From: Mel Gorman <mgorman@suse.de>
To: Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
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 10:47:31 +0100 [thread overview]
Message-ID: <20130412094731.GI11656@suse.de> (raw)
In-Reply-To: <20130412025708.GB7445@thunk.org>
On Thu, Apr 11, 2013 at 10:57:08PM -0400, Theodore Ts'o wrote:
> On Thu, Apr 11, 2013 at 11:33:35PM +0200, Jan Kara wrote:
> > I think it might be more enlightening if Mel traced which process in
> > which funclion is holding the buffer lock. I suspect we'll find out that
> > the flusher thread has submitted the buffer for IO as an async write and
> > thus it takes a long time to complete in presence of reads which have
> > higher priority.
>
> That's an interesting theory. If the workload is one which is very
> heavy on reads and writes, that could explain the high latency. That
> would explain why those of us who are using primarily SSD's are seeing
> the problems, because would be reads are nice and fast.
>
> 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.
>
> The only problem I can see with this hypothesis is that if this is the
> explanation for what Mel and Jiri are seeing, it's something that
> would have been around for a long time, and would affect ext3 as well
> as ext4. That isn't quite consistent, however, with Mel's observation
> that this is a probablem which has gotten worse in relatively
> recently.
>
According to the tests I've run, multi-second stalls have been a problem for
a while but never really bothered me. I'm not sure why it felt particularly
bad around -rc2 or why it seems to be better now. Maybe I just had my
cranky pants on.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2013-04-12 9:47 UTC|newest]
Thread overview: 52+ 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 15:00 ` Jiri Slaby
2013-04-02 15:03 ` Zheng Liu
2013-04-02 15:15 ` Mel Gorman
2013-04-02 15:06 ` Theodore Ts'o
2013-04-02 15:14 ` Theodore Ts'o
2013-04-02 18:19 ` Theodore Ts'o
2013-04-07 21:59 ` Frank Ch. Eigler
2013-04-08 8:36 ` Mel Gorman
2013-04-08 10:52 ` Frank Ch. Eigler
2013-04-08 11:01 ` Theodore Ts'o
2013-04-03 10:19 ` Mel Gorman
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 23:16 ` Theodore Ts'o
2013-04-06 7:29 ` Jiri Slaby
2013-04-06 7:37 ` Jiri Slaby
2013-04-06 8:19 ` Jiri Slaby
2013-04-06 13:15 ` Theodore Ts'o
2013-04-10 10:56 ` Mel Gorman
2013-04-10 13:12 ` Theodore Ts'o
2013-04-11 17:04 ` Mel Gorman
2013-04-11 18:35 ` Theodore Ts'o
2013-04-11 21:33 ` Jan Kara
2013-04-12 2:57 ` Theodore Ts'o
2013-04-12 4:50 ` Dave Chinner
2013-04-12 15:19 ` Theodore Ts'o
2013-04-13 1:23 ` Dave Chinner
2013-04-22 14:38 ` Mel Gorman
2013-04-22 22:42 ` Jeff Moyer
2013-04-23 0:02 ` Theodore Ts'o
2013-04-23 9:31 ` Jan Kara
2013-04-23 14:01 ` Mel Gorman
2013-04-24 19:09 ` Jeff Moyer
2013-04-25 12:21 ` Mel Gorman
2013-04-12 9:47 ` Mel Gorman [this message]
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 ` [PATCH 2/3] buffer: add BH_Prio and BH_Meta flags Theodore Ts'o
2013-04-21 0:07 ` [PATCH 3/3] ext4: mark metadata blocks using bh flags Theodore Ts'o
2013-04-21 6:09 ` Jiri Slaby
2013-04-21 19:55 ` Theodore Ts'o
2013-04-21 20:48 ` [PATCH 3/3 -v2] " Theodore Ts'o
2013-04-22 12:06 ` [PATCH 1/3] ext4: mark all metadata I/O with REQ_META Zheng Liu
2013-04-23 15:33 ` Excessive stall times on ext4 in 3.9-rc2 Mel Gorman
2013-04-23 15:50 ` Theodore Ts'o
2013-04-23 16:13 ` Mel Gorman
2013-04-12 10:18 ` Tvrtko Ursulin
2013-04-12 9:45 ` Mel Gorman
2013-04-02 23:16 ` Theodore Ts'o
2013-04-03 15:22 ` Mel Gorman
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