Re: [dm-devel] [PATCH UPDATED 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm

[Tejun Heo <tj kernel org>]

Hello,

On 09/01/2010 12:31 PM, Mikulas Patocka wrote:
> My recommended approach to this (on non-request-based dm) is to simply let 
> the current barrier infrastructure be as it is --- you don't need to 
> change it now, you can simply map FUA write to barrier write and FLUSH to 
> zero-data barrier --- and it won't cause any data corruption. It will just 
> force unneeded I/O queue draining.
> 
> Once FLUSH+FUA interface is finalized and committed upstream, we can 
> remove that I/O queue draining from dm to improve performance.

Unfortunately, it doesn't work that way.  The current dm
implementation depends on block layer holding the queue while a
barrier sequence is in progress which the new implementation doesn't
do anymore (the whole point of this conversion BTW).

Thanks.

-- 
tejun