linux-kernel - Re: Machine lockups on extreme memory pressure

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Message-ID: <20200922170106.GE12990@dhcp22.suse.cz>
Date:   Tue, 22 Sep 2020 19:01:06 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Thelen <gthelen@...gle.com>
Subject: Re: Machine lockups on extreme memory pressure

On Tue 22-09-20 09:51:30, Shakeel Butt wrote:
> On Tue, Sep 22, 2020 at 9:34 AM Michal Hocko <mhocko@...e.com> wrote:
> >
> > On Tue 22-09-20 09:29:48, Shakeel Butt wrote:
[...]
> > > Anyways, what do you think of the in-kernel PSI based
> > > oom-kill trigger. I think Johannes had a prototype as well.
> >
> > We have talked about something like that in the past and established
> > that auto tuning for oom killer based on PSI is almost impossible to get
> > right for all potential workloads and that so this belongs to userspace.
> > The kernel's oom killer is there as a last resort when system gets close
> > to meltdown.
> 
> The system is already in meltdown state from the users perspective. I
> still think allowing the users to optionally set the oom-kill trigger
> based on PSI makes sense. Something like 'if all processes on the
> system are stuck for 60 sec, trigger oom-killer'.

We already do have watchdogs for that no? If you cannot really schedule
anything then soft lockup detector should fire. In a meltdown state like
that the reboot is likely the best way forward anyway.
-- 
Michal Hocko
SUSE Labs