From: Eric Sandeen Subject: Re: delalloc fragmenting files? Date: Thu, 01 Nov 2007 10:20:18 -0500 Message-ID: <4729EEB2.9090406@redhat.com> References: <47225B1E.2060708@redhat.com> <20071026221938.GV3042@webber.adilger.int> <4728ED3B.1060407@redhat.com> <47291F62.3000008@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andreas Dilger , ext4 development To: Alex Tomas Return-path: Received: from mx1.redhat.com ([66.187.233.31]:38286 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751159AbXKAPUX (ORCPT ); Thu, 1 Nov 2007 11:20:23 -0400 In-Reply-To: <47291F62.3000008@gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Alex Tomas wrote: > please, try the patch attached. Looks quite a bit better: http://people.redhat.com/esandeen/seekwatcher/ext4-alex.png http://people.redhat.com/esandeen/seekwatcher/ext4-alex-ext4-dd-write.png http://people.redhat.com/esandeen/seekwatcher/ext4-alex-ext4-xfs-dd-write.png It is much less fragmented, although still not exactly the nice linear allocation I'd expect from a single threaded large write on a fresh fs... -Eric > thanks, Alex > > Eric Sandeen wrote: >> One thing that seems to be happening is that thanks to delalloc, a nice >> big request is coming in (only 1036 blocks of the 4096, not quite sure >> why), but then it gets into ext4_mb_normalize_request(), which finds the >> most blocks it can "preallocate" is 256, and chops down the request to >> 256 blocks. Shouldn't this preallocation be over & above what was asked >> for, vs. reducing the request? >> >> Ok, so, we get allocations in 256-block chunks... Why they don't all >> come out contiguous, I don't know yet... >> >> -Eric >