[dm-devel] [PATCH, RFC 2/2] dm: support REQ_FLUSH directly
Christoph Hellwig
hch at lst.de
Wed Aug 4 08:54:23 UTC 2010
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.
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