,
375 FAULT_FLAG_WRITE);
376 else
377 ret = VM_FAULT_WRITE;
378 put_page(page);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700379 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
380 /*
381 * We must loop because handle_mm_fault() may back out if there's
382 * any difficulty e.g. if pte accessed bit gets updated concurrently.
383 *
384 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
385 * COW has been broken, even if the vma does not permit VM_WRITE;
386 * but note that a concurrent fault might break PageKsm for us.
387 *
388 * VM_FAULT_SIGBUS could occur if we race with truncation of the
389 * backing file, which also invalidates anonymous pages: that's
390 * okay, that truncation will have unmapped the PageKsm for us.
391 *
392 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
393 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
394 * current task has TIF_MEMDIE set, and will be OOM killed on return
395 * to user; and ksmd, having no mm, would never be chosen for that.
396 *
397 * But if the mm is in a limited mem_cgroup, then the fault may fail
398 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
399 * even ksmd can fail in this way - though it's usually breaking ksm
400 * just to undo a merge it made a moment before, so unlikely to oom.
401 *
402 * That's a pity: we might therefore have more kernel pages allocated
403 * than we're counting as nodes in the stable tree; but ksm_do_scan
404 * will retry to break_cow on each pass, so should recover the page
405 * in due course. The important thing is to not let VM_MERGEABLE
406 * be cleared while any such pages might remain in the area.
407 */
408 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700409}
410
Bob Liuef694222012-03-21 16:34:11 -0700411static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
412 unsigned long addr)
413{
414 struct vm_area_struct *vma;
415 if (ksm_test_exit(mm))
416 return NULL;
417 vma = find_vma(mm, addr);
418 if (!vma || vma->vm_start > addr)
419 return NULL;
420 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
421 return NULL;
422 return vma;
423}
424
Hugh Dickins8dd35572009-12-14 17:59:18 -0800425static void break_cow(struct rmap_item *rmap_item)
Izik Eidus31dbd012009-09-21 17:02:03 -0700426{
Hugh Dickins8dd35572009-12-14 17:59:18 -0800427 struct mm_struct *mm = rmap_item->mm;
428 unsigned long addr = rmap_item->address;
Izik Eidus31dbd012009-09-21 17:02:03 -0700429 struct vm_area_struct *vma;
430
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800431 /*
432 * It is not an accident that whenever we want to break COW
433 * to undo, we also need to drop a reference to the anon_vma.
434 */
Peter Zijlstra9e601092011-03-22 16:32:46 -0700435 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800436
Hugh Dickins81464e302009-09-21 17:02:15 -0700437 down_read(&mm->mmap_sem);
Bob Liuef694222012-03-21 16:34:11 -0700438 vma = find_mergeable_vma(mm, addr);
439 if (vma)
440 break_ksm(vma, addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700441 up_read(&mm->mmap_sem);
442}
443
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800444static struct page *page_trans_compound_anon(struct page *page)
445{
446 if (PageTransCompound(page)) {
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800447 struct page *head = compound_trans_head(page);
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800448 /*
Andrea Arcangeli22e5c472011-01-13 15:47:20 -0800449 * head may actually be splitted and freed from under
450 * us but it's ok here.
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800451 */
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800452 if (PageAnon(head))
453 return head;
454 }
455 return NULL;
456}
457
Izik Eidus31dbd012009-09-21 17:02:03 -0700458static struct page *get_mergeable_page(struct rmap_item *rmap_item)
459{
460 struct mm_struct *mm = rmap_item->mm;
461 unsigned long addr = rmap_item->address;
462 struct vm_area_struct *vma;
463 struct page *page;
464
465 down_read(&mm->mmap_sem);
Bob Liuef694222012-03-21 16:34:11 -0700466 vma = find_mergeable_vma(mm, addr);
467 if (!vma)
Izik Eidus31dbd012009-09-21 17:02:03 -0700468 goto out;
469
470 page = follow_page(vma, addr, FOLL_GET);
Dan Carpenter22eccdd2010-04-23 13:18:10 -0400471 if (IS_ERR_OR_NULL(page))
Izik Eidus31dbd012009-09-21 17:02:03 -0700472 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800473 if (PageAnon(page) || page_trans_compound_anon(page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700474 flush_anon_page(vma, page, addr);
475 flush_dcache_page(page);
476 } else {
477 put_page(page);
478out: page = NULL;
479 }
480 up_read(&mm->mmap_sem);
481 return page;
482}
483
Petr Holasek90bd6fd2013-02-22 16:35:00 -0800484/*
485 * This helper is used for getting right index into array of tree roots.
486 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
487 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
488 * every node has its own stable and unstable tree.
489 */
490static inline int get_kpfn_nid(unsigned long kpfn)
491{
Hugh Dickinsd8fc16a2013-03-08 12:43:34 -0800492 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
Petr Holasek90bd6fd2013-02-22 16:35:00 -0800493}
494
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800495static void remove_node_from_stable_tree(struct stable_node *stable_node)
496{
497 struct rmap_item *rmap_item;
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800498
Sasha Levinb67bfe02013-02-27 17:06:00 -0800499 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800500 if (rmap_item->hlist.next)
501 ksm_pages_sharing--;
502 else
503 ksm_pages_shared--;
Peter Zijlstra9e601092011-03-22 16:32:46 -0700504 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800505 rmap_item->address &= PAGE_MASK;
506 cond_resched();
507 }
508
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800509 if (stable_node->head == &migrate_nodes)
510 list_del(&stable_node->list);
511 else
512 rb_erase(&stable_node->node,
Hugh Dickinsef53d162013-02-22 16:36:12 -0800513 root_stable_tree + NUMA(stable_node->nid));
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800514 free_stable_node(stable_node);
515}
516
517/*
518 * get_ksm_page: checks if the page indicated by the stable node
519 * is still its ksm page, despite having held no reference to it.
520 * In which case we can trust the content of the page, and it
521 * returns the gotten page; but if the page has now been zapped,
522 * remove the stale node from the stable tree and return NULL.
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800523 * But beware, the stable node's page might be being migrated.
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800524 *
525 * You would expect the stable_node to hold a reference to the ksm page.
526 * But if it increments the page's count, swapping out has to wait for
527 * ksmd to come around again before it can free the page, which may take
528 * seconds or even minutes: much too unresponsive. So instead we use a
529 * "keyhole reference": access to the ksm page from the stable node peeps
530 * out through its keyhole to see if that page still holds the right key,
531 * pointing back to this stable node. This relies on freeing a PageAnon
532 * page to reset its page->mapping to NULL, and relies on no other use of
533 * a page to put something that might look like our key in page->mapping.
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800534 * is on its way to being freed; but it is an anomaly to bear in mind.
535 */
Hugh Dickins8fdb3db2013-02-22 16:36:03 -0800536static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800537{
538 struct page *page;
539 void *expected_mapping;
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800540 unsigned long kpfn;
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800541
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800542 expected_mapping = (void *)stable_node +
543 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800544again:
545 kpfn = ACCESS_ONCE(stable_node->kpfn);
546 page = pfn_to_page(kpfn);
547
548 /*
549 * page is computed from kpfn, so on most architectures reading
550 * page->mapping is naturally ordered after reading node->kpfn,
551 * but on Alpha we need to be more careful.
552 */
553 smp_read_barrier_depends();
554 if (ACCESS_ONCE(page->mapping) != expected_mapping)
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800555 goto stale;
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800556
557 /*
558 * We cannot do anything with the page while its refcount is 0.
559 * Usually 0 means free, or tail of a higher-order page: in which
560 * case this node is no longer referenced, and should be freed;
561 * however, it might mean that the page is under page_freeze_refs().
562 * The __remove_mapping() case is easy, again the node is now stale;
563 * but if page is swapcache in migrate_page_move_mapping(), it might
564 * still be our page, in which case it's essential to keep the node.
565 */
566 while (!get_page_unless_zero(page)) {
567 /*
568 * Another check for page->mapping != expected_mapping would
569 * work here too. We have chosen the !PageSwapCache test to
570 * optimize the common case, when the page is or is about to
571 * be freed: PageSwapCache is cleared (under spin_lock_irq)
572 * in the freeze_refs section of __remove_mapping(); but Anon
573 * page->mapping reset to NULL later, in free_pages_prepare().
574 */
575 if (!PageSwapCache(page))
576 goto stale;
577 cpu_relax();
578 }
579
580 if (ACCESS_ONCE(page->mapping) != expected_mapping) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800581 put_page(page);
582 goto stale;
583 }
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800584
Hugh Dickins8fdb3db2013-02-22 16:36:03 -0800585 if (lock_it) {
Hugh Dickins8aafa6a2013-02-22 16:35:06 -0800586 lock_page(page);
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800587 if (ACCESS_ONCE(page->mapping) != expected_mapping) {
Hugh Dickins8aafa6a2013-02-22 16:35:06 -0800588 unlock_page(page);
589 put_page(page);
590 goto stale;
591 }
592 }
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800593 return page;
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800594
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800595stale:
Hugh Dickinsc8d65532013-02-22 16:35:10 -0800596 /*
597 * We come here from above when page->mapping or !PageSwapCache
598 * suggests that the node is stale; but it might be under migration.
599 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
600 * before checking whether node->kpfn has been changed.
601 */
602 smp_rmb();
603 if (ACCESS_ONCE(stable_node->kpfn) != kpfn)
604 goto again;
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800605 remove_node_from_stable_tree(stable_node);
606 return NULL;
607}
608
Izik Eidus31dbd012009-09-21 17:02:03 -0700609/*
Izik Eidus31dbd012009-09-21 17:02:03 -0700610 * Removing rmap_item from stable or unstable tree.
611 * This function will clean the information from the stable/unstable tree.
612 */
613static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
614{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800615 if (rmap_item->address & STABLE_FLAG) {
616 struct stable_node *stable_node;
Hugh Dickins5ad64682009-12-14 17:59:24 -0800617 struct page *page;
Izik Eidus31dbd012009-09-21 17:02:03 -0700618
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800619 stable_node = rmap_item->head;
Hugh Dickins8aafa6a2013-02-22 16:35:06 -0800620 page = get_ksm_page(stable_node, true);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800621 if (!page)
622 goto out;
623
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800624 hlist_del(&rmap_item->hlist);
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800625 unlock_page(page);
626 put_page(page);
Hugh Dickins08beca42009-12-14 17:59:21 -0800627
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800628 if (stable_node->hlist.first)
629 ksm_pages_sharing--;
630 else
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800631 ksm_pages_shared--;
Izik Eidus31dbd012009-09-21 17:02:03 -0700632
Peter Zijlstra9e601092011-03-22 16:32:46 -0700633 put_anon_vma(rmap_item->anon_vma);
Hugh Dickins93d17712009-12-14 17:59:16 -0800634 rmap_item->address &= PAGE_MASK;
Izik Eidus31dbd012009-09-21 17:02:03 -0700635
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -0800636 } else if (rmap_item->address & UNSTABLE_FLAG) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700637 unsigned char age;
638 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -0700639 * Usually ksmd can and must skip the rb_erase, because
Izik Eidus31dbd012009-09-21 17:02:03 -0700640 * root_unstable_tree was already reset to RB_ROOT.
Hugh Dickins9ba69292009-09-21 17:02:20 -0700641 * But be careful when an mm is exiting: do the rb_erase
642 * if this rmap_item was inserted by this scan, rather
643 * than left over from before.
Izik Eidus31dbd012009-09-21 17:02:03 -0700644 */
645 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
Hugh Dickinscd551f92009-09-21 17:02:17 -0700646 BUG_ON(age > 1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700647 if (!age)
Petr Holasek90bd6fd2013-02-22 16:35:00 -0800648 rb_erase(&rmap_item->node,
Hugh Dickinsef53d162013-02-22 16:36:12 -0800649 root_unstable_tree + NUMA(rmap_item->nid));
Hugh Dickins93d17712009-12-14 17:59:16 -0800650 ksm_pages_unshared--;
651 rmap_item->address &= PAGE_MASK;
652 }
Hugh Dickins4035c07a2009-12-14 17:59:27 -0800653out:
Izik Eidus31dbd012009-09-21 17:02:03 -0700654 cond_resched(); /* we're called from many long loops */
655}
656
Izik Eidus31dbd012009-09-21 17:02:03 -0700657static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -0800658 struct rmap_item **rmap_list)
Izik Eidus31dbd012009-09-21 17:02:03 -0700659{
Hugh Dickins6514d512009-12-14 17:59:19 -0800660 while (*rmap_list) {
661 struct rmap_item *rmap_item = *rmap_list;
662 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -0700663 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -0700664 free_rmap_item(rmap_item);
665 }
666}
667
668/*
Hugh Dickinse850dcf2013-02-22 16:35:03 -0800669 * Though it's very tempting to unmerge rmap_items from stable tree rather
Izik Eidus31dbd012009-09-21 17:02:03 -0700670 * than check every pte of a given vma, the locking doesn't quite work for
671 * that - an rmap_item is assigned to the stable tree after inserting ksm
672 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
673 * rmap_items from parent to child at fork time (so as not to waste time
674 * if exit comes before the next scan reaches it).
Hugh Dickins81464e302009-09-21 17:02:15 -0700675 *
676 * Similarly, although we'd like to remove rmap_items (so updating counts
677 * and freeing memory) when unmerging an area, it's easier to leave that
678 * to the next pass of ksmd - consider, for example, how ksmd might be
679 * in cmp_and_merge_page on one of the rmap_items we would be removing.
Izik Eidus31dbd012009-09-21 17:02:03 -0700680 */
Hugh Dickinsd952b792009-09-21 17:02:16 -0700681static int unmerge_ksm_pages(struct vm_area_struct *vma,
682 unsigned long start, unsigned long end)
Izik Eidus31dbd012009-09-21 17:02:03 -0700683{
684 unsigned long addr;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700685 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700686
Hugh Dickinsd952b792009-09-21 17:02:16 -0700687 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700688 if (ksm_test_exit(vma->vm_mm))
689 break;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700690 if (signal_pending(current))
691 err = -ERESTARTSYS;
692 else
693 err = break_ksm(vma, addr);
694 }
695 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700696}
697
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700698#ifdef CONFIG_SYSFS
699/*
700 * Only called through the sysfs control interface:
701 */
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800702static int remove_stable_node(struct stable_node *stable_node)
703{
704 struct page *page;
705 int err;
706
707 page = get_ksm_page(stable_node, true);
708 if (!page) {
709 /*
710 * get_ksm_page did remove_node_from_stable_tree itself.
711 */
712 return 0;
713 }
714
Hugh Dickins8fdb3db2013-02-22 16:36:03 -0800715 if (WARN_ON_ONCE(page_mapped(page))) {
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800716 /*
Hugh Dickins8fdb3db2013-02-22 16:36:03 -0800717 * This should not happen: but if it does, just refuse to let
718 * merge_across_nodes be switched - there is no need to panic.
719 */
720 err = -EBUSY;
721 } else {
722 /*
723 * The stable node did not yet appear stale to get_ksm_page(),
724 * since that allows for an unmapped ksm page to be recognized
725 * right up until it is freed; but the node is safe to remove.
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800726 * This page might be in a pagevec waiting to be freed,
727 * or it might be PageSwapCache (perhaps under writeback),
728 * or it might have been removed from swapcache a moment ago.
729 */
730 set_page_stable_node(page, NULL);
731 remove_node_from_stable_tree(stable_node);
732 err = 0;
733 }
734
735 unlock_page(page);
736 put_page(page);
737 return err;
738}
739
740static int remove_all_stable_nodes(void)
741{
742 struct stable_node *stable_node;
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800743 struct list_head *this, *next;
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800744 int nid;
745 int err = 0;
746
Hugh Dickinsef53d162013-02-22 16:36:12 -0800747 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800748 while (root_stable_tree[nid].rb_node) {
749 stable_node = rb_entry(root_stable_tree[nid].rb_node,
750 struct stable_node, node);
751 if (remove_stable_node(stable_node)) {
752 err = -EBUSY;
753 break; /* proceed to next nid */
754 }
755 cond_resched();
756 }
757 }
Hugh Dickins4146d2d2013-02-22 16:35:11 -0800758 list_for_each_safe(this, next, &migrate_nodes) {
759 stable_node = list_entry(this, struct stable_node, list);
760 if (remove_stable_node(stable_node))
761 err = -EBUSY;
762 cond_resched();
763 }
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800764 return err;
765}
766
Hugh Dickinsd952b792009-09-21 17:02:16 -0700767static int unmerge_and_remove_all_rmap_items(void)
Izik Eidus31dbd012009-09-21 17:02:03 -0700768{
769 struct mm_slot *mm_slot;
770 struct mm_struct *mm;
771 struct vm_area_struct *vma;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700772 int err = 0;
Izik Eidus31dbd012009-09-21 17:02:03 -0700773
Hugh Dickinsd952b792009-09-21 17:02:16 -0700774 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700775 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700776 struct mm_slot, mm_list);
777 spin_unlock(&ksm_mmlist_lock);
778
Hugh Dickins9ba69292009-09-21 17:02:20 -0700779 for (mm_slot = ksm_scan.mm_slot;
780 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700781 mm = mm_slot->mm;
782 down_read(&mm->mmap_sem);
783 for (vma = mm->mmap; vma; vma = vma->vm_next) {
Hugh Dickins9ba69292009-09-21 17:02:20 -0700784 if (ksm_test_exit(mm))
785 break;
Izik Eidus31dbd012009-09-21 17:02:03 -0700786 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
787 continue;
Hugh Dickinsd952b792009-09-21 17:02:16 -0700788 err = unmerge_ksm_pages(vma,
789 vma->vm_start, vma->vm_end);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700790 if (err)
791 goto error;
Izik Eidus31dbd012009-09-21 17:02:03 -0700792 }
Hugh Dickins9ba69292009-09-21 17:02:20 -0700793
Hugh Dickins6514d512009-12-14 17:59:19 -0800794 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700795
796 spin_lock(&ksm_mmlist_lock);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700797 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
Hugh Dickinsd952b792009-09-21 17:02:16 -0700798 struct mm_slot, mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700799 if (ksm_test_exit(mm)) {
Sasha Levin4ca3a692013-02-22 16:32:28 -0800800 hash_del(&mm_slot->link);
Hugh Dickins9ba69292009-09-21 17:02:20 -0700801 list_del(&mm_slot->mm_list);
802 spin_unlock(&ksm_mmlist_lock);
803
804 free_mm_slot(mm_slot);
805 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
806 up_read(&mm->mmap_sem);
807 mmdrop(mm);
808 } else {
809 spin_unlock(&ksm_mmlist_lock);
810 up_read(&mm->mmap_sem);
811 }
Izik Eidus31dbd012009-09-21 17:02:03 -0700812 }
813
Hugh Dickinscbf86cf2013-02-22 16:35:08 -0800814 /* Clean up stable nodes, but don't worry if some are still busy */
815 remove_all_stable_nodes();
Hugh Dickinsd952b792009-09-21 17:02:16 -0700816 ksm_scan.seqnr = 0;
Hugh Dickins9ba69292009-09-21 17:02:20 -0700817 return 0;
818
819error:
820 up_read(&mm->mmap_sem);
Izik Eidus31dbd012009-09-21 17:02:03 -0700821 spin_lock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700822 ksm_scan.mm_slot = &ksm_mm_head;
Izik Eidus31dbd012009-09-21 17:02:03 -0700823 spin_unlock(&ksm_mmlist_lock);
Hugh Dickinsd952b792009-09-21 17:02:16 -0700824 return err;
Izik Eidus31dbd012009-09-21 17:02:03 -0700825}
Hugh Dickins2ffd8672009-09-21 17:02:23 -0700826#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -0700827
Izik Eidus31dbd012009-09-21 17:02:03 -0700828static u32 calc_checksum(struct page *page)
829{
830 u32 checksum;
Cong Wang9b04c5f2011-11-25 23:14:39 +0800831 void *addr = kmap_atomic(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700832 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
Cong Wang9b04c5f2011-11-25 23:14:39 +0800833 kunmap_atomic(addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700834 return checksum;
835}
836
837static int memcmp_pages(struct page *page1, struct page *page2)
838{
839 char *addr1, *addr2;
840 int ret;
841
Cong Wang9b04c5f2011-11-25 23:14:39 +0800842 addr1 = kmap_atomic(page1);
843 addr2 = kmap_atomic(page2);
Izik Eidus31dbd012009-09-21 17:02:03 -0700844 ret = memcmp(addr1, addr2, PAGE_SIZE);
Cong Wang9b04c5f2011-11-25 23:14:39 +0800845 kunmap_atomic(addr2);
846 kunmap_atomic(addr1);
Izik Eidus31dbd012009-09-21 17:02:03 -0700847 return ret;
848}
849
850static inline int pages_identical(struct page *page1, struct page *page2)
851{
852 return !memcmp_pages(page1, page2);
853}
854
855static int write_protect_page(struct vm_area_struct *vma, struct page *page,
856 pte_t *orig_pte)
857{
858 struct mm_struct *mm = vma->vm_mm;
859 unsigned long addr;
860 pte_t *ptep;
861 spinlock_t *ptl;
862 int swapped;
863 int err = -EFAULT;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700864 unsigned long mmun_start; /* For mmu_notifiers */
865 unsigned long mmun_end; /* For mmu_notifiers */
Izik Eidus31dbd012009-09-21 17:02:03 -0700866
867 addr = page_address_in_vma(page, vma);
868 if (addr == -EFAULT)
869 goto out;
870
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800871 BUG_ON(PageTransCompound(page));
Haggai Eran6bdb9132012-10-08 16:33:35 -0700872
873 mmun_start = addr;
874 mmun_end = addr + PAGE_SIZE;
875 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
876
Izik Eidus31dbd012009-09-21 17:02:03 -0700877 ptep = page_check_address(page, mm, addr, &ptl, 0);
878 if (!ptep)
Haggai Eran6bdb9132012-10-08 16:33:35 -0700879 goto out_mn;
Izik Eidus31dbd012009-09-21 17:02:03 -0700880
Hugh Dickins4e316352010-10-02 17:49:08 -0700881 if (pte_write(*ptep) || pte_dirty(*ptep)) {
Izik Eidus31dbd012009-09-21 17:02:03 -0700882 pte_t entry;
883
884 swapped = PageSwapCache(page);
885 flush_cache_page(vma, addr, page_to_pfn(page));
886 /*
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300887 * Ok this is tricky, when get_user_pages_fast() run it doesn't
Izik Eidus31dbd012009-09-21 17:02:03 -0700888 * take any lock, therefore the check that we are going to make
889 * with the pagecount against the mapcount is racey and
890 * O_DIRECT can happen right after the check.
891 * So we clear the pte and flush the tlb before the check
892 * this assure us that no O_DIRECT can happen after the check
893 * or in the middle of the check.
894 */
895 entry = ptep_clear_flush(vma, addr, ptep);
896 /*
897 * Check that no O_DIRECT or similar I/O is in progress on the
898 * page
899 */
Hugh Dickins31e855e2009-12-14 17:59:17 -0800900 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
Robin Holtcb532372010-03-23 13:35:26 -0700901 set_pte_at(mm, addr, ptep, entry);
Izik Eidus31dbd012009-09-21 17:02:03 -0700902 goto out_unlock;
903 }
Hugh Dickins4e316352010-10-02 17:49:08 -0700904 if (pte_dirty(entry))
905 set_page_dirty(page);
906 entry = pte_mkclean(pte_wrprotect(entry));
Izik Eidus31dbd012009-09-21 17:02:03 -0700907 set_pte_at_notify(mm, addr, ptep, entry);
908 }
909 *orig_pte = *ptep;
910 err = 0;
911
912out_unlock:
913 pte_unmap_unlock(ptep, ptl);
Haggai Eran6bdb9132012-10-08 16:33:35 -0700914out_mn:
915 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
Izik Eidus31dbd012009-09-21 17:02:03 -0700916out:
917 return err;
918}
919
920/**
921 * replace_page - replace page in vma by new ksm page
Hugh Dickins8dd35572009-12-14 17:59:18 -0800922 * @vma: vma that holds the pte pointing to page
923 * @page: the page we are replacing by kpage
924 * @kpage: the ksm page we replace page by
Izik Eidus31dbd012009-09-21 17:02:03 -0700925 * @orig_pte: the original value of the pte
926 *
927 * Returns 0 on success, -EFAULT on failure.
928 */
Hugh Dickins8dd35572009-12-14 17:59:18 -0800929static int replace_page(struct vm_area_struct *vma, struct page *page,
930 struct page *kpage, pte_t orig_pte)
Izik Eidus31dbd012009-09-21 17:02:03 -0700931{
932 struct mm_struct *mm = vma->vm_mm;
Izik Eidus31dbd012009-09-21 17:02:03 -0700933 pmd_t *pmd;
934 pte_t *ptep;
935 spinlock_t *ptl;
936 unsigned long addr;
Izik Eidus31dbd012009-09-21 17:02:03 -0700937 int err = -EFAULT;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700938 unsigned long mmun_start; /* For mmu_notifiers */
939 unsigned long mmun_end; /* For mmu_notifiers */
Izik Eidus31dbd012009-09-21 17:02:03 -0700940
Hugh Dickins8dd35572009-12-14 17:59:18 -0800941 addr = page_address_in_vma(page, vma);
Izik Eidus31dbd012009-09-21 17:02:03 -0700942 if (addr == -EFAULT)
943 goto out;
944
Bob Liu62190492012-12-11 16:00:37 -0800945 pmd = mm_find_pmd(mm, addr);
946 if (!pmd)
Izik Eidus31dbd012009-09-21 17:02:03 -0700947 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800948 BUG_ON(pmd_trans_huge(*pmd));
Izik Eidus31dbd012009-09-21 17:02:03 -0700949
Haggai Eran6bdb9132012-10-08 16:33:35 -0700950 mmun_start = addr;
951 mmun_end = addr + PAGE_SIZE;
952 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
953
Izik Eidus31dbd012009-09-21 17:02:03 -0700954 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
955 if (!pte_same(*ptep, orig_pte)) {
956 pte_unmap_unlock(ptep, ptl);
Haggai Eran6bdb9132012-10-08 16:33:35 -0700957 goto out_mn;
Izik Eidus31dbd012009-09-21 17:02:03 -0700958 }
959
Hugh Dickins8dd35572009-12-14 17:59:18 -0800960 get_page(kpage);
Hugh Dickins5ad64682009-12-14 17:59:24 -0800961 page_add_anon_rmap(kpage, vma, addr);
Izik Eidus31dbd012009-09-21 17:02:03 -0700962
963 flush_cache_page(vma, addr, pte_pfn(*ptep));
964 ptep_clear_flush(vma, addr, ptep);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800965 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
Izik Eidus31dbd012009-09-21 17:02:03 -0700966
Hugh Dickins8dd35572009-12-14 17:59:18 -0800967 page_remove_rmap(page);
Hugh Dickinsae52a2a2011-01-13 15:46:28 -0800968 if (!page_mapped(page))
969 try_to_free_swap(page);
Hugh Dickins8dd35572009-12-14 17:59:18 -0800970 put_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -0700971
972 pte_unmap_unlock(ptep, ptl);
973 err = 0;
Haggai Eran6bdb9132012-10-08 16:33:35 -0700974out_mn:
975 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
Izik Eidus31dbd012009-09-21 17:02:03 -0700976out:
977 return err;
978}
979
Andrea Arcangeli29ad7682011-01-13 15:47:19 -0800980static int page_trans_compound_anon_split(struct page *page)
981{
982 int ret = 0;
983 struct page *transhuge_head = page_trans_compound_anon(page);
984 if (transhuge_head) {
985 /* Get the reference on the head to split it. */
986 if (get_page_unless_zero(transhuge_head)) {
987 /*
988 * Recheck we got the reference while the head
989 * was still anonymous.
990 */
991 if (PageAnon(transhuge_head))
992 ret = split_huge_page(transhuge_head);
993 else
994 /*
995 * Retry later if split_huge_page run
996 * from under us.
997 */
998 ret = 1;
999 put_page(transhuge_head);
1000 } else
1001 /* Retry later if split_huge_page run from under us. */
1002 ret = 1;
1003 }
1004 return ret;
1005}
1006
Izik Eidus31dbd012009-09-21 17:02:03 -07001007/*
1008 * try_to_merge_one_page - take two pages and merge them into one
Hugh Dickins8dd35572009-12-14 17:59:18 -08001009 * @vma: the vma that holds the pte pointing to page
1010 * @page: the PageAnon page that we want to replace with kpage
Hugh Dickins80e148222009-12-14 17:59:29 -08001011 * @kpage: the PageKsm page that we want to map instead of page,
1012 * or NULL the first time when we want to use page as kpage.
Izik Eidus31dbd012009-09-21 17:02:03 -07001013 *
1014 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1015 */
1016static int try_to_merge_one_page(struct vm_area_struct *vma,
Hugh Dickins8dd35572009-12-14 17:59:18 -08001017 struct page *page, struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -07001018{
1019 pte_t orig_pte = __pte(0);
1020 int err = -EFAULT;
1021
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001022 if (page == kpage) /* ksm page forked */
1023 return 0;
1024
Izik Eidus31dbd012009-09-21 17:02:03 -07001025 if (!(vma->vm_flags & VM_MERGEABLE))
1026 goto out;
Andrea Arcangeli29ad7682011-01-13 15:47:19 -08001027 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
1028 goto out;
1029 BUG_ON(PageTransCompound(page));
Hugh Dickins8dd35572009-12-14 17:59:18 -08001030 if (!PageAnon(page))
Izik Eidus31dbd012009-09-21 17:02:03 -07001031 goto out;
1032
Izik Eidus31dbd012009-09-21 17:02:03 -07001033 /*
1034 * We need the page lock to read a stable PageSwapCache in
1035 * write_protect_page(). We use trylock_page() instead of
1036 * lock_page() because we don't want to wait here - we
1037 * prefer to continue scanning and merging different pages,
1038 * then come back to this page when it is unlocked.
1039 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001040 if (!trylock_page(page))
Hugh Dickins31e855e2009-12-14 17:59:17 -08001041 goto out;
Izik Eidus31dbd012009-09-21 17:02:03 -07001042 /*
1043 * If this anonymous page is mapped only here, its pte may need
1044 * to be write-protected. If it's mapped elsewhere, all of its
1045 * ptes are necessarily already write-protected. But in either
1046 * case, we need to lock and check page_count is not raised.
1047 */
Hugh Dickins80e148222009-12-14 17:59:29 -08001048 if (write_protect_page(vma, page, &orig_pte) == 0) {
1049 if (!kpage) {
1050 /*
1051 * While we hold page lock, upgrade page from
1052 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1053 * stable_tree_insert() will update stable_node.
1054 */
1055 set_page_stable_node(page, NULL);
1056 mark_page_accessed(page);
1057 err = 0;
1058 } else if (pages_identical(page, kpage))
1059 err = replace_page(vma, page, kpage, orig_pte);
1060 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001061
Hugh Dickins80e148222009-12-14 17:59:29 -08001062 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
Hugh Dickins73848b42009-12-14 17:59:22 -08001063 munlock_vma_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001064 if (!PageMlocked(kpage)) {
1065 unlock_page(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001066 lock_page(kpage);
1067 mlock_vma_page(kpage);
1068 page = kpage; /* for final unlock */
1069 }
1070 }
Hugh Dickins73848b42009-12-14 17:59:22 -08001071
Hugh Dickins8dd35572009-12-14 17:59:18 -08001072 unlock_page(page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001073out:
1074 return err;
1075}
1076
1077/*
Hugh Dickins81464e302009-09-21 17:02:15 -07001078 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1079 * but no new kernel page is allocated: kpage must already be a ksm page.
Hugh Dickins8dd35572009-12-14 17:59:18 -08001080 *
1081 * This function returns 0 if the pages were merged, -EFAULT otherwise.
Hugh Dickins81464e302009-09-21 17:02:15 -07001082 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001083static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1084 struct page *page, struct page *kpage)
Hugh Dickins81464e302009-09-21 17:02:15 -07001085{
Hugh Dickins8dd35572009-12-14 17:59:18 -08001086 struct mm_struct *mm = rmap_item->mm;
Hugh Dickins81464e302009-09-21 17:02:15 -07001087 struct vm_area_struct *vma;
1088 int err = -EFAULT;
1089
Hugh Dickins8dd35572009-12-14 17:59:18 -08001090 down_read(&mm->mmap_sem);
1091 if (ksm_test_exit(mm))
1092 goto out;
1093 vma = find_vma(mm, rmap_item->address);
1094 if (!vma || vma->vm_start > rmap_item->address)
Hugh Dickins9ba69292009-09-21 17:02:20 -07001095 goto out;
1096
Hugh Dickins8dd35572009-12-14 17:59:18 -08001097 err = try_to_merge_one_page(vma, page, kpage);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001098 if (err)
1099 goto out;
1100
Hugh Dickinsbc566202013-02-22 16:36:06 -08001101 /* Unstable nid is in union with stable anon_vma: remove first */
1102 remove_rmap_item_from_tree(rmap_item);
1103
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001104 /* Must get reference to anon_vma while still holding mmap_sem */
Peter Zijlstra9e601092011-03-22 16:32:46 -07001105 rmap_item->anon_vma = vma->anon_vma;
1106 get_anon_vma(vma->anon_vma);
Hugh Dickins81464e302009-09-21 17:02:15 -07001107out:
Hugh Dickins8dd35572009-12-14 17:59:18 -08001108 up_read(&mm->mmap_sem);
Hugh Dickins81464e302009-09-21 17:02:15 -07001109 return err;
1110}
1111
1112/*
Izik Eidus31dbd012009-09-21 17:02:03 -07001113 * try_to_merge_two_pages - take two identical pages and prepare them
1114 * to be merged into one page.
1115 *
Hugh Dickins8dd35572009-12-14 17:59:18 -08001116 * This function returns the kpage if we successfully merged two identical
1117 * pages into one ksm page, NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -07001118 *
Hugh Dickins80e148222009-12-14 17:59:29 -08001119 * Note that this function upgrades page to ksm page: if one of the pages
Izik Eidus31dbd012009-09-21 17:02:03 -07001120 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1121 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001122static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1123 struct page *page,
1124 struct rmap_item *tree_rmap_item,
1125 struct page *tree_page)
Izik Eidus31dbd012009-09-21 17:02:03 -07001126{
Hugh Dickins80e148222009-12-14 17:59:29 -08001127 int err;
Izik Eidus31dbd012009-09-21 17:02:03 -07001128
Hugh Dickins80e148222009-12-14 17:59:29 -08001129 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
Izik Eidus31dbd012009-09-21 17:02:03 -07001130 if (!err) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001131 err = try_to_merge_with_ksm_page(tree_rmap_item,
Hugh Dickins80e148222009-12-14 17:59:29 -08001132 tree_page, page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001133 /*
Hugh Dickins81464e302009-09-21 17:02:15 -07001134 * If that fails, we have a ksm page with only one pte
1135 * pointing to it: so break it.
Izik Eidus31dbd012009-09-21 17:02:03 -07001136 */
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001137 if (err)
Hugh Dickins8dd35572009-12-14 17:59:18 -08001138 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001139 }
Hugh Dickins80e148222009-12-14 17:59:29 -08001140 return err ? NULL : page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001141}
1142
1143/*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001144 * stable_tree_search - search for page inside the stable tree
Izik Eidus31dbd012009-09-21 17:02:03 -07001145 *
1146 * This function checks if there is a page inside the stable tree
1147 * with identical content to the page that we are scanning right now.
1148 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001149 * This function returns the stable tree node of identical content if found,
Izik Eidus31dbd012009-09-21 17:02:03 -07001150 * NULL otherwise.
1151 */
Hugh Dickins62b61f62009-12-14 17:59:33 -08001152static struct page *stable_tree_search(struct page *page)
Izik Eidus31dbd012009-09-21 17:02:03 -07001153{
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001154 int nid;
Hugh Dickinsef53d162013-02-22 16:36:12 -08001155 struct rb_root *root;
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001156 struct rb_node **new;
1157 struct rb_node *parent;
1158 struct stable_node *stable_node;
1159 struct stable_node *page_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001160
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001161 page_node = page_stable_node(page);
1162 if (page_node && page_node->head != &migrate_nodes) {
1163 /* ksm page forked */
Hugh Dickins08beca42009-12-14 17:59:21 -08001164 get_page(page);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001165 return page;
Hugh Dickins08beca42009-12-14 17:59:21 -08001166 }
1167
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001168 nid = get_kpfn_nid(page_to_pfn(page));
Hugh Dickinsef53d162013-02-22 16:36:12 -08001169 root = root_stable_tree + nid;
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001170again:
Hugh Dickinsef53d162013-02-22 16:36:12 -08001171 new = &root->rb_node;
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001172 parent = NULL;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001173
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001174 while (*new) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001175 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001176 int ret;
1177
Hugh Dickins08beca42009-12-14 17:59:21 -08001178 cond_resched();
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001179 stable_node = rb_entry(*new, struct stable_node, node);
Hugh Dickins8aafa6a2013-02-22 16:35:06 -08001180 tree_page = get_ksm_page(stable_node, false);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001181 if (!tree_page)
1182 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001183
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001184 ret = memcmp_pages(page, tree_page);
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001185 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001186
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001187 parent = *new;
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001188 if (ret < 0)
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001189 new = &parent->rb_left;
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001190 else if (ret > 0)
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001191 new = &parent->rb_right;
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001192 else {
1193 /*
1194 * Lock and unlock the stable_node's page (which
1195 * might already have been migrated) so that page
1196 * migration is sure to notice its raised count.
1197 * It would be more elegant to return stable_node
1198 * than kpage, but that involves more changes.
1199 */
1200 tree_page = get_ksm_page(stable_node, true);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001201 if (tree_page) {
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001202 unlock_page(tree_page);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001203 if (get_kpfn_nid(stable_node->kpfn) !=
1204 NUMA(stable_node->nid)) {
1205 put_page(tree_page);
1206 goto replace;
1207 }
1208 return tree_page;
1209 }
1210 /*
1211 * There is now a place for page_node, but the tree may
1212 * have been rebalanced, so re-evaluate parent and new.
1213 */
1214 if (page_node)
1215 goto again;
1216 return NULL;
Hugh Dickinsc8d65532013-02-22 16:35:10 -08001217 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001218 }
1219
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001220 if (!page_node)
1221 return NULL;
1222
1223 list_del(&page_node->list);
1224 DO_NUMA(page_node->nid = nid);
1225 rb_link_node(&page_node->node, parent, new);
Hugh Dickinsef53d162013-02-22 16:36:12 -08001226 rb_insert_color(&page_node->node, root);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001227 get_page(page);
1228 return page;
1229
1230replace:
1231 if (page_node) {
1232 list_del(&page_node->list);
1233 DO_NUMA(page_node->nid = nid);
Hugh Dickinsef53d162013-02-22 16:36:12 -08001234 rb_replace_node(&stable_node->node, &page_node->node, root);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001235 get_page(page);
1236 } else {
Hugh Dickinsef53d162013-02-22 16:36:12 -08001237 rb_erase(&stable_node->node, root);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001238 page = NULL;
1239 }
1240 stable_node->head = &migrate_nodes;
1241 list_add(&stable_node->list, stable_node->head);
1242 return page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001243}
1244
1245/*
Hugh Dickinse850dcf2013-02-22 16:35:03 -08001246 * stable_tree_insert - insert stable tree node pointing to new ksm page
Izik Eidus31dbd012009-09-21 17:02:03 -07001247 * into the stable tree.
1248 *
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001249 * This function returns the stable tree node just allocated on success,
1250 * NULL otherwise.
Izik Eidus31dbd012009-09-21 17:02:03 -07001251 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001252static struct stable_node *stable_tree_insert(struct page *kpage)
Izik Eidus31dbd012009-09-21 17:02:03 -07001253{
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001254 int nid;
1255 unsigned long kpfn;
Hugh Dickinsef53d162013-02-22 16:36:12 -08001256 struct rb_root *root;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001257 struct rb_node **new;
Izik Eidus31dbd012009-09-21 17:02:03 -07001258 struct rb_node *parent = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001259 struct stable_node *stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001260
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001261 kpfn = page_to_pfn(kpage);
1262 nid = get_kpfn_nid(kpfn);
Hugh Dickinsef53d162013-02-22 16:36:12 -08001263 root = root_stable_tree + nid;
1264 new = &root->rb_node;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001265
Izik Eidus31dbd012009-09-21 17:02:03 -07001266 while (*new) {
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001267 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001268 int ret;
1269
Hugh Dickins08beca42009-12-14 17:59:21 -08001270 cond_resched();
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001271 stable_node = rb_entry(*new, struct stable_node, node);
Hugh Dickins8aafa6a2013-02-22 16:35:06 -08001272 tree_page = get_ksm_page(stable_node, false);
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001273 if (!tree_page)
1274 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001275
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001276 ret = memcmp_pages(kpage, tree_page);
1277 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001278
1279 parent = *new;
1280 if (ret < 0)
1281 new = &parent->rb_left;
1282 else if (ret > 0)
1283 new = &parent->rb_right;
1284 else {
1285 /*
1286 * It is not a bug that stable_tree_search() didn't
1287 * find this node: because at that time our page was
1288 * not yet write-protected, so may have changed since.
1289 */
1290 return NULL;
1291 }
1292 }
1293
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001294 stable_node = alloc_stable_node();
1295 if (!stable_node)
1296 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001297
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001298 INIT_HLIST_HEAD(&stable_node->hlist);
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001299 stable_node->kpfn = kpfn;
Hugh Dickins08beca42009-12-14 17:59:21 -08001300 set_page_stable_node(kpage, stable_node);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001301 DO_NUMA(stable_node->nid = nid);
Hugh Dickinse850dcf2013-02-22 16:35:03 -08001302 rb_link_node(&stable_node->node, parent, new);
Hugh Dickinsef53d162013-02-22 16:36:12 -08001303 rb_insert_color(&stable_node->node, root);
Hugh Dickins08beca42009-12-14 17:59:21 -08001304
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001305 return stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001306}
1307
1308/*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001309 * unstable_tree_search_insert - search for identical page,
1310 * else insert rmap_item into the unstable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001311 *
1312 * This function searches for a page in the unstable tree identical to the
1313 * page currently being scanned; and if no identical page is found in the
1314 * tree, we insert rmap_item as a new object into the unstable tree.
1315 *
1316 * This function returns pointer to rmap_item found to be identical
1317 * to the currently scanned page, NULL otherwise.
1318 *
1319 * This function does both searching and inserting, because they share
1320 * the same walking algorithm in an rbtree.
1321 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001322static
1323struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1324 struct page *page,
1325 struct page **tree_pagep)
Izik Eidus31dbd012009-09-21 17:02:03 -07001326{
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001327 struct rb_node **new;
1328 struct rb_root *root;
Izik Eidus31dbd012009-09-21 17:02:03 -07001329 struct rb_node *parent = NULL;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001330 int nid;
1331
1332 nid = get_kpfn_nid(page_to_pfn(page));
Hugh Dickinsef53d162013-02-22 16:36:12 -08001333 root = root_unstable_tree + nid;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001334 new = &root->rb_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001335
1336 while (*new) {
1337 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001338 struct page *tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001339 int ret;
1340
Hugh Dickinsd178f272009-11-09 15:58:23 +00001341 cond_resched();
Izik Eidus31dbd012009-09-21 17:02:03 -07001342 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
Hugh Dickins8dd35572009-12-14 17:59:18 -08001343 tree_page = get_mergeable_page(tree_rmap_item);
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001344 if (IS_ERR_OR_NULL(tree_page))
Izik Eidus31dbd012009-09-21 17:02:03 -07001345 return NULL;
1346
1347 /*
Hugh Dickins8dd35572009-12-14 17:59:18 -08001348 * Don't substitute a ksm page for a forked page.
Izik Eidus31dbd012009-09-21 17:02:03 -07001349 */
Hugh Dickins8dd35572009-12-14 17:59:18 -08001350 if (page == tree_page) {
1351 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001352 return NULL;
1353 }
1354
Hugh Dickins8dd35572009-12-14 17:59:18 -08001355 ret = memcmp_pages(page, tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001356
1357 parent = *new;
1358 if (ret < 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001359 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001360 new = &parent->rb_left;
1361 } else if (ret > 0) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001362 put_page(tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001363 new = &parent->rb_right;
Hugh Dickinsb599cbd2013-02-22 16:36:05 -08001364 } else if (!ksm_merge_across_nodes &&
1365 page_to_nid(tree_page) != nid) {
1366 /*
1367 * If tree_page has been migrated to another NUMA node,
1368 * it will be flushed out and put in the right unstable
1369 * tree next time: only merge with it when across_nodes.
1370 */
1371 put_page(tree_page);
1372 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001373 } else {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001374 *tree_pagep = tree_page;
Izik Eidus31dbd012009-09-21 17:02:03 -07001375 return tree_rmap_item;
1376 }
1377 }
1378
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001379 rmap_item->address |= UNSTABLE_FLAG;
Izik Eidus31dbd012009-09-21 17:02:03 -07001380 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
Hugh Dickinse850dcf2013-02-22 16:35:03 -08001381 DO_NUMA(rmap_item->nid = nid);
Izik Eidus31dbd012009-09-21 17:02:03 -07001382 rb_link_node(&rmap_item->node, parent, new);
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001383 rb_insert_color(&rmap_item->node, root);
Izik Eidus31dbd012009-09-21 17:02:03 -07001384
Hugh Dickins473b0ce2009-09-21 17:02:11 -07001385 ksm_pages_unshared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001386 return NULL;
1387}
1388
1389/*
1390 * stable_tree_append - add another rmap_item to the linked list of
1391 * rmap_items hanging off a given node of the stable tree, all sharing
1392 * the same ksm page.
1393 */
1394static void stable_tree_append(struct rmap_item *rmap_item,
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001395 struct stable_node *stable_node)
Izik Eidus31dbd012009-09-21 17:02:03 -07001396{
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001397 rmap_item->head = stable_node;
Izik Eidus31dbd012009-09-21 17:02:03 -07001398 rmap_item->address |= STABLE_FLAG;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001399 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
Hugh Dickinse178dfd2009-09-21 17:02:10 -07001400
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001401 if (rmap_item->hlist.next)
1402 ksm_pages_sharing++;
1403 else
1404 ksm_pages_shared++;
Izik Eidus31dbd012009-09-21 17:02:03 -07001405}
1406
1407/*
Hugh Dickins81464e302009-09-21 17:02:15 -07001408 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1409 * if not, compare checksum to previous and if it's the same, see if page can
1410 * be inserted into the unstable tree, or merged with a page already there and
1411 * both transferred to the stable tree.
Izik Eidus31dbd012009-09-21 17:02:03 -07001412 *
1413 * @page: the page that we are searching identical page to.
1414 * @rmap_item: the reverse mapping into the virtual address of this page
1415 */
1416static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1417{
Izik Eidus31dbd012009-09-21 17:02:03 -07001418 struct rmap_item *tree_rmap_item;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001419 struct page *tree_page = NULL;
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001420 struct stable_node *stable_node;
Hugh Dickins8dd35572009-12-14 17:59:18 -08001421 struct page *kpage;
Izik Eidus31dbd012009-09-21 17:02:03 -07001422 unsigned int checksum;
1423 int err;
1424
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001425 stable_node = page_stable_node(page);
1426 if (stable_node) {
1427 if (stable_node->head != &migrate_nodes &&
1428 get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1429 rb_erase(&stable_node->node,
Hugh Dickinsef53d162013-02-22 16:36:12 -08001430 root_stable_tree + NUMA(stable_node->nid));
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001431 stable_node->head = &migrate_nodes;
1432 list_add(&stable_node->list, stable_node->head);
1433 }
1434 if (stable_node->head != &migrate_nodes &&
1435 rmap_item->head == stable_node)
1436 return;
1437 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001438
1439 /* We first start with searching the page inside the stable tree */
Hugh Dickins62b61f62009-12-14 17:59:33 -08001440 kpage = stable_tree_search(page);
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001441 if (kpage == page && rmap_item->head == stable_node) {
1442 put_page(kpage);
1443 return;
1444 }
1445
1446 remove_rmap_item_from_tree(rmap_item);
1447
Hugh Dickins62b61f62009-12-14 17:59:33 -08001448 if (kpage) {
Hugh Dickins08beca42009-12-14 17:59:21 -08001449 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001450 if (!err) {
1451 /*
1452 * The page was successfully merged:
1453 * add its rmap_item to the stable tree.
1454 */
Hugh Dickins5ad64682009-12-14 17:59:24 -08001455 lock_page(kpage);
Hugh Dickins62b61f62009-12-14 17:59:33 -08001456 stable_tree_append(rmap_item, page_stable_node(kpage));
Hugh Dickins5ad64682009-12-14 17:59:24 -08001457 unlock_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001458 }
Hugh Dickins8dd35572009-12-14 17:59:18 -08001459 put_page(kpage);
Izik Eidus31dbd012009-09-21 17:02:03 -07001460 return;
1461 }
1462
1463 /*
Hugh Dickins4035c07a2009-12-14 17:59:27 -08001464 * If the hash value of the page has changed from the last time
1465 * we calculated it, this page is changing frequently: therefore we
1466 * don't want to insert it in the unstable tree, and we don't want
1467 * to waste our time searching for something identical to it there.
Izik Eidus31dbd012009-09-21 17:02:03 -07001468 */
1469 checksum = calc_checksum(page);
1470 if (rmap_item->oldchecksum != checksum) {
1471 rmap_item->oldchecksum = checksum;
1472 return;
1473 }
1474
Hugh Dickins8dd35572009-12-14 17:59:18 -08001475 tree_rmap_item =
1476 unstable_tree_search_insert(rmap_item, page, &tree_page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001477 if (tree_rmap_item) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001478 kpage = try_to_merge_two_pages(rmap_item, page,
1479 tree_rmap_item, tree_page);
1480 put_page(tree_page);
Hugh Dickins8dd35572009-12-14 17:59:18 -08001481 if (kpage) {
Hugh Dickinsbc566202013-02-22 16:36:06 -08001482 /*
1483 * The pages were successfully merged: insert new
1484 * node in the stable tree and add both rmap_items.
1485 */
Hugh Dickins5ad64682009-12-14 17:59:24 -08001486 lock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001487 stable_node = stable_tree_insert(kpage);
1488 if (stable_node) {
1489 stable_tree_append(tree_rmap_item, stable_node);
1490 stable_tree_append(rmap_item, stable_node);
1491 }
Hugh Dickins5ad64682009-12-14 17:59:24 -08001492 unlock_page(kpage);
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001493
Izik Eidus31dbd012009-09-21 17:02:03 -07001494 /*
1495 * If we fail to insert the page into the stable tree,
1496 * we will have 2 virtual addresses that are pointing
1497 * to a ksm page left outside the stable tree,
1498 * in which case we need to break_cow on both.
1499 */
Hugh Dickins7b6ba2c2009-12-14 17:59:20 -08001500 if (!stable_node) {
Hugh Dickins8dd35572009-12-14 17:59:18 -08001501 break_cow(tree_rmap_item);
1502 break_cow(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001503 }
1504 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001505 }
1506}
1507
1508static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001509 struct rmap_item **rmap_list,
Izik Eidus31dbd012009-09-21 17:02:03 -07001510 unsigned long addr)
1511{
1512 struct rmap_item *rmap_item;
1513
Hugh Dickins6514d512009-12-14 17:59:19 -08001514 while (*rmap_list) {
1515 rmap_item = *rmap_list;
Hugh Dickins93d17712009-12-14 17:59:16 -08001516 if ((rmap_item->address & PAGE_MASK) == addr)
Izik Eidus31dbd012009-09-21 17:02:03 -07001517 return rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001518 if (rmap_item->address > addr)
1519 break;
Hugh Dickins6514d512009-12-14 17:59:19 -08001520 *rmap_list = rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001521 remove_rmap_item_from_tree(rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001522 free_rmap_item(rmap_item);
1523 }
1524
1525 rmap_item = alloc_rmap_item();
1526 if (rmap_item) {
1527 /* It has already been zeroed */
1528 rmap_item->mm = mm_slot->mm;
1529 rmap_item->address = addr;
Hugh Dickins6514d512009-12-14 17:59:19 -08001530 rmap_item->rmap_list = *rmap_list;
1531 *rmap_list = rmap_item;
Izik Eidus31dbd012009-09-21 17:02:03 -07001532 }
1533 return rmap_item;
1534}
1535
1536static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1537{
1538 struct mm_struct *mm;
1539 struct mm_slot *slot;
1540 struct vm_area_struct *vma;
1541 struct rmap_item *rmap_item;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001542 int nid;
Izik Eidus31dbd012009-09-21 17:02:03 -07001543
1544 if (list_empty(&ksm_mm_head.mm_list))
1545 return NULL;
1546
1547 slot = ksm_scan.mm_slot;
1548 if (slot == &ksm_mm_head) {
Hugh Dickins2919bfd2011-01-13 15:47:29 -08001549 /*
1550 * A number of pages can hang around indefinitely on per-cpu
1551 * pagevecs, raised page count preventing write_protect_page
1552 * from merging them. Though it doesn't really matter much,
1553 * it is puzzling to see some stuck in pages_volatile until
1554 * other activity jostles them out, and they also prevented
1555 * LTP's KSM test from succeeding deterministically; so drain
1556 * them here (here rather than on entry to ksm_do_scan(),
1557 * so we don't IPI too often when pages_to_scan is set low).
1558 */
1559 lru_add_drain_all();
1560
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001561 /*
1562 * Whereas stale stable_nodes on the stable_tree itself
1563 * get pruned in the regular course of stable_tree_search(),
1564 * those moved out to the migrate_nodes list can accumulate:
1565 * so prune them once before each full scan.
1566 */
1567 if (!ksm_merge_across_nodes) {
1568 struct stable_node *stable_node;
1569 struct list_head *this, *next;
1570 struct page *page;
1571
1572 list_for_each_safe(this, next, &migrate_nodes) {
1573 stable_node = list_entry(this,
1574 struct stable_node, list);
1575 page = get_ksm_page(stable_node, false);
1576 if (page)
1577 put_page(page);
1578 cond_resched();
1579 }
1580 }
1581
Hugh Dickinsef53d162013-02-22 16:36:12 -08001582 for (nid = 0; nid < ksm_nr_node_ids; nid++)
Petr Holasek90bd6fd2013-02-22 16:35:00 -08001583 root_unstable_tree[nid] = RB_ROOT;
Izik Eidus31dbd012009-09-21 17:02:03 -07001584
1585 spin_lock(&ksm_mmlist_lock);
1586 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1587 ksm_scan.mm_slot = slot;
1588 spin_unlock(&ksm_mmlist_lock);
Hugh Dickins2b472612011-06-15 15:08:58 -07001589 /*
1590 * Although we tested list_empty() above, a racing __ksm_exit
1591 * of the last mm on the list may have removed it since then.
1592 */
1593 if (slot == &ksm_mm_head)
1594 return NULL;
Izik Eidus31dbd012009-09-21 17:02:03 -07001595next_mm:
1596 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001597 ksm_scan.rmap_list = &slot->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001598 }
1599
1600 mm = slot->mm;
1601 down_read(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001602 if (ksm_test_exit(mm))
1603 vma = NULL;
1604 else
1605 vma = find_vma(mm, ksm_scan.address);
1606
1607 for (; vma; vma = vma->vm_next) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001608 if (!(vma->vm_flags & VM_MERGEABLE))
1609 continue;
1610 if (ksm_scan.address < vma->vm_start)
1611 ksm_scan.address = vma->vm_start;
1612 if (!vma->anon_vma)
1613 ksm_scan.address = vma->vm_end;
1614
1615 while (ksm_scan.address < vma->vm_end) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001616 if (ksm_test_exit(mm))
1617 break;
Izik Eidus31dbd012009-09-21 17:02:03 -07001618 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001619 if (IS_ERR_OR_NULL(*page)) {
1620 ksm_scan.address += PAGE_SIZE;
1621 cond_resched();
1622 continue;
1623 }
Andrea Arcangeli29ad7682011-01-13 15:47:19 -08001624 if (PageAnon(*page) ||
1625 page_trans_compound_anon(*page)) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001626 flush_anon_page(vma, *page, ksm_scan.address);
1627 flush_dcache_page(*page);
1628 rmap_item = get_next_rmap_item(slot,
Hugh Dickins6514d512009-12-14 17:59:19 -08001629 ksm_scan.rmap_list, ksm_scan.address);
Izik Eidus31dbd012009-09-21 17:02:03 -07001630 if (rmap_item) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001631 ksm_scan.rmap_list =
1632 &rmap_item->rmap_list;
Izik Eidus31dbd012009-09-21 17:02:03 -07001633 ksm_scan.address += PAGE_SIZE;
1634 } else
1635 put_page(*page);
1636 up_read(&mm->mmap_sem);
1637 return rmap_item;
1638 }
Andrea Arcangeli21ae5b02011-01-13 15:47:00 -08001639 put_page(*page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001640 ksm_scan.address += PAGE_SIZE;
1641 cond_resched();
1642 }
1643 }
1644
Hugh Dickins9ba69292009-09-21 17:02:20 -07001645 if (ksm_test_exit(mm)) {
1646 ksm_scan.address = 0;
Hugh Dickins6514d512009-12-14 17:59:19 -08001647 ksm_scan.rmap_list = &slot->rmap_list;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001648 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001649 /*
1650 * Nuke all the rmap_items that are above this current rmap:
1651 * because there were no VM_MERGEABLE vmas with such addresses.
1652 */
Hugh Dickins6514d512009-12-14 17:59:19 -08001653 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
Izik Eidus31dbd012009-09-21 17:02:03 -07001654
1655 spin_lock(&ksm_mmlist_lock);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001656 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1657 struct mm_slot, mm_list);
1658 if (ksm_scan.address == 0) {
1659 /*
1660 * We've completed a full scan of all vmas, holding mmap_sem
1661 * throughout, and found no VM_MERGEABLE: so do the same as
1662 * __ksm_exit does to remove this mm from all our lists now.
Hugh Dickins9ba69292009-09-21 17:02:20 -07001663 * This applies either when cleaning up after __ksm_exit
1664 * (but beware: we can reach here even before __ksm_exit),
1665 * or when all VM_MERGEABLE areas have been unmapped (and
1666 * mmap_sem then protects against race with MADV_MERGEABLE).
Hugh Dickinscd551f92009-09-21 17:02:17 -07001667 */
Sasha Levin4ca3a692013-02-22 16:32:28 -08001668 hash_del(&slot->link);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001669 list_del(&slot->mm_list);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001670 spin_unlock(&ksm_mmlist_lock);
1671
Hugh Dickinscd551f92009-09-21 17:02:17 -07001672 free_mm_slot(slot);
1673 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001674 up_read(&mm->mmap_sem);
1675 mmdrop(mm);
1676 } else {
1677 spin_unlock(&ksm_mmlist_lock);
1678 up_read(&mm->mmap_sem);
Hugh Dickinscd551f92009-09-21 17:02:17 -07001679 }
Izik Eidus31dbd012009-09-21 17:02:03 -07001680
1681 /* Repeat until we've completed scanning the whole list */
Hugh Dickinscd551f92009-09-21 17:02:17 -07001682 slot = ksm_scan.mm_slot;
Izik Eidus31dbd012009-09-21 17:02:03 -07001683 if (slot != &ksm_mm_head)
1684 goto next_mm;
1685
Izik Eidus31dbd012009-09-21 17:02:03 -07001686 ksm_scan.seqnr++;
1687 return NULL;
1688}
1689
1690/**
1691 * ksm_do_scan - the ksm scanner main worker function.
1692 * @scan_npages - number of pages we want to scan before we return.
1693 */
1694static void ksm_do_scan(unsigned int scan_npages)
1695{
1696 struct rmap_item *rmap_item;
Dan Carpenter22eccdd2010-04-23 13:18:10 -04001697 struct page *uninitialized_var(page);
Izik Eidus31dbd012009-09-21 17:02:03 -07001698
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001699 while (scan_npages-- && likely(!freezing(current))) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001700 cond_resched();
1701 rmap_item = scan_get_next_rmap_item(&page);
1702 if (!rmap_item)
1703 return;
Hugh Dickins4146d2d2013-02-22 16:35:11 -08001704 cmp_and_merge_page(page, rmap_item);
Izik Eidus31dbd012009-09-21 17:02:03 -07001705 put_page(page);
1706 }
1707}
1708
Hugh Dickins6e1583842009-09-21 17:02:14 -07001709static int ksmd_should_run(void)
1710{
1711 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1712}
1713
Izik Eidus31dbd012009-09-21 17:02:03 -07001714static int ksm_scan_thread(void *nothing)
1715{
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001716 set_freezable();
Izik Eidus339aa622009-09-21 17:02:07 -07001717 set_user_nice(current, 5);
Izik Eidus31dbd012009-09-21 17:02:03 -07001718
1719 while (!kthread_should_stop()) {
Hugh Dickins6e1583842009-09-21 17:02:14 -07001720 mutex_lock(&ksm_thread_mutex);
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08001721 wait_while_offlining();
Hugh Dickins6e1583842009-09-21 17:02:14 -07001722 if (ksmd_should_run())
Izik Eidus31dbd012009-09-21 17:02:03 -07001723 ksm_do_scan(ksm_thread_pages_to_scan);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001724 mutex_unlock(&ksm_thread_mutex);
1725
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001726 try_to_freeze();
1727
Hugh Dickins6e1583842009-09-21 17:02:14 -07001728 if (ksmd_should_run()) {
Izik Eidus31dbd012009-09-21 17:02:03 -07001729 schedule_timeout_interruptible(
1730 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1731 } else {
Andrea Arcangeli878aee72011-01-13 15:47:10 -08001732 wait_event_freezable(ksm_thread_wait,
Hugh Dickins6e1583842009-09-21 17:02:14 -07001733 ksmd_should_run() || kthread_should_stop());
Izik Eidus31dbd012009-09-21 17:02:03 -07001734 }
1735 }
1736 return 0;
1737}
1738
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001739int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1740 unsigned long end, int advice, unsigned long *vm_flags)
1741{
1742 struct mm_struct *mm = vma->vm_mm;
Hugh Dickinsd952b792009-09-21 17:02:16 -07001743 int err;
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001744
1745 switch (advice) {
1746 case MADV_MERGEABLE:
1747 /*
1748 * Be somewhat over-protective for now!
1749 */
1750 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1751 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
Konstantin Khlebnikov314e51b2012-10-08 16:29:02 -07001752 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001753 return 0; /* just ignore the advice */
1754
Konstantin Khlebnikovcc2383e2012-10-08 16:28:37 -07001755#ifdef VM_SAO
1756 if (*vm_flags & VM_SAO)
1757 return 0;
1758#endif
1759
Hugh Dickinsd952b792009-09-21 17:02:16 -07001760 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1761 err = __ksm_enter(mm);
1762 if (err)
1763 return err;
1764 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001765
1766 *vm_flags |= VM_MERGEABLE;
1767 break;
1768
1769 case MADV_UNMERGEABLE:
1770 if (!(*vm_flags & VM_MERGEABLE))
1771 return 0; /* just ignore the advice */
1772
Hugh Dickinsd952b792009-09-21 17:02:16 -07001773 if (vma->anon_vma) {
1774 err = unmerge_ksm_pages(vma, start, end);
1775 if (err)
1776 return err;
1777 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001778
1779 *vm_flags &= ~VM_MERGEABLE;
1780 break;
1781 }
1782
1783 return 0;
1784}
1785
1786int __ksm_enter(struct mm_struct *mm)
1787{
Hugh Dickins6e1583842009-09-21 17:02:14 -07001788 struct mm_slot *mm_slot;
1789 int needs_wakeup;
1790
1791 mm_slot = alloc_mm_slot();
Izik Eidus31dbd012009-09-21 17:02:03 -07001792 if (!mm_slot)
1793 return -ENOMEM;
1794
Hugh Dickins6e1583842009-09-21 17:02:14 -07001795 /* Check ksm_run too? Would need tighter locking */
1796 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1797
Izik Eidus31dbd012009-09-21 17:02:03 -07001798 spin_lock(&ksm_mmlist_lock);
1799 insert_to_mm_slots_hash(mm, mm_slot);
1800 /*
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001801 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1802 * insert just behind the scanning cursor, to let the area settle
Izik Eidus31dbd012009-09-21 17:02:03 -07001803 * down a little; when fork is followed by immediate exec, we don't
1804 * want ksmd to waste time setting up and tearing down an rmap_list.
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001805 *
1806 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1807 * scanning cursor, otherwise KSM pages in newly forked mms will be
1808 * missed: then we might as well insert at the end of the list.
Izik Eidus31dbd012009-09-21 17:02:03 -07001809 */
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001810 if (ksm_run & KSM_RUN_UNMERGE)
1811 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1812 else
1813 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
Izik Eidus31dbd012009-09-21 17:02:03 -07001814 spin_unlock(&ksm_mmlist_lock);
1815
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001816 set_bit(MMF_VM_MERGEABLE, &mm->flags);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001817 atomic_inc(&mm->mm_count);
Hugh Dickins6e1583842009-09-21 17:02:14 -07001818
1819 if (needs_wakeup)
1820 wake_up_interruptible(&ksm_thread_wait);
1821
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001822 return 0;
1823}
1824
Andrea Arcangeli1c2fb7a2009-09-21 17:02:22 -07001825void __ksm_exit(struct mm_struct *mm)
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001826{
Hugh Dickinscd551f92009-09-21 17:02:17 -07001827 struct mm_slot *mm_slot;
Hugh Dickins9ba69292009-09-21 17:02:20 -07001828 int easy_to_free = 0;
Hugh Dickinscd551f92009-09-21 17:02:17 -07001829
Izik Eidus31dbd012009-09-21 17:02:03 -07001830 /*
Hugh Dickins9ba69292009-09-21 17:02:20 -07001831 * This process is exiting: if it's straightforward (as is the
1832 * case when ksmd was never running), free mm_slot immediately.
1833 * But if it's at the cursor or has rmap_items linked to it, use
1834 * mmap_sem to synchronize with any break_cows before pagetables
1835 * are freed, and leave the mm_slot on the list for ksmd to free.
1836 * Beware: ksm may already have noticed it exiting and freed the slot.
Izik Eidus31dbd012009-09-21 17:02:03 -07001837 */
Hugh Dickins9ba69292009-09-21 17:02:20 -07001838
Hugh Dickinscd551f92009-09-21 17:02:17 -07001839 spin_lock(&ksm_mmlist_lock);
1840 mm_slot = get_mm_slot(mm);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001841 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
Hugh Dickins6514d512009-12-14 17:59:19 -08001842 if (!mm_slot->rmap_list) {
Sasha Levin4ca3a692013-02-22 16:32:28 -08001843 hash_del(&mm_slot->link);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001844 list_del(&mm_slot->mm_list);
1845 easy_to_free = 1;
1846 } else {
1847 list_move(&mm_slot->mm_list,
1848 &ksm_scan.mm_slot->mm_list);
1849 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001850 }
Hugh Dickinscd551f92009-09-21 17:02:17 -07001851 spin_unlock(&ksm_mmlist_lock);
1852
Hugh Dickins9ba69292009-09-21 17:02:20 -07001853 if (easy_to_free) {
1854 free_mm_slot(mm_slot);
1855 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1856 mmdrop(mm);
1857 } else if (mm_slot) {
Hugh Dickins9ba69292009-09-21 17:02:20 -07001858 down_write(&mm->mmap_sem);
1859 up_write(&mm->mmap_sem);
Hugh Dickins9ba69292009-09-21 17:02:20 -07001860 }
Hugh Dickinsf8af4da2009-09-21 17:01:57 -07001861}
Izik Eidus31dbd012009-09-21 17:02:03 -07001862
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001863struct page *ksm_might_need_to_copy(struct page *page,
Hugh Dickins5ad64682009-12-14 17:59:24 -08001864 struct vm_area_struct *vma, unsigned long address)
1865{
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001866 struct anon_vma *anon_vma = page_anon_vma(page);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001867 struct page *new_page;
1868
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08001869 if (PageKsm(page)) {
1870 if (page_stable_node(page) &&
1871 !(ksm_run & KSM_RUN_UNMERGE))
1872 return page; /* no need to copy it */
1873 } else if (!anon_vma) {
1874 return page; /* no need to copy it */
1875 } else if (anon_vma->root == vma->anon_vma->root &&
1876 page->index == linear_page_index(vma, address)) {
1877 return page; /* still no need to copy it */
1878 }
1879 if (!PageUptodate(page))
1880 return page; /* let do_swap_page report the error */
1881
Hugh Dickins5ad64682009-12-14 17:59:24 -08001882 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1883 if (new_page) {
1884 copy_user_highpage(new_page, page, address, vma);
1885
1886 SetPageDirty(new_page);
1887 __SetPageUptodate(new_page);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001888 __set_page_locked(new_page);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001889 }
1890
Hugh Dickins5ad64682009-12-14 17:59:24 -08001891 return new_page;
1892}
1893
1894int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1895 unsigned long *vm_flags)
1896{
1897 struct stable_node *stable_node;
1898 struct rmap_item *rmap_item;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001899 unsigned int mapcount = page_mapcount(page);
1900 int referenced = 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001901 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001902
1903 VM_BUG_ON(!PageKsm(page));
1904 VM_BUG_ON(!PageLocked(page));
1905
1906 stable_node = page_stable_node(page);
1907 if (!stable_node)
1908 return 0;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001909again:
Sasha Levinb67bfe02013-02-27 17:06:00 -08001910 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001911 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001912 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001913 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001914
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001915 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07001916 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1917 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08001918 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001919 if (rmap_item->address < vma->vm_start ||
1920 rmap_item->address >= vma->vm_end)
1921 continue;
1922 /*
1923 * Initially we examine only the vma which covers this
1924 * rmap_item; but later, if there is still work to do,
1925 * we examine covering vmas in other mms: in case they
1926 * were forked from the original since ksmd passed.
1927 */
1928 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1929 continue;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001930
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001931 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1932 continue;
1933
1934 referenced += page_referenced_one(page, vma,
Hugh Dickins5ad64682009-12-14 17:59:24 -08001935 rmap_item->address, &mapcount, vm_flags);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001936 if (!search_new_forks || !mapcount)
1937 break;
1938 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001939 anon_vma_unlock_read(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001940 if (!mapcount)
1941 goto out;
1942 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001943 if (!search_new_forks++)
1944 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001945out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001946 return referenced;
1947}
1948
1949int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1950{
1951 struct stable_node *stable_node;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001952 struct rmap_item *rmap_item;
1953 int ret = SWAP_AGAIN;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001954 int search_new_forks = 0;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001955
1956 VM_BUG_ON(!PageKsm(page));
1957 VM_BUG_ON(!PageLocked(page));
1958
1959 stable_node = page_stable_node(page);
1960 if (!stable_node)
1961 return SWAP_FAIL;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001962again:
Sasha Levinb67bfe02013-02-27 17:06:00 -08001963 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001964 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08001965 struct anon_vma_chain *vmac;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001966 struct vm_area_struct *vma;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001967
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001968 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07001969 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1970 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08001971 vma = vmac->vma;
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001972 if (rmap_item->address < vma->vm_start ||
1973 rmap_item->address >= vma->vm_end)
1974 continue;
1975 /*
1976 * Initially we examine only the vma which covers this
1977 * rmap_item; but later, if there is still work to do,
1978 * we examine covering vmas in other mms: in case they
1979 * were forked from the original since ksmd passed.
1980 */
1981 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1982 continue;
1983
1984 ret = try_to_unmap_one(page, vma,
1985 rmap_item->address, flags);
1986 if (ret != SWAP_AGAIN || !page_mapped(page)) {
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001987 anon_vma_unlock_read(anon_vma);
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001988 goto out;
1989 }
1990 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08001991 anon_vma_unlock_read(anon_vma);
Hugh Dickins5ad64682009-12-14 17:59:24 -08001992 }
Hugh Dickinsdb114b82009-12-14 17:59:25 -08001993 if (!search_new_forks++)
1994 goto again;
Hugh Dickins5ad64682009-12-14 17:59:24 -08001995out:
Hugh Dickins5ad64682009-12-14 17:59:24 -08001996 return ret;
1997}
1998
Hugh Dickinse9995ef2009-12-14 17:59:31 -08001999#ifdef CONFIG_MIGRATION
2000int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
2001 struct vm_area_struct *, unsigned long, void *), void *arg)
2002{
2003 struct stable_node *stable_node;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002004 struct rmap_item *rmap_item;
2005 int ret = SWAP_AGAIN;
2006 int search_new_forks = 0;
2007
2008 VM_BUG_ON(!PageKsm(page));
2009 VM_BUG_ON(!PageLocked(page));
2010
2011 stable_node = page_stable_node(page);
2012 if (!stable_node)
2013 return ret;
2014again:
Sasha Levinb67bfe02013-02-27 17:06:00 -08002015 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002016 struct anon_vma *anon_vma = rmap_item->anon_vma;
Rik van Riel5beb4932010-03-05 13:42:07 -08002017 struct anon_vma_chain *vmac;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002018 struct vm_area_struct *vma;
2019
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08002020 anon_vma_lock_read(anon_vma);
Michel Lespinassebf181b92012-10-08 16:31:39 -07002021 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2022 0, ULONG_MAX) {
Rik van Riel5beb4932010-03-05 13:42:07 -08002023 vma = vmac->vma;
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002024 if (rmap_item->address < vma->vm_start ||
2025 rmap_item->address >= vma->vm_end)
2026 continue;
2027 /*
2028 * Initially we examine only the vma which covers this
2029 * rmap_item; but later, if there is still work to do,
2030 * we examine covering vmas in other mms: in case they
2031 * were forked from the original since ksmd passed.
2032 */
2033 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2034 continue;
2035
2036 ret = rmap_one(page, vma, rmap_item->address, arg);
2037 if (ret != SWAP_AGAIN) {
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08002038 anon_vma_unlock_read(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002039 goto out;
2040 }
2041 }
Hugh Dickinsb6b19f22012-12-19 17:44:29 -08002042 anon_vma_unlock_read(anon_vma);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002043 }
2044 if (!search_new_forks++)
2045 goto again;
2046out:
2047 return ret;
2048}
2049
2050void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2051{
2052 struct stable_node *stable_node;
2053
2054 VM_BUG_ON(!PageLocked(oldpage));
2055 VM_BUG_ON(!PageLocked(newpage));
2056 VM_BUG_ON(newpage->mapping != oldpage->mapping);
2057
2058 stable_node = page_stable_node(newpage);
2059 if (stable_node) {
Hugh Dickins62b61f62009-12-14 17:59:33 -08002060 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
2061 stable_node->kpfn = page_to_pfn(newpage);
Hugh Dickinsc8d65532013-02-22 16:35:10 -08002062 /*
2063 * newpage->mapping was set in advance; now we need smp_wmb()
2064 * to make sure that the new stable_node->kpfn is visible
2065 * to get_ksm_page() before it can see that oldpage->mapping
2066 * has gone stale (or that PageSwapCache has been cleared).
2067 */
2068 smp_wmb();
2069 set_page_stable_node(oldpage, NULL);
Hugh Dickinse9995ef2009-12-14 17:59:31 -08002070 }
2071}
2072#endif /* CONFIG_MIGRATION */
2073
Hugh Dickins62b61f62009-12-14 17:59:33 -08002074#ifdef CONFIG_MEMORY_HOTREMOVE
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002075static int just_wait(void *word)
2076{
2077 schedule();
2078 return 0;
2079}
2080
2081static void wait_while_offlining(void)
2082{
2083 while (ksm_run & KSM_RUN_OFFLINE) {
2084 mutex_unlock(&ksm_thread_mutex);
2085 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2086 just_wait, TASK_UNINTERRUPTIBLE);
2087 mutex_lock(&ksm_thread_mutex);
2088 }
2089}
2090
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002091static void ksm_check_stable_tree(unsigned long start_pfn,
2092 unsigned long end_pfn)
Hugh Dickins62b61f62009-12-14 17:59:33 -08002093{
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002094 struct stable_node *stable_node;
Hugh Dickins4146d2d2013-02-22 16:35:11 -08002095 struct list_head *this, *next;
Hugh Dickins62b61f62009-12-14 17:59:33 -08002096 struct rb_node *node;
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002097 int nid;
Hugh Dickins62b61f62009-12-14 17:59:33 -08002098
Hugh Dickinsef53d162013-02-22 16:36:12 -08002099 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2100 node = rb_first(root_stable_tree + nid);
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002101 while (node) {
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002102 stable_node = rb_entry(node, struct stable_node, node);
2103 if (stable_node->kpfn >= start_pfn &&
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002104 stable_node->kpfn < end_pfn) {
2105 /*
2106 * Don't get_ksm_page, page has already gone:
2107 * which is why we keep kpfn instead of page*
2108 */
2109 remove_node_from_stable_tree(stable_node);
Hugh Dickinsef53d162013-02-22 16:36:12 -08002110 node = rb_first(root_stable_tree + nid);
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002111 } else
2112 node = rb_next(node);
2113 cond_resched();
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002114 }
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002115 }
Hugh Dickins4146d2d2013-02-22 16:35:11 -08002116 list_for_each_safe(this, next, &migrate_nodes) {
2117 stable_node = list_entry(this, struct stable_node, list);
2118 if (stable_node->kpfn >= start_pfn &&
2119 stable_node->kpfn < end_pfn)
2120 remove_node_from_stable_tree(stable_node);
2121 cond_resched();
2122 }
Hugh Dickins62b61f62009-12-14 17:59:33 -08002123}
2124
2125static int ksm_memory_callback(struct notifier_block *self,
2126 unsigned long action, void *arg)
2127{
2128 struct memory_notify *mn = arg;
Hugh Dickins62b61f62009-12-14 17:59:33 -08002129
2130 switch (action) {
2131 case MEM_GOING_OFFLINE:
2132 /*
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002133 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2134 * and remove_all_stable_nodes() while memory is going offline:
2135 * it is unsafe for them to touch the stable tree at this time.
2136 * But unmerge_ksm_pages(), rmap lookups and other entry points
2137 * which do not need the ksm_thread_mutex are all safe.
Hugh Dickins62b61f62009-12-14 17:59:33 -08002138 */
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002139 mutex_lock(&ksm_thread_mutex);
2140 ksm_run |= KSM_RUN_OFFLINE;
2141 mutex_unlock(&ksm_thread_mutex);
Hugh Dickins62b61f62009-12-14 17:59:33 -08002142 break;
2143
2144 case MEM_OFFLINE:
2145 /*
2146 * Most of the work is done by page migration; but there might
2147 * be a few stable_nodes left over, still pointing to struct
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002148 * pages which have been offlined: prune those from the tree,
2149 * otherwise get_ksm_page() might later try to access a
2150 * non-existent struct page.
Hugh Dickins62b61f62009-12-14 17:59:33 -08002151 */
Hugh Dickinsee0ea592013-02-22 16:35:05 -08002152 ksm_check_stable_tree(mn->start_pfn,
2153 mn->start_pfn + mn->nr_pages);
Hugh Dickins62b61f62009-12-14 17:59:33 -08002154 /* fallthrough */
2155
2156 case MEM_CANCEL_OFFLINE:
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002157 mutex_lock(&ksm_thread_mutex);
2158 ksm_run &= ~KSM_RUN_OFFLINE;
Hugh Dickins62b61f62009-12-14 17:59:33 -08002159 mutex_unlock(&ksm_thread_mutex);
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002160
2161 smp_mb(); /* wake_up_bit advises this */
2162 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
Hugh Dickins62b61f62009-12-14 17:59:33 -08002163 break;
2164 }
2165 return NOTIFY_OK;
2166}
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002167#else
2168static void wait_while_offlining(void)
2169{
2170}
Hugh Dickins62b61f62009-12-14 17:59:33 -08002171#endif /* CONFIG_MEMORY_HOTREMOVE */
2172
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002173#ifdef CONFIG_SYSFS
2174/*
2175 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2176 */
2177
Izik Eidus31dbd012009-09-21 17:02:03 -07002178#define KSM_ATTR_RO(_name) \
2179 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2180#define KSM_ATTR(_name) \
2181 static struct kobj_attribute _name##_attr = \
2182 __ATTR(_name, 0644, _name##_show, _name##_store)
2183
2184static ssize_t sleep_millisecs_show(struct kobject *kobj,
2185 struct kobj_attribute *attr, char *buf)
2186{
2187 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2188}
2189
2190static ssize_t sleep_millisecs_store(struct kobject *kobj,
2191 struct kobj_attribute *attr,
2192 const char *buf, size_t count)
2193{
2194 unsigned long msecs;
2195 int err;
2196
2197 err = strict_strtoul(buf, 10, &msecs);
2198 if (err || msecs > UINT_MAX)
2199 return -EINVAL;
2200
2201 ksm_thread_sleep_millisecs = msecs;
2202
2203 return count;
2204}
2205KSM_ATTR(sleep_millisecs);
2206
2207static ssize_t pages_to_scan_show(struct kobject *kobj,
2208 struct kobj_attribute *attr, char *buf)
2209{
2210 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2211}
2212
2213static ssize_t pages_to_scan_store(struct kobject *kobj,
2214 struct kobj_attribute *attr,
2215 const char *buf, size_t count)
2216{
2217 int err;
2218 unsigned long nr_pages;
2219
2220 err = strict_strtoul(buf, 10, &nr_pages);
2221 if (err || nr_pages > UINT_MAX)
2222 return -EINVAL;
2223
2224 ksm_thread_pages_to_scan = nr_pages;
2225
2226 return count;
2227}
2228KSM_ATTR(pages_to_scan);
2229
2230static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2231 char *buf)
2232{
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002233 return sprintf(buf, "%lu\n", ksm_run);
Izik Eidus31dbd012009-09-21 17:02:03 -07002234}
2235
2236static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2237 const char *buf, size_t count)
2238{
2239 int err;
2240 unsigned long flags;
2241
2242 err = strict_strtoul(buf, 10, &flags);
2243 if (err || flags > UINT_MAX)
2244 return -EINVAL;
2245 if (flags > KSM_RUN_UNMERGE)
2246 return -EINVAL;
2247
2248 /*
2249 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2250 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
Hugh Dickinsd0f209f2009-12-14 17:59:34 -08002251 * breaking COW to free the pages_shared (but leaves mm_slots
2252 * on the list for when ksmd may be set running again).
Izik Eidus31dbd012009-09-21 17:02:03 -07002253 */
2254
2255 mutex_lock(&ksm_thread_mutex);
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002256 wait_while_offlining();
Izik Eidus31dbd012009-09-21 17:02:03 -07002257 if (ksm_run != flags) {
2258 ksm_run = flags;
Hugh Dickinsd952b792009-09-21 17:02:16 -07002259 if (flags & KSM_RUN_UNMERGE) {
David Rientjese1e12d22012-12-11 16:02:56 -08002260 set_current_oom_origin();
Hugh Dickinsd952b792009-09-21 17:02:16 -07002261 err = unmerge_and_remove_all_rmap_items();
David Rientjese1e12d22012-12-11 16:02:56 -08002262 clear_current_oom_origin();
Hugh Dickinsd952b792009-09-21 17:02:16 -07002263 if (err) {
2264 ksm_run = KSM_RUN_STOP;
2265 count = err;
2266 }
2267 }
Izik Eidus31dbd012009-09-21 17:02:03 -07002268 }
2269 mutex_unlock(&ksm_thread_mutex);
2270
2271 if (flags & KSM_RUN_MERGE)
2272 wake_up_interruptible(&ksm_thread_wait);
2273
2274 return count;
2275}
2276KSM_ATTR(run);
2277
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002278#ifdef CONFIG_NUMA
2279static ssize_t merge_across_nodes_show(struct kobject *kobj,
2280 struct kobj_attribute *attr, char *buf)
2281{
2282 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2283}
2284
2285static ssize_t merge_across_nodes_store(struct kobject *kobj,
2286 struct kobj_attribute *attr,
2287 const char *buf, size_t count)
2288{
2289 int err;
2290 unsigned long knob;
2291
2292 err = kstrtoul(buf, 10, &knob);
2293 if (err)
2294 return err;
2295 if (knob > 1)
2296 return -EINVAL;
2297
2298 mutex_lock(&ksm_thread_mutex);
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002299 wait_while_offlining();
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002300 if (ksm_merge_across_nodes != knob) {
Hugh Dickinscbf86cf2013-02-22 16:35:08 -08002301 if (ksm_pages_shared || remove_all_stable_nodes())
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002302 err = -EBUSY;
Hugh Dickinsef53d162013-02-22 16:36:12 -08002303 else if (root_stable_tree == one_stable_tree) {
2304 struct rb_root *buf;
2305 /*
2306 * This is the first time that we switch away from the
2307 * default of merging across nodes: must now allocate
2308 * a buffer to hold as many roots as may be needed.
2309 * Allocate stable and unstable together:
2310 * MAXSMP NODES_SHIFT 10 will use 16kB.
2311 */
2312 buf = kcalloc(nr_node_ids + nr_node_ids,
2313 sizeof(*buf), GFP_KERNEL | __GFP_ZERO);
2314 /* Let us assume that RB_ROOT is NULL is zero */
2315 if (!buf)
2316 err = -ENOMEM;
2317 else {
2318 root_stable_tree = buf;
2319 root_unstable_tree = buf + nr_node_ids;
2320 /* Stable tree is empty but not the unstable */
2321 root_unstable_tree[0] = one_unstable_tree[0];
2322 }
2323 }
2324 if (!err) {
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002325 ksm_merge_across_nodes = knob;
Hugh Dickinsef53d162013-02-22 16:36:12 -08002326 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2327 }
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002328 }
2329 mutex_unlock(&ksm_thread_mutex);
2330
2331 return err ? err : count;
2332}
2333KSM_ATTR(merge_across_nodes);
2334#endif
2335
Hugh Dickinsb4028262009-09-21 17:02:09 -07002336static ssize_t pages_shared_show(struct kobject *kobj,
2337 struct kobj_attribute *attr, char *buf)
2338{
2339 return sprintf(buf, "%lu\n", ksm_pages_shared);
2340}
2341KSM_ATTR_RO(pages_shared);
2342
2343static ssize_t pages_sharing_show(struct kobject *kobj,
2344 struct kobj_attribute *attr, char *buf)
2345{
Hugh Dickinse178dfd2009-09-21 17:02:10 -07002346 return sprintf(buf, "%lu\n", ksm_pages_sharing);
Hugh Dickinsb4028262009-09-21 17:02:09 -07002347}
2348KSM_ATTR_RO(pages_sharing);
2349
Hugh Dickins473b0ce2009-09-21 17:02:11 -07002350static ssize_t pages_unshared_show(struct kobject *kobj,
2351 struct kobj_attribute *attr, char *buf)
2352{
2353 return sprintf(buf, "%lu\n", ksm_pages_unshared);
2354}
2355KSM_ATTR_RO(pages_unshared);
2356
2357static ssize_t pages_volatile_show(struct kobject *kobj,
2358 struct kobj_attribute *attr, char *buf)
2359{
2360 long ksm_pages_volatile;
2361
2362 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2363 - ksm_pages_sharing - ksm_pages_unshared;
2364 /*
2365 * It was not worth any locking to calculate that statistic,
2366 * but it might therefore sometimes be negative: conceal that.
2367 */
2368 if (ksm_pages_volatile < 0)
2369 ksm_pages_volatile = 0;
2370 return sprintf(buf, "%ld\n", ksm_pages_volatile);
2371}
2372KSM_ATTR_RO(pages_volatile);
2373
2374static ssize_t full_scans_show(struct kobject *kobj,
2375 struct kobj_attribute *attr, char *buf)
2376{
2377 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2378}
2379KSM_ATTR_RO(full_scans);
2380
Izik Eidus31dbd012009-09-21 17:02:03 -07002381static struct attribute *ksm_attrs[] = {
2382 &sleep_millisecs_attr.attr,
2383 &pages_to_scan_attr.attr,
2384 &run_attr.attr,
Hugh Dickinsb4028262009-09-21 17:02:09 -07002385 &pages_shared_attr.attr,
2386 &pages_sharing_attr.attr,
Hugh Dickins473b0ce2009-09-21 17:02:11 -07002387 &pages_unshared_attr.attr,
2388 &pages_volatile_attr.attr,
2389 &full_scans_attr.attr,
Petr Holasek90bd6fd2013-02-22 16:35:00 -08002390#ifdef CONFIG_NUMA
2391 &merge_across_nodes_attr.attr,
2392#endif
Izik Eidus31dbd012009-09-21 17:02:03 -07002393 NULL,
2394};
2395
2396static struct attribute_group ksm_attr_group = {
2397 .attrs = ksm_attrs,
2398 .name = "ksm",
2399};
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002400#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07002401
2402static int __init ksm_init(void)
2403{
2404 struct task_struct *ksm_thread;
2405 int err;
2406
2407 err = ksm_slab_init();
2408 if (err)
2409 goto out;
2410
Izik Eidus31dbd012009-09-21 17:02:03 -07002411 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2412 if (IS_ERR(ksm_thread)) {
2413 printk(KERN_ERR "ksm: creating kthread failed\n");
2414 err = PTR_ERR(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07002415 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07002416 }
2417
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002418#ifdef CONFIG_SYSFS
Izik Eidus31dbd012009-09-21 17:02:03 -07002419 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2420 if (err) {
2421 printk(KERN_ERR "ksm: register sysfs failed\n");
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002422 kthread_stop(ksm_thread);
Lai Jiangshand9f89842010-08-09 17:20:02 -07002423 goto out_free;
Izik Eidus31dbd012009-09-21 17:02:03 -07002424 }
Hugh Dickinsc73602a2009-10-07 16:32:22 -07002425#else
2426 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2427
Hugh Dickins2ffd8672009-09-21 17:02:23 -07002428#endif /* CONFIG_SYSFS */
Izik Eidus31dbd012009-09-21 17:02:03 -07002429
Hugh Dickins62b61f62009-12-14 17:59:33 -08002430#ifdef CONFIG_MEMORY_HOTREMOVE
Hugh Dickinsef4d43a2013-02-22 16:35:16 -08002431 /* There is no significance to this priority 100 */
Hugh Dickins62b61f62009-12-14 17:59:33 -08002432 hotplug_memory_notifier(ksm_memory_callback, 100);
2433#endif
Izik Eidus31dbd012009-09-21 17:02:03 -07002434 return 0;
2435
Lai Jiangshand9f89842010-08-09 17:20:02 -07002436out_free:
Izik Eidus31dbd012009-09-21 17:02:03 -07002437 ksm_slab_free();
2438out:
2439 return err;
2440}
2441module_init(ksm_init)