linux-kernel - Re: [PATCH v2 2/2] mm, oom: remove 'prefer children over parent' heuristic

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Date:   Tue, 22 Jan 2019 06:10:07 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2 2/2] mm, oom: remove 'prefer children over parent'
 heuristic

On 2019/01/22 3:50, Shakeel Butt wrote:
>>>From the start of the git history of Linux, the kernel after selecting
> the worst process to be oom-killed, prefer to kill its child (if the
> child does not share mm with the parent). Later it was changed to prefer
> to kill a child who is worst. If the parent is still the worst then the
> parent will be killed.
> 
> This heuristic assumes that the children did less work than their parent
> and by killing one of them, the work lost will be less. However this is
> very workload dependent. If there is a workload which can benefit from
> this heuristic, can use oom_score_adj to prefer children to be killed
> before the parent.
> 
> The select_bad_process() has already selected the worst process in the
> system/memcg. There is no need to recheck the badness of its children
> and hoping to find a worse candidate. That's a lot of unneeded racy
> work. Also the heuristic is dangerous because it make fork bomb like
> workloads to recover much later because we constantly pick and kill
> processes which are not memory hogs. So, let's remove this whole
> heuristic.
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Cc: Roman Gushchin <guro@...com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> 
> ---
> Changelog since v1:
> - Improved commit message based on mhocko's comment.
> - Replaced 'p' with 'victim'.
> - Removed extra pr_err message.

But this version omits printing one of "Out of memory (oom_kill_allocating_task)",
"Out of memory" and "Memory cgroup out of memory" message which is unexpected.
We want to propagate that message to __oom_kill_process() ? ;-)