From: Shakeel Butt <shakeel.butt@linux.dev>
To: Hui Zhu <hui.zhu@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Qi Zheng <qi.zheng@linux.dev>, Lorenzo Stoakes <ljs@kernel.org>,
Kairui Song <kasong@tencent.com>, Barry Song <baohua@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Hui Zhu <zhuhui@kylinos.cn>
Subject: Re: [PATCH v2 3/3] mm: memcg: skip the RCU lock when the memcg is not dying
Date: Thu, 3 Sep 2026 10:57:08 -0700 [thread overview]
Message-ID: <apm0372x4vOtJvSs@linux.dev> (raw)
In-Reply-To: <3fc10f32131097bb57efaec72d049d635b227cf1.1788169145.git.zhuhui@kylinos.cn>
On Mon, Aug 31, 2026 at 05:46:11PM +0800, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
>
> get_non_dying_memcg_start() takes rcu_read_lock() on every stat update, but
> the lock only protects the upward walk to a non-dying ancestor, which
> happens solely while a memcg is being offlined. The dying check itself
> reads the CSS_DYING flag of a memcg the caller already holds a reference
> to, so it is safe without the lock.
>
> Check memcg_is_dying() first and return immediately when the memcg is
> alive, taking the RCU lock only on the rare dying path. On an anon
> fault/charge churn workload in a memcg this recovers the ~0.6% overhead
> added by the previous patch (4368077 vs 4343159 pages/s before, back to
> ~4377000 pages/s after).
>
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
next prev parent reply other threads:[~2026-09-03 17:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-31 9:46 [PATCH v2 0/3] mm: workingset: fix the shadow node budget under MGLRU Hui Zhu
2026-08-31 9:46 ` [PATCH v2 1/3] mm: workingset: use lruvec_page_state_local() to count lru pages Hui Zhu
2026-09-03 17:51 ` Shakeel Butt
2026-09-03 17:55 ` Shakeel Butt
2026-08-31 9:46 ` [PATCH v2 2/3] mm: memcg: redirect stats updates of dying memcgs for all hierarchies Hui Zhu
2026-09-03 17:52 ` Shakeel Butt
2026-09-03 17:56 ` Shakeel Butt
2026-08-31 9:46 ` [PATCH v2 3/3] mm: memcg: skip the RCU lock when the memcg is not dying Hui Zhu
2026-09-03 17:57 ` Shakeel Butt [this message]
2026-09-03 17:53 ` [PATCH v2 0/3] mm: workingset: fix the shadow node budget under MGLRU Shakeel Butt
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