From: Ric Wheeler Subject: Re: [PATCH, RFC] ext4: Use preallocation when reading from the inode table Date: Tue, 23 Sep 2008 08:18:54 -0400 Message-ID: <48D8DEAE.4080309@redhat.com> References: <20080923101613.58768083@lxorguk.ukuu.org.uk> <20080923115045.GI10950@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Alan Cox , "Theodore Ts'o" , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Andreas Dilger Return-path: Received: from mx2.redhat.com ([66.187.237.31]:47790 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751324AbYIWMTI (ORCPT ); Tue, 23 Sep 2008 08:19:08 -0400 In-Reply-To: <20080923115045.GI10950@webber.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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" 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" >>> >> Acked-by: Alan Cox >> >> 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