linux-kernel - Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

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Message-ID: <20100823140823.GA23490@lst.de>
Date:	Mon, 23 Aug 2010 16:08:23 +0200
From:	Christoph Hellwig <hch@....de>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Ric Wheeler <rwheeler@...hat.com>, Christoph Hellwig <hch@....de>,
	Tejun Heo <tj@...nel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"James.Bottomley@...e.de" <James.Bottomley@...e.de>,
	"tytso@....edu" <tytso@....edu>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"swhiteho@...hat.com" <swhiteho@...hat.com>,
	"konishi.ryusuke@....ntt.co.jp" <konishi.ryusuke@....ntt.co.jp>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"vst@...b.net" <vst@...b.net>, "jack@...e.cz" <jack@...e.cz>,
	"hare@...e.de" <hare@...e.de>
Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

On Mon, Aug 23, 2010 at 04:01:15PM +0200, Jens Axboe wrote:
> The problem purely exists on arrays that report write back cache enabled
> AND don't implement SYNC_CACHE as a noop. Do any of them exist, or are
> they purely urban legend?

I haven't seen it.  I don't care particularly about this case, but once
it a while people want to disable flushing for testing or because they
really don't care.

What about adding a sysfs attribue to every request_queue that allows
disabling the cache flushing feature?  Compared to the barrier option
this controls the feature at the right level and makes it available
to everyone instead of beeing duplicated.  After a while we can then
simply ignore the barrier/nobarrier options.
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