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Date: Fri, 13 Nov 2009 17:34:46 +0000
From: Mel Gorman <mel@....ul.ie>
To: Chris Mason <chris.mason@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>,
Sven Geggus <lists@...hsschwanzdomain.de>,
Karol Lewandowski <karol.k.lewandowski@...il.com>,
Tobias Oetiker <tobi@...iker.ch>, linux-kernel@...r.kernel.org,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Pekka Enberg <penberg@...helsinki.fi>,
Rik van Riel <riel@...hat.com>,
Christoph Lameter <cl@...ux-foundation.org>,
Stephan von Krawczynski <skraw@...net.com>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [PATCH] make crypto unplug fix V3
On Fri, Nov 13, 2009 at 07:58:12AM -0500, Chris Mason wrote:
> This is still likely to set your dm data on fire. It is only meant for
> testers that start with mkfs and don't have any valuable dm data.
>
The good news is that my room remains fire-free. Despite swap also
running from dm-crypt, I had no corruption or instability issues.
Here is an updated set of results for fake-gitk running.
X86
2.6.30-0000000-force-highorder Elapsed:12:08.908 Failures:0
2.6.31-0000000-force-highorder Elapsed:10:56.283 Failures:0
2.6.31-0000006-dm-crypt-unplug Elapsed:11:51.653 Failures:0
2.6.31-0000012-pgalloc-2.6.30 Elapsed:12:26.587 Failures:0
2.6.31-0000123-congestion-both Elapsed:10:55.298 Failures:0
2.6.31-0001234-kswapd-quick-recheck Elapsed:18:01.523 Failures:0
2.6.31-0123456-dm-crypt-unplug Elapsed:10:45.720 Failures:0
2.6.31-revert-8aa7e847 Elapsed:15:08.020 Failures:0
2.6.32-rc6-0000000-force-highorder Elapsed:16:20.765 Failures:4
2.6.32-rc6-0000006-dm-crypt-unplug Elapsed:13:42.920 Failures:0
2.6.32-rc6-0000012-pgalloc-2.6.30 Elapsed:16:13.380 Failures:1
2.6.32-rc6-0000123-congestion-both Elapsed:18:39.118 Failures:0
2.6.32-rc6-0001234-kswapd-quick-recheck Elapsed:15:04.398 Failures:0
2.6.32-rc6-0123456-dm-crypt-unplug Elapsed:12:50.438 Failures:0
2.6.32-rc6-revert-8aa7e847 Elapsed:20:50.888 Failures:0
X86-64
2.6.30-0000000-force-highorder Elapsed:10:37.300 Failures:0
2.6.31-0000000-force-highorder Elapsed:08:49.338 Failures:0
2.6.31-0000006-dm-crypt-unplug Elapsed:09:37.840 Failures:0
2.6.31-0000012-pgalloc-2.6.30 Elapsed:15:49.690 Failures:0
2.6.31-0000123-congestion-both Elapsed:09:18.790 Failures:0
2.6.31-0001234-kswapd-quick-recheck Elapsed:08:39.268 Failures:0
2.6.31-0123456-dm-crypt-unplug Elapsed:08:20.965 Failures:0
2.6.31-revert-8aa7e847 Elapsed:08:07.457 Failures:0
2.6.32-rc6-0000000-force-highorder Elapsed:18:29.103 Failures:1
2.6.32-rc6-0000006-dm-crypt-unplug Elapsed:25:53.515 Failures:3
2.6.32-rc6-0000012-pgalloc-2.6.30 Elapsed:19:55.570 Failures:6
2.6.32-rc6-0000123-congestion-both Elapsed:17:29.255 Failures:2
2.6.32-rc6-0001234-kswapd-quick-recheck Elapsed:14:41.068 Failures:0
2.6.32-rc6-0123456-dm-crypt-unplug Elapsed:15:48.028 Failures:1
2.6.32-rc6-revert-8aa7e847 Elapsed:14:48.647 Failures:0
The numbering in the kernel indicates what patches are applied. I tested
the dm-crypt patch both in isolation and in combination with the patches
in this series.
Basically, the dm-crypt-unplug makes a small difference in performance
overall, mostly slight gains and losses. There was one massive regression
with the dm-crypt patch applied to 2.6.32-rc6 but at the moment, I don't
know what that is.
In general, the patch reduces the amount of time direct reclaimers are
spending on congestion_wait.
> It includes my patch from last night, along with changes to force dm to
> unplug when its IO queues empty.
>
> The problem goes like this:
>
> Process: submit read bio
> dm: put bio onto work queue
> process: unplug
> dm: work queue finds bio, does a generic_make_request
>
> The end result is that we miss the unplug completely. dm-crypt needs to
> unplug for sync bios. This patch also changes it to unplug whenever the
> queue is empty, which is far from ideal but better than missing the
> unplugs.
>
> This doesn't completely fix io stalls I'm seeing with dm-crypt, but its
> my best guess. If it works, I'll break it up and submit for real to
> the dm people.
>
Out of curiousity, how are you measuring IO stalls? In the tests I'm doing,
the worker processes output their progress and it should be at a steady
rate. I considered a stall to be an excessive delay between updates which
is a pretty indirect measure.
> -chris
>
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index ed10381..729ae01 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -94,8 +94,12 @@ struct crypt_config {
> struct bio_set *bs;
>
> struct workqueue_struct *io_queue;
> + struct workqueue_struct *async_io_queue;
> struct workqueue_struct *crypt_queue;
>
> + atomic_t sync_bios_in_queue;
> + atomic_t async_bios_in_queue;
> +
> /*
> * crypto related data
> */
> @@ -679,11 +683,29 @@ static void kcryptd_io_write(struct dm_crypt_io *io)
> static void kcryptd_io(struct work_struct *work)
> {
> struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
> + struct crypt_config *cc = io->target->private;
> + int zero_sync = 0;
> + int zero_async = 0;
> + int was_sync = 0;
> +
> + if (io->base_bio->bi_rw & (1 << BIO_RW_SYNCIO)) {
> + zero_sync = atomic_dec_and_test(&cc->sync_bios_in_queue);
> + was_sync = 1;
> + } else
> + zero_async = atomic_dec_and_test(&cc->async_bios_in_queue);
>
> if (bio_data_dir(io->base_bio) == READ)
> kcryptd_io_read(io);
> else
> kcryptd_io_write(io);
> +
> + if ((was_sync && zero_sync) ||
> + (!was_sync && zero_async &&
> + atomic_read(&cc->sync_bios_in_queue) == 0)) {
> + struct backing_dev_info *bdi;
> + bdi = blk_get_backing_dev_info(io->base_bio->bi_bdev);
> + blk_run_backing_dev(bdi, NULL);
> + }
> }
>
> static void kcryptd_queue_io(struct dm_crypt_io *io)
> @@ -691,7 +713,13 @@ static void kcryptd_queue_io(struct dm_crypt_io *io)
> struct crypt_config *cc = io->target->private;
>
> INIT_WORK(&io->work, kcryptd_io);
> - queue_work(cc->io_queue, &io->work);
> + if (io->base_bio->bi_rw & (1 << BIO_RW_SYNCIO)) {
> + atomic_inc(&cc->sync_bios_in_queue);
> + queue_work(cc->io_queue, &io->work);
> + } else {
> + atomic_inc(&cc->async_bios_in_queue);
> + queue_work(cc->async_io_queue, &io->work);
> + }
> }
>
> static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io,
> @@ -759,8 +787,7 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)
>
> /* Encryption was already finished, submit io now */
> if (crypt_finished) {
> - kcryptd_crypt_write_io_submit(io, r, 0);
> -
> + kcryptd_crypt_write_io_submit(io, r, 1);
> /*
> * If there was an error, do not try next fragments.
> * For async, error is processed in async handler.
> @@ -1120,6 +1147,15 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> } else
> cc->iv_mode = NULL;
>
> + atomic_set(&cc->sync_bios_in_queue, 0);
> + atomic_set(&cc->async_bios_in_queue, 0);
> +
> + cc->async_io_queue = create_singlethread_workqueue("kcryptd_async_io");
> + if (!cc->async_io_queue) {
> + ti->error = "Couldn't create kcryptd io queue";
> + goto bad_async_io_queue;
> + }
> +
> cc->io_queue = create_singlethread_workqueue("kcryptd_io");
> if (!cc->io_queue) {
> ti->error = "Couldn't create kcryptd io queue";
> @@ -1139,6 +1175,8 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> bad_crypt_queue:
> destroy_workqueue(cc->io_queue);
> bad_io_queue:
> + destroy_workqueue(cc->async_io_queue);
> +bad_async_io_queue:
> kfree(cc->iv_mode);
> bad_ivmode_string:
> dm_put_device(ti, cc->dev);
> @@ -1166,6 +1204,7 @@ static void crypt_dtr(struct dm_target *ti)
> struct crypt_config *cc = (struct crypt_config *) ti->private;
>
> destroy_workqueue(cc->io_queue);
> + destroy_workqueue(cc->async_io_queue);
> destroy_workqueue(cc->crypt_queue);
>
> if (cc->req)
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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