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

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Message-ID: <20101206133924.GB9235@infradead.org>
Date:	Mon, 6 Dec 2010 08:39:24 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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

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.  

> 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
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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