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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 <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki
2008-02-07 00:14:10 -08:00
committed by Linus Torvalds
parent 9175e0311e
commit ae41be3742
3 changed files with 72 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

43
mm/memcontrol.c
View File

@ -492,6 +492,49 @@ void mem_cgroup_uncharge(struct page_cgroup *pc)
}
}
}
/*
* Returns non-zero if a page (under migration) has valid page_cgroup member.
* Refcnt of page_cgroup is incremented.
*/
int mem_cgroup_prepare_migration(struct page *page)
{
struct page_cgroup *pc;
int ret = 0;
lock_page_cgroup(page);
pc = page_get_page_cgroup(page);
if (pc && atomic_inc_not_zero(&pc->ref_cnt))
ret = 1;
unlock_page_cgroup(page);
return ret;
}
void mem_cgroup_end_migration(struct page *page)
{
struct page_cgroup *pc = page_get_page_cgroup(page);
mem_cgroup_uncharge(pc);
}
/*
* We know both *page* and *newpage* are now not-on-LRU and Pg_locked.
* And no race with uncharge() routines because page_cgroup for *page*
* has extra one reference by mem_cgroup_prepare_migration.
*/
void mem_cgroup_page_migration(struct page *page, struct page *newpage)
{
struct page_cgroup *pc;
retry:
pc = page_get_page_cgroup(page);
if (!pc)
return;
if (clear_page_cgroup(page, pc) != pc)
goto retry;
pc->page = newpage;
lock_page_cgroup(newpage);
page_assign_page_cgroup(newpage, pc);
unlock_page_cgroup(newpage);
return;
}
int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
{