From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: [PATCH] ext4: don't load the block bitmap for block groups which have no space Date: Mon, 13 Aug 2012 14:49:16 -0400 Message-ID: <20120813184916.GF32484@thunk.org> References: <20120809181059.A5BAA11FC69@bugzilla.kernel.org> <1344622885-14982-1-git-send-email-tytso@mit.edu> <50292500.1070807@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ext4 Developers List To: Eric Sandeen Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:44473 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304Ab2HMStU (ORCPT ); Mon, 13 Aug 2012 14:49:20 -0400 Content-Disposition: inline In-Reply-To: <50292500.1070807@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Aug 13, 2012 at 11:02:08AM -0500, Eric Sandeen wrote: > > Looks ok to me; I think this just further optimizes what was done > in > > 8a57d9d61a6e361c7bb159dda797672c1df1a691 > ext4: check for a good block group before loading buddy pages > > correct? Yes, that's right; it's a further optimization. I can think of an additional optimization where if we are reading the block bitmap for block group N, and the block bitmap for block group N+1 hasn't been read before (so we don't have buddy bitmap stats), and the block bitmap for bg N+1 is adjacent for bg N, we should read both at the same time. (And this could be generalized for N+2, N+3, etc.) I'm not entirely sure whether it's worth the effort, but I suspect for very full file systems, it might be very well be. This is a more general case of the problem where most people only benchmark mostly empty file systems, and my experience has been that above 70-80% utilization, our performance starts to fall off. And while disk space is cheap, it's not _that_ cheap, and there are always customers who insist on using file systems up to a utilization of 99%, and expect the same performance as when the file system was freshly formated. :-( - Ted