linux-kernel - Re: [PATCH] mm,oom: Try last second allocation before and after selecting an OOM victim.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201710312213.BDB35457.MtFJOQVLOFSOHF@I-love.SAKURA.ne.jp>
Date:   Tue, 31 Oct 2017 22:13:05 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
Cc:     aarcange@...hat.com, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, rientjes@...gle.com,
        hannes@...xchg.org, mjaggi@...iumnetworks.com, mgorman@...e.de,
        oleg@...hat.com, vdavydov.dev@...il.com, vbabka@...e.cz
Subject: Re: [PATCH] mm,oom: Try last second allocation before and after selecting an OOM victim.

Michal Hocko wrote:
> On Tue 31-10-17 21:42:23, Tetsuo Handa wrote:
> > > While both have some merit, the first reason is mostly historical
> > > because we have the explicit locking now and it is really unlikely that
> > > the memory would be available right after we have given up trying.
> > > Last attempt allocation makes some sense of course but considering that
> > > the oom victim selection is quite an expensive operation which can take
> > > a considerable amount of time it makes much more sense to retry the
> > > allocation after the most expensive part rather than before. Therefore
> > > move the last attempt right before we are trying to kill an oom victim
> > > to rule potential races when somebody could have freed a lot of memory
> > > in the meantime. This will reduce the time window for potentially
> > > pre-mature OOM killing considerably.
> > 
> > But this is about "doing last second allocation attempt after selecting
> > an OOM victim". This is not about "allowing OOM victims to try ALLOC_OOM
> > before selecting next OOM victim" which is the actual problem I'm trying
> > to deal with.
> 
> then split it into two. First make the general case and then add a more
> sophisticated on top. Dealing with multiple issues at once is what makes
> all those brain cells suffer.

I'm failing to understand. I was dealing with single issue at once.
The single issue is "MMF_OOM_SKIP prematurely prevents OOM victims from trying
ALLOC_OOM before selecting next OOM victims". Then, what are the general case and
a more sophisticated? I wonder what other than "MMF_OOM_SKIP should allow OOM
victims to try ALLOC_OOM for once before selecting next OOM victims" can exist...