diff mbox series

[RFC,v2,02/18] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm

Message ID 20210409122959.82264-3-songmuchun@bytedance.com (mailing list archive)
State New, archived
Headers show
Series Use obj_cgroup APIs to charge the LRU pages | expand

Commit Message

Muchun Song April 9, 2021, 12:29 p.m. UTC 
When mm is NULL, we do not need to hold rcu lock and call css_tryget for
the root memcg. And we also do not need to check !mm in every loop of
while. So bail out early when !mm.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

Comments

Shakeel Butt April 10, 2021, 5:47 p.m. UTC | #1 
On Fri, Apr 9, 2021 at 5:32 AM Muchun Song <songmuchun@bytedance.com> wrote:
>
> When mm is NULL, we do not need to hold rcu lock and call css_tryget for
> the root memcg. And we also do not need to check !mm in every loop of
> while. So bail out early when !mm.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Shakeel Butt <shakeelb@google.com>
diff mbox series

Patch

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f229de925aa5..9cbfff59b171 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -901,20 +901,19 @@  struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 	if (mem_cgroup_disabled())
 		return NULL;
 
+	/*
+	 * Page cache insertions can happen without an
+	 * actual mm context, e.g. during disk probing
+	 * on boot, loopback IO, acct() writes etc.
+	 */
+	if (unlikely(!mm))
+		return root_mem_cgroup;
+
 	rcu_read_lock();
 	do {
-		/*
-		 * Page cache insertions can happen without an
-		 * actual mm context, e.g. during disk probing
-		 * on boot, loopback IO, acct() writes etc.
-		 */
-		if (unlikely(!mm))
+		memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
+		if (unlikely(!memcg))
 			memcg = root_mem_cgroup;
-		else {
-			memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
-			if (unlikely(!memcg))
-				memcg = root_mem_cgroup;
-		}
 	} while (!css_tryget(&memcg->css));
 	rcu_read_unlock();
 	return memcg;