From: Chris Mason <chris.mason@oracle.com>
To: "Ted Ts'o" <tytso@mit.edu>
Cc: Jeff Moyer <jmoyer@redhat.com>,
Boaz Harrosh <bharrosh@panasas.com>, Zach Brown <zab@zabbo.net>,
Eric Sandeen <sandeen@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [PATCH, RFC] Don't do page stablization if !CONFIG_BLKDEV_INTEGRITY
Date: Thu, 8 Mar 2012 16:20:54 -0500 [thread overview]
Message-ID: <20120308212054.GI29510@shiny> (raw)
In-Reply-To: <20120308211221.GB11861@thunk.org>
On Thu, Mar 08, 2012 at 04:12:21PM -0500, Ted Ts'o wrote:
> On Thu, Mar 08, 2012 at 03:42:52PM -0500, Jeff Moyer wrote:
> >
> > So now we're back to figuring out how to tell how long I/O will take?
> > If writeback is issuing random access I/Os to spinning media, you can
> > bet it might be a while. Today, you could lower nr_requests to some
> > obscenely small number to improve worst-case latency. I thought there
> > was some talk about improving the intelligence of writeback in this
> > regard, but it's a tough problem, especially given that writeback isn't
> > the only cook in the kitchen.
>
> ... and it gets worse if there is any kind of I/O prioritization going
> on via ionice(), or (as was the case in our example) I/O cgroups were
> being used to provide proportional I/O rate controls. I don't think
> it's realistic to assume the writeback code can predict how long I/O
> will take when it does a submission.
cgroups do make it much harder because it could be a simple IO priority
inversion. The latencies are just going to be a fact of life for now
and the best choice is to skip the stable pages.
-chris
next prev parent reply other threads:[~2012-03-08 21:21 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-07 23:40 [PATCH, RFC] Don't do page stablization if !CONFIG_BLKDEV_INTEGRITY Theodore Ts'o
2012-03-07 23:54 ` Eric Sandeen
2012-03-08 0:05 ` Darrick J. Wong
2012-03-08 2:18 ` Darrick J. Wong
2012-03-08 3:00 ` Boaz Harrosh
2012-03-08 3:21 ` Boaz Harrosh
2012-03-08 2:39 ` Zach Brown
2012-03-08 15:54 ` Ted Ts'o
2012-03-08 18:09 ` Chris Mason
2012-03-08 20:20 ` Boaz Harrosh
2012-03-08 20:37 ` Chris Mason
2012-03-08 20:42 ` Jeff Moyer
2012-03-08 20:55 ` Chris Mason
2012-03-08 21:12 ` Ted Ts'o
2012-03-08 21:20 ` Chris Mason [this message]
2012-03-09 8:11 ` Dave Chinner
2012-03-08 20:50 ` Boaz Harrosh
2012-03-08 23:32 ` Dave Chinner
2012-03-08 21:24 ` Ted Ts'o
2012-03-08 21:38 ` Chris Mason
2012-03-08 21:41 ` Ted Ts'o
2012-03-09 1:02 ` Chris Mason
2012-03-09 1:08 ` Martin K. Petersen
2012-03-09 16:20 ` Ted Ts'o
2012-03-08 21:52 ` Boaz Harrosh
2012-03-08 0:23 ` Boaz Harrosh
2012-03-08 3:45 ` Martin K. Petersen
2012-03-08 4:37 ` Boaz Harrosh
2012-03-08 6:27 ` Sage Weil
2012-03-08 15:43 ` Ted Ts'o
2012-03-08 16:36 ` Martin K. Petersen
2012-03-08 16:43 ` Sage Weil
2012-03-15 2:10 ` Andy Lutomirski
2012-03-15 4:46 ` Boaz Harrosh
2012-03-15 5:02 ` Andy Lutomirski
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