linux-kernel - Re: [RESEND v12 0/6] cgroup-aware OOM killer

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Message-ID: <20171031075408.67au22uk6dkpu7vv@dhcp22.suse.cz>
Date:   Tue, 31 Oct 2017 08:54:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Tejun Heo <tj@...nel.org>, kernel-team@...com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND v12 0/6] cgroup-aware OOM killer

On Mon 30-10-17 14:36:39, David Rientjes wrote:
> On Fri, 27 Oct 2017, Roman Gushchin wrote:
> 
> > The thing is that the hierarchical approach (as in v8), which are you pushing,
> > has it's own limitations, which we've discussed in details earlier. There are
> > reasons why v12 is different, and we can't really simple go back. I mean if
> > there are better ideas how to resolve concerns raised in discussions around v8,
> > let me know, but ignoring them is not an option.
> > 
> 
> I'm not ignoring them, I have stated that we need the ability to protect 
> important cgroups on the system without oom disabling all attached 
> processes.  If that is implemented as a memory.oom_score_adj with the same 
> semantics as /proc/pid/oom_score_adj, i.e. a proportion of available 
> memory (the limit), it can also address the issues pointed out with the 
> hierarchical approach in v8.

No it cannot and it would be a terrible interface to have as well. You
do not want to permanently tune oom_score_adj to compensate for
structural restrictions on the hierarchy.

> If this is not the case, could you elaborate 
> on what your exact concern is and why we do not care that users can 
> completely circumvent victim selection by creating child cgroups for other 
> controllers?
> 
> Since the ability to protect important cgroups on the system may require a 
> heuristic change, I think it should be solved now rather than constantly 
> insisting that we can make this patchset complete later and in the 
> meantime force the user to set all attached processes to be oom disabled.

I believe, and Roman has pointed that out as well already, that further
improvements can be implemented without changing user visible behavior
as and add-on. If you disagree then you better come with a solid proof
that all of us wrong and reasonable semantic cannot be achieved that
way.
-- 
Michal Hocko
SUSE Labs