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From: Muchun Song <songmuchun@bytedance.com>
To: hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com,
	akpm@linux-foundation.org
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH 3/4] mm: memcontrol: bail out early when id is zero
Date: Sat, 13 Feb 2021 01:01:58 +0800	[thread overview]
Message-ID: <20210212170159.32153-3-songmuchun@bytedance.com> (raw)
In-Reply-To: <20210212170159.32153-1-songmuchun@bytedance.com>

The memcg ID cannot be zero, but we can pass zero to mem_cgroup_from_id,
so idr_find() is pointless and wastes CPU cycles.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/memcontrol.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3f26522765a..68ed4b297c13 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5173,6 +5173,9 @@ static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
 struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 {
 	WARN_ON_ONCE(!rcu_read_lock_held());
+	/* The memcg ID cannot be zero. */
+	if (id == 0)
+		return NULL;
 	return idr_find(&mem_cgroup_idr, id);
 }
 
-- 
2.11.0



  parent reply	other threads:[~2021-02-12 17:02 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12 17:01 [PATCH 1/4] mm: memcontrol: remove memcg check from memcg_oom_recover Muchun Song
2021-02-12 17:01 ` [PATCH 2/4] mm: memcontrol: add missing memcg_oom_recover() when uncharge slab page Muchun Song
2021-02-15  9:37   ` Michal Hocko
2021-02-12 17:01 ` Muchun Song [this message]
2021-02-15  9:39   ` [PATCH 3/4] mm: memcontrol: bail out early when id is zero Michal Hocko
2021-02-15 10:09     ` [External] " Muchun Song
2021-02-15 10:27       ` Michal Hocko
2021-02-15 11:34         ` Muchun Song
2021-02-12 17:01 ` [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2 Muchun Song
2021-02-12 18:56   ` Shakeel Butt
2021-02-13  6:48     ` [External] " Muchun Song
2021-02-16 17:16       ` Shakeel Butt
2021-02-15  9:47   ` Michal Hocko
2021-02-15 10:15     ` [External] " Muchun Song
2021-02-15 10:24       ` Michal Hocko
2021-02-16 16:59   ` Johannes Weiner
2021-02-16 17:17     ` Shakeel Butt
2021-02-16 17:19     ` Michal Hocko
2021-02-16 17:28     ` Johannes Weiner
2021-02-17  5:15       ` [External] " Muchun Song
2021-02-17  5:11     ` Muchun Song
2021-02-15  9:24 ` [PATCH 1/4] mm: memcontrol: remove memcg check from memcg_oom_recover Michal Hocko

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