From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vladislav Bolkhovitin <vst@vlnb.net>
Subject: Re: [RFC] relaxed barrier semantics
Date: Fri, 30 Jul 2010 17:25:52 +0400
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Cc: Ted Ts'o <tytso@mit.edu>, Andreas Dilger <adilger@dilger.ca>,
	Ric Wheeler <rwheeler@redhat.com>, Tejun Heo <tj@kernel.org>,
	Vivek Goyal <vgoyal@redhat.com>, Jan Kara <jack@suse.cz>,
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	chris.mason@oracle.com, swhiteho@redhat.com,
	konishi.ryusuke@lab.ntt.co.jp
To: Christoph Hellwig <hch@lst.de>
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Christoph Hellwig, on 07/30/2010 05:09 PM wrote:
> 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.

Sure. It was only a naive example to illustrate my points. But the FS is 
still waiting for the requests, so "draining" its "local queue"?

Vlad