From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:51278 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725783AbeLTHHn (ORCPT ); Thu, 20 Dec 2018 02:07:43 -0500 Date: Thu, 20 Dec 2018 08:07:41 +0100 From: Christoph Hellwig Subject: Re: [PATCH 11/11] xfs: introduce an always_cow mode Message-ID: <20181220070741.GA9803@lst.de> References: <20181203222503.30649-1-hch@lst.de> <20181203222503.30649-12-hch@lst.de> <20181218232437.GS27208@magnolia> <20181219224335.GB4205@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219224335.GB4205@dastard> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: "Darrick J. Wong" , Christoph Hellwig , linux-xfs@vger.kernel.org On Thu, Dec 20, 2018 at 09:43:35AM +1100, Dave Chinner wrote: > On Tue, Dec 18, 2018 at 03:24:37PM -0800, Darrick J. Wong wrote: > > On Mon, Dec 03, 2018 at 05:25:03PM -0500, Christoph Hellwig wrote: > > Granted, I'm still rather fuzzy on what exactly is supposed to happen > > with preallocating fallocate when all writes require an allocation to > > succeed? > > For always_cow mode, perhaps we could consider preallocating into > the COW fork rather than the data fork? That way when we go to write > the data, we've already got the space allocated regardless of > whether it is over a hole or existing data? For a speculative preallocation that is what we already do. But for persistent preallocation that doesn't help as the COW fork is not persistent.