linux-kernel - Re: [PATCH 0/4] mm, oom: get rid of TIF

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Message-ID: <20161005120415.GD7138@dhcp22.suse.cz>
Date:   Wed, 5 Oct 2016 14:04:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     linux-mm@...ck.org
Cc:     David Rientjes <rientjes@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/4] mm, oom: get rid of TIF_MEMDIE

On Tue 04-10-16 11:00:05, Michal Hocko wrote:
[...]
> Recent changes in the oom proper allows for that finally, I believe. Now
> that all the oom victims are reapable we are no longer depending on
> ALLOC_NO_WATERMARKS because the memory held by the victim is reclaimed
> asynchronously. A partial access to memory reserves should be sufficient
> just to guarantee that the oom victim is not starved due to other
> memory consumers. This also means that we do not have to pretend to be
> conservative and give access to memory reserves only to one thread from
> the process at the time. This is patch 1.
> 
> Patch 2 is a simple cleanup which turns TIF_MEMDIE users to tsk_is_oom_victim
> which is process rather than thread centric. None of those callers really
> requires to be thread aware AFAICS.
> 
> The tricky part then is exit_oom_victim vs. oom_killer_disable because
> TIF_MEMDIE acted as a token there so we had a way to count threads from
> the process. It didn't work 100% reliably and had its own issues but we
> have to replace it with something which doesn't rely on counting threads
> but rather find a moment when all threads have reached steady state in
> do_exit. This is what patch 3 does and I would really appreciate if Oleg
> could double check my thinking there. I am also CCing Al on that one
> because I am moving exit_io_context up in do_exit right before exit_notify.

It became apparent that the last part was wrong after Oleg's review. I
definitely want to come up with something that works eventually. I am
just wondering whether patches 1-2 are worth accepting without the rest.
I fully realize those patches are less attractive when TIF_MEMDIE stays
but I would argue that reducing the TIF_MEMDIE users will make the code
slightly better and easier to understand.

What do you think?
-- 
Michal Hocko
SUSE Labs