linux-ext4 - Re: [PATCH] ext4: Set barrier=0 when block device does not advertise flush support

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Message-ID: <20101206180942.GL18195@tux1.beaverton.ibm.com>
Date:	Mon, 6 Dec 2010 10:09:42 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: Set barrier=0 when block device does not
	advertise flush support

On Mon, Dec 06, 2010 at 08:39:24AM -0500, Christoph Hellwig wrote:
> barrier=0 really means losemydata=1.  The plan I discussed with Jens was
> to allow to disable the flush and fua semantics in the block layer, so
> we'll have one new tunable for that, which is documented to causes these
> issues.  

Oh.  I wasn't aware that anyone was planning to put in a tuning knob for
flush/fua, red warning light or otherwise.  What is the name of the tunable,
and when will it appear?  Or has it already?

> > picks the safe option by default.  However, I'd prefer /proc/mounts not
> > misrepresent the status of flush support, to the best of ext4's knowledge.
> 
> That's bullshit.  The barrier option has traditionally meant that we

Well then, let's remove the barrier= mount flag altogether.  No need for strong
language over a minor issue. :)  When I see some patches I will push this
through my testing setup and report back what data I collect.

--D

> sent barrier requests, and now means thatwe send flush+fua requests.
> There's no reason for a warning and option mislabling just because you
> got the most efficient implementation of it.
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