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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d6183f0..7b4d9d7 100644 (file)
--- 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 1947218..4748966 100644 (file)
--- 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