linux-kernel - Re: [RFC PATCH] mm: silence soft lockups from unlock

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Message-ID: <20200721112529.GJ4061@dhcp22.suse.cz>
Date:   Tue, 21 Jul 2020 13:25:29 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page

On Tue 21-07-20 07:10:14, Qian Cai wrote:
> 
> 
> > On Jul 21, 2020, at 2:33 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > on a large ppc machine. The very likely cause is a suboptimal
> > configuration when systed-udev spawns way too many workders to bring the
> > system up.
> 
> This is strange. The problem description is missing quite a few
> important details. For example, what systems exactly are those? How
> many CPUs, memory and NUMA nodes were you talking about?

Are these really important? I believe I can dig that out from the bug
report but I didn't really consider that important enough.

> Which kernel version was it reported?

It is a SLES 4.12 based kernel with the said commit backported. The page
lock internals are thus in line with the upstream kernel.

> How many workers from systemd-udev was “misconfigured”?

I do not know that information. I believe that it used whatever systemd
comes with as a default. And that can be a lot.

Do you have any actual feedback to the patch?

-- 
Michal Hocko
SUSE Labs