From: Ric Wheeler Subject: Re: [PATCHSET] Refactor barrier=/nobarrier flags from fs to block layer Date: Wed, 26 Jan 2011 06:47:16 -0500 Message-ID: <4D4009C4.3080007@redhat.com> References: <20110126071200.GE32261@tux1.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Tejun Heo , Vivek Goyal , axboe@kernel.dk, tytso@mit.edu, shli@kernel.org, neilb@suse.de, adilger.kernel@dilger.ca, jack@suse.cz, snitzer@redhat.com, linux-kernel@vger.kernel.org, kmannth@us.ibm.com, cmm@us.ibm.com, linux-ext4@vger.kernel.org, hch@lst.de, josef@redhat.com To: djwong@us.ibm.com Return-path: In-Reply-To: <20110126071200.GE32261@tux1.beaverton.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 01/26/2011 02:12 AM, Darrick J. Wong wrote: > Hello, > > From what I can tell, most of the filesystems that know how to issue commands > to flush the write cache also have some mechanism for the user to override > whether or not the filesystem actually issues those flushes. Unfortunately, > the term "barrier" is obsolete having been changed into flushes in 2.6.36, and > many of the filesystems implement the mount options with slightly different > syntaxes (barrier=[0|1|none|flush], nobarrier, etc). Why remove the mount option? We have been using that term and educating users about how to use it for many, many years. I see no reason to remove mount options at all. Ric > This patchset adds to the block layer a sysfs knob that an administrator can > use to disable flushes, and removes the mount options from the filesystem code. > As a starting point, I'm removing the mount options and flush toggle from > jbd2/ext4. > > Anyway, I'm looking for some feedback about refactoring the barrier/flush > control knob into the block layer. It sounds like we want a knob that picks > the safest option (issue flushes when supported) unless the administrator > decides that it is appropriate to do otherwise. I suspect that there are good > arguments for not having a knob at all, and good arguments for a safe knob. > However, since I don't see the barrier options being removed en masse, I'm > assuming that we still want a knob somewhere. Do we need the ignore_fua knob > too? Is this the proper way to deprecate mount options out of filesystems? > > --D