From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754223Ab2DRQPV (ORCPT ); Wed, 18 Apr 2012 12:15:21 -0400 Received: from li9-11.members.linode.com ([67.18.176.11]:36159 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752909Ab2DRQPU (ORCPT ); Wed, 18 Apr 2012 12:15:20 -0400 Date: Wed, 18 Apr 2012 12:07:17 -0400 From: "Ted Ts'o" To: Dave Chinner Cc: Eric Sandeen , Ric Wheeler , Zheng Liu , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Zheng Liu Subject: Re: [RFC][PATCH 0/3] add FALLOC_FL_NO_HIDE_STALE flag in fallocate Message-ID: <20120418160717.GE5916@thunk.org> Mail-Followup-To: Ted Ts'o , Dave Chinner , Eric Sandeen , Ric Wheeler , Zheng Liu , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Zheng Liu References: <1334681618-9452-1-git-send-email-wenqing.lz@taobao.com> <4F8DAF89.5070805@redhat.com> <20120417184306.GA5916@thunk.org> <4F8DBC20.5010401@redhat.com> <20120418030208.GO6734@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120418030208.GO6734@dastard> User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on test.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 18, 2012 at 01:02:08PM +1000, Dave Chinner wrote: > In actual fact, on my 12 disk RAID0 array, XFS is faster with > unwritten extents *enabled* than when hacked to turn them off. Can you explain why this is the case? It seems... counterintuitive. The only explanation I can think of is that your code paths when unwritten extents are disabled haven't been optimized, in which case the comparison between using and not using unwritten extents might not be valid. Is there anything going on other than _not_ mutating the extent tree (and all of the logical journaling that would go along with it)? Hacking to turn them off means it should be doing *less* work, so I would expect at worst it would be the same speed as using extent written extents. If it's faster to use unwritten extents, something very wierd must be going on.... - Ted