From: David Rientjes <rientjes@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Oleg Nesterov <oleg@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Andrea Argangeli <andrea@kernel.org>,
Rik van Riel <riel@redhat.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH 1/5] mm, oom: introduce oom reaper
Date: Wed, 3 Feb 2016 15:48:18 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.10.1602031543250.10331@chino.kir.corp.google.com> (raw)
In-Reply-To: <1454505240-23446-2-git-send-email-mhocko@kernel.org>
On Wed, 3 Feb 2016, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> This is based on the idea from Mel Gorman discussed during LSFMM 2015 and
> independently brought up by Oleg Nesterov.
>
> The OOM killer currently allows to kill only a single task in a good
> hope that the task will terminate in a reasonable time and frees up its
> memory. Such a task (oom victim) will get an access to memory reserves
> via mark_oom_victim to allow a forward progress should there be a need
> for additional memory during exit path.
>
> It has been shown (e.g. by Tetsuo Handa) that it is not that hard to
> construct workloads which break the core assumption mentioned above and
> the OOM victim might take unbounded amount of time to exit because it
> might be blocked in the uninterruptible state waiting for an event
> (e.g. lock) which is blocked by another task looping in the page
> allocator.
>
> This patch reduces the probability of such a lockup by introducing a
> specialized kernel thread (oom_reaper) which tries to reclaim additional
> memory by preemptively reaping the anonymous or swapped out memory
> owned by the oom victim under an assumption that such a memory won't
> be needed when its owner is killed and kicked from the userspace anyway.
> There is one notable exception to this, though, if the OOM victim was
> in the process of coredumping the result would be incomplete. This is
> considered a reasonable constrain because the overall system health is
> more important than debugability of a particular application.
>
> A kernel thread has been chosen because we need a reliable way of
> invocation so workqueue context is not appropriate because all the
> workers might be busy (e.g. allocating memory). Kswapd which sounds
> like another good fit is not appropriate as well because it might get
> blocked on locks during reclaim as well.
>
> oom_reaper has to take mmap_sem on the target task for reading so the
> solution is not 100% because the semaphore might be held or blocked for
> write but the probability is reduced considerably wrt. basically any
> lock blocking forward progress as described above. In order to prevent
> from blocking on the lock without any forward progress we are using only
> a trylock and retry 10 times with a short sleep in between.
> Users of mmap_sem which need it for write should be carefully reviewed
> to use _killable waiting as much as possible and reduce allocations
> requests done with the lock held to absolute minimum to reduce the risk
> even further.
>
> The API between oom killer and oom reaper is quite trivial. wake_oom_reaper
> updates mm_to_reap with cmpxchg to guarantee only NULL->mm transition
> and oom_reaper clear this atomically once it is done with the work. This
> means that only a single mm_struct can be reaped at the time. As the
> operation is potentially disruptive we are trying to limit it to the
> ncessary minimum and the reaper blocks any updates while it operates on
> an mm. mm_struct is pinned by mm_count to allow parallel exit_mmap and a
> race is detected by atomic_inc_not_zero(mm_users).
>
> Chnages since v4
> - drop MAX_RT_PRIO-1 as per David - memcg/cpuset/mempolicy OOM killing
> might interfere with the rest of the system
> Changes since v3
> - many style/compile fixups by Andrew
> - unmap_mapping_range_tree needs full initialization of zap_details
> to prevent from missing unmaps and follow up BUG_ON during truncate
> resp. misaccounting - Kirill/Andrew
> - exclude mlocked pages because they need an explicit munlock by Kirill
> - use subsys_initcall instead of module_init - Paul Gortmaker
> - do not tear down mm if it is shared with the global init because this
> could lead to SEGV and panic - Tetsuo
> Changes since v2
> - fix mm_count refernce leak reported by Tetsuo
> - make sure oom_reaper_th is NULL after kthread_run fails - Tetsuo
> - use wait_event_freezable rather than open coded wait loop - suggested
> by Tetsuo
> Changes since v1
> - fix the screwed up detail->check_swap_entries - Johannes
> - do not use kthread_should_stop because that would need a cleanup
> and we do not have anybody to stop us - Tetsuo
> - move wake_oom_reaper to oom_kill_process because we have to wait
> for all tasks sharing the same mm to get killed - Tetsuo
> - do not reap mm structs which are shared with unkillable tasks - Tetsuo
>
> Suggested-by: Oleg Nesterov <oleg@redhat.com>
> Suggested-by: Mel Gorman <mgorman@suse.de>
> Acked-by: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
I think all the patches could really have been squashed together because
subsequent patches just overwrite already added code. I was going to
suggest not doing atomic_inc(&mm->mm_count) in wake_oom_reaper() and
change oom_kill_process() to do
if (can_oom_reap)
wake_oom_reaper(mm);
else
mmdrop(mm);
but I see that we don't even touch mm->mm_count after the third patch.
next prev parent reply other threads:[~2016-02-03 23:48 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-03 13:13 [PATCH 0/5] oom reaper v5 Michal Hocko
2016-02-03 13:13 ` [PATCH 1/5] mm, oom: introduce oom reaper Michal Hocko
2016-02-03 23:48 ` David Rientjes [this message]
2016-02-04 6:41 ` Michal Hocko
2016-02-06 13:22 ` Tetsuo Handa
2016-02-15 20:50 ` Michal Hocko
2016-02-03 13:13 ` [PATCH 2/5] oom reaper: handle mlocked pages Michal Hocko
2016-02-03 23:57 ` David Rientjes
2016-02-23 1:36 ` David Rientjes
2016-02-23 13:21 ` Michal Hocko
2016-02-29 3:19 ` Hugh Dickins
2016-02-29 13:41 ` Michal Hocko
2016-03-08 13:40 ` Michal Hocko
2016-03-08 20:07 ` Hugh Dickins
2016-03-09 8:26 ` Michal Hocko
2016-02-03 13:13 ` [PATCH 3/5] oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space Michal Hocko
2016-02-04 14:22 ` Tetsuo Handa
2016-02-04 14:43 ` Michal Hocko
2016-02-04 15:08 ` Tetsuo Handa
2016-02-04 16:31 ` Michal Hocko
2016-02-05 11:14 ` Tetsuo Handa
2016-02-06 8:30 ` Michal Hocko
2016-02-06 11:23 ` Tetsuo Handa
2016-02-15 20:47 ` Michal Hocko
2016-02-06 6:45 ` Michal Hocko
2016-02-06 14:33 ` Tetsuo Handa
2016-02-15 20:40 ` [PATCH 3.1/5] oom: make oom_reaper freezable Michal Hocko
2016-02-03 13:13 ` [PATCH 4/5] mm, oom_reaper: report success/failure Michal Hocko
2016-02-03 23:10 ` David Rientjes
2016-02-04 6:46 ` Michal Hocko
2016-02-04 22:31 ` David Rientjes
2016-02-05 9:26 ` Michal Hocko
2016-02-06 6:34 ` Michal Hocko
2016-02-03 13:14 ` [PATCH 5/5] mm, oom_reaper: implement OOM victims queuing Michal Hocko
2016-02-04 10:49 ` Tetsuo Handa
2016-02-04 14:53 ` Michal Hocko
2016-02-06 5:54 ` Tetsuo Handa
2016-02-06 8:37 ` Michal Hocko
2016-02-06 15:33 ` Tetsuo Handa
2016-02-15 20:15 ` Michal Hocko
2016-02-16 11:11 ` Tetsuo Handa
2016-02-16 15:53 ` Michal Hocko
2016-02-17 9:48 ` [PATCH 6/5] oom, oom_reaper: disable oom_reaper for Michal Hocko
2016-02-17 10:41 ` Tetsuo Handa
2016-02-17 11:33 ` Michal Hocko
2016-02-19 18:34 ` Michal Hocko
2016-02-20 2:32 ` [PATCH 6/5] oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task Tetsuo Handa
2016-02-22 9:41 ` Michal Hocko
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