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Date:	Sat, 19 Jan 2008 20:10:20 -0800
From:	Daniel Phillips <phillips@...nq.net>
To:	"Abhishek Rai" <abhishekrai@...gle.com>
Cc:	"Theodore Tso" <tytso@....edu>,
	"Christoph Hellwig" <hch@...radead.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, rohitseth@...gle.com,
	linux-ext4@...r.kernel.org
Subject: Re: [CALL FOR TESTING] Make Ext3 fsck way faster [2.6.24-rc6 -mm patch]

On Thursday 17 January 2008 04:47, Abhishek Rai wrote:
> > if Abhishek wants to pursue it, would be to pull in all of the
> > indirect blocks when the file is opened, and create an in-memory
> > extent tree that would speed up access to the file.  It's rarely
> > worth doing this without metaclustering, since it doesn't help for
> > sequential I/O, only random I/O, but with metaclustering it would
> > also be a win for sequential I/O.  (This would also remove the
> > minor performance degradation for sequential I/O imposed by
> > metaclustering, and in fact improve it slightly for really big
> > files.)
>
> Also, since the in memory extent tree will now occupy much less
> space, we can keep them cached for a much longer time which will
> improve performance of random reads. The new metaclustering patch is
> more amenable to this trick since it reduces fragmentation thereby
> reducing the number of extents.

I can see value in preemptively loading indirect blocks into the buffer 
cache, but is building a second-order extent tree really worth the 
effort?  Probing the buffer cache is very fast.

Regards,

Daniel
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