Messages in this thread | | | Date | Tue, 23 Sep 2008 08:18:54 -0400 | From | Ric Wheeler <> | Subject | Re: [PATCH, RFC] ext4: Use preallocation when reading from the inode table |
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Andreas Dilger wrote: > 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. > >
I think that Alan is probably right - the magic number for modern drives is probably closer to 256K. Having it be a /sys tunable (with a larger default) would be a nice way to verify this.
Ric
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