memcg: add accessor to mem_cgroup.css

So that an outside user can free the reference count grabbed by
try_get_mem_cgroup_from_page().

CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Hugh Dickins <hugh.dickins@tiscali.co.uk>
CC: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
CC: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index fc9bae82ac42..2c30a1116d84 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -81,6 +81,8 @@ int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
         return cgroup == mem;
 }
 
+extern struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem);
+
 extern int
 mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr);
 extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
@@ -206,6 +208,11 @@ static inline int task_in_mem_cgroup(struct task_struct *task,
         return 1;
 }
 
+static inline struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem)
+{
+        return NULL;
+}
+
 static inline int
 mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
 {