From: Konstantin Khlebnikov <koct9i@gmail.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Michal Hocko <mhocko@suse.com>,
Mel Gorman <mgorman@techsingularity.net>,
linux-raid@vger.kernel.org, Dave Chinner <dchinner@redhat.com>,
Tejun Heo <tj@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Shaohua Li <shli@kernel.org>
Subject: Re: [PATCH RFC] mm, writeback: flush plugged IO in wakeup_flusher_threads()
Date: Fri, 5 Aug 2016 08:44:25 +0300 [thread overview]
Message-ID: <CALYGNiMM-LWAqX2AuH-Su4EykL7fybV9EaW6V_VoGw9HiBXMDg@mail.gmail.com> (raw)
In-Reply-To: <3ee639d7-2371-c27d-3639-e4b1315d6663@kernel.dk>
On Thu, Aug 4, 2016 at 10:21 PM, Jens Axboe <axboe@kernel.dk> wrote:
> On 08/04/2016 12:36 PM, Konstantin Khlebnikov wrote:
>>
>> I've found funny live-lock between raid10 barriers during resync and
>> memory
>> controller hard limits. Inside mpage_readpages() task holds on its plug
>> bio
>> which blocks barrier in raid10. Its memory cgroup have no free memory thus
>> task goes into reclaimer but all reclaimable pages are dirty and cannot be
>> written because raid10 is rebuilding and stuck on barrier.
>>
>> Common flush of such IO in schedule() never happens because machine where
>> that happened has a lot of free cpus and task never goes sleep.
>>
>> Lock is 'live' because changing memory limit or killing tasks which holds
>> that stuck bio unblock whole progress.
>>
>> That was happened in 3.18.x but I see no difference in upstream logic.
>> Theoretically this might happen even without memory cgroup.
>
>
> So the issue is that the caller of wakeup_flusher_threads() ends up never
> going to sleep, hence the plug is never auto-flushed. I didn't quite
> understand your reasoning for why it never sleeps above, but that must be
> the gist of it.
Ah right, simple context switch doesn't flush plug, so count of cpus
is irrelevant.
>
> I don't see anything inherently wrong with the fix.
>
> --
> Jens Axboe
>
>
> --
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prev parent reply other threads:[~2016-08-05 5:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-04 18:36 Konstantin Khlebnikov
2016-08-04 19:21 ` Jens Axboe
2016-08-05 5:44 ` Konstantin Khlebnikov [this message]
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