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

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Date:   Wed, 17 Jan 2018 14:18:33 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
cc:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        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, Michal Hocko wrote:

> Absolutely agreed! And moreover, there are not all that many ways what
> to do as an action. You just kill a logical entity - be it a process or
> a logical group of processes. But you have way too many policies how
> to select that entity. Do you want to chose the youngest process/group
> because all the older ones have been computing real stuff and you would
> lose days of your cpu time? Or should those who pay more should be
> protected (aka give them static priorities), or you name it...
> 

That's an argument for making the interface extensible, yes.

> I am sorry, I still didn't grasp the full semantic of the proposed
> soluton but the mere fact it is starting by conflating selection and the
> action is a no go and a wrong API. This is why I've said that what you
> (David) outlined yesterday is probably going to suffer from a much
> longer discussion and most likely to be not acceptable. Your patchset
> proves me correct...

I'm very happy to change the API if there are better suggestions.  That 
may end up just being an memory.oom_policy file, as this implements, and 
separating out a new memory.oom_action that isn't a boolean value to 
either do a full group kill or only a single process.  Or it could be what 
I suggested in my mail to Tejun, such as "hierarchy killall" written to
memory.oom_policy, which would specify a single policy and then an 
optional mechanism.  With my proposed patchset, there would then be three 
policies: "none", "cgroup", and "tree" and one possible optional 
mechanism: "killall".