From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Roman Gushchin <guro@fb.com>,
David Rientjes <rientjes@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish
Date: Tue, 30 Oct 2018 22:57:37 +0900 [thread overview]
Message-ID: <0b1a8c3b-8346-ba7d-da7b-3c79354e11d7@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20181030121012.GC32673@dhcp22.suse.cz>
On 2018/10/30 21:10, Michal Hocko wrote:
> I misunderstood your concern. oom_reaper would back off without
> MMF_OOF_SKIP as well. You are right we cannot assume anything about
> close callbacks so MMF_OOM_SKIP has to come before that. I will move it
> behind the pagetable freeing.
>
And at that point, your patch can at best wait for only __free_pgtables(),
at the cost/risk of complicating exit_mmap() and arch specific code. Also,
you are asking for comments to wrong audiences. It is arch maintainers who
need to precisely understand the OOM behavior / possibility of OOM lockup,
and you must persuade them about restricting/complicating future changes in
their arch code due to your wish to allow handover. Without "up-to-dated
big fat comments to all relevant functions affected by your change" and
"acks from all arch maintainers", I'm sure that people keep making
errors/mistakes/overlooks.
My patch can wait for completion of (not only exit_mmap() but also) __mmput(),
by using simple polling approach. My patch can allow NOMMU kernels to avoid
possibility of OOM lockup by setting MMF_OOM_SKIP at __mmput() (and future
patch will implement timeout based back off for NOMMU kernels), and allows you
to get rid of TIF_MEMDIE (which you recently added to your TODO list) by getting
rid of conditional handling of oom_reserves_allowed() and ALLOC_OOM.
Your "refusing timeout based next OOM victim selection" keeps everyone unable
to safely make forward progress. OOM handling is too much complicated, and
nobody can become free from errors/mistakes/overlooks. Look at the reality!
next prev parent reply other threads:[~2018-10-30 13:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-25 8:24 [RFC PATCH v2 0/3] oom: rework oom_reaper vs. exit_mmap handoff Michal Hocko
2018-10-25 8:24 ` [RFC PATCH v2 1/3] mm, oom: rework mmap_exit vs. oom_reaper synchronization Michal Hocko
2018-10-25 8:24 ` [RFC PATCH v2 2/3] mm, oom: keep retrying the oom_reap operation as long as there is substantial memory left Michal Hocko
2018-10-25 8:24 ` [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish Michal Hocko
2018-10-30 4:45 ` Tetsuo Handa
2018-10-30 6:31 ` Michal Hocko
2018-10-30 9:47 ` Tetsuo Handa
2018-10-30 11:39 ` Michal Hocko
2018-10-30 12:02 ` Tetsuo Handa
2018-10-30 12:10 ` Michal Hocko
2018-10-30 13:57 ` Tetsuo Handa [this message]
2018-10-30 14:23 ` Michal Hocko
2018-11-08 9:32 ` [RFC PATCH v2 0/3] oom: rework oom_reaper vs. exit_mmap handoff Michal Hocko
2018-11-14 9:46 ` Tetsuo Handa
2018-11-14 10:16 ` Michal Hocko
2018-11-15 9:54 ` Tetsuo Handa
2018-11-15 11:36 ` Michal Hocko
2018-11-16 10:06 ` Tetsuo Handa
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