linux-kernel - Re: [PATCH RESEND] mm/oom_kill: don't kill exiting tasks in oom_kill_memcg

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Message-ID: <ZBBJZx3Em9L9/3jn@dhcp22.suse.cz>
Date:   Tue, 14 Mar 2023 11:16:07 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Haifeng Xu <haifeng.xu@...pee.com>
Cc:     shakeelb@...gle.com, hannes@...xchg.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] mm/oom_kill: don't kill exiting tasks in
 oom_kill_memcg_member

On Tue 14-03-23 18:07:42, Haifeng Xu wrote:
> 
> 
> On 2023/3/14 17:19, Michal Hocko wrote:
> > On Tue 14-03-23 09:11:36, Haifeng Xu wrote:
> >> If oom_group is set, oom_kill_process() invokes oom_kill_memcg_member()
> >> to kill all processes in the memcg. When scanning tasks in memcg, maybe
> >> the provided task is marked as oom victim. Also, some tasks are likely
> >> to release their address space. There is no need to kill the exiting tasks.
> > 
> > This doesn't state any actual problem. Could you be more specific? Is
> > this a bug fix, a behavior change or an optimization?
> 
> 
> 1) oom_kill_process() has inovked __oom_kill_process() to kill the selected victim, but it will be scanned
> in mem_cgroup_scan_tasks(). It's pointless to kill the victim twice. 

Why does that matter though? The purpose of task_will_free_mem in
oom_kill_process is different. It would bail out from a potentially
noisy OOM report when the selected oom victim is expected to terminate
soon. __oom_kill_process called for the whole memcg doesn't aim at
avoiding any oom victims. It merely sends a kill signal too all of them.

> 2) for those exiting processes, reaping them directly is also a faster way to free memory compare with invoking
> __oom_kill_process().

Is it? What if the terminating task is blocked on lock? Async oom
reaping might release those resources in that case.
-- 
Michal Hocko
SUSE Labs