Re: [dm-devel] [PATCH, RFC 2/2] dm: support REQ_FLUSH directly

[Christoph Hellwig <hch lst de>]

On Wed, Aug 04, 2010 at 01:57:37PM +0900, Kiyoshi Ueda wrote:
> > -		if (unlikely(dm_rq_is_flush_request(rq))) {
> > +		if (rq->cmd_flags & REQ_FLUSH) {
> >  			BUG_ON(md->flush_request);
> >  			md->flush_request = rq;
> >  			blk_start_request(rq);
> 
> Current request-based device-mapper's flush code depends on
> the block-layer's barrier behavior which dispatches only one request
> at a time when flush is needed.
> In other words, current request-based device-mapper can't handle
> other requests while a flush request is in progress.
> 
> I'll take a look how I can fix the request-based device-mapper to
> cope with it.  I think it'll take time for carefull investigation.

Given that request based device mapper doesn't even look at the
block numbers from what I can see just removing any special casing
for REQ_FLUSH should probably do it.