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

[Tejun Heo <tj kernel org>]

Hello,

On 08/23/2010 04:08 PM, Christoph Hellwig wrote:
> 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.

Yeah, that sounds reasonable.  blk_queue_flush() can be called anytime
without locking anyway, so it should be really easy to implement too.

Thanks.

-- 
tejun