Re: [PATCH 4/4] mm, oom: Fix unnecessary killing of additional processes.

From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: David Rientjes <rientjes@google.com>,
	linux-mm@kvack.org, Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH 4/4] mm, oom: Fix unnecessary killing of additional processes.
Date: Thu, 6 Sep 2018 15:56:15 +0200	[thread overview]
Message-ID: <20180906135615.GA14951@dhcp22.suse.cz> (raw)
In-Reply-To: <37b763c1-b83e-1632-3187-55fb360a914e@i-love.sakura.ne.jp>

On Thu 06-09-18 22:40:24, Tetsuo Handa wrote:
> On 2018/09/06 21:05, Michal Hocko wrote:
> >> If you are too busy, please show "the point of no-blocking" using source code
> >> instead. If such "the point of no-blocking" really exists, it can be executed
> >> by allocating threads.
> > 
> > I would have to study this much deeper but I _suspect_ that we are not
> > taking any blocking locks right after we return from unmap_vmas. In
> > other words the place we used to have synchronization with the
> > oom_reaper in the past.
> 
> See commit 97b1255cb27c551d ("mm,oom_reaper: check for MMF_OOM_SKIP before
> complaining"). Since this dependency is inode-based (i.e. irrelevant with
> OOM victims), waiting for this lock can livelock.
> 
> So, where is safe "the point of no-blocking" ?

Ohh, right unlink_file_vma and its i_mmap_rwsem lock. As I've said I
have to think about that some more. Maybe we can split those into two parts.

-- 
Michal Hocko
SUSE Labs