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bugfix for memory cgroup controller: migration under memory controller fix

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While using memory control cgroup, page-migration under it works as following.
==
 1. uncharge all refs at try to unmap.
 2. charge regs again remove_migration_ptes()
==
This is simple but has following problems.
==
 The page is uncharged and charged back again if *mapped*.
    - This means that cgroup before migration can be different from one after
      migration
    - If page is not mapped but charged as page cache, charge is just ignored
      (because not mapped, it will not be uncharged before migration)
      This is memory leak.
==
This patch tries to keep memory cgroup at page migration by increasing
one refcnt during it. 3 functions are added.

 mem_cgroup_prepare_migration() --- increase refcnt of page->page_cgroup
 mem_cgroup_end_migration()     --- decrease refcnt of page->page_cgroup
 mem_cgroup_page_migration() --- copy page->page_cgroup from old page to
                                 new page.

During migration
  - old page is under PG_locked.
  - new page is under PG_locked, too.
  - both old page and new page is not on LRU.

These 3 facts guarantee that page_cgroup() migration has no race.

Tested and worked well in x86_64/fake-NUMA box.

Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Pavel Emelianov <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Kirill Korotaev <[email protected]>
Cc: Herbert Poetzl <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Vaidyanathan Srinivasan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KAMEZAWA Hiroyuki 2008-02-07 00:14:10 -08:00 • committed by Linus Torvalds
commit ae41be3742
3 changed files with 72 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

13
mm/migrate.c
View file

@ -593,9 +593,10 @@ static int move_to_new_page(struct page *newpage, struct page *page)
else
rc = fallback_migrate_page(mapping, newpage, page);
if (!rc)
if (!rc) {
mem_cgroup_page_migration(page, newpage);
remove_migration_ptes(page, newpage);
else
} else
newpage->mapping = NULL;
unlock_page(newpage);
@ -614,6 +615,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
int *result = NULL;
struct page *newpage = get_new_page(page, private, &result);
int rcu_locked = 0;
int charge = 0;
if (!newpage)
return -ENOMEM;
@ -673,14 +675,19 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
goto rcu_unlock;
}
charge = mem_cgroup_prepare_migration(page);
/* Establish migration ptes or remove ptes */
try_to_unmap(page, 1);
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
if (rc)
if (rc) {
remove_migration_ptes(page, page);
if (charge)
mem_cgroup_end_migration(page);
} else if (charge)
mem_cgroup_end_migration(newpage);
rcu_unlock:
if (rcu_locked)
rcu_read_unlock();