linux-kernel - Re: [PATCH] fs: fix for core dumping of a process getting oom-killed

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Message-ID: <YUrkwbQ9d6vvh0Ta@dhcp22.suse.cz>
Date:   Wed, 22 Sep 2021 10:09:37 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vishnu Rangayyan <vishnu.rangayyan@...le.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: fix for core dumping of a process getting oom-killed

On Tue 21-09-21 20:12:08, Vishnu Rangayyan wrote:
> 
> 
> On 9/21/21 5:59 AM, Michal Hocko wrote:
[...]
> > Why
> > is fsync helping at all? Why do we need a new sysctl to address the
> > problem and how does it help to prevent the memcg OOM. Also why is this
> > a problem in the first place.
> The simple intent is to allow the core dumping to succeed in low memory
> situations where the dump_emit doesn't tip over the thing and trigger the
> oom-killer. This change avoids only that particular issue.

How does it avoid that?

> Agree, its not the actual problem at all. If the core dumping fails, that
> sometimes prevents or delays looking into the actual issue.
> The sysctl was to allow disabling this behavior or to fine tune for special
> cases such as limited memory environments.

Please note that any sysctl is an userspace API that has to be
maintained effectivelly for ever so there should be a very good reason
and a strong justification to add one. I do not see that to be case
here.

-- 
Michal Hocko
SUSE Labs