From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC] relaxed barrier semantics
Date: Fri, 30 Jul 2010 15:09:57 +0200
Message-ID: <20100730130957.GA26894@lst.de>
References: <20100728090025.GA9252@lst.de> <4C4FF592.9090800@kernel.org> <20100728092859.GA11096@lst.de> <20100729014431.GD4506@thunk.org> <4C51DA1F.2040701@redhat.com> <20100729194904.GA17098@lst.de> <4C51DCF1.3010507@redhat.com> <25F5E16E-968D-4FEF-8187-70453985B19B@dilger.ca> <20100729230406.GI4506@thunk.org> <4C52CBFF.6090406@vlnb.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <4C52CBFF.6090406@vlnb.net>
Sender: linux-fsdevel-owner@vger.kernel.org
To: Vladislav Bolkhovitin <vst@vlnb.net>
Cc: Ted Ts'o <tytso@mit.edu>, Andreas Dilger <adilger@dilger.ca>, Ric Wheeler <rwheeler@redhat.com>, Christoph Hellwig <hch@lst.de>, Tejun Heo <tj@kernel.org>, Vivek Goyal <vgoyal@redhat.com>, Jan Kara <jack@suse.cz>, jaxboe@fusionio.com, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp
List-Id: linux-scsi@vger.kernel.org

On Fri, Jul 30, 2010 at 04:56:31PM +0400, Vladislav Bolkhovitin wrote:
> For a simpler device (a disk without support for ORDERED queuing) the 
> same meta-data updates would be:
> 
> 1. 1st journal write command
> 
> 2. 2d  journal write command
> 
> 3. 3d  journal write command
> 
> 4. The queue draining.

Which is complete overkill.  We have state machines for everything we do
block I/O on (both data and the journal), which allows us to just wait
on the I/O requests we need inside the filesystem instead of draining
the queue, or enforce global ordering using ordered tags.