From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay1.corp.sgi.com [137.38.102.111]) by oss.sgi.com (Postfix) with ESMTP id 85F0A7F88 for ; Fri, 21 Mar 2014 18:18:05 -0500 (CDT) Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by relay1.corp.sgi.com (Postfix) with ESMTP id 79B9E8F804B for ; Fri, 21 Mar 2014 16:18:05 -0700 (PDT) Received: from ipmail06.adl6.internode.on.net (ipmail06.adl6.internode.on.net [150.101.137.145]) by cuda.sgi.com with ESMTP id vkXgEtHCV2myrVCM for ; Fri, 21 Mar 2014 16:18:03 -0700 (PDT) Date: Sat, 22 Mar 2014 10:18:01 +1100 From: Dave Chinner Subject: Re: [FAQ] XFS speculative preallocation Message-ID: <20140321231801.GE1389@dastard> References: <20140321162920.GA3087@laptop.bfoster> <87eh1vuxam.fsf@mid.deneb.enyo.de> <20140321231032.GC1389@dastard> <532CC79A.8050908@sandeen.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <532CC79A.8050908@sandeen.net> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: Brian Foster , Florian Weimer , xfs@oss.sgi.com On Fri, Mar 21, 2014 at 06:13:30PM -0500, Eric Sandeen wrote: > On 3/21/14, 6:10 PM, Dave Chinner wrote: > > On Fri, Mar 21, 2014 at 09:11:29PM +0100, Florian Weimer wrote: > >> * Brian Foster: > >> > >>> Although speculative preallocation can lead to reports of excess space > >>> usage, the preallocated space is not permanent unless explicitly made so > >>> via fallocate or a similar interface. > >> > >> How does an explicit allocation with posix_fallocate interact with > >> speculative preallocation? Does it disable it? > > > > fallocate is permanent preallocation using unwritten extents. > > Speculative preallocation is an extension of delayed allocation that > > is done when extending the file and the EOF falls into a hole. If > > there is unwritten extents beyond EOF, speulative preallocation is > > not performed. > > > >> I see rather dramatic fragmentation of the systemd journal when it is > >> stored on XFS, and it calls posix_fallocate before writing data to the > >> file. > > > > There's your problem - systemd is preventing delayed allocation, and > > so it fragmenting the file itself with it's write pattern. > > Basically, that's a bug in systemd, and not something the filesystem > > can avoid because userspace is directly controlling block > > allocation. > > hohum, I guess we should look into this. > > OTOH: nothing wrong with calling posix_fallocate() if you need the space > guarantees it provides for proper operation... Right, but it's something that the filesystem has no real control over. We've been asked to allocate blocks immediately by fallocate(), and so we get what we get.... Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs