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Subject[patch] 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>
---
include/linux/memcontrol.h | 9 +++++----
mm/memcontrol.c | 11 ++++++-----
2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
--- 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
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1443,11 +1443,12 @@ 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) {
@@ -1459,14 +1460,14 @@ 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

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