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From: Mikulas Patocka <mpatocka@redhat.com>
To: Kent Overstreet <koverstreet@google.com>
Cc: Vivek Goyal <vgoyal@redhat.com>,
	linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
	dm-devel@redhat.com, tj@kernel.org, bharrosh@panasas.com,
	Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers
Date: Tue, 4 Sep 2012 15:26:19 -0400 (EDT)	[thread overview]
Message-ID: <Pine.LNX.4.64.1209041509160.22689@file.rdu.redhat.com> (raw)
In-Reply-To: <20120904034100.GA21602@moria.home.lan>



On Mon, 3 Sep 2012, Kent Overstreet wrote:

> On Mon, Sep 03, 2012 at 04:41:37PM -0400, Mikulas Patocka wrote:
> > ... or another possibility - start a timer when something is put to 
> > current->bio_list and use that timer to pop entries off current->bio_list 
> > and submit them to a workqueue. The timer can be cpu-local so only 
> > interrupt masking is required to synchronize against the timer.
> > 
> > This would normally run just like the current kernel and in case of 
> > deadlock, the timer would kick in and resolve the deadlock.
> 
> Ugh. That's a _terrible_ idea.
> 
> Remember the old plugging code? You ever have to debug performance
> issues caused by it?

Yes, I do remember it (and I fixed one bug that resulted in missed unplug 
and degraded performance).

But currently, deadlocks due to exhausted mempools and bios being stalled 
in current->bio_list don't happen (or do happen below so rarely that they 
aren't reported).

If we add a timer, it will turn a deadlock into an i/o delay, but it can't 
make things any worse.

BTW. can these new-style timerless plugs introduce deadlocks too? What 
happens when some bios are indefinitely delayed because their requests are 
held in a plug and a mempool runs out?

> > > I could be convinced, but right now I prefer my solution.
> > 
> > It fixes bio allocation problem, but not other similar mempool problems in 
> > dm and md.
> 
> I looked a bit more, and actually I think the rest of the problem is
> pretty limited in scope - most of those mempool allocations are per
> request, not per split.
> 
> I'm willing to put some time into converting dm/md over to bioset's
> front_pad. I'm having to learn the code for the immutable biovec work,
> anyways.

Currently, dm targets allocate request-specific data from target-specific 
mempool. mempools are in dm-crypt, dm-delay, dm-mirror, dm-snapshot, 
dm-thin, dm-verity. You can change it to allocate request-specific data 
with the bio.

Mikulas

  parent reply	other threads:[~2012-09-04 19:26 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-28 17:37 [PATCH v7 0/9] Block cleanups, deadlock fix Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 1/9] block: Generalized bio pool freeing Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 2/9] dm: Use bioset's front_pad for dm_rq_clone_bio_info Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 3/9] block: Add bio_reset() Kent Overstreet
2012-08-28 20:31   ` Tejun Heo
2012-08-28 22:17     ` Kent Overstreet
2012-08-28 22:53       ` Kent Overstreet
2012-09-01  2:23       ` Tejun Heo
2012-09-05 20:13         ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 4/9] pktcdvd: Switch to bio_kmalloc() Kent Overstreet
2012-08-28 20:32   ` Tejun Heo
2012-08-28 22:24     ` Kent Overstreet
2012-09-04  9:05     ` Jiri Kosina
2012-09-05 19:44       ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 5/9] block: Kill bi_destructor Kent Overstreet
2012-08-28 20:36   ` Tejun Heo
2012-08-28 22:07     ` Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 6/9] block: Consolidate bio_alloc_bioset(), bio_kmalloc() Kent Overstreet
2012-08-28 20:41   ` Tejun Heo
2012-08-28 22:03     ` Kent Overstreet
2012-09-01  2:17       ` Tejun Heo
2012-08-28 17:37 ` [PATCH v7 7/9] block: Add bio_clone_bioset(), bio_clone_kmalloc() Kent Overstreet
2012-08-28 20:44   ` Tejun Heo
2012-08-28 22:05     ` Kent Overstreet
2012-09-01  2:19       ` Tejun Heo
2012-08-28 17:37 ` [PATCH v7 8/9] block: Reorder struct bio_set Kent Overstreet
2012-08-28 17:37 ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Kent Overstreet
2012-08-28 20:49   ` Tejun Heo
2012-08-28 22:28     ` Kent Overstreet
2012-08-28 23:01       ` Kent Overstreet
2012-08-29  1:31         ` Vivek Goyal
2012-08-29  3:25           ` Kent Overstreet
2012-08-29 12:57             ` Vivek Goyal
2012-08-29 14:39               ` [dm-devel] " Alasdair G Kergon
2012-08-29 16:26                 ` Kent Overstreet
2012-08-29 21:01                   ` John Stoffel
2012-08-29 21:08                     ` Kent Overstreet
2012-08-28 22:06   ` Vivek Goyal
2012-08-28 22:23     ` Kent Overstreet
2012-08-29 16:24   ` Mikulas Patocka
2012-08-29 16:50     ` Kent Overstreet
2012-08-29 16:57       ` [dm-devel] " Alasdair G Kergon
2012-08-29 17:07       ` Vivek Goyal
2012-08-29 17:13         ` Kent Overstreet
2012-08-29 17:23           ` [dm-devel] " Alasdair G Kergon
2012-08-29 17:32             ` Kent Overstreet
2012-08-30 22:07           ` Vivek Goyal
2012-08-31  1:43             ` Kent Overstreet
2012-08-31  1:55               ` Kent Overstreet
2012-08-31 15:01               ` Vivek Goyal
2012-09-03  1:26                 ` Kent Overstreet
2012-09-03 20:41               ` Mikulas Patocka
2012-09-04  3:41                 ` Kent Overstreet
2012-09-04 18:55                   ` Tejun Heo
2012-09-04 19:01                     ` Tejun Heo
2012-09-04 19:43                       ` Kent Overstreet
2012-09-04 19:42                     ` Kent Overstreet
2012-09-04 21:03                       ` Tejun Heo
2012-09-04 19:26                   ` Mikulas Patocka [this message]
2012-09-04 19:39                     ` Vivek Goyal
2012-09-04 19:51                     ` [PATCH] dm: Use bioset's front_pad for dm_target_io Kent Overstreet
2012-09-04 21:20                       ` Tejun Heo
2012-09-11 19:28                       ` [PATCH 2] " Mikulas Patocka
2012-09-11 19:50                         ` Kent Overstreet
2012-09-12 22:31                           ` Mikulas Patocka
2012-09-14 23:09                             ` [dm-devel] " Alasdair G Kergon
2012-09-01  2:13             ` [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers Tejun Heo
2012-09-03  1:34               ` [PATCH v2] " Kent Overstreet
2012-09-04 15:00               ` [PATCH v7 9/9] " Vivek Goyal
2012-09-03  0:49             ` Dave Chinner
2012-09-03  1:17               ` Kent Overstreet
2012-09-04 13:54               ` Vivek Goyal
2012-09-04 18:26                 ` Tejun Heo
2012-09-05  3:57                   ` Dave Chinner
2012-09-05  4:37                     ` Tejun Heo

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