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authorMel Gorman <mel@csn.ul.ie>2010-05-24 17:32:20 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-25 11:06:59 -0400
commit3fe2011ff51e92500010a495df4be86745fbbda9 (patch)
treef3dc07b9d41ce5ba15805c2d3b4bc0a1a7916832 /mm/migrate.c
parent67b9509b2c68ae38cecb83a239881cb0ddf087dc (diff)
mm: migration: allow the migration of PageSwapCache pages
PageAnon pages that are unmapped may or may not have an anon_vma so are not currently migrated. However, a swap cache page can be migrated and fits this description. This patch identifies page swap caches and allows them to be migrated but ensures that no attempt to made to remap the pages would would potentially try to access an already freed anon_vma. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/migrate.c')
-rw-r--r--mm/migrate.c53
1 files changed, 36 insertions, 17 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index b114635962dc..4afd6fe3c074 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -485,7 +485,8 @@ static int fallback_migrate_page(struct address_space *mapping,
485 * < 0 - error code 485 * < 0 - error code
486 * == 0 - success 486 * == 0 - success
487 */ 487 */
488static int move_to_new_page(struct page *newpage, struct page *page) 488static int move_to_new_page(struct page *newpage, struct page *page,
489 int remap_swapcache)
489{ 490{
490 struct address_space *mapping; 491 struct address_space *mapping;
491 int rc; 492 int rc;
@@ -520,10 +521,12 @@ static int move_to_new_page(struct page *newpage, struct page *page)
520 else 521 else
521 rc = fallback_migrate_page(mapping, newpage, page); 522 rc = fallback_migrate_page(mapping, newpage, page);
522 523
523 if (!rc) 524 if (rc) {
524 remove_migration_ptes(page, newpage);
525 else
526 newpage->mapping = NULL; 525 newpage->mapping = NULL;
526 } else {
527 if (remap_swapcache)
528 remove_migration_ptes(page, newpage);
529 }
527 530
528 unlock_page(newpage); 531 unlock_page(newpage);
529 532
@@ -540,6 +543,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
540 int rc = 0; 543 int rc = 0;
541 int *result = NULL; 544 int *result = NULL;
542 struct page *newpage = get_new_page(page, private, &result); 545 struct page *newpage = get_new_page(page, private, &result);
546 int remap_swapcache = 1;
543 int rcu_locked = 0; 547 int rcu_locked = 0;
544 int charge = 0; 548 int charge = 0;
545 struct mem_cgroup *mem = NULL; 549 struct mem_cgroup *mem = NULL;
@@ -601,18 +605,33 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
601 rcu_read_lock(); 605 rcu_read_lock();
602 rcu_locked = 1; 606 rcu_locked = 1;
603 607
604 /* 608 /* Determine how to safely use anon_vma */
605 * If the page has no mappings any more, just bail. An 609 if (!page_mapped(page)) {
606 * unmapped anon page is likely to be freed soon but worse, 610 if (!PageSwapCache(page))
607 * it's possible its anon_vma disappeared between when 611 goto rcu_unlock;
608 * the page was isolated and when we reached here while
609 * the RCU lock was not held
610 */
611 if (!page_mapped(page))
612 goto rcu_unlock;
613 612
614 anon_vma = page_anon_vma(page); 613 /*
615 atomic_inc(&anon_vma->external_refcount); 614 * We cannot be sure that the anon_vma of an unmapped
615 * swapcache page is safe to use because we don't
616 * know in advance if the VMA that this page belonged
617 * to still exists. If the VMA and others sharing the
618 * data have been freed, then the anon_vma could
619 * already be invalid.
620 *
621 * To avoid this possibility, swapcache pages get
622 * migrated but are not remapped when migration
623 * completes
624 */
625 remap_swapcache = 0;
626 } else {
627 /*
628 * Take a reference count on the anon_vma if the
629 * page is mapped so that it is guaranteed to
630 * exist when the page is remapped later
631 */
632 anon_vma = page_anon_vma(page);
633 atomic_inc(&anon_vma->external_refcount);
634 }
616 } 635 }
617 636
618 /* 637 /*
@@ -647,9 +666,9 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
647 666
648skip_unmap: 667skip_unmap:
649 if (!page_mapped(page)) 668 if (!page_mapped(page))
650 rc = move_to_new_page(newpage, page); 669 rc = move_to_new_page(newpage, page, remap_swapcache);
651 670
652 if (rc) 671 if (rc && remap_swapcache)
653 remove_migration_ptes(page, page); 672 remove_migration_ptes(page, page);
654rcu_unlock: 673rcu_unlock:
655 674