linux-kernel - Re: [PATCH 2/2] mm,oom: Use ALLOC_OOM for OOM victim's last second allocation.

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Message-ID: <20171101151600.olalzdipejtylkok@dhcp22.suse.cz>
Date:   Wed, 1 Nov 2017 16:16:00 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, rientjes@...gle.com,
        mjaggi@...iumnetworks.com, oleg@...hat.com, vdavydov@...tuozzo.com
Subject: Re: [PATCH 2/2] mm,oom: Use ALLOC_OOM for OOM victim's last second
 allocation.

On Thu 02-11-17 00:08:59, Tetsuo Handa wrote:
> Michal Hocko wrote:
[...]
> > I am not sure about this part though. If the oom_reaper cannot take the
> > mmap_sem then it retries for 1s. Have you ever seen the race to be that
> > large?
> 
> Like shown in [2], khugepaged can prevent oom_reaper from taking the mmap_sem
> for 1 second. Also, it won't be impossible for OOM victims to spend 1 second
> between post __gfp_pfmemalloc_flags(gfp_mask) and pre mutex_trylock(&oom_lock)
> (in other words, the race window (1-2) above). Therefore, non artificial
> workloads could hit the same result.

but this is a speculation so I wouldn't mention it in the changelog. It
might confuse readers.
-- 
Michal Hocko
SUSE Labs