~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/mm/ksm.c

Version: ~ [ linux-5.14-rc1 ] ~ [ linux-5.13.1 ] ~ [ linux-5.12.16 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.49 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.131 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.197 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.239 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.275 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.275 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  * Memory merging support.
  3  *
  4  * This code enables dynamic sharing of identical pages found in different
  5  * memory areas, even if they are not shared by fork()
  6  *
  7  * Copyright (C) 2008-2009 Red Hat, Inc.
  8  * Authors:
  9  *      Izik Eidus
 10  *      Andrea Arcangeli
 11  *      Chris Wright
 12  *      Hugh Dickins
 13  *
 14  * This work is licensed under the terms of the GNU GPL, version 2.
 15  */
 16 
 17 #include <linux/errno.h>
 18 #include <linux/mm.h>
 19 #include <linux/fs.h>
 20 #include <linux/mman.h>
 21 #include <linux/sched.h>
 22 #include <linux/rwsem.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/rmap.h>
 25 #include <linux/spinlock.h>
 26 #include <linux/jhash.h>
 27 #include <linux/delay.h>
 28 #include <linux/kthread.h>
 29 #include <linux/wait.h>
 30 #include <linux/slab.h>
 31 #include <linux/rbtree.h>
 32 #include <linux/memory.h>
 33 #include <linux/mmu_notifier.h>
 34 #include <linux/swap.h>
 35 #include <linux/ksm.h>
 36 #include <linux/hashtable.h>
 37 #include <linux/freezer.h>
 38 #include <linux/oom.h>
 39 #include <linux/numa.h>
 40 
 41 #include <asm/tlbflush.h>
 42 #include "internal.h"
 43 
 44 #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 
 52 /*
 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.)
 90  *
 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.
 93  */
 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
 99  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
100  * @mm: the mm that this information is valid for
101  */
102 struct mm_slot {
103         struct hlist_node link;
104         struct list_head mm_list;
105         struct rmap_item *rmap_list;
106         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
113  * @rmap_list: link to the next rmap to be scanned in the rmap_list
114  * @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  */
118 struct ksm_scan {
119         struct mm_slot *mm_slot;
120         unsigned long address;
121         struct rmap_item **rmap_list;
122         unsigned long seqnr;
123 };
124 
125 /**
126  * struct stable_node - node of the stable rbtree
127  * @node: rb node of this ksm page in the stable tree
128  * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129  * @list: linked into migrate_nodes, pending placement in the proper node tree
130  * @hlist: hlist head of rmap_items using this ksm page
131  * @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)
133  */
134 struct stable_node {
135         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         };
142         struct hlist_head hlist;
143         unsigned long kpfn;
144 #ifdef CONFIG_NUMA
145         int nid;
146 #endif
147 };
148 
149 /**
150  * struct rmap_item - reverse mapping item for virtual addresses
151  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
152  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
153  * @nid: NUMA node id of unstable tree in which linked (may not match page)
154  * @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
157  * @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
160  */
161 struct rmap_item {
162         struct rmap_item *rmap_list;
163         union {
164                 struct anon_vma *anon_vma;      /* when stable */
165 #ifdef CONFIG_NUMA
166                 int nid;                /* when node of unstable tree */
167 #endif
168         };
169         struct mm_struct *mm;
170         unsigned long address;          /* + low bits used for flags below */
171         unsigned int oldchecksum;       /* when unstable */
172         union {
173                 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                 };
178         };
179 };
180 
181 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
182 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
183 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
184 
185 /* The stable and unstable tree heads */
186 static struct rb_root one_stable_tree[1] = { RB_ROOT };
187 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188 static struct rb_root *root_stable_tree = one_stable_tree;
189 static struct rb_root *root_unstable_tree = one_unstable_tree;
190 
191 /* Recently migrated nodes of stable tree, pending proper placement */
192 static LIST_HEAD(migrate_nodes);
193 
194 #define MM_SLOTS_HASH_BITS 10
195 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
196 
197 static struct mm_slot ksm_mm_head = {
198         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
199 };
200 static struct ksm_scan ksm_scan = {
201         .mm_slot = &ksm_mm_head,
202 };
203 
204 static struct kmem_cache *rmap_item_cache;
205 static struct kmem_cache *stable_node_cache;
206 static struct kmem_cache *mm_slot_cache;
207 
208 /* The number of nodes in the stable tree */
209 static unsigned long ksm_pages_shared;
210 
211 /* The number of page slots additionally sharing those nodes */
212 static unsigned long ksm_pages_sharing;
213 
214 /* The number of nodes in the unstable tree */
215 static unsigned long ksm_pages_unshared;
216 
217 /* The number of rmap_items in use: to calculate pages_volatile */
218 static unsigned long ksm_rmap_items;
219 
220 /* Number of pages ksmd should scan in one batch */
221 static unsigned int ksm_thread_pages_to_scan = 100;
222 
223 /* Milliseconds ksmd should sleep between batches */
224 static unsigned int ksm_thread_sleep_millisecs = 20;
225 
226 #ifdef CONFIG_NUMA
227 /* Zeroed when merging across nodes is not allowed */
228 static unsigned int ksm_merge_across_nodes = 1;
229 static int ksm_nr_node_ids = 1;
230 #else
231 #define ksm_merge_across_nodes  1U
232 #define ksm_nr_node_ids         1
233 #endif
234 
235 #define KSM_RUN_STOP    0
236 #define KSM_RUN_MERGE   1
237 #define KSM_RUN_UNMERGE 2
238 #define KSM_RUN_OFFLINE 4
239 static unsigned long ksm_run = KSM_RUN_STOP;
240 static void wait_while_offlining(void);
241 
242 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243 static DEFINE_MUTEX(ksm_thread_mutex);
244 static 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 
250 static 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 
256         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257         if (!stable_node_cache)
258                 goto out_free1;
259 
260         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261         if (!mm_slot_cache)
262                 goto out_free2;
263 
264         return 0;
265 
266 out_free2:
267         kmem_cache_destroy(stable_node_cache);
268 out_free1:
269         kmem_cache_destroy(rmap_item_cache);
270 out:
271         return -ENOMEM;
272 }
273 
274 static void __init ksm_slab_free(void)
275 {
276         kmem_cache_destroy(mm_slot_cache);
277         kmem_cache_destroy(stable_node_cache);
278         kmem_cache_destroy(rmap_item_cache);
279         mm_slot_cache = NULL;
280 }
281 
282 static inline struct rmap_item *alloc_rmap_item(void)
283 {
284         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;
290 }
291 
292 static inline void free_rmap_item(struct rmap_item *rmap_item)
293 {
294         ksm_rmap_items--;
295         rmap_item->mm = NULL;   /* debug safety */
296         kmem_cache_free(rmap_item_cache, rmap_item);
297 }
298 
299 static inline struct stable_node *alloc_stable_node(void)
300 {
301         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
302 }
303 
304 static inline void free_stable_node(struct stable_node *stable_node)
305 {
306         kmem_cache_free(stable_node_cache, stable_node);
307 }
308 
309 static 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 
316 static inline void free_mm_slot(struct mm_slot *mm_slot)
317 {
318         kmem_cache_free(mm_slot_cache, mm_slot);
319 }
320 
321 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
322 {
323         struct mm_slot *slot;
324 
325         hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
326                 if (slot->mm == mm)
327                         return slot;
328 
329         return NULL;
330 }
331 
332 static void insert_to_mm_slots_hash(struct mm_struct *mm,
333                                     struct mm_slot *mm_slot)
334 {
335         mm_slot->mm = mm;
336         hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
337 }
338 
339 /*
340  * 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  */
347 static inline bool ksm_test_exit(struct mm_struct *mm)
348 {
349         return atomic_read(&mm->mm_users) == 0;
350 }
351 
352 /*
353  * We use break_ksm to break COW on a ksm page: it's a stripped down
354  *
355  *      if (get_user_pages(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  *
363  * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
364  * of the process that owns 'vma'.  We also do not want to enforce
365  * protection keys here anyway.
366  */
367 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
368 {
369         struct page *page;
370         int ret = 0;
371 
372         do {
373                 cond_resched();
374                 page = follow_page(vma, addr,
375                                 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
376                 if (IS_ERR_OR_NULL(page))
377                         break;
378                 if (PageKsm(page))
379                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
380                                                         FAULT_FLAG_WRITE |
381                                                         FAULT_FLAG_REMOTE);
382                 else
383                         ret = VM_FAULT_WRITE;
384                 put_page(page);
385         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
386         /*
387          * We must loop because handle_mm_fault() may back out if there's
388          * any difficulty e.g. if pte accessed bit gets updated concurrently.
389          *
390          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
391          * COW has been broken, even if the vma does not permit VM_WRITE;
392          * but note that a concurrent fault might break PageKsm for us.
393          *
394          * VM_FAULT_SIGBUS could occur if we race with truncation of the
395          * backing file, which also invalidates anonymous pages: that's
396          * okay, that truncation will have unmapped the PageKsm for us.
397          *
398          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
399          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
400          * current task has TIF_MEMDIE set, and will be OOM killed on return
401          * to user; and ksmd, having no mm, would never be chosen for that.
402          *
403          * But if the mm is in a limited mem_cgroup, then the fault may fail
404          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
405          * even ksmd can fail in this way - though it's usually breaking ksm
406          * just to undo a merge it made a moment before, so unlikely to oom.
407          *
408          * That's a pity: we might therefore have more kernel pages allocated
409          * than we're counting as nodes in the stable tree; but ksm_do_scan
410          * will retry to break_cow on each pass, so should recover the page
411          * in due course.  The important thing is to not let VM_MERGEABLE
412          * be cleared while any such pages might remain in the area.
413          */
414         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
415 }
416 
417 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
418                 unsigned long addr)
419 {
420         struct vm_area_struct *vma;
421         if (ksm_test_exit(mm))
422                 return NULL;
423         vma = find_vma(mm, addr);
424         if (!vma || vma->vm_start > addr)
425                 return NULL;
426         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
427                 return NULL;
428         return vma;
429 }
430 
431 static void break_cow(struct rmap_item *rmap_item)
432 {
433         struct mm_struct *mm = rmap_item->mm;
434         unsigned long addr = rmap_item->address;
435         struct vm_area_struct *vma;
436 
437         /*
438          * It is not an accident that whenever we want to break COW
439          * to undo, we also need to drop a reference to the anon_vma.
440          */
441         put_anon_vma(rmap_item->anon_vma);
442 
443         down_read(&mm->mmap_sem);
444         vma = find_mergeable_vma(mm, addr);
445         if (vma)
446                 break_ksm(vma, addr);
447         up_read(&mm->mmap_sem);
448 }
449 
450 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
451 {
452         struct mm_struct *mm = rmap_item->mm;
453         unsigned long addr = rmap_item->address;
454         struct vm_area_struct *vma;
455         struct page *page;
456 
457         down_read(&mm->mmap_sem);
458         vma = find_mergeable_vma(mm, addr);
459         if (!vma)
460                 goto out;
461 
462         page = follow_page(vma, addr, FOLL_GET);
463         if (IS_ERR_OR_NULL(page))
464                 goto out;
465         if (PageAnon(page)) {
466                 flush_anon_page(vma, page, addr);
467                 flush_dcache_page(page);
468         } else {
469                 put_page(page);
470 out:
471                 page = NULL;
472         }
473         up_read(&mm->mmap_sem);
474         return page;
475 }
476 
477 /*
478  * This helper is used for getting right index into array of tree roots.
479  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
480  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
481  * every node has its own stable and unstable tree.
482  */
483 static inline int get_kpfn_nid(unsigned long kpfn)
484 {
485         return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
486 }
487 
488 static void remove_node_from_stable_tree(struct stable_node *stable_node)
489 {
490         struct rmap_item *rmap_item;
491 
492         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
493                 if (rmap_item->hlist.next)
494                         ksm_pages_sharing--;
495                 else
496                         ksm_pages_shared--;
497                 put_anon_vma(rmap_item->anon_vma);
498                 rmap_item->address &= PAGE_MASK;
499                 cond_resched();
500         }
501 
502         if (stable_node->head == &migrate_nodes)
503                 list_del(&stable_node->list);
504         else
505                 rb_erase(&stable_node->node,
506                          root_stable_tree + NUMA(stable_node->nid));
507         free_stable_node(stable_node);
508 }
509 
510 /*
511  * get_ksm_page: checks if the page indicated by the stable node
512  * is still its ksm page, despite having held no reference to it.
513  * In which case we can trust the content of the page, and it
514  * returns the gotten page; but if the page has now been zapped,
515  * remove the stale node from the stable tree and return NULL.
516  * But beware, the stable node's page might be being migrated.
517  *
518  * You would expect the stable_node to hold a reference to the ksm page.
519  * But if it increments the page's count, swapping out has to wait for
520  * ksmd to come around again before it can free the page, which may take
521  * seconds or even minutes: much too unresponsive.  So instead we use a
522  * "keyhole reference": access to the ksm page from the stable node peeps
523  * out through its keyhole to see if that page still holds the right key,
524  * pointing back to this stable node.  This relies on freeing a PageAnon
525  * page to reset its page->mapping to NULL, and relies on no other use of
526  * a page to put something that might look like our key in page->mapping.
527  * is on its way to being freed; but it is an anomaly to bear in mind.
528  */
529 static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
530 {
531         struct page *page;
532         void *expected_mapping;
533         unsigned long kpfn;
534 
535         expected_mapping = (void *)stable_node +
536                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
537 again:
538         kpfn = READ_ONCE(stable_node->kpfn);
539         page = pfn_to_page(kpfn);
540 
541         /*
542          * page is computed from kpfn, so on most architectures reading
543          * page->mapping is naturally ordered after reading node->kpfn,
544          * but on Alpha we need to be more careful.
545          */
546         smp_read_barrier_depends();
547         if (READ_ONCE(page->mapping) != expected_mapping)
548                 goto stale;
549 
550         /*
551          * We cannot do anything with the page while its refcount is 0.
552          * Usually 0 means free, or tail of a higher-order page: in which
553          * case this node is no longer referenced, and should be freed;
554          * however, it might mean that the page is under page_freeze_refs().
555          * The __remove_mapping() case is easy, again the node is now stale;
556          * but if page is swapcache in migrate_page_move_mapping(), it might
557          * still be our page, in which case it's essential to keep the node.
558          */
559         while (!get_page_unless_zero(page)) {
560                 /*
561                  * Another check for page->mapping != expected_mapping would
562                  * work here too.  We have chosen the !PageSwapCache test to
563                  * optimize the common case, when the page is or is about to
564                  * be freed: PageSwapCache is cleared (under spin_lock_irq)
565                  * in the freeze_refs section of __remove_mapping(); but Anon
566                  * page->mapping reset to NULL later, in free_pages_prepare().
567                  */
568                 if (!PageSwapCache(page))
569                         goto stale;
570                 cpu_relax();
571         }
572 
573         if (READ_ONCE(page->mapping) != expected_mapping) {
574                 put_page(page);
575                 goto stale;
576         }
577 
578         if (lock_it) {
579                 lock_page(page);
580                 if (READ_ONCE(page->mapping) != expected_mapping) {
581                         unlock_page(page);
582                         put_page(page);
583                         goto stale;
584                 }
585         }
586         return page;
587 
588 stale:
589         /*
590          * We come here from above when page->mapping or !PageSwapCache
591          * suggests that the node is stale; but it might be under migration.
592          * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
593          * before checking whether node->kpfn has been changed.
594          */
595         smp_rmb();
596         if (READ_ONCE(stable_node->kpfn) != kpfn)
597                 goto again;
598         remove_node_from_stable_tree(stable_node);
599         return NULL;
600 }
601 
602 /*
603  * Removing rmap_item from stable or unstable tree.
604  * This function will clean the information from the stable/unstable tree.
605  */
606 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
607 {
608         if (rmap_item->address & STABLE_FLAG) {
609                 struct stable_node *stable_node;
610                 struct page *page;
611 
612                 stable_node = rmap_item->head;
613                 page = get_ksm_page(stable_node, true);
614                 if (!page)
615                         goto out;
616 
617                 hlist_del(&rmap_item->hlist);
618                 unlock_page(page);
619                 put_page(page);
620 
621                 if (!hlist_empty(&stable_node->hlist))
622                         ksm_pages_sharing--;
623                 else
624                         ksm_pages_shared--;
625 
626                 put_anon_vma(rmap_item->anon_vma);
627                 rmap_item->address &= PAGE_MASK;
628 
629         } else if (rmap_item->address & UNSTABLE_FLAG) {
630                 unsigned char age;
631                 /*
632                  * Usually ksmd can and must skip the rb_erase, because
633                  * root_unstable_tree was already reset to RB_ROOT.
634                  * But be careful when an mm is exiting: do the rb_erase
635                  * if this rmap_item was inserted by this scan, rather
636                  * than left over from before.
637                  */
638                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
639                 BUG_ON(age > 1);
640                 if (!age)
641                         rb_erase(&rmap_item->node,
642                                  root_unstable_tree + NUMA(rmap_item->nid));
643                 ksm_pages_unshared--;
644                 rmap_item->address &= PAGE_MASK;
645         }
646 out:
647         cond_resched();         /* we're called from many long loops */
648 }
649 
650 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
651                                        struct rmap_item **rmap_list)
652 {
653         while (*rmap_list) {
654                 struct rmap_item *rmap_item = *rmap_list;
655                 *rmap_list = rmap_item->rmap_list;
656                 remove_rmap_item_from_tree(rmap_item);
657                 free_rmap_item(rmap_item);
658         }
659 }
660 
661 /*
662  * Though it's very tempting to unmerge rmap_items from stable tree rather
663  * than check every pte of a given vma, the locking doesn't quite work for
664  * that - an rmap_item is assigned to the stable tree after inserting ksm
665  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
666  * rmap_items from parent to child at fork time (so as not to waste time
667  * if exit comes before the next scan reaches it).
668  *
669  * Similarly, although we'd like to remove rmap_items (so updating counts
670  * and freeing memory) when unmerging an area, it's easier to leave that
671  * to the next pass of ksmd - consider, for example, how ksmd might be
672  * in cmp_and_merge_page on one of the rmap_items we would be removing.
673  */
674 static int unmerge_ksm_pages(struct vm_area_struct *vma,
675                              unsigned long start, unsigned long end)
676 {
677         unsigned long addr;
678         int err = 0;
679 
680         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
681                 if (ksm_test_exit(vma->vm_mm))
682                         break;
683                 if (signal_pending(current))
684                         err = -ERESTARTSYS;
685                 else
686                         err = break_ksm(vma, addr);
687         }
688         return err;
689 }
690 
691 #ifdef CONFIG_SYSFS
692 /*
693  * Only called through the sysfs control interface:
694  */
695 static int remove_stable_node(struct stable_node *stable_node)
696 {
697         struct page *page;
698         int err;
699 
700         page = get_ksm_page(stable_node, true);
701         if (!page) {
702                 /*
703                  * get_ksm_page did remove_node_from_stable_tree itself.
704                  */
705                 return 0;
706         }
707 
708         if (WARN_ON_ONCE(page_mapped(page))) {
709                 /*
710                  * This should not happen: but if it does, just refuse to let
711                  * merge_across_nodes be switched - there is no need to panic.
712                  */
713                 err = -EBUSY;
714         } else {
715                 /*
716                  * The stable node did not yet appear stale to get_ksm_page(),
717                  * since that allows for an unmapped ksm page to be recognized
718                  * right up until it is freed; but the node is safe to remove.
719                  * This page might be in a pagevec waiting to be freed,
720                  * or it might be PageSwapCache (perhaps under writeback),
721                  * or it might have been removed from swapcache a moment ago.
722                  */
723                 set_page_stable_node(page, NULL);
724                 remove_node_from_stable_tree(stable_node);
725                 err = 0;
726         }
727 
728         unlock_page(page);
729         put_page(page);
730         return err;
731 }
732 
733 static int remove_all_stable_nodes(void)
734 {
735         struct stable_node *stable_node, *next;
736         int nid;
737         int err = 0;
738 
739         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
740                 while (root_stable_tree[nid].rb_node) {
741                         stable_node = rb_entry(root_stable_tree[nid].rb_node,
742                                                 struct stable_node, node);
743                         if (remove_stable_node(stable_node)) {
744                                 err = -EBUSY;
745                                 break;  /* proceed to next nid */
746                         }
747                         cond_resched();
748                 }
749         }
750         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
751                 if (remove_stable_node(stable_node))
752                         err = -EBUSY;
753                 cond_resched();
754         }
755         return err;
756 }
757 
758 static int unmerge_and_remove_all_rmap_items(void)
759 {
760         struct mm_slot *mm_slot;
761         struct mm_struct *mm;
762         struct vm_area_struct *vma;
763         int err = 0;
764 
765         spin_lock(&ksm_mmlist_lock);
766         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
767                                                 struct mm_slot, mm_list);
768         spin_unlock(&ksm_mmlist_lock);
769 
770         for (mm_slot = ksm_scan.mm_slot;
771                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
772                 mm = mm_slot->mm;
773                 down_read(&mm->mmap_sem);
774                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
775                         if (ksm_test_exit(mm))
776                                 break;
777                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
778                                 continue;
779                         err = unmerge_ksm_pages(vma,
780                                                 vma->vm_start, vma->vm_end);
781                         if (err)
782                                 goto error;
783                 }
784 
785                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
786                 up_read(&mm->mmap_sem);
787 
788                 spin_lock(&ksm_mmlist_lock);
789                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
790                                                 struct mm_slot, mm_list);
791                 if (ksm_test_exit(mm)) {
792                         hash_del(&mm_slot->link);
793                         list_del(&mm_slot->mm_list);
794                         spin_unlock(&ksm_mmlist_lock);
795 
796                         free_mm_slot(mm_slot);
797                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
798                         mmdrop(mm);
799                 } else
800                         spin_unlock(&ksm_mmlist_lock);
801         }
802 
803         /* Clean up stable nodes, but don't worry if some are still busy */
804         remove_all_stable_nodes();
805         ksm_scan.seqnr = 0;
806         return 0;
807 
808 error:
809         up_read(&mm->mmap_sem);
810         spin_lock(&ksm_mmlist_lock);
811         ksm_scan.mm_slot = &ksm_mm_head;
812         spin_unlock(&ksm_mmlist_lock);
813         return err;
814 }
815 #endif /* CONFIG_SYSFS */
816 
817 static u32 calc_checksum(struct page *page)
818 {
819         u32 checksum;
820         void *addr = kmap_atomic(page);
821         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
822         kunmap_atomic(addr);
823         return checksum;
824 }
825 
826 static int memcmp_pages(struct page *page1, struct page *page2)
827 {
828         char *addr1, *addr2;
829         int ret;
830 
831         addr1 = kmap_atomic(page1);
832         addr2 = kmap_atomic(page2);
833         ret = memcmp(addr1, addr2, PAGE_SIZE);
834         kunmap_atomic(addr2);
835         kunmap_atomic(addr1);
836         return ret;
837 }
838 
839 static inline int pages_identical(struct page *page1, struct page *page2)
840 {
841         return !memcmp_pages(page1, page2);
842 }
843 
844 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
845                               pte_t *orig_pte)
846 {
847         struct mm_struct *mm = vma->vm_mm;
848         unsigned long addr;
849         pte_t *ptep;
850         spinlock_t *ptl;
851         int swapped;
852         int err = -EFAULT;
853         unsigned long mmun_start;       /* For mmu_notifiers */
854         unsigned long mmun_end;         /* For mmu_notifiers */
855 
856         addr = page_address_in_vma(page, vma);
857         if (addr == -EFAULT)
858                 goto out;
859 
860         BUG_ON(PageTransCompound(page));
861 
862         mmun_start = addr;
863         mmun_end   = addr + PAGE_SIZE;
864         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
865 
866         ptep = page_check_address(page, mm, addr, &ptl, 0);
867         if (!ptep)
868                 goto out_mn;
869 
870         if (pte_write(*ptep) || pte_dirty(*ptep)) {
871                 pte_t entry;
872 
873                 swapped = PageSwapCache(page);
874                 flush_cache_page(vma, addr, page_to_pfn(page));
875                 /*
876                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
877                  * take any lock, therefore the check that we are going to make
878                  * with the pagecount against the mapcount is racey and
879                  * O_DIRECT can happen right after the check.
880                  * So we clear the pte and flush the tlb before the check
881                  * this assure us that no O_DIRECT can happen after the check
882                  * or in the middle of the check.
883                  */
884                 entry = ptep_clear_flush_notify(vma, addr, ptep);
885                 /*
886                  * Check that no O_DIRECT or similar I/O is in progress on the
887                  * page
888                  */
889                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
890                         set_pte_at(mm, addr, ptep, entry);
891                         goto out_unlock;
892                 }
893                 if (pte_dirty(entry))
894                         set_page_dirty(page);
895                 entry = pte_mkclean(pte_wrprotect(entry));
896                 set_pte_at_notify(mm, addr, ptep, entry);
897         }
898         *orig_pte = *ptep;
899         err = 0;
900 
901 out_unlock:
902         pte_unmap_unlock(ptep, ptl);
903 out_mn:
904         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
905 out:
906         return err;
907 }
908 
909 /**
910  * replace_page - replace page in vma by new ksm page
911  * @vma:      vma that holds the pte pointing to page
912  * @page:     the page we are replacing by kpage
913  * @kpage:    the ksm page we replace page by
914  * @orig_pte: the original value of the pte
915  *
916  * Returns 0 on success, -EFAULT on failure.
917  */
918 static int replace_page(struct vm_area_struct *vma, struct page *page,
919                         struct page *kpage, pte_t orig_pte)
920 {
921         struct mm_struct *mm = vma->vm_mm;
922         pmd_t *pmd;
923         pte_t *ptep;
924         spinlock_t *ptl;
925         unsigned long addr;
926         int err = -EFAULT;
927         unsigned long mmun_start;       /* For mmu_notifiers */
928         unsigned long mmun_end;         /* For mmu_notifiers */
929 
930         addr = page_address_in_vma(page, vma);
931         if (addr == -EFAULT)
932                 goto out;
933 
934         pmd = mm_find_pmd(mm, addr);
935         if (!pmd)
936                 goto out;
937 
938         mmun_start = addr;
939         mmun_end   = addr + PAGE_SIZE;
940         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
941 
942         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
943         if (!pte_same(*ptep, orig_pte)) {
944                 pte_unmap_unlock(ptep, ptl);
945                 goto out_mn;
946         }
947 
948         get_page(kpage);
949         page_add_anon_rmap(kpage, vma, addr, false);
950 
951         flush_cache_page(vma, addr, pte_pfn(*ptep));
952         ptep_clear_flush_notify(vma, addr, ptep);
953         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
954 
955         page_remove_rmap(page, false);
956         if (!page_mapped(page))
957                 try_to_free_swap(page);
958         put_page(page);
959 
960         pte_unmap_unlock(ptep, ptl);
961         err = 0;
962 out_mn:
963         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
964 out:
965         return err;
966 }
967 
968 /*
969  * try_to_merge_one_page - take two pages and merge them into one
970  * @vma: the vma that holds the pte pointing to page
971  * @page: the PageAnon page that we want to replace with kpage
972  * @kpage: the PageKsm page that we want to map instead of page,
973  *         or NULL the first time when we want to use page as kpage.
974  *
975  * This function returns 0 if the pages were merged, -EFAULT otherwise.
976  */
977 static int try_to_merge_one_page(struct vm_area_struct *vma,
978                                  struct page *page, struct page *kpage)
979 {
980         pte_t orig_pte = __pte(0);
981         int err = -EFAULT;
982 
983         if (page == kpage)                      /* ksm page forked */
984                 return 0;
985 
986         if (!PageAnon(page))
987                 goto out;
988 
989         /*
990          * We need the page lock to read a stable PageSwapCache in
991          * write_protect_page().  We use trylock_page() instead of
992          * lock_page() because we don't want to wait here - we
993          * prefer to continue scanning and merging different pages,
994          * then come back to this page when it is unlocked.
995          */
996         if (!trylock_page(page))
997                 goto out;
998 
999         if (PageTransCompound(page)) {
1000                 err = split_huge_page(page);
1001                 if (err)
1002                         goto out_unlock;
1003         }
1004 
1005         /*
1006          * If this anonymous page is mapped only here, its pte may need
1007          * to be write-protected.  If it's mapped elsewhere, all of its
1008          * ptes are necessarily already write-protected.  But in either
1009          * case, we need to lock and check page_count is not raised.
1010          */
1011         if (write_protect_page(vma, page, &orig_pte) == 0) {
1012                 if (!kpage) {
1013                         /*
1014                          * While we hold page lock, upgrade page from
1015                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
1016                          * stable_tree_insert() will update stable_node.
1017                          */
1018                         set_page_stable_node(page, NULL);
1019                         mark_page_accessed(page);
1020                         /*
1021                          * Page reclaim just frees a clean page with no dirty
1022                          * ptes: make sure that the ksm page would be swapped.
1023                          */
1024                         if (!PageDirty(page))
1025                                 SetPageDirty(page);
1026                         err = 0;
1027                 } else if (pages_identical(page, kpage))
1028                         err = replace_page(vma, page, kpage, orig_pte);
1029         }
1030 
1031         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1032                 munlock_vma_page(page);
1033                 if (!PageMlocked(kpage)) {
1034                         unlock_page(page);
1035                         lock_page(kpage);
1036                         mlock_vma_page(kpage);
1037                         page = kpage;           /* for final unlock */
1038                 }
1039         }
1040 
1041 out_unlock:
1042         unlock_page(page);
1043 out:
1044         return err;
1045 }
1046 
1047 /*
1048  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1049  * but no new kernel page is allocated: kpage must already be a ksm page.
1050  *
1051  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1052  */
1053 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1054                                       struct page *page, struct page *kpage)
1055 {
1056         struct mm_struct *mm = rmap_item->mm;
1057         struct vm_area_struct *vma;
1058         int err = -EFAULT;
1059 
1060         down_read(&mm->mmap_sem);
1061         vma = find_mergeable_vma(mm, rmap_item->address);
1062         if (!vma)
1063                 goto out;
1064 
1065         err = try_to_merge_one_page(vma, page, kpage);
1066         if (err)
1067                 goto out;
1068 
1069         /* Unstable nid is in union with stable anon_vma: remove first */
1070         remove_rmap_item_from_tree(rmap_item);
1071 
1072         /* Must get reference to anon_vma while still holding mmap_sem */
1073         rmap_item->anon_vma = vma->anon_vma;
1074         get_anon_vma(vma->anon_vma);
1075 out:
1076         up_read(&mm->mmap_sem);
1077         return err;
1078 }
1079 
1080 /*
1081  * try_to_merge_two_pages - take two identical pages and prepare them
1082  * to be merged into one page.
1083  *
1084  * This function returns the kpage if we successfully merged two identical
1085  * pages into one ksm page, NULL otherwise.
1086  *
1087  * Note that this function upgrades page to ksm page: if one of the pages
1088  * is already a ksm page, try_to_merge_with_ksm_page should be used.
1089  */
1090 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1091                                            struct page *page,
1092                                            struct rmap_item *tree_rmap_item,
1093                                            struct page *tree_page)
1094 {
1095         int err;
1096 
1097         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1098         if (!err) {
1099                 err = try_to_merge_with_ksm_page(tree_rmap_item,
1100                                                         tree_page, page);
1101                 /*
1102                  * If that fails, we have a ksm page with only one pte
1103                  * pointing to it: so break it.
1104                  */
1105                 if (err)
1106                         break_cow(rmap_item);
1107         }
1108         return err ? NULL : page;
1109 }
1110 
1111 /*
1112  * stable_tree_search - search for page inside the stable tree
1113  *
1114  * This function checks if there is a page inside the stable tree
1115  * with identical content to the page that we are scanning right now.
1116  *
1117  * This function returns the stable tree node of identical content if found,
1118  * NULL otherwise.
1119  */
1120 static struct page *stable_tree_search(struct page *page)
1121 {
1122         int nid;
1123         struct rb_root *root;
1124         struct rb_node **new;
1125         struct rb_node *parent;
1126         struct stable_node *stable_node;
1127         struct stable_node *page_node;
1128 
1129         page_node = page_stable_node(page);
1130         if (page_node && page_node->head != &migrate_nodes) {
1131                 /* ksm page forked */
1132                 get_page(page);
1133                 return page;
1134         }
1135 
1136         nid = get_kpfn_nid(page_to_pfn(page));
1137         root = root_stable_tree + nid;
1138 again:
1139         new = &root->rb_node;
1140         parent = NULL;
1141 
1142         while (*new) {
1143                 struct page *tree_page;
1144                 int ret;
1145 
1146                 cond_resched();
1147                 stable_node = rb_entry(*new, struct stable_node, node);
1148                 tree_page = get_ksm_page(stable_node, false);
1149                 if (!tree_page) {
1150                         /*
1151                          * If we walked over a stale stable_node,
1152                          * get_ksm_page() will call rb_erase() and it
1153                          * may rebalance the tree from under us. So
1154                          * restart the search from scratch. Returning
1155                          * NULL would be safe too, but we'd generate
1156                          * false negative insertions just because some
1157                          * stable_node was stale.
1158                          */
1159                         goto again;
1160                 }
1161 
1162                 ret = memcmp_pages(page, tree_page);
1163                 put_page(tree_page);
1164 
1165                 parent = *new;
1166                 if (ret < 0)
1167                         new = &parent->rb_left;
1168                 else if (ret > 0)
1169                         new = &parent->rb_right;
1170                 else {
1171                         /*
1172                          * Lock and unlock the stable_node's page (which
1173                          * might already have been migrated) so that page
1174                          * migration is sure to notice its raised count.
1175                          * It would be more elegant to return stable_node
1176                          * than kpage, but that involves more changes.
1177                          */
1178                         tree_page = get_ksm_page(stable_node, true);
1179                         if (tree_page) {
1180                                 unlock_page(tree_page);
1181                                 if (get_kpfn_nid(stable_node->kpfn) !=
1182                                                 NUMA(stable_node->nid)) {
1183                                         put_page(tree_page);
1184                                         goto replace;
1185                                 }
1186                                 return tree_page;
1187                         }
1188                         /*
1189                          * There is now a place for page_node, but the tree may
1190                          * have been rebalanced, so re-evaluate parent and new.
1191                          */
1192                         if (page_node)
1193                                 goto again;
1194                         return NULL;
1195                 }
1196         }
1197 
1198         if (!page_node)
1199                 return NULL;
1200 
1201         list_del(&page_node->list);
1202         DO_NUMA(page_node->nid = nid);
1203         rb_link_node(&page_node->node, parent, new);
1204         rb_insert_color(&page_node->node, root);
1205         get_page(page);
1206         return page;
1207 
1208 replace:
1209         if (page_node) {
1210                 list_del(&page_node->list);
1211                 DO_NUMA(page_node->nid = nid);
1212                 rb_replace_node(&stable_node->node, &page_node->node, root);
1213                 get_page(page);
1214         } else {
1215                 rb_erase(&stable_node->node, root);
1216                 page = NULL;
1217         }
1218         stable_node->head = &migrate_nodes;
1219         list_add(&stable_node->list, stable_node->head);
1220         return page;
1221 }
1222 
1223 /*
1224  * stable_tree_insert - insert stable tree node pointing to new ksm page
1225  * into the stable tree.
1226  *
1227  * This function returns the stable tree node just allocated on success,
1228  * NULL otherwise.
1229  */
1230 static struct stable_node *stable_tree_insert(struct page *kpage)
1231 {
1232         int nid;
1233         unsigned long kpfn;
1234         struct rb_root *root;
1235         struct rb_node **new;
1236         struct rb_node *parent;
1237         struct stable_node *stable_node;
1238 
1239         kpfn = page_to_pfn(kpage);
1240         nid = get_kpfn_nid(kpfn);
1241         root = root_stable_tree + nid;
1242 again:
1243         parent = NULL;
1244         new = &root->rb_node;
1245 
1246         while (*new) {
1247                 struct page *tree_page;
1248                 int ret;
1249 
1250                 cond_resched();
1251                 stable_node = rb_entry(*new, struct stable_node, node);
1252                 tree_page = get_ksm_page(stable_node, false);
1253                 if (!tree_page) {
1254                         /*
1255                          * If we walked over a stale stable_node,
1256                          * get_ksm_page() will call rb_erase() and it
1257                          * may rebalance the tree from under us. So
1258                          * restart the search from scratch. Returning
1259                          * NULL would be safe too, but we'd generate
1260                          * false negative insertions just because some
1261                          * stable_node was stale.
1262                          */
1263                         goto again;
1264                 }
1265 
1266                 ret = memcmp_pages(kpage, tree_page);
1267                 put_page(tree_page);
1268 
1269                 parent = *new;
1270                 if (ret < 0)
1271                         new = &parent->rb_left;
1272                 else if (ret > 0)
1273                         new = &parent->rb_right;
1274                 else {
1275                         /*
1276                          * It is not a bug that stable_tree_search() didn't
1277                          * find this node: because at that time our page was
1278                          * not yet write-protected, so may have changed since.
1279                          */
1280                         return NULL;
1281                 }
1282         }
1283 
1284         stable_node = alloc_stable_node();
1285         if (!stable_node)
1286                 return NULL;
1287 
1288         INIT_HLIST_HEAD(&stable_node->hlist);
1289         stable_node->kpfn = kpfn;
1290         set_page_stable_node(kpage, stable_node);
1291         DO_NUMA(stable_node->nid = nid);
1292         rb_link_node(&stable_node->node, parent, new);
1293         rb_insert_color(&stable_node->node, root);
1294 
1295         return stable_node;
1296 }
1297 
1298 /*
1299  * unstable_tree_search_insert - search for identical page,
1300  * else insert rmap_item into the unstable tree.
1301  *
1302  * This function searches for a page in the unstable tree identical to the
1303  * page currently being scanned; and if no identical page is found in the
1304  * tree, we insert rmap_item as a new object into the unstable tree.
1305  *
1306  * This function returns pointer to rmap_item found to be identical
1307  * to the currently scanned page, NULL otherwise.
1308  *
1309  * This function does both searching and inserting, because they share
1310  * the same walking algorithm in an rbtree.
1311  */
1312 static
1313 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1314                                               struct page *page,
1315                                               struct page **tree_pagep)
1316 {
1317         struct rb_node **new;
1318         struct rb_root *root;
1319         struct rb_node *parent = NULL;
1320         int nid;
1321 
1322         nid = get_kpfn_nid(page_to_pfn(page));
1323         root = root_unstable_tree + nid;
1324         new = &root->rb_node;
1325 
1326         while (*new) {
1327                 struct rmap_item *tree_rmap_item;
1328                 struct page *tree_page;
1329                 int ret;
1330 
1331                 cond_resched();
1332                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1333                 tree_page = get_mergeable_page(tree_rmap_item);
1334                 if (!tree_page)
1335                         return NULL;
1336 
1337                 /*
1338                  * Don't substitute a ksm page for a forked page.
1339                  */
1340                 if (page == tree_page) {
1341                         put_page(tree_page);
1342                         return NULL;
1343                 }
1344 
1345                 ret = memcmp_pages(page, tree_page);
1346 
1347                 parent = *new;
1348                 if (ret < 0) {
1349                         put_page(tree_page);
1350                         new = &parent->rb_left;
1351                 } else if (ret > 0) {
1352                         put_page(tree_page);
1353                         new = &parent->rb_right;
1354                 } else if (!ksm_merge_across_nodes &&
1355                            page_to_nid(tree_page) != nid) {
1356                         /*
1357                          * If tree_page has been migrated to another NUMA node,
1358                          * it will be flushed out and put in the right unstable
1359                          * tree next time: only merge with it when across_nodes.
1360                          */
1361                         put_page(tree_page);
1362                         return NULL;
1363                 } else {
1364                         *tree_pagep = tree_page;
1365                         return tree_rmap_item;
1366                 }
1367         }
1368 
1369         rmap_item->address |= UNSTABLE_FLAG;
1370         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1371         DO_NUMA(rmap_item->nid = nid);
1372         rb_link_node(&rmap_item->node, parent, new);
1373         rb_insert_color(&rmap_item->node, root);
1374 
1375         ksm_pages_unshared++;
1376         return NULL;
1377 }
1378 
1379 /*
1380  * stable_tree_append - add another rmap_item to the linked list of
1381  * rmap_items hanging off a given node of the stable tree, all sharing
1382  * the same ksm page.
1383  */
1384 static void stable_tree_append(struct rmap_item *rmap_item,
1385                                struct stable_node *stable_node)
1386 {
1387         rmap_item->head = stable_node;
1388         rmap_item->address |= STABLE_FLAG;
1389         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1390 
1391         if (rmap_item->hlist.next)
1392                 ksm_pages_sharing++;
1393         else
1394                 ksm_pages_shared++;
1395 }
1396 
1397 /*
1398  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1399  * if not, compare checksum to previous and if it's the same, see if page can
1400  * be inserted into the unstable tree, or merged with a page already there and
1401  * both transferred to the stable tree.
1402  *
1403  * @page: the page that we are searching identical page to.
1404  * @rmap_item: the reverse mapping into the virtual address of this page
1405  */
1406 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1407 {
1408         struct rmap_item *tree_rmap_item;
1409         struct page *tree_page = NULL;
1410         struct stable_node *stable_node;
1411         struct page *kpage;
1412         unsigned int checksum;
1413         int err;
1414 
1415         stable_node = page_stable_node(page);
1416         if (stable_node) {
1417                 if (stable_node->head != &migrate_nodes &&
1418                     get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1419                         rb_erase(&stable_node->node,
1420                                  root_stable_tree + NUMA(stable_node->nid));
1421                         stable_node->head = &migrate_nodes;
1422                         list_add(&stable_node->list, stable_node->head);
1423                 }
1424                 if (stable_node->head != &migrate_nodes &&
1425                     rmap_item->head == stable_node)
1426                         return;
1427         }
1428 
1429         /* We first start with searching the page inside the stable tree */
1430         kpage = stable_tree_search(page);
1431         if (kpage == page && rmap_item->head == stable_node) {
1432                 put_page(kpage);
1433                 return;
1434         }
1435 
1436         remove_rmap_item_from_tree(rmap_item);
1437 
1438         if (kpage) {
1439                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1440                 if (!err) {
1441                         /*
1442                          * The page was successfully merged:
1443                          * add its rmap_item to the stable tree.
1444                          */
1445                         lock_page(kpage);
1446                         stable_tree_append(rmap_item, page_stable_node(kpage));
1447                         unlock_page(kpage);
1448                 }
1449                 put_page(kpage);
1450                 return;
1451         }
1452 
1453         /*
1454          * If the hash value of the page has changed from the last time
1455          * we calculated it, this page is changing frequently: therefore we
1456          * don't want to insert it in the unstable tree, and we don't want
1457          * to waste our time searching for something identical to it there.
1458          */
1459         checksum = calc_checksum(page);
1460         if (rmap_item->oldchecksum != checksum) {
1461                 rmap_item->oldchecksum = checksum;
1462                 return;
1463         }
1464 
1465         tree_rmap_item =
1466                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1467         if (tree_rmap_item) {
1468                 kpage = try_to_merge_two_pages(rmap_item, page,
1469                                                 tree_rmap_item, tree_page);
1470                 put_page(tree_page);
1471                 if (kpage) {
1472                         /*
1473                          * The pages were successfully merged: insert new
1474                          * node in the stable tree and add both rmap_items.
1475                          */
1476                         lock_page(kpage);
1477                         stable_node = stable_tree_insert(kpage);
1478                         if (stable_node) {
1479                                 stable_tree_append(tree_rmap_item, stable_node);
1480                                 stable_tree_append(rmap_item, stable_node);
1481                         }
1482                         unlock_page(kpage);
1483 
1484                         /*
1485                          * If we fail to insert the page into the stable tree,
1486                          * we will have 2 virtual addresses that are pointing
1487                          * to a ksm page left outside the stable tree,
1488                          * in which case we need to break_cow on both.
1489                          */
1490                         if (!stable_node) {
1491                                 break_cow(tree_rmap_item);
1492                                 break_cow(rmap_item);
1493                         }
1494                 }
1495         }
1496 }
1497 
1498 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1499                                             struct rmap_item **rmap_list,
1500                                             unsigned long addr)
1501 {
1502         struct rmap_item *rmap_item;
1503 
1504         while (*rmap_list) {
1505                 rmap_item = *rmap_list;
1506                 if ((rmap_item->address & PAGE_MASK) == addr)
1507                         return rmap_item;
1508                 if (rmap_item->address > addr)
1509                         break;
1510                 *rmap_list = rmap_item->rmap_list;
1511                 remove_rmap_item_from_tree(rmap_item);
1512                 free_rmap_item(rmap_item);
1513         }
1514 
1515         rmap_item = alloc_rmap_item();
1516         if (rmap_item) {
1517                 /* It has already been zeroed */
1518                 rmap_item->mm = mm_slot->mm;
1519                 rmap_item->address = addr;
1520                 rmap_item->rmap_list = *rmap_list;
1521                 *rmap_list = rmap_item;
1522         }
1523         return rmap_item;
1524 }
1525 
1526 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1527 {
1528         struct mm_struct *mm;
1529         struct mm_slot *slot;
1530         struct vm_area_struct *vma;
1531         struct rmap_item *rmap_item;
1532         int nid;
1533 
1534         if (list_empty(&ksm_mm_head.mm_list))
1535                 return NULL;
1536 
1537         slot = ksm_scan.mm_slot;
1538         if (slot == &ksm_mm_head) {
1539                 /*
1540                  * A number of pages can hang around indefinitely on per-cpu
1541                  * pagevecs, raised page count preventing write_protect_page
1542                  * from merging them.  Though it doesn't really matter much,
1543                  * it is puzzling to see some stuck in pages_volatile until
1544                  * other activity jostles them out, and they also prevented
1545                  * LTP's KSM test from succeeding deterministically; so drain
1546                  * them here (here rather than on entry to ksm_do_scan(),
1547                  * so we don't IPI too often when pages_to_scan is set low).
1548                  */
1549                 lru_add_drain_all();
1550 
1551                 /*
1552                  * Whereas stale stable_nodes on the stable_tree itself
1553                  * get pruned in the regular course of stable_tree_search(),
1554                  * those moved out to the migrate_nodes list can accumulate:
1555                  * so prune them once before each full scan.
1556                  */
1557                 if (!ksm_merge_across_nodes) {
1558                         struct stable_node *stable_node, *next;
1559                         struct page *page;
1560 
1561                         list_for_each_entry_safe(stable_node, next,
1562                                                  &migrate_nodes, list) {
1563                                 page = get_ksm_page(stable_node, false);
1564                                 if (page)
1565                                         put_page(page);
1566                                 cond_resched();
1567                         }
1568                 }
1569 
1570                 for (nid = 0; nid < ksm_nr_node_ids; nid++)
1571                         root_unstable_tree[nid] = RB_ROOT;
1572 
1573                 spin_lock(&ksm_mmlist_lock);
1574                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1575                 ksm_scan.mm_slot = slot;
1576                 spin_unlock(&ksm_mmlist_lock);
1577                 /*
1578                  * Although we tested list_empty() above, a racing __ksm_exit
1579                  * of the last mm on the list may have removed it since then.
1580                  */
1581                 if (slot == &ksm_mm_head)
1582                         return NULL;
1583 next_mm:
1584                 ksm_scan.address = 0;
1585                 ksm_scan.rmap_list = &slot->rmap_list;
1586         }
1587 
1588         mm = slot->mm;
1589         down_read(&mm->mmap_sem);
1590         if (ksm_test_exit(mm))
1591                 vma = NULL;
1592         else
1593                 vma = find_vma(mm, ksm_scan.address);
1594 
1595         for (; vma; vma = vma->vm_next) {
1596                 if (!(vma->vm_flags & VM_MERGEABLE))
1597                         continue;
1598                 if (ksm_scan.address < vma->vm_start)
1599                         ksm_scan.address = vma->vm_start;
1600                 if (!vma->anon_vma)
1601                         ksm_scan.address = vma->vm_end;
1602 
1603                 while (ksm_scan.address < vma->vm_end) {
1604                         if (ksm_test_exit(mm))
1605                                 break;
1606                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1607                         if (IS_ERR_OR_NULL(*page)) {
1608                                 ksm_scan.address += PAGE_SIZE;
1609                                 cond_resched();
1610                                 continue;
1611                         }
1612                         if (PageAnon(*page)) {
1613                                 flush_anon_page(vma, *page, ksm_scan.address);
1614                                 flush_dcache_page(*page);
1615                                 rmap_item = get_next_rmap_item(slot,
1616                                         ksm_scan.rmap_list, ksm_scan.address);
1617                                 if (rmap_item) {
1618                                         ksm_scan.rmap_list =
1619                                                         &rmap_item->rmap_list;
1620                                         ksm_scan.address += PAGE_SIZE;
1621                                 } else
1622                                         put_page(*page);
1623                                 up_read(&mm->mmap_sem);
1624                                 return rmap_item;
1625                         }
1626                         put_page(*page);
1627                         ksm_scan.address += PAGE_SIZE;
1628                         cond_resched();
1629                 }
1630         }
1631 
1632         if (ksm_test_exit(mm)) {
1633                 ksm_scan.address = 0;
1634                 ksm_scan.rmap_list = &slot->rmap_list;
1635         }
1636         /*
1637          * Nuke all the rmap_items that are above this current rmap:
1638          * because there were no VM_MERGEABLE vmas with such addresses.
1639          */
1640         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1641 
1642         spin_lock(&ksm_mmlist_lock);
1643         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1644                                                 struct mm_slot, mm_list);
1645         if (ksm_scan.address == 0) {
1646                 /*
1647                  * We've completed a full scan of all vmas, holding mmap_sem
1648                  * throughout, and found no VM_MERGEABLE: so do the same as
1649                  * __ksm_exit does to remove this mm from all our lists now.
1650                  * This applies either when cleaning up after __ksm_exit
1651                  * (but beware: we can reach here even before __ksm_exit),
1652                  * or when all VM_MERGEABLE areas have been unmapped (and
1653                  * mmap_sem then protects against race with MADV_MERGEABLE).
1654                  */
1655                 hash_del(&slot->link);
1656                 list_del(&slot->mm_list);
1657                 spin_unlock(&ksm_mmlist_lock);
1658 
1659                 free_mm_slot(slot);
1660                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1661                 up_read(&mm->mmap_sem);
1662                 mmdrop(mm);
1663         } else {
1664                 up_read(&mm->mmap_sem);
1665                 /*
1666                  * up_read(&mm->mmap_sem) first because after
1667                  * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
1668                  * already have been freed under us by __ksm_exit()
1669                  * because the "mm_slot" is still hashed and
1670                  * ksm_scan.mm_slot doesn't point to it anymore.
1671                  */
1672                 spin_unlock(&ksm_mmlist_lock);
1673         }
1674 
1675         /* Repeat until we've completed scanning the whole list */
1676         slot = ksm_scan.mm_slot;
1677         if (slot != &ksm_mm_head)
1678                 goto next_mm;
1679 
1680         ksm_scan.seqnr++;
1681         return NULL;
1682 }
1683 
1684 /**
1685  * ksm_do_scan  - the ksm scanner main worker function.
1686  * @scan_npages - number of pages we want to scan before we return.
1687  */
1688 static void ksm_do_scan(unsigned int scan_npages)
1689 {
1690         struct rmap_item *rmap_item;
1691         struct page *uninitialized_var(page);
1692 
1693         while (scan_npages-- && likely(!freezing(current))) {
1694                 cond_resched();
1695                 rmap_item = scan_get_next_rmap_item(&page);
1696                 if (!rmap_item)
1697                         return;
1698                 cmp_and_merge_page(page, rmap_item);
1699                 put_page(page);
1700         }
1701 }
1702 
1703 static int ksmd_should_run(void)
1704 {
1705         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1706 }
1707 
1708 static int ksm_scan_thread(void *nothing)
1709 {
1710         set_freezable();
1711         set_user_nice(current, 5);
1712 
1713         while (!kthread_should_stop()) {
1714                 mutex_lock(&ksm_thread_mutex);
1715                 wait_while_offlining();
1716                 if (ksmd_should_run())
1717                         ksm_do_scan(ksm_thread_pages_to_scan);
1718                 mutex_unlock(&ksm_thread_mutex);
1719 
1720                 try_to_freeze();
1721 
1722                 if (ksmd_should_run()) {
1723                         schedule_timeout_interruptible(
1724                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1725                 } else {
1726                         wait_event_freezable(ksm_thread_wait,
1727                                 ksmd_should_run() || kthread_should_stop());
1728                 }
1729         }
1730         return 0;
1731 }
1732 
1733 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1734                 unsigned long end, int advice, unsigned long *vm_flags)
1735 {
1736         struct mm_struct *mm = vma->vm_mm;
1737         int err;
1738 
1739         switch (advice) {
1740         case MADV_MERGEABLE:
1741                 /*
1742                  * Be somewhat over-protective for now!
1743                  */
1744                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1745                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1746                                  VM_HUGETLB | VM_MIXEDMAP))
1747                         return 0;               /* just ignore the advice */
1748 
1749 #ifdef VM_SAO
1750                 if (*vm_flags & VM_SAO)
1751                         return 0;
1752 #endif
1753 
1754                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1755                         err = __ksm_enter(mm);
1756                         if (err)
1757                                 return err;
1758                 }
1759 
1760                 *vm_flags |= VM_MERGEABLE;
1761                 break;
1762 
1763         case MADV_UNMERGEABLE:
1764                 if (!(*vm_flags & VM_MERGEABLE))
1765                         return 0;               /* just ignore the advice */
1766 
1767                 if (vma->anon_vma) {
1768                         err = unmerge_ksm_pages(vma, start, end);
1769                         if (err)
1770                                 return err;
1771                 }
1772 
1773                 *vm_flags &= ~VM_MERGEABLE;
1774                 break;
1775         }
1776 
1777         return 0;
1778 }
1779 
1780 int __ksm_enter(struct mm_struct *mm)
1781 {
1782         struct mm_slot *mm_slot;
1783         int needs_wakeup;
1784 
1785         mm_slot = alloc_mm_slot();
1786         if (!mm_slot)
1787                 return -ENOMEM;
1788 
1789         /* Check ksm_run too?  Would need tighter locking */
1790         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1791 
1792         spin_lock(&ksm_mmlist_lock);
1793         insert_to_mm_slots_hash(mm, mm_slot);
1794         /*
1795          * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1796          * insert just behind the scanning cursor, to let the area settle
1797          * down a little; when fork is followed by immediate exec, we don't
1798          * want ksmd to waste time setting up and tearing down an rmap_list.
1799          *
1800          * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1801          * scanning cursor, otherwise KSM pages in newly forked mms will be
1802          * missed: then we might as well insert at the end of the list.
1803          */
1804         if (ksm_run & KSM_RUN_UNMERGE)
1805                 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1806         else
1807                 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1808         spin_unlock(&ksm_mmlist_lock);
1809 
1810         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1811         atomic_inc(&mm->mm_count);
1812 
1813         if (needs_wakeup)
1814                 wake_up_interruptible(&ksm_thread_wait);
1815 
1816         return 0;
1817 }
1818 
1819 void __ksm_exit(struct mm_struct *mm)
1820 {
1821         struct mm_slot *mm_slot;
1822         int easy_to_free = 0;
1823 
1824         /*
1825          * This process is exiting: if it's straightforward (as is the
1826          * case when ksmd was never running), free mm_slot immediately.
1827          * But if it's at the cursor or has rmap_items linked to it, use
1828          * mmap_sem to synchronize with any break_cows before pagetables
1829          * are freed, and leave the mm_slot on the list for ksmd to free.
1830          * Beware: ksm may already have noticed it exiting and freed the slot.
1831          */
1832 
1833         spin_lock(&ksm_mmlist_lock);
1834         mm_slot = get_mm_slot(mm);
1835         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1836                 if (!mm_slot->rmap_list) {
1837                         hash_del(&mm_slot->link);
1838                         list_del(&mm_slot->mm_list);
1839                         easy_to_free = 1;
1840                 } else {
1841                         list_move(&mm_slot->mm_list,
1842                                   &ksm_scan.mm_slot->mm_list);
1843                 }
1844         }
1845         spin_unlock(&ksm_mmlist_lock);
1846 
1847         if (easy_to_free) {
1848                 free_mm_slot(mm_slot);
1849                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1850                 mmdrop(mm);
1851         } else if (mm_slot) {
1852                 down_write(&mm->mmap_sem);
1853                 up_write(&mm->mmap_sem);
1854         }
1855 }
1856 
1857 struct page *ksm_might_need_to_copy(struct page *page,
1858                         struct vm_area_struct *vma, unsigned long address)
1859 {
1860         struct anon_vma *anon_vma = page_anon_vma(page);
1861         struct page *new_page;
1862 
1863         if (PageKsm(page)) {
1864                 if (page_stable_node(page) &&
1865                     !(ksm_run & KSM_RUN_UNMERGE))
1866                         return page;    /* no need to copy it */
1867         } else if (!anon_vma) {
1868                 return page;            /* no need to copy it */
1869         } else if (anon_vma->root == vma->anon_vma->root &&
1870                  page->index == linear_page_index(vma, address)) {
1871                 return page;            /* still no need to copy it */
1872         }
1873         if (!PageUptodate(page))
1874                 return page;            /* let do_swap_page report the error */
1875 
1876         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1877         if (new_page) {
1878                 copy_user_highpage(new_page, page, address, vma);
1879 
1880                 SetPageDirty(new_page);
1881                 __SetPageUptodate(new_page);
1882                 __SetPageLocked(new_page);
1883         }
1884 
1885         return new_page;
1886 }
1887 
1888 int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
1889 {
1890         struct stable_node *stable_node;
1891         struct rmap_item *rmap_item;
1892         int ret = SWAP_AGAIN;
1893         int search_new_forks = 0;
1894 
1895         VM_BUG_ON_PAGE(!PageKsm(page), page);
1896 
1897         /*
1898          * Rely on the page lock to protect against concurrent modifications
1899          * to that page's node of the stable tree.
1900          */
1901         VM_BUG_ON_PAGE(!PageLocked(page), page);
1902 
1903         stable_node = page_stable_node(page);
1904         if (!stable_node)
1905                 return ret;
1906 again:
1907         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1908                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1909                 struct anon_vma_chain *vmac;
1910                 struct vm_area_struct *vma;
1911 
1912                 cond_resched();
1913                 anon_vma_lock_read(anon_vma);
1914                 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1915                                                0, ULONG_MAX) {
1916                         cond_resched();
1917                         vma = vmac->vma;
1918                         if (rmap_item->address < vma->vm_start ||
1919                             rmap_item->address >= vma->vm_end)
1920                                 continue;
1921                         /*
1922                          * Initially we examine only the vma which covers this
1923                          * rmap_item; but later, if there is still work to do,
1924                          * we examine covering vmas in other mms: in case they
1925                          * were forked from the original since ksmd passed.
1926                          */
1927                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1928                                 continue;
1929 
1930                         if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1931                                 continue;
1932 
1933                         ret = rwc->rmap_one(page, vma,
1934                                         rmap_item->address, rwc->arg);
1935                         if (ret != SWAP_AGAIN) {
1936                                 anon_vma_unlock_read(anon_vma);
1937                                 goto out;
1938                         }
1939                         if (rwc->done && rwc->done(page)) {
1940                                 anon_vma_unlock_read(anon_vma);
1941                                 goto out;
1942                         }
1943                 }
1944                 anon_vma_unlock_read(anon_vma);
1945         }
1946         if (!search_new_forks++)
1947                 goto again;
1948 out:
1949         return ret;
1950 }
1951 
1952 #ifdef CONFIG_MIGRATION
1953 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1954 {
1955         struct stable_node *stable_node;
1956 
1957         VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
1958         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1959         VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
1960 
1961         stable_node = page_stable_node(newpage);
1962         if (stable_node) {
1963                 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
1964                 stable_node->kpfn = page_to_pfn(newpage);
1965                 /*
1966                  * newpage->mapping was set in advance; now we need smp_wmb()
1967                  * to make sure that the new stable_node->kpfn is visible
1968                  * to get_ksm_page() before it can see that oldpage->mapping
1969                  * has gone stale (or that PageSwapCache has been cleared).
1970                  */
1971                 smp_wmb();
1972                 set_page_stable_node(oldpage, NULL);
1973         }
1974 }
1975 #endif /* CONFIG_MIGRATION */
1976 
1977 #ifdef CONFIG_MEMORY_HOTREMOVE
1978 static void wait_while_offlining(void)
1979 {
1980         while (ksm_run & KSM_RUN_OFFLINE) {
1981                 mutex_unlock(&ksm_thread_mutex);
1982                 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
1983                             TASK_UNINTERRUPTIBLE);
1984                 mutex_lock(&ksm_thread_mutex);
1985         }
1986 }
1987 
1988 static void ksm_check_stable_tree(unsigned long start_pfn,
1989                                   unsigned long end_pfn)
1990 {
1991         struct stable_node *stable_node, *next;
1992         struct rb_node *node;
1993         int nid;
1994 
1995         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
1996                 node = rb_first(root_stable_tree + nid);
1997                 while (node) {
1998                         stable_node = rb_entry(node, struct stable_node, node);
1999                         if (stable_node->kpfn >= start_pfn &&
2000                             stable_node->kpfn < end_pfn) {
2001                                 /*
2002                                  * Don't get_ksm_page, page has already gone:
2003                                  * which is why we keep kpfn instead of page*
2004                                  */
2005                                 remove_node_from_stable_tree(stable_node);
2006                                 node = rb_first(root_stable_tree + nid);
2007                         } else
2008                                 node = rb_next(node);
2009                         cond_resched();
2010                 }
2011         }
2012         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2013                 if (stable_node->kpfn >= start_pfn &&
2014                     stable_node->kpfn < end_pfn)
2015                         remove_node_from_stable_tree(stable_node);
2016                 cond_resched();
2017         }
2018 }
2019 
2020 static int ksm_memory_callback(struct notifier_block *self,
2021                                unsigned long action, void *arg)
2022 {
2023         struct memory_notify *mn = arg;
2024 
2025         switch (action) {
2026         case MEM_GOING_OFFLINE:
2027                 /*
2028                  * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2029                  * and remove_all_stable_nodes() while memory is going offline:
2030                  * it is unsafe for them to touch the stable tree at this time.
2031                  * But unmerge_ksm_pages(), rmap lookups and other entry points
2032                  * which do not need the ksm_thread_mutex are all safe.
2033                  */
2034                 mutex_lock(&ksm_thread_mutex);
2035                 ksm_run |= KSM_RUN_OFFLINE;
2036                 mutex_unlock(&ksm_thread_mutex);
2037                 break;
2038 
2039         case MEM_OFFLINE:
2040                 /*
2041                  * Most of the work is done by page migration; but there might
2042                  * be a few stable_nodes left over, still pointing to struct
2043                  * pages which have been offlined: prune those from the tree,
2044                  * otherwise get_ksm_page() might later try to access a
2045                  * non-existent struct page.
2046                  */
2047                 ksm_check_stable_tree(mn->start_pfn,
2048                                       mn->start_pfn + mn->nr_pages);
2049                 /* fallthrough */
2050 
2051         case MEM_CANCEL_OFFLINE:
2052                 mutex_lock(&ksm_thread_mutex);
2053                 ksm_run &= ~KSM_RUN_OFFLINE;
2054                 mutex_unlock(&ksm_thread_mutex);
2055 
2056                 smp_mb();       /* wake_up_bit advises this */
2057                 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2058                 break;
2059         }
2060         return NOTIFY_OK;
2061 }
2062 #else
2063 static void wait_while_offlining(void)
2064 {
2065 }
2066 #endif /* CONFIG_MEMORY_HOTREMOVE */
2067 
2068 #ifdef CONFIG_SYSFS
2069 /*
2070  * This all compiles without CONFIG_SYSFS, but is a waste of space.
2071  */
2072 
2073 #define KSM_ATTR_RO(_name) \
2074         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2075 #define KSM_ATTR(_name) \
2076         static struct kobj_attribute _name##_attr = \
2077                 __ATTR(_name, 0644, _name##_show, _name##_store)
2078 
2079 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2080                                     struct kobj_attribute *attr, char *buf)
2081 {
2082         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2083 }
2084 
2085 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2086                                      struct kobj_attribute *attr,
2087                                      const char *buf, size_t count)
2088 {
2089         unsigned long msecs;
2090         int err;
2091 
2092         err = kstrtoul(buf, 10, &msecs);
2093         if (err || msecs > UINT_MAX)
2094                 return -EINVAL;
2095 
2096         ksm_thread_sleep_millisecs = msecs;
2097 
2098         return count;
2099 }
2100 KSM_ATTR(sleep_millisecs);
2101 
2102 static ssize_t pages_to_scan_show(struct kobject *kobj,
2103                                   struct kobj_attribute *attr, char *buf)
2104 {
2105         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2106 }
2107 
2108 static ssize_t pages_to_scan_store(struct kobject *kobj,
2109                                    struct kobj_attribute *attr,
2110                                    const char *buf, size_t count)
2111 {
2112         int err;
2113         unsigned long nr_pages;
2114 
2115         err = kstrtoul(buf, 10, &nr_pages);
2116         if (err || nr_pages > UINT_MAX)
2117                 return -EINVAL;
2118 
2119         ksm_thread_pages_to_scan = nr_pages;
2120 
2121         return count;
2122 }
2123 KSM_ATTR(pages_to_scan);
2124 
2125 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2126                         char *buf)
2127 {
2128         return sprintf(buf, "%lu\n", ksm_run);
2129 }
2130 
2131 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2132                          const char *buf, size_t count)
2133 {
2134         int err;
2135         unsigned long flags;
2136 
2137         err = kstrtoul(buf, 10, &flags);
2138         if (err || flags > UINT_MAX)
2139                 return -EINVAL;
2140         if (flags > KSM_RUN_UNMERGE)
2141                 return -EINVAL;
2142 
2143         /*
2144          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2145          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2146          * breaking COW to free the pages_shared (but leaves mm_slots
2147          * on the list for when ksmd may be set running again).
2148          */
2149 
2150         mutex_lock(&ksm_thread_mutex);
2151         wait_while_offlining();
2152         if (ksm_run != flags) {
2153                 ksm_run = flags;
2154                 if (flags & KSM_RUN_UNMERGE) {
2155                         set_current_oom_origin();
2156                         err = unmerge_and_remove_all_rmap_items();
2157                         clear_current_oom_origin();
2158                         if (err) {
2159                                 ksm_run = KSM_RUN_STOP;
2160                                 count = err;
2161                         }
2162                 }
2163         }
2164         mutex_unlock(&ksm_thread_mutex);
2165 
2166         if (flags & KSM_RUN_MERGE)
2167                 wake_up_interruptible(&ksm_thread_wait);
2168 
2169         return count;
2170 }
2171 KSM_ATTR(run);
2172 
2173 #ifdef CONFIG_NUMA
2174 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2175                                 struct kobj_attribute *attr, char *buf)
2176 {
2177         return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2178 }
2179 
2180 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2181                                    struct kobj_attribute *attr,
2182                                    const char *buf, size_t count)
2183 {
2184         int err;
2185         unsigned long knob;
2186 
2187         err = kstrtoul(buf, 10, &knob);
2188         if (err)
2189                 return err;
2190         if (knob > 1)
2191                 return -EINVAL;
2192 
2193         mutex_lock(&ksm_thread_mutex);
2194         wait_while_offlining();
2195         if (ksm_merge_across_nodes != knob) {
2196                 if (ksm_pages_shared || remove_all_stable_nodes())
2197                         err = -EBUSY;
2198                 else if (root_stable_tree == one_stable_tree) {
2199                         struct rb_root *buf;
2200                         /*
2201                          * This is the first time that we switch away from the
2202                          * default of merging across nodes: must now allocate
2203                          * a buffer to hold as many roots as may be needed.
2204                          * Allocate stable and unstable together:
2205                          * MAXSMP NODES_SHIFT 10 will use 16kB.
2206                          */
2207                         buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2208                                       GFP_KERNEL);
2209                         /* Let us assume that RB_ROOT is NULL is zero */
2210                         if (!buf)
2211                                 err = -ENOMEM;
2212                         else {
2213                                 root_stable_tree = buf;
2214                                 root_unstable_tree = buf + nr_node_ids;
2215                                 /* Stable tree is empty but not the unstable */
2216                                 root_unstable_tree[0] = one_unstable_tree[0];
2217                         }
2218                 }
2219                 if (!err) {
2220                         ksm_merge_across_nodes = knob;
2221                         ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2222                 }
2223         }
2224         mutex_unlock(&ksm_thread_mutex);
2225 
2226         return err ? err : count;
2227 }
2228 KSM_ATTR(merge_across_nodes);
2229 #endif
2230 
2231 static ssize_t pages_shared_show(struct kobject *kobj,
2232                                  struct kobj_attribute *attr, char *buf)
2233 {
2234         return sprintf(buf, "%lu\n", ksm_pages_shared);
2235 }
2236 KSM_ATTR_RO(pages_shared);
2237 
2238 static ssize_t pages_sharing_show(struct kobject *kobj,
2239                                   struct kobj_attribute *attr, char *buf)
2240 {
2241         return sprintf(buf, "%lu\n", ksm_pages_sharing);
2242 }
2243 KSM_ATTR_RO(pages_sharing);
2244 
2245 static ssize_t pages_unshared_show(struct kobject *kobj,
2246                                    struct kobj_attribute *attr, char *buf)
2247 {
2248         return sprintf(buf, "%lu\n", ksm_pages_unshared);
2249 }
2250 KSM_ATTR_RO(pages_unshared);
2251 
2252 static ssize_t pages_volatile_show(struct kobject *kobj,
2253                                    struct kobj_attribute *attr, char *buf)
2254 {
2255         long ksm_pages_volatile;
2256 
2257         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2258                                 - ksm_pages_sharing - ksm_pages_unshared;
2259         /*
2260          * It was not worth any locking to calculate that statistic,
2261          * but it might therefore sometimes be negative: conceal that.
2262          */
2263         if (ksm_pages_volatile < 0)
2264                 ksm_pages_volatile = 0;
2265         return sprintf(buf, "%ld\n", ksm_pages_volatile);
2266 }
2267 KSM_ATTR_RO(pages_volatile);
2268 
2269 static ssize_t full_scans_show(struct kobject *kobj,
2270                                struct kobj_attribute *attr, char *buf)
2271 {
2272         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2273 }
2274 KSM_ATTR_RO(full_scans);
2275 
2276 static struct attribute *ksm_attrs[] = {
2277         &sleep_millisecs_attr.attr,
2278         &pages_to_scan_attr.attr,
2279         &run_attr.attr,
2280         &pages_shared_attr.attr,
2281         &pages_sharing_attr.attr,
2282         &pages_unshared_attr.attr,
2283         &pages_volatile_attr.attr,
2284         &full_scans_attr.attr,
2285 #ifdef CONFIG_NUMA
2286         &merge_across_nodes_attr.attr,
2287 #endif
2288         NULL,
2289 };
2290 
2291 static struct attribute_group ksm_attr_group = {
2292         .attrs = ksm_attrs,
2293         .name = "ksm",
2294 };
2295 #endif /* CONFIG_SYSFS */
2296 
2297 static int __init ksm_init(void)
2298 {
2299         struct task_struct *ksm_thread;
2300         int err;
2301 
2302         err = ksm_slab_init();
2303         if (err)
2304                 goto out;
2305 
2306         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2307         if (IS_ERR(ksm_thread)) {
2308                 pr_err("ksm: creating kthread failed\n");
2309                 err = PTR_ERR(ksm_thread);
2310                 goto out_free;
2311         }
2312 
2313 #ifdef CONFIG_SYSFS
2314         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2315         if (err) {
2316                 pr_err("ksm: register sysfs failed\n");
2317                 kthread_stop(ksm_thread);
2318                 goto out_free;
2319         }
2320 #else
2321         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2322 
2323 #endif /* CONFIG_SYSFS */
2324 
2325 #ifdef CONFIG_MEMORY_HOTREMOVE
2326         /* There is no significance to this priority 100 */
2327         hotplug_memory_notifier(ksm_memory_callback, 100);
2328 #endif
2329         return 0;
2330 
2331 out_free:
2332         ksm_slab_free();
2333 out:
2334         return err;
2335 }
2336 subsys_initcall(ksm_init);
2337 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp