From: David Rientjes <rientjes@google.com>
Date: Wed, 19 Jun 2013 00:05:49 +0000 (+1000)
Subject: mm, memcg: don't take task_lock in task_in_mem_cgroup
X-Git-Tag: next-20130619~2^2~569
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=4bc7e93fbbcd9aaf6f923f2f67f9450c4fdb2151;p=karo-tx-linux.git

mm, memcg: don't take task_lock in task_in_mem_cgroup

For processes that have detached their mm's, task_in_mem_cgroup()
unnecessarily takes task_lock() when rcu_read_lock() is all that is
necessary to call mem_cgroup_from_task().

While we're here, switch task_in_mem_cgroup() to return bool.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d6183f06d8c1..7b4d9d79570b 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -77,7 +77,8 @@ extern void mem_cgroup_uncharge_cache_page(struct page *page);
 
 bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 				  struct mem_cgroup *memcg);
-int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg);
+bool task_in_mem_cgroup(struct task_struct *task,
+			const struct mem_cgroup *memcg);
 
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
@@ -273,10 +274,10 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
 	return true;
 }
 
-static inline int task_in_mem_cgroup(struct task_struct *task,
-				     const struct mem_cgroup *memcg)
+static inline bool task_in_mem_cgroup(struct task_struct *task,
+				      const struct mem_cgroup *memcg)
 {
-	return 1;
+	return true;
 }
 
 static inline struct cgroup_subsys_state
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 194721839cf5..4748966b1511 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1448,11 +1448,12 @@ static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 	return ret;
 }
 
-int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
+bool task_in_mem_cgroup(struct task_struct *task,
+			const struct mem_cgroup *memcg)
 {
-	int ret;
 	struct mem_cgroup *curr = NULL;
 	struct task_struct *p;
+	bool ret;
 
 	p = find_lock_task_mm(task);
 	if (p) {
@@ -1464,14 +1465,14 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
 		 * killer still needs to detect if they have already been oom
 		 * killed to prevent needlessly killing additional tasks.
 		 */
-		task_lock(task);
+		rcu_read_lock();
 		curr = mem_cgroup_from_task(task);
 		if (curr)
 			css_get(&curr->css);
-		task_unlock(task);
+		rcu_read_unlock();
 	}
 	if (!curr)
-		return 0;
+		return false;
 	/*
 	 * We should check use_hierarchy of "memcg" not "curr". Because checking
 	 * use_hierarchy of "curr" here make this function true if hierarchy is