Re: [PATCH] blk-mq: don't allocate driver tag beforehand for flush rq

[Ming Lei <ming.lei@redhat.com>]

On Wed, Sep 13, 2017 at 09:32:30PM +0800, Ming Lei wrote:
> The behind idea is simple:
> 
> 1) for none scheduler, driver tag has to be borrowed for flush
> rq, otherwise we may run out of tag, and IO hang is caused.
> get/put driver tag is actually a nop, so reorder tags isn't
> necessary at all.
> 
> 2) for real I/O scheduler, we needn't to allocate driver tag
> beforehand for flush rq, and it works just fine to follow the
> way for normal requests: allocate driver tag for each rq just
> before calling .queue_rq().
> 
> Then flush rq isn't treated specially wrt. get/put driver tag,
> codes get cleanup much, such as, reorder_tags_to_front() is
> removed, needn't to worry about request order in dispatch list
> any more.
> 
> One visible change to driver is that flush rq's tag may not be
> same with the data rq in flush sequence, that won't be a
> problem, since we always do that in legacy path.

Please ignore this patch, since looks there is one issue.

-- 
Ming