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TOMOYO Linux Cross Reference
Linux/mm/migrate.c

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  1 /*
  2  * Memory Migration functionality - linux/mm/migration.c
  3  *
  4  * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
  5  *
  6  * Page migration was first developed in the context of the memory hotplug
  7  * project. The main authors of the migration code are:
  8  *
  9  * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
 10  * Hirokazu Takahashi <taka@valinux.co.jp>
 11  * Dave Hansen <haveblue@us.ibm.com>
 12  * Christoph Lameter
 13  */
 14 
 15 #include <linux/migrate.h>
 16 #include <linux/export.h>
 17 #include <linux/swap.h>
 18 #include <linux/swapops.h>
 19 #include <linux/pagemap.h>
 20 #include <linux/buffer_head.h>
 21 #include <linux/mm_inline.h>
 22 #include <linux/nsproxy.h>
 23 #include <linux/pagevec.h>
 24 #include <linux/ksm.h>
 25 #include <linux/rmap.h>
 26 #include <linux/topology.h>
 27 #include <linux/cpu.h>
 28 #include <linux/cpuset.h>
 29 #include <linux/writeback.h>
 30 #include <linux/mempolicy.h>
 31 #include <linux/vmalloc.h>
 32 #include <linux/security.h>
 33 #include <linux/memcontrol.h>
 34 #include <linux/syscalls.h>
 35 #include <linux/hugetlb.h>
 36 #include <linux/hugetlb_cgroup.h>
 37 #include <linux/gfp.h>
 38 #include <linux/balloon_compaction.h>
 39 
 40 #include <asm/tlbflush.h>
 41 
 42 #define CREATE_TRACE_POINTS
 43 #include <trace/events/migrate.h>
 44 
 45 #include "internal.h"
 46 
 47 /*
 48  * migrate_prep() needs to be called before we start compiling a list of pages
 49  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
 50  * undesirable, use migrate_prep_local()
 51  */
 52 int migrate_prep(void)
 53 {
 54         /*
 55          * Clear the LRU lists so pages can be isolated.
 56          * Note that pages may be moved off the LRU after we have
 57          * drained them. Those pages will fail to migrate like other
 58          * pages that may be busy.
 59          */
 60         lru_add_drain_all();
 61 
 62         return 0;
 63 }
 64 
 65 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
 66 int migrate_prep_local(void)
 67 {
 68         lru_add_drain();
 69 
 70         return 0;
 71 }
 72 
 73 /*
 74  * Add isolated pages on the list back to the LRU under page lock
 75  * to avoid leaking evictable pages back onto unevictable list.
 76  */
 77 void putback_lru_pages(struct list_head *l)
 78 {
 79         struct page *page;
 80         struct page *page2;
 81 
 82         list_for_each_entry_safe(page, page2, l, lru) {
 83                 list_del(&page->lru);
 84                 dec_zone_page_state(page, NR_ISOLATED_ANON +
 85                                 page_is_file_cache(page));
 86                         putback_lru_page(page);
 87         }
 88 }
 89 
 90 /*
 91  * Put previously isolated pages back onto the appropriate lists
 92  * from where they were once taken off for compaction/migration.
 93  *
 94  * This function shall be used instead of putback_lru_pages(),
 95  * whenever the isolated pageset has been built by isolate_migratepages_range()
 96  */
 97 void putback_movable_pages(struct list_head *l)
 98 {
 99         struct page *page;
100         struct page *page2;
101 
102         list_for_each_entry_safe(page, page2, l, lru) {
103                 list_del(&page->lru);
104                 dec_zone_page_state(page, NR_ISOLATED_ANON +
105                                 page_is_file_cache(page));
106                 if (unlikely(balloon_page_movable(page)))
107                         balloon_page_putback(page);
108                 else
109                         putback_lru_page(page);
110         }
111 }
112 
113 /*
114  * Restore a potential migration pte to a working pte entry
115  */
116 static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
117                                  unsigned long addr, void *old)
118 {
119         struct mm_struct *mm = vma->vm_mm;
120         swp_entry_t entry;
121         pmd_t *pmd;
122         pte_t *ptep, pte;
123         spinlock_t *ptl;
124 
125         if (unlikely(PageHuge(new))) {
126                 ptep = huge_pte_offset(mm, addr);
127                 if (!ptep)
128                         goto out;
129                 ptl = &mm->page_table_lock;
130         } else {
131                 pmd = mm_find_pmd(mm, addr);
132                 if (!pmd)
133                         goto out;
134                 if (pmd_trans_huge(*pmd))
135                         goto out;
136 
137                 ptep = pte_offset_map(pmd, addr);
138 
139                 /*
140                  * Peek to check is_swap_pte() before taking ptlock?  No, we
141                  * can race mremap's move_ptes(), which skips anon_vma lock.
142                  */
143 
144                 ptl = pte_lockptr(mm, pmd);
145         }
146 
147         spin_lock(ptl);
148         pte = *ptep;
149         if (!is_swap_pte(pte))
150                 goto unlock;
151 
152         entry = pte_to_swp_entry(pte);
153 
154         if (!is_migration_entry(entry) ||
155             migration_entry_to_page(entry) != old)
156                 goto unlock;
157 
158         get_page(new);
159         pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
160         if (is_write_migration_entry(entry))
161                 pte = pte_mkwrite(pte);
162 #ifdef CONFIG_HUGETLB_PAGE
163         if (PageHuge(new)) {
164                 pte = pte_mkhuge(pte);
165                 pte = arch_make_huge_pte(pte, vma, new, 0);
166         }
167 #endif
168         flush_cache_page(vma, addr, pte_pfn(pte));
169         set_pte_at(mm, addr, ptep, pte);
170 
171         if (PageHuge(new)) {
172                 if (PageAnon(new))
173                         hugepage_add_anon_rmap(new, vma, addr);
174                 else
175                         page_dup_rmap(new);
176         } else if (PageAnon(new))
177                 page_add_anon_rmap(new, vma, addr);
178         else
179                 page_add_file_rmap(new);
180 
181         /* No need to invalidate - it was non-present before */
182         update_mmu_cache(vma, addr, ptep);
183 unlock:
184         pte_unmap_unlock(ptep, ptl);
185 out:
186         return SWAP_AGAIN;
187 }
188 
189 /*
190  * Get rid of all migration entries and replace them by
191  * references to the indicated page.
192  */
193 static void remove_migration_ptes(struct page *old, struct page *new)
194 {
195         rmap_walk(new, remove_migration_pte, old);
196 }
197 
198 /*
199  * Something used the pte of a page under migration. We need to
200  * get to the page and wait until migration is finished.
201  * When we return from this function the fault will be retried.
202  */
203 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
204                                 unsigned long address)
205 {
206         pte_t *ptep, pte;
207         spinlock_t *ptl;
208         swp_entry_t entry;
209         struct page *page;
210 
211         ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
212         pte = *ptep;
213         if (!is_swap_pte(pte))
214                 goto out;
215 
216         entry = pte_to_swp_entry(pte);
217         if (!is_migration_entry(entry))
218                 goto out;
219 
220         page = migration_entry_to_page(entry);
221 
222         /*
223          * Once radix-tree replacement of page migration started, page_count
224          * *must* be zero. And, we don't want to call wait_on_page_locked()
225          * against a page without get_page().
226          * So, we use get_page_unless_zero(), here. Even failed, page fault
227          * will occur again.
228          */
229         if (!get_page_unless_zero(page))
230                 goto out;
231         pte_unmap_unlock(ptep, ptl);
232         wait_on_page_locked(page);
233         put_page(page);
234         return;
235 out:
236         pte_unmap_unlock(ptep, ptl);
237 }
238 
239 #ifdef CONFIG_BLOCK
240 /* Returns true if all buffers are successfully locked */
241 static bool buffer_migrate_lock_buffers(struct buffer_head *head,
242                                                         enum migrate_mode mode)
243 {
244         struct buffer_head *bh = head;
245 
246         /* Simple case, sync compaction */
247         if (mode != MIGRATE_ASYNC) {
248                 do {
249                         get_bh(bh);
250                         lock_buffer(bh);
251                         bh = bh->b_this_page;
252 
253                 } while (bh != head);
254 
255                 return true;
256         }
257 
258         /* async case, we cannot block on lock_buffer so use trylock_buffer */
259         do {
260                 get_bh(bh);
261                 if (!trylock_buffer(bh)) {
262                         /*
263                          * We failed to lock the buffer and cannot stall in
264                          * async migration. Release the taken locks
265                          */
266                         struct buffer_head *failed_bh = bh;
267                         put_bh(failed_bh);
268                         bh = head;
269                         while (bh != failed_bh) {
270                                 unlock_buffer(bh);
271                                 put_bh(bh);
272                                 bh = bh->b_this_page;
273                         }
274                         return false;
275                 }
276 
277                 bh = bh->b_this_page;
278         } while (bh != head);
279         return true;
280 }
281 #else
282 static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
283                                                         enum migrate_mode mode)
284 {
285         return true;
286 }
287 #endif /* CONFIG_BLOCK */
288 
289 /*
290  * Replace the page in the mapping.
291  *
292  * The number of remaining references must be:
293  * 1 for anonymous pages without a mapping
294  * 2 for pages with a mapping
295  * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
296  */
297 static int migrate_page_move_mapping(struct address_space *mapping,
298                 struct page *newpage, struct page *page,
299                 struct buffer_head *head, enum migrate_mode mode)
300 {
301         int expected_count = 0;
302         void **pslot;
303 
304         if (!mapping) {
305                 /* Anonymous page without mapping */
306                 if (page_count(page) != 1)
307                         return -EAGAIN;
308                 return MIGRATEPAGE_SUCCESS;
309         }
310 
311         spin_lock_irq(&mapping->tree_lock);
312 
313         pslot = radix_tree_lookup_slot(&mapping->page_tree,
314                                         page_index(page));
315 
316         expected_count = 2 + page_has_private(page);
317         if (page_count(page) != expected_count ||
318                 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
319                 spin_unlock_irq(&mapping->tree_lock);
320                 return -EAGAIN;
321         }
322 
323         if (!page_freeze_refs(page, expected_count)) {
324                 spin_unlock_irq(&mapping->tree_lock);
325                 return -EAGAIN;
326         }
327 
328         /*
329          * In the async migration case of moving a page with buffers, lock the
330          * buffers using trylock before the mapping is moved. If the mapping
331          * was moved, we later failed to lock the buffers and could not move
332          * the mapping back due to an elevated page count, we would have to
333          * block waiting on other references to be dropped.
334          */
335         if (mode == MIGRATE_ASYNC && head &&
336                         !buffer_migrate_lock_buffers(head, mode)) {
337                 page_unfreeze_refs(page, expected_count);
338                 spin_unlock_irq(&mapping->tree_lock);
339                 return -EAGAIN;
340         }
341 
342         /*
343          * Now we know that no one else is looking at the page.
344          */
345         get_page(newpage);      /* add cache reference */
346         if (PageSwapCache(page)) {
347                 SetPageSwapCache(newpage);
348                 set_page_private(newpage, page_private(page));
349         }
350 
351         radix_tree_replace_slot(pslot, newpage);
352 
353         /*
354          * Drop cache reference from old page by unfreezing
355          * to one less reference.
356          * We know this isn't the last reference.
357          */
358         page_unfreeze_refs(page, expected_count - 1);
359 
360         /*
361          * If moved to a different zone then also account
362          * the page for that zone. Other VM counters will be
363          * taken care of when we establish references to the
364          * new page and drop references to the old page.
365          *
366          * Note that anonymous pages are accounted for
367          * via NR_FILE_PAGES and NR_ANON_PAGES if they
368          * are mapped to swap space.
369          */
370         __dec_zone_page_state(page, NR_FILE_PAGES);
371         __inc_zone_page_state(newpage, NR_FILE_PAGES);
372         if (!PageSwapCache(page) && PageSwapBacked(page)) {
373                 __dec_zone_page_state(page, NR_SHMEM);
374                 __inc_zone_page_state(newpage, NR_SHMEM);
375         }
376         spin_unlock_irq(&mapping->tree_lock);
377 
378         return MIGRATEPAGE_SUCCESS;
379 }
380 
381 /*
382  * The expected number of remaining references is the same as that
383  * of migrate_page_move_mapping().
384  */
385 int migrate_huge_page_move_mapping(struct address_space *mapping,
386                                    struct page *newpage, struct page *page)
387 {
388         int expected_count;
389         void **pslot;
390 
391         if (!mapping) {
392                 if (page_count(page) != 1)
393                         return -EAGAIN;
394                 return MIGRATEPAGE_SUCCESS;
395         }
396 
397         spin_lock_irq(&mapping->tree_lock);
398 
399         pslot = radix_tree_lookup_slot(&mapping->page_tree,
400                                         page_index(page));
401 
402         expected_count = 2 + page_has_private(page);
403         if (page_count(page) != expected_count ||
404                 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
405                 spin_unlock_irq(&mapping->tree_lock);
406                 return -EAGAIN;
407         }
408 
409         if (!page_freeze_refs(page, expected_count)) {
410                 spin_unlock_irq(&mapping->tree_lock);
411                 return -EAGAIN;
412         }
413 
414         get_page(newpage);
415 
416         radix_tree_replace_slot(pslot, newpage);
417 
418         page_unfreeze_refs(page, expected_count - 1);
419 
420         spin_unlock_irq(&mapping->tree_lock);
421         return MIGRATEPAGE_SUCCESS;
422 }
423 
424 /*
425  * Copy the page to its new location
426  */
427 void migrate_page_copy(struct page *newpage, struct page *page)
428 {
429         if (PageHuge(page) || PageTransHuge(page))
430                 copy_huge_page(newpage, page);
431         else
432                 copy_highpage(newpage, page);
433 
434         if (PageError(page))
435                 SetPageError(newpage);
436         if (PageReferenced(page))
437                 SetPageReferenced(newpage);
438         if (PageUptodate(page))
439                 SetPageUptodate(newpage);
440         if (TestClearPageActive(page)) {
441                 VM_BUG_ON(PageUnevictable(page));
442                 SetPageActive(newpage);
443         } else if (TestClearPageUnevictable(page))
444                 SetPageUnevictable(newpage);
445         if (PageChecked(page))
446                 SetPageChecked(newpage);
447         if (PageMappedToDisk(page))
448                 SetPageMappedToDisk(newpage);
449 
450         if (PageDirty(page)) {
451                 clear_page_dirty_for_io(page);
452                 /*
453                  * Want to mark the page and the radix tree as dirty, and
454                  * redo the accounting that clear_page_dirty_for_io undid,
455                  * but we can't use set_page_dirty because that function
456                  * is actually a signal that all of the page has become dirty.
457                  * Whereas only part of our page may be dirty.
458                  */
459                 if (PageSwapBacked(page))
460                         SetPageDirty(newpage);
461                 else
462                         __set_page_dirty_nobuffers(newpage);
463         }
464 
465         mlock_migrate_page(newpage, page);
466         ksm_migrate_page(newpage, page);
467 
468         ClearPageSwapCache(page);
469         ClearPagePrivate(page);
470         set_page_private(page, 0);
471 
472         /*
473          * If any waiters have accumulated on the new page then
474          * wake them up.
475          */
476         if (PageWriteback(newpage))
477                 end_page_writeback(newpage);
478 }
479 
480 /************************************************************
481  *                    Migration functions
482  ***********************************************************/
483 
484 /* Always fail migration. Used for mappings that are not movable */
485 int fail_migrate_page(struct address_space *mapping,
486                         struct page *newpage, struct page *page)
487 {
488         return -EIO;
489 }
490 EXPORT_SYMBOL(fail_migrate_page);
491 
492 /*
493  * Common logic to directly migrate a single page suitable for
494  * pages that do not use PagePrivate/PagePrivate2.
495  *
496  * Pages are locked upon entry and exit.
497  */
498 int migrate_page(struct address_space *mapping,
499                 struct page *newpage, struct page *page,
500                 enum migrate_mode mode)
501 {
502         int rc;
503 
504         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
505 
506         rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
507 
508         if (rc != MIGRATEPAGE_SUCCESS)
509                 return rc;
510 
511         migrate_page_copy(newpage, page);
512         return MIGRATEPAGE_SUCCESS;
513 }
514 EXPORT_SYMBOL(migrate_page);
515 
516 #ifdef CONFIG_BLOCK
517 /*
518  * Migration function for pages with buffers. This function can only be used
519  * if the underlying filesystem guarantees that no other references to "page"
520  * exist.
521  */
522 int buffer_migrate_page(struct address_space *mapping,
523                 struct page *newpage, struct page *page, enum migrate_mode mode)
524 {
525         struct buffer_head *bh, *head;
526         int rc;
527 
528         if (!page_has_buffers(page))
529                 return migrate_page(mapping, newpage, page, mode);
530 
531         head = page_buffers(page);
532 
533         rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
534 
535         if (rc != MIGRATEPAGE_SUCCESS)
536                 return rc;
537 
538         /*
539          * In the async case, migrate_page_move_mapping locked the buffers
540          * with an IRQ-safe spinlock held. In the sync case, the buffers
541          * need to be locked now
542          */
543         if (mode != MIGRATE_ASYNC)
544                 BUG_ON(!buffer_migrate_lock_buffers(head, mode));
545 
546         ClearPagePrivate(page);
547         set_page_private(newpage, page_private(page));
548         set_page_private(page, 0);
549         put_page(page);
550         get_page(newpage);
551 
552         bh = head;
553         do {
554                 set_bh_page(bh, newpage, bh_offset(bh));
555                 bh = bh->b_this_page;
556 
557         } while (bh != head);
558 
559         SetPagePrivate(newpage);
560 
561         migrate_page_copy(newpage, page);
562 
563         bh = head;
564         do {
565                 unlock_buffer(bh);
566                 put_bh(bh);
567                 bh = bh->b_this_page;
568 
569         } while (bh != head);
570 
571         return MIGRATEPAGE_SUCCESS;
572 }
573 EXPORT_SYMBOL(buffer_migrate_page);
574 #endif
575 
576 /*
577  * Writeback a page to clean the dirty state
578  */
579 static int writeout(struct address_space *mapping, struct page *page)
580 {
581         struct writeback_control wbc = {
582                 .sync_mode = WB_SYNC_NONE,
583                 .nr_to_write = 1,
584                 .range_start = 0,
585                 .range_end = LLONG_MAX,
586                 .for_reclaim = 1
587         };
588         int rc;
589 
590         if (!mapping->a_ops->writepage)
591                 /* No write method for the address space */
592                 return -EINVAL;
593 
594         if (!clear_page_dirty_for_io(page))
595                 /* Someone else already triggered a write */
596                 return -EAGAIN;
597 
598         /*
599          * A dirty page may imply that the underlying filesystem has
600          * the page on some queue. So the page must be clean for
601          * migration. Writeout may mean we loose the lock and the
602          * page state is no longer what we checked for earlier.
603          * At this point we know that the migration attempt cannot
604          * be successful.
605          */
606         remove_migration_ptes(page, page);
607 
608         rc = mapping->a_ops->writepage(page, &wbc);
609 
610         if (rc != AOP_WRITEPAGE_ACTIVATE)
611                 /* unlocked. Relock */
612                 lock_page(page);
613 
614         return (rc < 0) ? -EIO : -EAGAIN;
615 }
616 
617 /*
618  * Default handling if a filesystem does not provide a migration function.
619  */
620 static int fallback_migrate_page(struct address_space *mapping,
621         struct page *newpage, struct page *page, enum migrate_mode mode)
622 {
623         if (PageDirty(page)) {
624                 /* Only writeback pages in full synchronous migration */
625                 if (mode != MIGRATE_SYNC)
626                         return -EBUSY;
627                 return writeout(mapping, page);
628         }
629 
630         /*
631          * Buffers may be managed in a filesystem specific way.
632          * We must have no buffers or drop them.
633          */
634         if (page_has_private(page) &&
635             !try_to_release_page(page, GFP_KERNEL))
636                 return -EAGAIN;
637 
638         return migrate_page(mapping, newpage, page, mode);
639 }
640 
641 /*
642  * Move a page to a newly allocated page
643  * The page is locked and all ptes have been successfully removed.
644  *
645  * The new page will have replaced the old page if this function
646  * is successful.
647  *
648  * Return value:
649  *   < 0 - error code
650  *  MIGRATEPAGE_SUCCESS - success
651  */
652 static int move_to_new_page(struct page *newpage, struct page *page,
653                                 int remap_swapcache, enum migrate_mode mode)
654 {
655         struct address_space *mapping;
656         int rc;
657 
658         /*
659          * Block others from accessing the page when we get around to
660          * establishing additional references. We are the only one
661          * holding a reference to the new page at this point.
662          */
663         if (!trylock_page(newpage))
664                 BUG();
665 
666         /* Prepare mapping for the new page.*/
667         newpage->index = page->index;
668         newpage->mapping = page->mapping;
669         if (PageSwapBacked(page))
670                 SetPageSwapBacked(newpage);
671 
672         mapping = page_mapping(page);
673         if (!mapping)
674                 rc = migrate_page(mapping, newpage, page, mode);
675         else if (mapping->a_ops->migratepage)
676                 /*
677                  * Most pages have a mapping and most filesystems provide a
678                  * migratepage callback. Anonymous pages are part of swap
679                  * space which also has its own migratepage callback. This
680                  * is the most common path for page migration.
681                  */
682                 rc = mapping->a_ops->migratepage(mapping,
683                                                 newpage, page, mode);
684         else
685                 rc = fallback_migrate_page(mapping, newpage, page, mode);
686 
687         if (rc != MIGRATEPAGE_SUCCESS) {
688                 newpage->mapping = NULL;
689         } else {
690                 if (remap_swapcache)
691                         remove_migration_ptes(page, newpage);
692                 page->mapping = NULL;
693         }
694 
695         unlock_page(newpage);
696 
697         return rc;
698 }
699 
700 static int __unmap_and_move(struct page *page, struct page *newpage,
701                         int force, bool offlining, enum migrate_mode mode)
702 {
703         int rc = -EAGAIN;
704         int remap_swapcache = 1;
705         struct mem_cgroup *mem;
706         struct anon_vma *anon_vma = NULL;
707 
708         if (!trylock_page(page)) {
709                 if (!force || mode == MIGRATE_ASYNC)
710                         goto out;
711 
712                 /*
713                  * It's not safe for direct compaction to call lock_page.
714                  * For example, during page readahead pages are added locked
715                  * to the LRU. Later, when the IO completes the pages are
716                  * marked uptodate and unlocked. However, the queueing
717                  * could be merging multiple pages for one bio (e.g.
718                  * mpage_readpages). If an allocation happens for the
719                  * second or third page, the process can end up locking
720                  * the same page twice and deadlocking. Rather than
721                  * trying to be clever about what pages can be locked,
722                  * avoid the use of lock_page for direct compaction
723                  * altogether.
724                  */
725                 if (current->flags & PF_MEMALLOC)
726                         goto out;
727 
728                 lock_page(page);
729         }
730 
731         /*
732          * Only memory hotplug's offline_pages() caller has locked out KSM,
733          * and can safely migrate a KSM page.  The other cases have skipped
734          * PageKsm along with PageReserved - but it is only now when we have
735          * the page lock that we can be certain it will not go KSM beneath us
736          * (KSM will not upgrade a page from PageAnon to PageKsm when it sees
737          * its pagecount raised, but only here do we take the page lock which
738          * serializes that).
739          */
740         if (PageKsm(page) && !offlining) {
741                 rc = -EBUSY;
742                 goto unlock;
743         }
744 
745         /* charge against new page */
746         mem_cgroup_prepare_migration(page, newpage, &mem);
747 
748         if (PageWriteback(page)) {
749                 /*
750                  * Only in the case of a full syncronous migration is it
751                  * necessary to wait for PageWriteback. In the async case,
752                  * the retry loop is too short and in the sync-light case,
753                  * the overhead of stalling is too much
754                  */
755                 if (mode != MIGRATE_SYNC) {
756                         rc = -EBUSY;
757                         goto uncharge;
758                 }
759                 if (!force)
760                         goto uncharge;
761                 wait_on_page_writeback(page);
762         }
763         /*
764          * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
765          * we cannot notice that anon_vma is freed while we migrates a page.
766          * This get_anon_vma() delays freeing anon_vma pointer until the end
767          * of migration. File cache pages are no problem because of page_lock()
768          * File Caches may use write_page() or lock_page() in migration, then,
769          * just care Anon page here.
770          */
771         if (PageAnon(page)) {
772                 /*
773                  * Only page_lock_anon_vma_read() understands the subtleties of
774                  * getting a hold on an anon_vma from outside one of its mms.
775                  */
776                 anon_vma = page_get_anon_vma(page);
777                 if (anon_vma) {
778                         /*
779                          * Anon page
780                          */
781                 } else if (PageSwapCache(page)) {
782                         /*
783                          * We cannot be sure that the anon_vma of an unmapped
784                          * swapcache page is safe to use because we don't
785                          * know in advance if the VMA that this page belonged
786                          * to still exists. If the VMA and others sharing the
787                          * data have been freed, then the anon_vma could
788                          * already be invalid.
789                          *
790                          * To avoid this possibility, swapcache pages get
791                          * migrated but are not remapped when migration
792                          * completes
793                          */
794                         remap_swapcache = 0;
795                 } else {
796                         goto uncharge;
797                 }
798         }
799 
800         if (unlikely(balloon_page_movable(page))) {
801                 /*
802                  * A ballooned page does not need any special attention from
803                  * physical to virtual reverse mapping procedures.
804                  * Skip any attempt to unmap PTEs or to remap swap cache,
805                  * in order to avoid burning cycles at rmap level, and perform
806                  * the page migration right away (proteced by page lock).
807                  */
808                 rc = balloon_page_migrate(newpage, page, mode);
809                 goto uncharge;
810         }
811 
812         /*
813          * Corner case handling:
814          * 1. When a new swap-cache page is read into, it is added to the LRU
815          * and treated as swapcache but it has no rmap yet.
816          * Calling try_to_unmap() against a page->mapping==NULL page will
817          * trigger a BUG.  So handle it here.
818          * 2. An orphaned page (see truncate_complete_page) might have
819          * fs-private metadata. The page can be picked up due to memory
820          * offlining.  Everywhere else except page reclaim, the page is
821          * invisible to the vm, so the page can not be migrated.  So try to
822          * free the metadata, so the page can be freed.
823          */
824         if (!page->mapping) {
825                 VM_BUG_ON(PageAnon(page));
826                 if (page_has_private(page)) {
827                         try_to_free_buffers(page);
828                         goto uncharge;
829                 }
830                 goto skip_unmap;
831         }
832 
833         /* Establish migration ptes or remove ptes */
834         try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
835 
836 skip_unmap:
837         if (!page_mapped(page))
838                 rc = move_to_new_page(newpage, page, remap_swapcache, mode);
839 
840         if (rc && remap_swapcache)
841                 remove_migration_ptes(page, page);
842 
843         /* Drop an anon_vma reference if we took one */
844         if (anon_vma)
845                 put_anon_vma(anon_vma);
846 
847 uncharge:
848         mem_cgroup_end_migration(mem, page, newpage,
849                                  (rc == MIGRATEPAGE_SUCCESS ||
850                                   rc == MIGRATEPAGE_BALLOON_SUCCESS));
851 unlock:
852         unlock_page(page);
853 out:
854         return rc;
855 }
856 
857 /*
858  * Obtain the lock on page, remove all ptes and migrate the page
859  * to the newly allocated page in newpage.
860  */
861 static int unmap_and_move(new_page_t get_new_page, unsigned long private,
862                         struct page *page, int force, bool offlining,
863                         enum migrate_mode mode)
864 {
865         int rc = 0;
866         int *result = NULL;
867         struct page *newpage = get_new_page(page, private, &result);
868 
869         if (!newpage)
870                 return -ENOMEM;
871 
872         if (page_count(page) == 1) {
873                 /* page was freed from under us. So we are done. */
874                 goto out;
875         }
876 
877         if (unlikely(PageTransHuge(page)))
878                 if (unlikely(split_huge_page(page)))
879                         goto out;
880 
881         rc = __unmap_and_move(page, newpage, force, offlining, mode);
882 
883         if (unlikely(rc == MIGRATEPAGE_BALLOON_SUCCESS)) {
884                 /*
885                  * A ballooned page has been migrated already.
886                  * Now, it's the time to wrap-up counters,
887                  * handle the page back to Buddy and return.
888                  */
889                 dec_zone_page_state(page, NR_ISOLATED_ANON +
890                                     page_is_file_cache(page));
891                 balloon_page_free(page);
892                 return MIGRATEPAGE_SUCCESS;
893         }
894 out:
895         if (rc != -EAGAIN) {
896                 /*
897                  * A page that has been migrated has all references
898                  * removed and will be freed. A page that has not been
899                  * migrated will have kepts its references and be
900                  * restored.
901                  */
902                 list_del(&page->lru);
903                 dec_zone_page_state(page, NR_ISOLATED_ANON +
904                                 page_is_file_cache(page));
905                 putback_lru_page(page);
906         }
907         /*
908          * Move the new page to the LRU. If migration was not successful
909          * then this will free the page.
910          */
911         putback_lru_page(newpage);
912         if (result) {
913                 if (rc)
914                         *result = rc;
915                 else
916                         *result = page_to_nid(newpage);
917         }
918         return rc;
919 }
920 
921 /*
922  * Counterpart of unmap_and_move_page() for hugepage migration.
923  *
924  * This function doesn't wait the completion of hugepage I/O
925  * because there is no race between I/O and migration for hugepage.
926  * Note that currently hugepage I/O occurs only in direct I/O
927  * where no lock is held and PG_writeback is irrelevant,
928  * and writeback status of all subpages are counted in the reference
929  * count of the head page (i.e. if all subpages of a 2MB hugepage are
930  * under direct I/O, the reference of the head page is 512 and a bit more.)
931  * This means that when we try to migrate hugepage whose subpages are
932  * doing direct I/O, some references remain after try_to_unmap() and
933  * hugepage migration fails without data corruption.
934  *
935  * There is also no race when direct I/O is issued on the page under migration,
936  * because then pte is replaced with migration swap entry and direct I/O code
937  * will wait in the page fault for migration to complete.
938  */
939 static int unmap_and_move_huge_page(new_page_t get_new_page,
940                                 unsigned long private, struct page *hpage,
941                                 int force, bool offlining,
942                                 enum migrate_mode mode)
943 {
944         int rc = 0;
945         int *result = NULL;
946         struct page *new_hpage = get_new_page(hpage, private, &result);
947         struct anon_vma *anon_vma = NULL;
948 
949         if (!new_hpage)
950                 return -ENOMEM;
951 
952         rc = -EAGAIN;
953 
954         if (!trylock_page(hpage)) {
955                 if (!force || mode != MIGRATE_SYNC)
956                         goto out;
957                 lock_page(hpage);
958         }
959 
960         if (PageAnon(hpage))
961                 anon_vma = page_get_anon_vma(hpage);
962 
963         try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
964 
965         if (!page_mapped(hpage))
966                 rc = move_to_new_page(new_hpage, hpage, 1, mode);
967 
968         if (rc)
969                 remove_migration_ptes(hpage, hpage);
970 
971         if (anon_vma)
972                 put_anon_vma(anon_vma);
973 
974         if (!rc)
975                 hugetlb_cgroup_migrate(hpage, new_hpage);
976 
977         unlock_page(hpage);
978 out:
979         put_page(new_hpage);
980         if (result) {
981                 if (rc)
982                         *result = rc;
983                 else
984                         *result = page_to_nid(new_hpage);
985         }
986         return rc;
987 }
988 
989 /*
990  * migrate_pages
991  *
992  * The function takes one list of pages to migrate and a function
993  * that determines from the page to be migrated and the private data
994  * the target of the move and allocates the page.
995  *
996  * The function returns after 10 attempts or if no pages
997  * are movable anymore because to has become empty
998  * or no retryable pages exist anymore.
999  * Caller should call putback_lru_pages to return pages to the LRU
1000  * or free list only if ret != 0.
1001  *
1002  * Return: Number of pages not migrated or error code.
1003  */
1004 int migrate_pages(struct list_head *from,
1005                 new_page_t get_new_page, unsigned long private, bool offlining,
1006                 enum migrate_mode mode, int reason)
1007 {
1008         int retry = 1;
1009         int nr_failed = 0;
1010         int nr_succeeded = 0;
1011         int pass = 0;
1012         struct page *page;
1013         struct page *page2;
1014         int swapwrite = current->flags & PF_SWAPWRITE;
1015         int rc;
1016 
1017         if (!swapwrite)
1018                 current->flags |= PF_SWAPWRITE;
1019 
1020         for(pass = 0; pass < 10 && retry; pass++) {
1021                 retry = 0;
1022 
1023                 list_for_each_entry_safe(page, page2, from, lru) {
1024                         cond_resched();
1025 
1026                         rc = unmap_and_move(get_new_page, private,
1027                                                 page, pass > 2, offlining,
1028                                                 mode);
1029 
1030                         switch(rc) {
1031                         case -ENOMEM:
1032                                 goto out;
1033                         case -EAGAIN:
1034                                 retry++;
1035                                 break;
1036                         case MIGRATEPAGE_SUCCESS:
1037                                 nr_succeeded++;
1038                                 break;
1039                         default:
1040                                 /* Permanent failure */
1041                                 nr_failed++;
1042                                 break;
1043                         }
1044                 }
1045         }
1046         rc = nr_failed + retry;
1047 out:
1048         if (nr_succeeded)
1049                 count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
1050         if (nr_failed)
1051                 count_vm_events(PGMIGRATE_FAIL, nr_failed);
1052         trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
1053 
1054         if (!swapwrite)
1055                 current->flags &= ~PF_SWAPWRITE;
1056 
1057         return rc;
1058 }
1059 
1060 int migrate_huge_page(struct page *hpage, new_page_t get_new_page,
1061                       unsigned long private, bool offlining,
1062                       enum migrate_mode mode)
1063 {
1064         int pass, rc;
1065 
1066         for (pass = 0; pass < 10; pass++) {
1067                 rc = unmap_and_move_huge_page(get_new_page,
1068                                               private, hpage, pass > 2, offlining,
1069                                               mode);
1070                 switch (rc) {
1071                 case -ENOMEM:
1072                         goto out;
1073                 case -EAGAIN:
1074                         /* try again */
1075                         cond_resched();
1076                         break;
1077                 case MIGRATEPAGE_SUCCESS:
1078                         goto out;
1079                 default:
1080                         rc = -EIO;
1081                         goto out;
1082                 }
1083         }
1084 out:
1085         return rc;
1086 }
1087 
1088 #ifdef CONFIG_NUMA
1089 /*
1090  * Move a list of individual pages
1091  */
1092 struct page_to_node {
1093         unsigned long addr;
1094         struct page *page;
1095         int node;
1096         int status;
1097 };
1098 
1099 static struct page *new_page_node(struct page *p, unsigned long private,
1100                 int **result)
1101 {
1102         struct page_to_node *pm = (struct page_to_node *)private;
1103 
1104         while (pm->node != MAX_NUMNODES && pm->page != p)
1105                 pm++;
1106 
1107         if (pm->node == MAX_NUMNODES)
1108                 return NULL;
1109 
1110         *result = &pm->status;
1111 
1112         return alloc_pages_exact_node(pm->node,
1113                                 GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
1114 }
1115 
1116 /*
1117  * Move a set of pages as indicated in the pm array. The addr
1118  * field must be set to the virtual address of the page to be moved
1119  * and the node number must contain a valid target node.
1120  * The pm array ends with node = MAX_NUMNODES.
1121  */
1122 static int do_move_page_to_node_array(struct mm_struct *mm,
1123                                       struct page_to_node *pm,
1124                                       int migrate_all)
1125 {
1126         int err;
1127         struct page_to_node *pp;
1128         LIST_HEAD(pagelist);
1129 
1130         down_read(&mm->mmap_sem);
1131 
1132         /*
1133          * Build a list of pages to migrate
1134          */
1135         for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
1136                 struct vm_area_struct *vma;
1137                 struct page *page;
1138 
1139                 err = -EFAULT;
1140                 vma = find_vma(mm, pp->addr);
1141                 if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
1142                         goto set_status;
1143 
1144                 page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);
1145 
1146                 err = PTR_ERR(page);
1147                 if (IS_ERR(page))
1148                         goto set_status;
1149 
1150                 err = -ENOENT;
1151                 if (!page)
1152                         goto set_status;
1153 
1154                 /* Use PageReserved to check for zero page */
1155                 if (PageReserved(page) || PageKsm(page))
1156                         goto put_and_set;
1157 
1158                 pp->page = page;
1159                 err = page_to_nid(page);
1160 
1161                 if (err == pp->node)
1162                         /*
1163                          * Node already in the right place
1164                          */
1165                         goto put_and_set;
1166 
1167                 err = -EACCES;
1168                 if (page_mapcount(page) > 1 &&
1169                                 !migrate_all)
1170                         goto put_and_set;
1171 
1172                 err = isolate_lru_page(page);
1173                 if (!err) {
1174                         list_add_tail(&page->lru, &pagelist);
1175                         inc_zone_page_state(page, NR_ISOLATED_ANON +
1176                                             page_is_file_cache(page));
1177                 }
1178 put_and_set:
1179                 /*
1180                  * Either remove the duplicate refcount from
1181                  * isolate_lru_page() or drop the page ref if it was
1182                  * not isolated.
1183                  */
1184                 put_page(page);
1185 set_status:
1186                 pp->status = err;
1187         }
1188 
1189         err = 0;
1190         if (!list_empty(&pagelist)) {
1191                 err = migrate_pages(&pagelist, new_page_node,
1192                                 (unsigned long)pm, 0, MIGRATE_SYNC,
1193                                 MR_SYSCALL);
1194                 if (err)
1195                         putback_lru_pages(&pagelist);
1196         }
1197 
1198         up_read(&mm->mmap_sem);
1199         return err;
1200 }
1201 
1202 /*
1203  * Migrate an array of page address onto an array of nodes and fill
1204  * the corresponding array of status.
1205  */
1206 static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1207                          unsigned long nr_pages,
1208                          const void __user * __user *pages,
1209                          const int __user *nodes,
1210                          int __user *status, int flags)
1211 {
1212         struct page_to_node *pm;
1213         unsigned long chunk_nr_pages;
1214         unsigned long chunk_start;
1215         int err;
1216 
1217         err = -ENOMEM;
1218         pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
1219         if (!pm)
1220                 goto out;
1221 
1222         migrate_prep();
1223 
1224         /*
1225          * Store a chunk of page_to_node array in a page,
1226          * but keep the last one as a marker
1227          */
1228         chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
1229 
1230         for (chunk_start = 0;
1231              chunk_start < nr_pages;
1232              chunk_start += chunk_nr_pages) {
1233                 int j;
1234 
1235                 if (chunk_start + chunk_nr_pages > nr_pages)
1236                         chunk_nr_pages = nr_pages - chunk_start;
1237 
1238                 /* fill the chunk pm with addrs and nodes from user-space */
1239                 for (j = 0; j < chunk_nr_pages; j++) {
1240                         const void __user *p;
1241                         int node;
1242 
1243                         err = -EFAULT;
1244                         if (get_user(p, pages + j + chunk_start))
1245                                 goto out_pm;
1246                         pm[j].addr = (unsigned long) p;
1247 
1248                         if (get_user(node, nodes + j + chunk_start))
1249                                 goto out_pm;
1250 
1251                         err = -ENODEV;
1252                         if (node < 0 || node >= MAX_NUMNODES)
1253                                 goto out_pm;
1254 
1255                         if (!node_state(node, N_MEMORY))
1256                                 goto out_pm;
1257 
1258                         err = -EACCES;
1259                         if (!node_isset(node, task_nodes))
1260                                 goto out_pm;
1261 
1262                         pm[j].node = node;
1263                 }
1264 
1265                 /* End marker for this chunk */
1266                 pm[chunk_nr_pages].node = MAX_NUMNODES;
1267 
1268                 /* Migrate this chunk */
1269                 err = do_move_page_to_node_array(mm, pm,
1270                                                  flags & MPOL_MF_MOVE_ALL);
1271                 if (err < 0)
1272                         goto out_pm;
1273 
1274                 /* Return status information */
1275                 for (j = 0; j < chunk_nr_pages; j++)
1276                         if (put_user(pm[j].status, status + j + chunk_start)) {
1277                                 err = -EFAULT;
1278                                 goto out_pm;
1279                         }
1280         }
1281         err = 0;
1282 
1283 out_pm:
1284         free_page((unsigned long)pm);
1285 out:
1286         return err;
1287 }
1288 
1289 /*
1290  * Determine the nodes of an array of pages and store it in an array of status.
1291  */
1292 static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1293                                 const void __user **pages, int *status)
1294 {
1295         unsigned long i;
1296 
1297         down_read(&mm->mmap_sem);
1298 
1299         for (i = 0; i < nr_pages; i++) {
1300                 unsigned long addr = (unsigned long)(*pages);
1301                 struct vm_area_struct *vma;
1302                 struct page *page;
1303                 int err = -EFAULT;
1304 
1305                 vma = find_vma(mm, addr);
1306                 if (!vma || addr < vma->vm_start)
1307                         goto set_status;
1308 
1309                 page = follow_page(vma, addr, 0);
1310 
1311                 err = PTR_ERR(page);
1312                 if (IS_ERR(page))
1313                         goto set_status;
1314 
1315                 err = -ENOENT;
1316                 /* Use PageReserved to check for zero page */
1317                 if (!page || PageReserved(page) || PageKsm(page))
1318                         goto set_status;
1319 
1320                 err = page_to_nid(page);
1321 set_status:
1322                 *status = err;
1323 
1324                 pages++;
1325                 status++;
1326         }
1327 
1328         up_read(&mm->mmap_sem);
1329 }
1330 
1331 /*
1332  * Determine the nodes of a user array of pages and store it in
1333  * a user array of status.
1334  */
1335 static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1336                          const void __user * __user *pages,
1337                          int __user *status)
1338 {
1339 #define DO_PAGES_STAT_CHUNK_NR 16
1340         const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1341         int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1342 
1343         while (nr_pages) {
1344                 unsigned long chunk_nr;
1345 
1346                 chunk_nr = nr_pages;
1347                 if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1348                         chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1349 
1350                 if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1351                         break;
1352 
1353                 do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1354 
1355                 if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1356                         break;
1357 
1358                 pages += chunk_nr;
1359                 status += chunk_nr;
1360                 nr_pages -= chunk_nr;
1361         }
1362         return nr_pages ? -EFAULT : 0;
1363 }
1364 
1365 /*
1366  * Move a list of pages in the address space of the currently executing
1367  * process.
1368  */
1369 SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1370                 const void __user * __user *, pages,
1371                 const int __user *, nodes,
1372                 int __user *, status, int, flags)
1373 {
1374         const struct cred *cred = current_cred(), *tcred;
1375         struct task_struct *task;
1376         struct mm_struct *mm;
1377         int err;
1378         nodemask_t task_nodes;
1379 
1380         /* Check flags */
1381         if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1382                 return -EINVAL;
1383 
1384         if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1385                 return -EPERM;
1386 
1387         /* Find the mm_struct */
1388         rcu_read_lock();
1389         task = pid ? find_task_by_vpid(pid) : current;
1390         if (!task) {
1391                 rcu_read_unlock();
1392                 return -ESRCH;
1393         }
1394         get_task_struct(task);
1395 
1396         /*
1397          * Check if this process has the right to modify the specified
1398          * process. The right exists if the process has administrative
1399          * capabilities, superuser privileges or the same
1400          * userid as the target process.
1401          */
1402         tcred = __task_cred(task);
1403         if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
1404             !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&
1405             !capable(CAP_SYS_NICE)) {
1406                 rcu_read_unlock();
1407                 err = -EPERM;
1408                 goto out;
1409         }
1410         rcu_read_unlock();
1411 
1412         err = security_task_movememory(task);
1413         if (err)
1414                 goto out;
1415 
1416         task_nodes = cpuset_mems_allowed(task);
1417         mm = get_task_mm(task);
1418         put_task_struct(task);
1419 
1420         if (!mm)
1421                 return -EINVAL;
1422 
1423         if (nodes)
1424                 err = do_pages_move(mm, task_nodes, nr_pages, pages,
1425                                     nodes, status, flags);
1426         else
1427                 err = do_pages_stat(mm, nr_pages, pages, status);
1428 
1429         mmput(mm);
1430         return err;
1431 
1432 out:
1433         put_task_struct(task);
1434         return err;
1435 }
1436 
1437 /*
1438  * Call migration functions in the vma_ops that may prepare
1439  * memory in a vm for migration. migration functions may perform
1440  * the migration for vmas that do not have an underlying page struct.
1441  */
1442 int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
1443         const nodemask_t *from, unsigned long flags)
1444 {
1445         struct vm_area_struct *vma;
1446         int err = 0;
1447 
1448         for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
1449                 if (vma->vm_ops && vma->vm_ops->migrate) {
1450                         err = vma->vm_ops->migrate(vma, to, from, flags);
1451                         if (err)
1452                                 break;
1453                 }
1454         }
1455         return err;
1456 }
1457 
1458 #ifdef CONFIG_NUMA_BALANCING
1459 /*
1460  * Returns true if this is a safe migration target node for misplaced NUMA
1461  * pages. Currently it only checks the watermarks which crude
1462  */
1463 static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
1464                                    int nr_migrate_pages)
1465 {
1466         int z;
1467         for (z = pgdat->nr_zones - 1; z >= 0; z--) {
1468                 struct zone *zone = pgdat->node_zones + z;
1469 
1470                 if (!populated_zone(zone))
1471                         continue;
1472 
1473                 if (zone->all_unreclaimable)
1474                         continue;
1475 
1476                 /* Avoid waking kswapd by allocating pages_to_migrate pages. */
1477                 if (!zone_watermark_ok(zone, 0,
1478                                        high_wmark_pages(zone) +
1479                                        nr_migrate_pages,
1480                                        0, 0))
1481                         continue;
1482                 return true;
1483         }
1484         return false;
1485 }
1486 
1487 static struct page *alloc_misplaced_dst_page(struct page *page,
1488                                            unsigned long data,
1489                                            int **result)
1490 {
1491         int nid = (int) data;
1492         struct page *newpage;
1493 
1494         newpage = alloc_pages_exact_node(nid,
1495                                          (GFP_HIGHUSER_MOVABLE | GFP_THISNODE |
1496                                           __GFP_NOMEMALLOC | __GFP_NORETRY |
1497                                           __GFP_NOWARN) &
1498                                          ~GFP_IOFS, 0);
1499         if (newpage)
1500                 page_xchg_last_nid(newpage, page_last_nid(page));
1501 
1502         return newpage;
1503 }
1504 
1505 /*
1506  * page migration rate limiting control.
1507  * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
1508  * window of time. Default here says do not migrate more than 1280M per second.
1509  * If a node is rate-limited then PTE NUMA updates are also rate-limited. However
1510  * as it is faults that reset the window, pte updates will happen unconditionally
1511  * if there has not been a fault since @pteupdate_interval_millisecs after the
1512  * throttle window closed.
1513  */
1514 static unsigned int migrate_interval_millisecs __read_mostly = 100;
1515 static unsigned int pteupdate_interval_millisecs __read_mostly = 1000;
1516 static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
1517 
1518 /* Returns true if NUMA migration is currently rate limited */
1519 bool migrate_ratelimited(int node)
1520 {
1521         pg_data_t *pgdat = NODE_DATA(node);
1522 
1523         if (time_after(jiffies, pgdat->numabalancing_migrate_next_window +
1524                                 msecs_to_jiffies(pteupdate_interval_millisecs)))
1525                 return false;
1526 
1527         if (pgdat->numabalancing_migrate_nr_pages < ratelimit_pages)
1528                 return false;
1529 
1530         return true;
1531 }
1532 
1533 /* Returns true if the node is migrate rate-limited after the update */
1534 bool numamigrate_update_ratelimit(pg_data_t *pgdat, unsigned long nr_pages)
1535 {
1536         bool rate_limited = false;
1537 
1538         /*
1539          * Rate-limit the amount of data that is being migrated to a node.
1540          * Optimal placement is no good if the memory bus is saturated and
1541          * all the time is being spent migrating!
1542          */
1543         spin_lock(&pgdat->numabalancing_migrate_lock);
1544         if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {
1545                 pgdat->numabalancing_migrate_nr_pages = 0;
1546                 pgdat->numabalancing_migrate_next_window = jiffies +
1547                         msecs_to_jiffies(migrate_interval_millisecs);
1548         }
1549         if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages)
1550                 rate_limited = true;
1551         else
1552                 pgdat->numabalancing_migrate_nr_pages += nr_pages;
1553         spin_unlock(&pgdat->numabalancing_migrate_lock);
1554         
1555         return rate_limited;
1556 }
1557 
1558 int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
1559 {
1560         int ret = 0;
1561 
1562         /* Avoid migrating to a node that is nearly full */
1563         if (migrate_balanced_pgdat(pgdat, 1)) {
1564                 int page_lru;
1565 
1566                 if (isolate_lru_page(page)) {
1567                         put_page(page);
1568                         return 0;
1569                 }
1570 
1571                 /* Page is isolated */
1572                 ret = 1;
1573                 page_lru = page_is_file_cache(page);
1574                 if (!PageTransHuge(page))
1575                         inc_zone_page_state(page, NR_ISOLATED_ANON + page_lru);
1576                 else
1577                         mod_zone_page_state(page_zone(page),
1578                                         NR_ISOLATED_ANON + page_lru,
1579                                         HPAGE_PMD_NR);
1580         }
1581 
1582         /*
1583          * Page is either isolated or there is not enough space on the target
1584          * node. If isolated, then it has taken a reference count and the
1585          * callers reference can be safely dropped without the page
1586          * disappearing underneath us during migration. Otherwise the page is
1587          * not to be migrated but the callers reference should still be
1588          * dropped so it does not leak.
1589          */
1590         put_page(page);
1591 
1592         return ret;
1593 }
1594 
1595 /*
1596  * Attempt to migrate a misplaced page to the specified destination
1597  * node. Caller is expected to have an elevated reference count on
1598  * the page that will be dropped by this function before returning.
1599  */
1600 int migrate_misplaced_page(struct page *page, int node)
1601 {
1602         pg_data_t *pgdat = NODE_DATA(node);
1603         int isolated = 0;
1604         int nr_remaining;
1605         LIST_HEAD(migratepages);
1606 
1607         /*
1608          * Don't migrate pages that are mapped in multiple processes.
1609          * TODO: Handle false sharing detection instead of this hammer
1610          */
1611         if (page_mapcount(page) != 1) {
1612                 put_page(page);
1613                 goto out;
1614         }
1615 
1616         /*
1617          * Rate-limit the amount of data that is being migrated to a node.
1618          * Optimal placement is no good if the memory bus is saturated and
1619          * all the time is being spent migrating!
1620          */
1621         if (numamigrate_update_ratelimit(pgdat, 1)) {
1622                 put_page(page);
1623                 goto out;
1624         }
1625 
1626         isolated = numamigrate_isolate_page(pgdat, page);
1627         if (!isolated)
1628                 goto out;
1629 
1630         list_add(&page->lru, &migratepages);
1631         nr_remaining = migrate_pages(&migratepages,
1632                         alloc_misplaced_dst_page,
1633                         node, false, MIGRATE_ASYNC,
1634                         MR_NUMA_MISPLACED);
1635         if (nr_remaining) {
1636                 putback_lru_pages(&migratepages);
1637                 isolated = 0;
1638         } else
1639                 count_vm_numa_event(NUMA_PAGE_MIGRATE);
1640         BUG_ON(!list_empty(&migratepages));
1641 out:
1642         return isolated;
1643 }
1644 #endif /* CONFIG_NUMA_BALANCING */
1645 
1646 #if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1647 int migrate_misplaced_transhuge_page(struct mm_struct *mm,
1648                                 struct vm_area_struct *vma,
1649                                 pmd_t *pmd, pmd_t entry,
1650                                 unsigned long address,
1651                                 struct page *page, int node)
1652 {
1653         unsigned long haddr = address & HPAGE_PMD_MASK;
1654         pg_data_t *pgdat = NODE_DATA(node);
1655         int isolated = 0;
1656         struct page *new_page = NULL;
1657         struct mem_cgroup *memcg = NULL;
1658         int page_lru = page_is_file_cache(page);
1659 
1660         /*
1661          * Don't migrate pages that are mapped in multiple processes.
1662          * TODO: Handle false sharing detection instead of this hammer
1663          */
1664         if (page_mapcount(page) != 1)
1665                 goto out_dropref;
1666 
1667         /*
1668          * Rate-limit the amount of data that is being migrated to a node.
1669          * Optimal placement is no good if the memory bus is saturated and
1670          * all the time is being spent migrating!
1671          */
1672         if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
1673                 goto out_dropref;
1674 
1675         new_page = alloc_pages_node(node,
1676                 (GFP_TRANSHUGE | GFP_THISNODE) & ~__GFP_WAIT, HPAGE_PMD_ORDER);
1677         if (!new_page) {
1678                 count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
1679                 goto out_dropref;
1680         }
1681         page_xchg_last_nid(new_page, page_last_nid(page));
1682 
1683         isolated = numamigrate_isolate_page(pgdat, page);
1684 
1685         /*
1686          * Failing to isolate or a GUP pin prevents migration. The expected
1687          * page count is 2. 1 for anonymous pages without a mapping and 1
1688          * for the callers pin. If the page was isolated, the page will
1689          * need to be put back on the LRU.
1690          */
1691         if (!isolated || page_count(page) != 2) {
1692                 count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
1693                 put_page(new_page);
1694                 if (isolated) {
1695                         putback_lru_page(page);
1696                         isolated = 0;
1697                         goto out;
1698                 }
1699                 goto out_keep_locked;
1700         }
1701 
1702         /* Prepare a page as a migration target */
1703         __set_page_locked(new_page);
1704         SetPageSwapBacked(new_page);
1705 
1706         /* anon mapping, we can simply copy page->mapping to the new page: */
1707         new_page->mapping = page->mapping;
1708         new_page->index = page->index;
1709         migrate_page_copy(new_page, page);
1710         WARN_ON(PageLRU(new_page));
1711 
1712         /* Recheck the target PMD */
1713         spin_lock(&mm->page_table_lock);
1714         if (unlikely(!pmd_same(*pmd, entry))) {
1715                 spin_unlock(&mm->page_table_lock);
1716 
1717                 /* Reverse changes made by migrate_page_copy() */
1718                 if (TestClearPageActive(new_page))
1719                         SetPageActive(page);
1720                 if (TestClearPageUnevictable(new_page))
1721                         SetPageUnevictable(page);
1722                 mlock_migrate_page(page, new_page);
1723 
1724                 unlock_page(new_page);
1725                 put_page(new_page);             /* Free it */
1726 
1727                 unlock_page(page);
1728                 putback_lru_page(page);
1729 
1730                 count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
1731                 goto out;
1732         }
1733 
1734         /*
1735          * Traditional migration needs to prepare the memcg charge
1736          * transaction early to prevent the old page from being
1737          * uncharged when installing migration entries.  Here we can
1738          * save the potential rollback and start the charge transfer
1739          * only when migration is already known to end successfully.
1740          */
1741         mem_cgroup_prepare_migration(page, new_page, &memcg);
1742 
1743         entry = mk_pmd(new_page, vma->vm_page_prot);
1744         entry = pmd_mknonnuma(entry);
1745         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1746         entry = pmd_mkhuge(entry);
1747 
1748         page_add_new_anon_rmap(new_page, vma, haddr);
1749 
1750         set_pmd_at(mm, haddr, pmd, entry);
1751         update_mmu_cache_pmd(vma, address, &entry);
1752         page_remove_rmap(page);
1753         /*
1754          * Finish the charge transaction under the page table lock to
1755          * prevent split_huge_page() from dividing up the charge
1756          * before it's fully transferred to the new page.
1757          */
1758         mem_cgroup_end_migration(memcg, page, new_page, true);
1759         spin_unlock(&mm->page_table_lock);
1760 
1761         unlock_page(new_page);
1762         unlock_page(page);
1763         put_page(page);                 /* Drop the rmap reference */
1764         put_page(page);                 /* Drop the LRU isolation reference */
1765 
1766         count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
1767         count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
1768 
1769 out:
1770         mod_zone_page_state(page_zone(page),
1771                         NR_ISOLATED_ANON + page_lru,
1772                         -HPAGE_PMD_NR);
1773         return isolated;
1774 
1775 out_dropref:
1776         put_page(page);
1777 out_keep_locked:
1778         return 0;
1779 }
1780 #endif /* CONFIG_NUMA_BALANCING */
1781 
1782 #endif /* CONFIG_NUMA */
1783 

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