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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

19
include/linux/memcontrol.h
View file

@ -60,6 +60,10 @@ static inline void mem_cgroup_uncharge_page(struct page *page)
mem_cgroup_uncharge(page_get_page_cgroup(page));
}
extern int mem_cgroup_prepare_migration(struct page *page);
extern void mem_cgroup_end_migration(struct page *page);
extern void mem_cgroup_page_migration(struct page *page, struct page *newpage);
#else /* CONFIG_CGROUP_MEM_CONT */
static inline void mm_init_cgroup(struct mm_struct *mm,
struct task_struct *p)
@ -117,6 +121,21 @@ static inline int task_in_mem_cgroup(struct task_struct *task,
return 1;
}
static inline int mem_cgroup_prepare_migration(struct page *page)
{
return 0;
}
static inline void mem_cgroup_end_migration(struct page *page)
{
}
static inline void
mem_cgroup_page_migration(struct page *page, struct page *newpage)
{
}
#endif /* CONFIG_CGROUP_MEM_CONT */
#endif /* _LINUX_MEMCONTROL_H */