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Date: Tue, 23 Sep 2008 05:50:45 -0600
From: Andreas Dilger <adilger@sun.com>
Subject: Re: [PATCH, RFC] ext4: Use preallocation when reading from the	inode
 table
In-reply-to: <20080923101613.58768083@lxorguk.ukuu.org.uk>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Theodore Ts'o" <tytso@mit.edu>, linux-ext4@vger.kernel.org,
       linux-kernel@vger.kernel.org
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On Sep 23, 2008  10:16 +0100, Alan Cox wrote:
> On Mon, 22 Sep 2008 20:35:23 -0400
> "Theodore Ts'o" <tytso@mit.edu> wrote:
> > With modern hard drives, reading 64k takes roughly the same time as
> > reading a 4k block.  So request adjacent inode table blocks to reduce
> > the time it takes when iterating over directories (especially when doing
> > this in htree sort order) in a cold cache case.  With this patch, the
> > time it takes to run "git status" on a kernel tree after flushing the
> > caches via "echo 3 > /proc/sys/vm/drop_caches", is reduced by 21%.
> > 
> > Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> 
> Acked-by: Alan Cox <alan@redhat.com>
> 
> I'm actually suprised that 16 is the magic tuning number you've used and
> a bigger one isn't even more of a win

I was going to suggest making this at least a #defined constant instead
of hard coding the values there.  Making it a mount option and/or /proc
value would allow further testing.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.