From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:44609 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbbFRCq2 (ORCPT ); Wed, 17 Jun 2015 22:46:28 -0400 Date: Thu, 18 Jun 2015 10:46:09 +0800 From: Liu Bo To: dsterba@suse.cz, linux-btrfs@vger.kernel.org, fdmanana@suse.com Subject: Re: [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION Message-ID: <20150618024607.GA8530@localhost.localdomain> Reply-To: bo.li.liu@oracle.com References: <1434527672-5762-1-git-send-email-bo.li.liu@oracle.com> <20150617153306.GY6761@twin.jikos.cz> <20150617155234.GB7773@localhost.localdomain> <20150617170118.GA6761@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20150617170118.GA6761@twin.jikos.cz> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Jun 17, 2015 at 07:01:18PM +0200, David Sterba wrote: > On Wed, Jun 17, 2015 at 11:52:36PM +0800, Liu Bo wrote: > > On Wed, Jun 17, 2015 at 05:33:06PM +0200, David Sterba wrote: > > > On Wed, Jun 17, 2015 at 03:54:31PM +0800, Liu Bo wrote: > > > > MS_I_VERSION is enabled by default for btrfs, this adds an alternative > > > > option to toggle it off. > > > > > > There's an existing generic iversion/noiversion mount option pair, no > > > need to extra add it to btrfs. > > > > I know, it doesn't work though. > > Sigh, I see, btrfs forces MS_I_VERSION flag, > 0c4d2d95d06e920e0c61707e62c7fffc9c57f63a. I read 'enabled by default' as > that there's a standard way to override the defaults. > > So the right way is not to do that but this will break everyhing that > relies on that behaviour at the moment. This means to add the exception > to the upper layers, either VFS or 'mount', which is not very likely to > happen. > > The generic options do not reach the filesystem specific callbacks, so > we can't check it. Ext4 also makes its own "i_version" option, so I think we can do the same thing until more filesystems require to do it in a generic way. The performance benefit with no_iversion is obvious for fsync related workloads since we would avoid some expensive log commits. Thanks, -liubo