linux-kernel - Re: [patch v3 -mm 3/6] mm, memcg: add hierarchical usage oom policy

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Date:   Mon, 23 Jul 2018 14:28:58 -0700
From:   Roman Gushchin <guro@...com>
To:     David Rientjes <rientjes@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, <cgroups@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [patch v3 -mm 3/6] mm, memcg: add hierarchical usage oom policy

On Mon, Jul 23, 2018 at 01:33:19PM -0700, David Rientjes wrote:
> On Mon, 16 Jul 2018, David Rientjes wrote:
> 
> > > And "tree" is different. It actually changes how the selection algorithm works,
> > > and sub-tree settings do matter in this case.
> > > 
> > 
> > "Tree" is considering the entity as a single indivisible memory consumer, 
> > it is compared with siblings based on its hierarhical usage.  It has 
> > cgroup oom policy.
> > 
> > It would be possible to separate this out, if you'd prefer, to account 
> > an intermediate cgroup as the largest descendant or the sum of all 
> > descendants.  I hadn't found a usecase for that, however, but it doesn't 
> > mean there isn't one.  If you'd like, I can introduce another tunable.
> > 
> 
> Roman, I'm trying to make progress so that the cgroup aware oom killer is 
> in a state that it can be merged.  Would you prefer a second tunable here 
> to specify a cgroup's points includes memory from its subtree?

Hi, David!

It's hard to tell, because I don't have a clear picture of what you're
suggesting now. My biggest concern about your last version was that it's hard
to tell what oom_policy really defines. Each value has it's own application
rules, which is a bit messy (some values are meaningful for OOMing cgroup only,
other are reading on hierarchy traversal).
If you know how to make it clear and non-contradictory,
please, describe the proposed interface.

> 
> It would be helpful if you would also review the rest of the patchset.

I think, that we should focus on interface semantics right now.
If we can't agree on how the things should work, it makes no sense
to discuss the implementation.

Thanks!