From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: xfs@oss.sgi.com, Florian Weimer <fweimer@bfk.de>
Subject: Re: XFS on 2.6.26: reading the first 4K of a large file takes ages
Date: Thu, 20 May 2010 09:27:31 +1000 [thread overview]
Message-ID: <20100519232731.GR8120@dastard> (raw)
In-Reply-To: <20100519114826.GA18224@infradead.org>
On Wed, May 19, 2010 at 07:48:26AM -0400, Christoph Hellwig wrote:
> On Wed, May 19, 2010 at 11:33:27AM +0000, Florian Weimer wrote:
> > We've got a couple of rather large files, and with a cold cache,
> > reading the first 4K bytes of the file (e.g., just running
> > "head --bytes 4096" on it) takes ages, up to several minutes,
> > sometimes triggering the hang check timer.
> >
> > I wonder if XFS reads the whole extent information into RAM when the
> > file is opened. Is this the case, at least on 2.6.26? Has this
> > changed in later versions, perhaps?
>
> Yes, XFS always reads in the extent map, and no this hasn't changed
> recently.
And demand paging the in-memory information is hard. It's on a to-do
list somewhere 'round here....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2010-05-19 23:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-19 11:33 XFS on 2.6.26: reading the first 4K of a large file takes ages Florian Weimer
2010-05-19 11:48 ` Christoph Hellwig
2010-05-19 23:27 ` Dave Chinner [this message]
2010-05-20 12:11 ` Florian Weimer
2010-05-21 6:20 ` Stewart Smith
2010-05-21 6:43 ` Florian Weimer
2010-05-21 8:26 ` Dave Chinner
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