linux-kernel - Re: [patch -mm 3/4] mm, memcg: replace memory.oom

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Message-ID: <alpine.DEB.2.10.1801191251080.177541@chino.kir.corp.google.com>
Date:   Fri, 19 Jan 2018 12:53:41 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Tejun Heo <tj@...nel.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        kernel-team@...com, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch -mm 3/4] mm, memcg: replace memory.oom_group with policy
 tunable

On Wed, 17 Jan 2018, David Rientjes wrote:

> Yes, this is a valid point.  The policy of "tree" and "all" are identical 
> policies and then the mechanism differs wrt to whether one process is 
> killed or all eligible processes are killed, respectively.  My motivation 
> for this was to avoid having two different tunables, especially because 
> later we'll need a way for userspace to influence the decisionmaking to 
> protect (bias against) important subtrees.  What would really be nice is 
> cgroup.subtree_control-type behavior where we could effect a policy and a 
> mechanism at the same time.  It's not clear how that would be handled to 
> allow only one policy and one mechanism, however, in a clean way.  The 
> simplest for the user would be a new file, to specify the mechanism and 
> leave memory.oom_policy alone.  Would another file really be warranted?  
> Not sure.
> 

Hearing no response, I'll implement this as a separate tunable in a v2 
series assuming there are no better ideas proposed before next week.  One 
of the nice things about a separate tunable is that an admin can control 
the overall policy and they can delegate the mechanism (killall vs one 
process) to a user subtree.  I agree with your earlier point that killall 
vs one process is a property of the workload and is better defined 
separately.

I'll also look to fix the breakage wrt root mem cgroup comparison with 
leaf mem cgroup comparison that is currently in -mm.