From: Johannes Weiner <hannes@cmpxchg.org>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: akpm@linux-foundation.org, mhocko@kernel.org,
chris@chrisdown.name, guro@fb.com, linux-mm@kvack.org
Subject: Re: [PATCH v2 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection
Date: Sat, 2 May 2020 10:44:22 -0400 [thread overview]
Message-ID: <20200502144422.GA51551@cmpxchg.org> (raw)
In-Reply-To: <20200502135910.7255-2-laoar.shao@gmail.com>
On Sat, May 02, 2020 at 09:59:09AM -0400, Yafang Shao wrote:
> A cgroup can have both memory protection and a memory limit to isolate
> it from its siblings in both directions - for example, to prevent it
> from being shrunk below 2G under high pressure from outside, but also
> from growing beyond 4G under low pressure.
>
> Commit 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
> implemented proportional scan pressure so that multiple siblings in
> excess of their protection settings don't get reclaimed equally but
> instead in accordance to their unprotected portion.
>
> During limit reclaim, this proportionality shouldn't apply of course:
> there is no competition, all pressure is from within the cgroup and
> should be applied as such. Reclaim should operate at full efficiency.
>
> However, mem_cgroup_protected() never expected anybody to look at the
> effective protection values when it indicated that the cgroup is above
> its protection. As a result, a query during limit reclaim may return
> stale protection values that were calculated by a previous reclaim cycle
> in which the cgroup did have siblings.
>
> When this happens, reclaim is unnecessarily hesitant and potentially
> slow to meet the desired limit. In theory this could lead to premature
> OOM kills, although it's not obvious this has occurred in practice.
>
> [hannes@cmpxchg.org: changelog]
> [mhocko@kernel.org: rework code comment]
> [chris@chrisdown.name: retitle]
> Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Acked-by: Roman Gushchin <guro@fb.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Chris Down <chris@chrisdown.name>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2020-05-02 14:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-02 13:59 [PATCH v2 0/2] mm: memcontrol: memory.{low,min} reclaim fix & cleanup Yafang Shao
2020-05-02 13:59 ` [PATCH v2 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection Yafang Shao
2020-05-02 14:12 ` Chris Down
2020-05-02 14:44 ` Johannes Weiner [this message]
2020-05-04 7:52 ` Michal Hocko
2020-05-02 13:59 ` [PATCH v2 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks Yafang Shao
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