From: "Theodore Ts'o" <tytso@mit.edu>
To: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>,
linux-ext4@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Jiri Slaby <jslaby@suse.cz>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2
Date: Fri, 12 Apr 2013 11:19:52 -0400 [thread overview]
Message-ID: <20130412151952.GA4944@thunk.org> (raw)
In-Reply-To: <20130412045042.GA30622@dastard>
On Fri, Apr 12, 2013 at 02:50:42PM +1000, Dave Chinner wrote:
> > If that is the case, one possible solution that comes to mind would be
> > to mark buffer_heads that contain metadata with a flag, so that the
> > flusher thread can write them back at the same priority as reads.
>
> Ext4 is already using REQ_META for this purpose.
We're using REQ_META | REQ_PRIO for reads, not writes.
> I'm surprised that no-one has suggested "change the IO elevator"
> yet.....
Well, testing to see if the stalls go away with the noop schedule is a
good thing to try just to validate the theory.
The thing is, we do want to make ext4 work well with cfq, and
prioritizing non-readahead read requests ahead of data writeback does
make sense. The issue is with is that metadata writes going through
the block device could in some cases effectively cause a priority
inversion when what had previously been an asynchronous writeback
starts blocking a foreground, user-visible process.
At least, that's the theory; we should confirm that this is indeed
what is causing the data stalls which Mel is reporting on HDD's before
we start figuring out how to fix this problem.
- Ted
WARNING: multiple messages have this Message-ID (diff)
From: Theodore Ts'o <tytso@mit.edu>
To: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>,
linux-ext4@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Jiri Slaby <jslaby@suse.cz>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2
Date: Fri, 12 Apr 2013 11:19:52 -0400 [thread overview]
Message-ID: <20130412151952.GA4944@thunk.org> (raw)
In-Reply-To: <20130412045042.GA30622@dastard>
On Fri, Apr 12, 2013 at 02:50:42PM +1000, Dave Chinner wrote:
> > If that is the case, one possible solution that comes to mind would be
> > to mark buffer_heads that contain metadata with a flag, so that the
> > flusher thread can write them back at the same priority as reads.
>
> Ext4 is already using REQ_META for this purpose.
We're using REQ_META | REQ_PRIO for reads, not writes.
> I'm surprised that no-one has suggested "change the IO elevator"
> yet.....
Well, testing to see if the stalls go away with the noop schedule is a
good thing to try just to validate the theory.
The thing is, we do want to make ext4 work well with cfq, and
prioritizing non-readahead read requests ahead of data writeback does
make sense. The issue is with is that metadata writes going through
the block device could in some cases effectively cause a priority
inversion when what had previously been an asynchronous writeback
starts blocking a foreground, user-visible process.
At least, that's the theory; we should confirm that this is indeed
what is causing the data stalls which Mel is reporting on HDD's before
we start figuring out how to fix this problem.
- Ted
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next prev parent reply other threads:[~2013-04-12 15:20 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-02 14:27 Excessive stall times on ext4 in 3.9-rc2 Mel Gorman
2013-04-02 14:27 ` Mel Gorman
2013-04-02 15:00 ` Jiri Slaby
2013-04-02 15:00 ` Jiri Slaby
2013-04-02 15:03 ` Zheng Liu
2013-04-02 15:03 ` Zheng Liu
2013-04-02 15:15 ` Mel Gorman
2013-04-02 15:15 ` Mel Gorman
2013-04-02 15:06 ` Theodore Ts'o
2013-04-02 15:06 ` Theodore Ts'o
2013-04-02 15:14 ` Theodore Ts'o
2013-04-02 15:14 ` Theodore Ts'o
2013-04-02 18:19 ` Theodore Ts'o
2013-04-02 18:19 ` Theodore Ts'o
2013-04-07 21:59 ` Frank Ch. Eigler
2013-04-07 21:59 ` Frank Ch. Eigler
2013-04-08 8:36 ` Mel Gorman
2013-04-08 8:36 ` Mel Gorman
2013-04-08 10:52 ` Frank Ch. Eigler
2013-04-08 10:52 ` Frank Ch. Eigler
2013-04-08 11:01 ` Theodore Ts'o
2013-04-08 11:01 ` Theodore Ts'o
2013-04-03 10:19 ` Mel Gorman
2013-04-03 10:19 ` Mel Gorman
2013-04-03 12:05 ` Theodore Ts'o
2013-04-03 12:05 ` Theodore Ts'o
2013-04-03 15:15 ` Mel Gorman
2013-04-05 22:18 ` Jiri Slaby
2013-04-05 22:18 ` Jiri Slaby
2013-04-05 23:16 ` Theodore Ts'o
2013-04-05 23:16 ` Theodore Ts'o
2013-04-06 7:29 ` Jiri Slaby
2013-04-06 7:29 ` Jiri Slaby
2013-04-06 7:37 ` Jiri Slaby
2013-04-06 7:37 ` Jiri Slaby
2013-04-06 8:19 ` Jiri Slaby
2013-04-06 13:15 ` Theodore Ts'o
2013-04-06 13:15 ` Theodore Ts'o
2013-04-10 10:56 ` Mel Gorman
2013-04-10 10:56 ` Mel Gorman
2013-04-10 13:12 ` Theodore Ts'o
2013-04-10 13:12 ` Theodore Ts'o
2013-04-11 17:04 ` Mel Gorman
2013-04-11 17:04 ` Mel Gorman
2013-04-11 18:35 ` Theodore Ts'o
2013-04-11 18:35 ` Theodore Ts'o
2013-04-11 21:33 ` Jan Kara
2013-04-11 21:33 ` Jan Kara
2013-04-12 2:57 ` Theodore Ts'o
2013-04-12 2:57 ` Theodore Ts'o
2013-04-12 4:50 ` Dave Chinner
2013-04-12 4:50 ` Dave Chinner
2013-04-12 15:19 ` Theodore Ts'o [this message]
2013-04-12 15:19 ` Theodore Ts'o
2013-04-13 1:23 ` Dave Chinner
2013-04-13 1:23 ` Dave Chinner
2013-04-22 14:38 ` Mel Gorman
2013-04-22 14:38 ` Mel Gorman
2013-04-22 22:42 ` Jeff Moyer
2013-04-22 22:42 ` Jeff Moyer
2013-04-23 0:02 ` Theodore Ts'o
2013-04-23 0:02 ` Theodore Ts'o
2013-04-23 9:31 ` Jan Kara
2013-04-23 9:31 ` Jan Kara
2013-04-23 14:01 ` Mel Gorman
2013-04-23 14:01 ` Mel Gorman
2013-04-24 19:09 ` Jeff Moyer
2013-04-24 19:09 ` Jeff Moyer
2013-04-25 12:21 ` Mel Gorman
2013-04-25 12:21 ` Mel Gorman
2013-04-12 9:47 ` Mel Gorman
2013-04-12 9:47 ` Mel Gorman
2013-04-21 0:05 ` Theodore Ts'o
2013-04-21 0:05 ` Theodore Ts'o
2013-04-21 0:07 ` [PATCH 1/3] ext4: mark all metadata I/O with REQ_META Theodore Ts'o
2013-04-21 0:07 ` Theodore Ts'o
2013-04-21 0:07 ` [PATCH 2/3] buffer: add BH_Prio and BH_Meta flags Theodore Ts'o
2013-04-21 0:07 ` Theodore Ts'o
2013-04-21 0:07 ` [PATCH 3/3] ext4: mark metadata blocks using bh flags Theodore Ts'o
2013-04-21 0:07 ` Theodore Ts'o
2013-04-21 6:09 ` Jiri Slaby
2013-04-21 6:09 ` Jiri Slaby
2013-04-21 6:09 ` Jiri Slaby
2013-04-21 19:55 ` Theodore Ts'o
2013-04-21 19:55 ` Theodore Ts'o
2013-04-21 19:55 ` Theodore Ts'o
2013-04-21 20:48 ` [PATCH 3/3 -v2] " Theodore Ts'o
2013-04-21 20:48 ` Theodore Ts'o
2013-04-21 20:48 ` Theodore Ts'o
2013-04-22 12:06 ` [PATCH 1/3] ext4: mark all metadata I/O with REQ_META Zheng Liu
2013-04-22 12:06 ` Zheng Liu
2013-04-23 15:33 ` Excessive stall times on ext4 in 3.9-rc2 Mel Gorman
2013-04-23 15:33 ` Mel Gorman
2013-04-23 15:50 ` Theodore Ts'o
2013-04-23 15:50 ` Theodore Ts'o
2013-04-23 16:13 ` Mel Gorman
2013-04-23 16:13 ` Mel Gorman
2013-04-12 10:18 ` Tvrtko Ursulin
2013-04-12 10:18 ` Tvrtko Ursulin
2013-04-12 9:45 ` Mel Gorman
2013-04-12 9:45 ` Mel Gorman
2013-04-02 23:16 ` Theodore Ts'o
2013-04-02 23:16 ` Theodore Ts'o
2013-04-03 15:22 ` Mel Gorman
2013-04-03 15:22 ` Mel Gorman
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