linux-kernel - Re: [PATCH 2/5] dm: implement REQ_FLUSH/FUA support for bio-based dm

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Message-ID: <4C7E5B79.3080709@kernel.org>
Date:	Wed, 01 Sep 2010 15:56:09 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
CC:	jaxboe@...ionio.com, k-ueda@...jp.nec.com, j-nomura@...jp.nec.com,
	jamie@...reable.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
	hch@....de, dm-devel@...hat.com
Subject: Re: [PATCH 2/5] dm: implement REQ_FLUSH/FUA support for bio-based
 dm

On 09/01/2010 03:54 PM, Mike Snitzer wrote:
>> It just doesn't happen anymore.  If the underlying device doesn't
>> support FLUSH/FUA, the block layer simply make those parts noop.  IOW,
>> it no longer distinguishes between writeback cache which doesn't
>> support cache flush at all and writethrough cache.  Devices which have
>> WB cache w/o flush very difficult to come by these days and there's
>> nothing much we can do anyway, so it doesn't make sense to require
>> everyone to implement -EOPNOTSUPP.
>>
>> One scheduled feature is to implement falling back to REQ_FLUSH when
>> the device advertises REQ_FUA but fails to process it, but one way or
>> the other, the goal is encapsulating REQ_FLUSH/FUA support in block
>> layer proper.  If FLUSH/FUA can be retried using a different strategy,
>> it should be done inside request_queue proper instead of pushing retry
>> logic to all its users.
> 
> OK, so maybe add this info to the patch header one of the primary
> FLUSH+FUA conversion patches?

Sure.

Thanks.

-- 
tejun
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