linux-kernel - Re: [v9 4/5] mm, oom: add cgroup v2 mount option for cgroup-aware OOM killer

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Date:   Tue, 3 Oct 2017 13:49:36 +0100
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     <linux-mm@...ck.org>, Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, <kernel-team@...com>,
        <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [v9 4/5] mm, oom: add cgroup v2 mount option for cgroup-aware
 OOM killer

On Tue, Oct 03, 2017 at 01:50:36PM +0200, Michal Hocko wrote:
> On Wed 27-09-17 14:09:35, Roman Gushchin wrote:
> > Add a "groupoom" cgroup v2 mount option to enable the cgroup-aware
> > OOM killer. If not set, the OOM selection is performed in
> > a "traditional" per-process way.
> > 
> > The behavior can be changed dynamically by remounting the cgroupfs.
> 
> I do not have a strong preference about this. I would just be worried
> that it is usually systemd which tries to own the whole hierarchy

I actually like this fact.

It gives us the opportunity to change the default behavior for most users
at the point when we'll be sure that new behavior is better; but at the same
time we'll save full compatibility on the kernel level.
With growing popularity of memory cgroups, I don't think that hiding
this functionality with a boot option makes any sense. It's just not
this type of feature, that should be hidden.