From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail03.adl6.internode.on.net ([150.101.137.143]:6573 "EHLO ipmail03.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752193AbdJPWcA (ORCPT ); Mon, 16 Oct 2017 18:32:00 -0400 Date: Tue, 17 Oct 2017 09:31:58 +1100 From: Dave Chinner Subject: Re: agcount for 2TB, 4TB and 8TB drives Message-ID: <20171016223158.GK15067@dastard> References: <20171009112306.GM3666@dastard> <89a7ae9a-9960-ae37-f6ca-0c1f2e33f65f@scylladb.com> <20171009220332.GP3666@dastard> <38bd7785-174d-fd09-fc1f-50a2d4e1dd69@scylladb.com> <20171010225524.GV3666@dastard> <86635b89-5016-5cd1-53a2-bf21b842ae04@scylladb.com> <20171014224224.GD15067@dastard> <20171015220018.GG3666@dastard> <10d04693-02ef-427f-95fe-cc7bcaf3ec6f@scylladb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <10d04693-02ef-427f-95fe-cc7bcaf3ec6f@scylladb.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Avi Kivity Cc: Eric Sandeen , "Darrick J. Wong" , Gandalf Corvotempesta , linux-xfs@vger.kernel.org On Mon, Oct 16, 2017 at 01:00:32PM +0300, Avi Kivity wrote: > On 10/16/2017 01:00 AM, Dave Chinner wrote: > >On Sun, Oct 15, 2017 at 12:36:03PM +0300, Avi Kivity wrote: > >>On 10/15/2017 01:42 AM, Dave Chinner wrote: > >>>On Fri, Oct 13, 2017 at 11:13:24AM +0300, Avi Kivity wrote: > >>Even better would be if XFS would detect the sequential write and > >>start allocating ahead of it. > >That's what delayed allocation does with buffered IO. We > >specifically do not do that with direct IO because it's direct IO > >and we only do exactly what the IO the user submits requires us to > >do. > > > >As it is, I'm not sure that it would gain us anything over extent > >size hints because they are effectively doing exactly the same thing > >(i.e. allocate ahead) on every write that hits a hole beyond > >EOF when extending the file.... > > If I understand correctly, you do get momentary serialization when > you cross a hint boundary, while with allocate ahead, you would not. Allocate ahead still requires a threshold to be crossed to trigger allocation. So it doesn't get rid of allocation, it just changes what IO triggers it. Cheers, Dave. -- Dave Chinner david@fromorbit.com