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:

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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.
 

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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