linux-kernel - Re: [PATCH 0/3] introduce memory.oom.group

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Message-ID: <20180810070351.GB1644@dhcp22.suse.cz>
Date:   Fri, 10 Aug 2018 09:03:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Tejun Heo <tj@...nel.org>, kernel-team@...com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] introduce memory.oom.group

On Thu 09-08-18 13:10:10, David Rientjes wrote:
> On Wed, 8 Aug 2018, Michal Hocko wrote:
> 
> > > > > In a cgroup-aware oom killer world, yes, we need the ability to specify 
> > > > > that the usage of the entire subtree should be compared as a single 
> > > > > entity with other cgroups.  That is necessary for user subtrees but may 
> > > > > not be necessary for top-level cgroups depending on how you structure your 
> > > > > unified cgroup hierarchy.  So it needs to be configurable, as you suggest, 
> > > > > and you are correct it can be different than oom.group.
> > > > > 
> > > > > That's not the only thing we need though, as I'm sure you were expecting 
> > > > > me to say :)
> > > > > 
> > > > > We need the ability to preserve existing behavior, i.e. process based and 
> > > > > not cgroup aware, for subtrees so that our users who have clear 
> > > > > expectations and tune their oom_score_adj accordingly based on how the oom 
> > > > > killer has always chosen processes for oom kill do not suddenly regress.
> > > > 
> > > > Isn't the combination of oom.group=0 and oom.evaluate_together=1 describing
> > > > this case? This basically means that if memcg is selected as target,
> > > > the process inside will be selected using traditional per-process approach.
> > > > 
> > > 
> > > No, that would overload the policy and mechanism.  We want the ability to 
> > > consider user-controlled subtrees as a single entity for comparison with 
> > > other user subtrees to select which subtree to target.  This does not 
> > > imply that users want their entire subtree oom killed.
> > 
> > Yeah, that's why oom.group == 0, no?
> > 
> > Anyway, can we separate this discussion from the current series please?
> > We are getting more and more tangent.
> > 
> > Or do you still see the current state to be not mergeable?
> 
> I've said three times in this series that I am fine with it.

OK, that wasn't really clear to me because I haven't see any explicit
ack from you (well except for the trivial helper patch). So I was not
sure.

> Roman and I 
> are discussing the API for making forward progress with the cgroup aware 
> oom killer itself.  When he responds, he can change the subject line if 
> that would be helpful to you.

I do not insist of course but it would be easier to follow if that
discussion was separate.

-- 
Michal Hocko
SUSE Labs