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

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Date:   Wed, 23 Jan 2019 04:41:42 +0000
From:   Roman Gushchin <guro@...com>
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>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.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 Mon, Jan 21, 2019 at 10:50:32AM -0800, 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.

This is a great cleanup, thanks!

Acked-by: Roman Gushchin <guro@...com>