linux-kernel - Re: [PATCH] memcg, oom: do not bypass oom killer for dying tasks

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Message-ID: <ad2ce9e6-1651-8170-f944-1ba4ce4c14c9@google.com>
Date: Sun, 6 Apr 2025 14:34:09 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Michal Hocko <mhocko@...nel.org>
cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, 
    Rik van Riel <riel@...riel.com>, Johannes Weiner <hannes@...xchg.org>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
    cgroups mailinglist <cgroups@...r.kernel.org>, 
    LKML <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] memcg, oom: do not bypass oom killer for dying tasks

On Wed, 2 Apr 2025, Michal Hocko wrote:

> From: Michal Hocko <mhocko@...e.com>
> 
> 7775face2079 ("memcg: killed threads should not invoke memcg OOM killer") has added
> a bypass of the oom killer path for dying threads because a very
> specific workload (described in the changelog) could hit "no killable
> tasks" path. This itself is not fatal condition but it could be annoying
> if this was a common case.
> 
> On the other hand the bypass has some issues on its own. Without
> triggering oom killer we won't be able to trigger async oom reclaim
> (oom_reaper) which can operate on killed tasks as well as long as they
> still have their mm available. This could be the case during futex
> cleanup when the memory as pointed out by Johannes in [1]. The said case
> is still not fully understood but let's drop this bypass that was mostly
> driven by an artificial workload and allow dying tasks to go into oom
> path. This will make the code easier to reason about and also help
> corner cases where oom_reaper could help to release memory.
> 
> [1] https://lore.kernel.org/all/20241212183012.GB1026@cmpxchg.org/T/#u
> 
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Acked-by: David Rientjes <rientjes@...gle.com>