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

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Message-ID: <CALvZod753Peyyg6aHUaFoiv3uXEPHqsyrSiariV8bF-vhH6iRA@mail.gmail.com>
Date:   Tue, 22 Sep 2020 09:51:30 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...e.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, Sep 22, 2020 at 9:34 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Tue 22-09-20 09:29:48, Shakeel Butt wrote:
> > On Tue, Sep 22, 2020 at 8:16 AM Michal Hocko <mhocko@...e.com> wrote:
> > >
> > > On Tue 22-09-20 06:37:02, Shakeel Butt wrote:
> [...]
> > > > I talked about this problem with Johannes at LPC 2019 and I think we
> > > > talked about two potential solutions. First was to somehow give memory
> > > > reserves to oomd and second was in-kernel PSI based oom-killer. I am
> > > > not sure the first one will work in this situation but the second one
> > > > might help.
> > >
> > > Why does your oomd depend on memory allocation?
> > >
> >
> > It does not but I think my concern was the potential allocations
> > during syscalls.
>
> So what is the problem then? Why your oomd cannot kill anything?
>

>From the dump, it seems like it is not able to get the CPU. I am still
trying to extract the reason though.

> > 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'.