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

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Message-ID: <20200922151654.GA12990@dhcp22.suse.cz>
Date:   Tue, 22 Sep 2020 17:16:54 +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 06:37:02, Shakeel Butt wrote:
[...]
> > I would recommend to focus on tracking down the who is blocking the
> > further progress.
> 
> I was able to find the CPU next in line for the list_lock from the
> dump. I don't think anyone is blocking the progress as such but more
> like the spinlock in the irq context is starving the spinlock in the
> process context. This is a high traffic machine and there are tens of
> thousands of potential network ACKs on the queue.

So there is a forward progress but it is too slow to have any reasonable
progress in userspace?

> 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?
-- 
Michal Hocko
SUSE Labs