Re: [PATCH, RFC] ext4: Use preallocation when reading from the inode table

[Andreas Dilger <adilger@sun.com>]

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.