From: KAMEZAWA Hiroyuki In general, mem_cgroup's charge on ANON page is removed when page_remove_rmap() is called. At migration, the newpage is remapped again by remove_migration_ptes(). But pte may be already changed (by task exits). It is charged at page allocation but have no chance to be uncharged in that case because it is never added to rmap. Handle that corner case in mem_cgroup_end_migration(). Signed-off-by: KAMEZAWA Hiroyuki Acked-by: Balbir Singh Signed-off-by: KOSAKI Motohiro Cc: "Eric W. Biederman" Cc: Pavel Emelyanov Cc: Li Zefan Cc: Hugh Dickins Cc: YAMAMOTO Takashi Cc: Paul Menage Cc: David Rientjes Signed-off-by: Andrew Morton --- mm/memcontrol.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff -puN mm/memcontrol.c~memcg-remove-refcnt-from-page_cgroup-fix-memcg-fix-mem_cgroup_end_migration-race mm/memcontrol.c --- a/mm/memcontrol.c~memcg-remove-refcnt-from-page_cgroup-fix-memcg-fix-mem_cgroup_end_migration-race +++ a/mm/memcontrol.c @@ -762,10 +762,22 @@ int mem_cgroup_prepare_migration(struct /* remove redundant charge if migration failed*/ void mem_cgroup_end_migration(struct page *newpage) { - /* At success, page->mapping is not NULL and nothing to do. */ + /* + * At success, page->mapping is not NULL. + * special rollback care is necessary when + * 1. at migration failure. (newpage->mapping is cleared in this case) + * 2. the newpage was moved but not remapped again because the task + * exits and the newpage is obsolete. In this case, the new page + * may be a swapcache. So, we just call mem_cgroup_uncharge_page() + * always for avoiding mess. The page_cgroup will be removed if + * unnecessary. File cache pages is still on radix-tree. Don't + * care it. + */ if (!newpage->mapping) __mem_cgroup_uncharge_common(newpage, MEM_CGROUP_CHARGE_TYPE_FORCE); + else if (PageAnon(newpage)) + mem_cgroup_uncharge_page(newpage); } /* _