linux-kernel - Re: [v7 5/5] mm, oom: cgroup v2 mount option to disable cgroup-aware OOM killer

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Message-ID: <20170906084242.l4rcx6n3hdzxvil6@dhcp22.suse.cz>
Date:   Wed, 6 Sep 2017 10:42:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
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: [v7 5/5] mm, oom: cgroup v2 mount option to disable cgroup-aware
 OOM killer

On Tue 05-09-17 20:16:09, Roman Gushchin wrote:
> On Tue, Sep 05, 2017 at 05:12:51PM +0200, Michal Hocko wrote:
[...]
> > > Then we should probably hide corresponding
> > > cgroup interface (oom_group and oom_priority knobs) by default,
> > > and it feels as unnecessary complication and is overall against
> > > cgroup v2 interface design.
> > 
> > Why. If we care enough, we could simply return EINVAL when those knobs
> > are written while the corresponding strategy is not used.
> 
> It doesn't look as a nice default interface.

I do not have a strong opinion on this. A printk_once could explain why
the knob is ignored and instruct the admin how to enable the feature
completely.
 
> > > > I think we should instead go with
> > > > oom_strategy=[alloc_task,biggest_task,cgroup]
> > > 
> > > It would be a really nice interface; although I've no idea how to implement it:
> > > "alloc_task" is an existing sysctl, which we have to preserve;
> > 
> > I would argue that we should simply deprecate and later drop the sysctl.
> > I _strongly_ suspect anybody is using this. If yes it is not that hard
> > to change the kernel command like rather than select the sysctl.
> 
> I agree. And if so, why do we need a new interface for an useless feature?

Well, I won't be opposed just deprecating the sysfs and only add a
"real" kill-allocate strategy if somebody explicitly asks for it.
-- 
Michal Hocko
SUSE Labs