From: Mikulas Patocka <mpatocka@redhat.com>
To: NeilBrown <neilb@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@kernel.org>,
linux-mm@kvack.org, dm-devel@redhat.com,
Mel Gorman <mgorman@suse.de>,
David Rientjes <rientjes@google.com>,
Ondrej Kozina <okozina@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks
Date: Wed, 27 Jul 2016 10:28:40 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.1607270948040.1779@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <87invr4tjm.fsf@notabene.neil.brown.name>
On Wed, 27 Jul 2016, NeilBrown wrote:
> On Tue, Jul 26 2016, Mikulas Patocka wrote:
>
> > On Sat, 23 Jul 2016, NeilBrown wrote:
> >
> >> "dirtying ... from the reclaim context" ??? What does that mean?
> >> According to
> >> Commit: 26eecbf3543b ("[PATCH] vm: pageout throttling")
> >> From the history tree, the purpose of throttle_vm_writeout() is to
> >> limit the amount of memory that is concurrently under I/O.
> >> That seems strange to me because I thought it was the responsibility of
> >> each backing device to impose a limit - a maximum queue size of some
> >> sort.
> >
> > Device mapper doesn't impose any limit for in-flight bios.
>
> I would suggest that it probably should. At least it should
> "set_wb_congested()" when the number of in-flight bios reaches some
> arbitrary threshold.
If we set the device mapper device as congested, it can again trigger that
mempool alloc throttling bug.
I.e. suppose that we swap to a dm-crypt device. The dm-crypt device
becomes clogged and sets its state as congested. The underlying block
device is not congested.
The mempool_alloc function in the dm-crypt workqueue sets the
PF_LESS_THROTTLE flag, and tries to allocate memory, but according to
Michal's patches, processes with PF_LESS_THROTTLE may still get throttled.
So if we set the dm-crypt device as congested, it can incorrectly throttle
the dm-crypt workqueue that does allocations of temporary pages and
encryption.
I think that approach with PF_LESS_THROTTLE in mempool_alloc is incorrect
and that mempool allocations should never be throttled.
> > I've made some patches that limit in-flight bios for device mapper in
> > the past, but there were not integrated into upstream.
>
> I second the motion to resurrect these.
I uploaded those patches here:
http://people.redhat.com/~mpatocka/patches/kernel/dm-limit-outstanding-bios/
Mikulas
> Thanks,
> NeilBrown
>
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next prev parent reply other threads:[~2016-07-27 14:28 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-18 8:39 [RFC PATCH 0/2] mempool vs. page allocator interaction Michal Hocko
2016-07-18 8:41 ` [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path Michal Hocko
2016-07-18 8:41 ` [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks Michal Hocko
2016-07-19 21:50 ` Mikulas Patocka
2016-07-22 8:46 ` NeilBrown
2016-07-22 9:04 ` NeilBrown
2016-07-22 9:15 ` Michal Hocko
2016-07-23 0:12 ` NeilBrown
2016-07-25 8:32 ` Michal Hocko
2016-07-25 19:23 ` Michal Hocko
2016-07-26 7:07 ` Michal Hocko
2016-07-27 3:43 ` [dm-devel] " NeilBrown
2016-07-27 18:24 ` Michal Hocko
2016-07-27 21:33 ` NeilBrown
2016-07-28 7:17 ` Michal Hocko
2016-08-03 12:53 ` Mikulas Patocka
2016-08-03 14:34 ` Michal Hocko
2016-08-04 18:49 ` Mikulas Patocka
2016-08-12 12:32 ` Michal Hocko
2016-08-13 17:34 ` Mikulas Patocka
2016-08-14 10:34 ` Michal Hocko
2016-08-15 16:15 ` Mikulas Patocka
2016-11-23 21:11 ` Mikulas Patocka
2016-11-24 13:29 ` Michal Hocko
2016-11-24 17:10 ` Mikulas Patocka
2016-11-28 14:06 ` Michal Hocko
2016-07-25 21:52 ` Mikulas Patocka
2016-07-26 7:25 ` Michal Hocko
2016-07-27 4:02 ` [dm-devel] " NeilBrown
2016-07-27 14:28 ` Mikulas Patocka [this message]
2016-07-27 18:40 ` Michal Hocko
2016-08-03 13:59 ` Mikulas Patocka
2016-08-03 14:42 ` Michal Hocko
2016-08-04 18:46 ` Mikulas Patocka
2016-07-27 21:36 ` NeilBrown
2016-07-19 2:00 ` [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path David Rientjes
2016-07-19 7:49 ` Michal Hocko
2016-07-19 13:54 ` Johannes Weiner
2016-07-19 14:19 ` Michal Hocko
2016-07-19 22:01 ` Mikulas Patocka
2016-07-19 20:45 ` David Rientjes
2016-07-20 8:15 ` Michal Hocko
2016-07-20 21:06 ` David Rientjes
2016-07-21 8:52 ` Michal Hocko
2016-07-21 12:13 ` Johannes Weiner
2016-07-21 14:53 ` Michal Hocko
2016-07-21 15:26 ` Johannes Weiner
2016-07-22 1:41 ` NeilBrown
2016-07-22 6:37 ` Michal Hocko
2016-07-22 12:26 ` Vlastimil Babka
2016-07-22 19:44 ` Andrew Morton
2016-07-23 18:52 ` Vlastimil Babka
2016-07-19 21:50 ` Mikulas Patocka
2016-07-20 6:44 ` Michal Hocko
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