From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: [PATCHSET] Refactor barrier=/nobarrier flags from fs to block layer Date: Wed, 26 Jan 2011 06:49:24 -0500 Message-ID: <4D400A44.6030502@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: Received: from mx1.redhat.com ([209.132.183.28]:39161 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752858Ab1AZLuC (ORCPT ); Wed, 26 Jan 2011 06:50:02 -0500 In-Reply-To: <20110126071200.GE32261@tux1.beaverton.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 the term "barrier" is obsolete having been changed into flushes in 2.6.36, and 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). > > 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 Just to be clear, I strongly object to remove the mount options. "Barrier" and "poke a control knob in the block" layer are both equally mysterious and meaningless to real users, so I do not see this as a gain, Ric