On Fri, Mar 17, 2023 at 11:28:13PM +0100, Jan Kara wrote:
> > - rq_list_add(&plug->mq_list, rq);
> > + last_p = &plug->mq_list;
> > + while (*last_p)
> > + last_p = &(*last_p)->rq_next;
> > + rq_list_add_tail(&last_p, rq);
> > plug->rq_count++;
> > }
>
> Uh, I don't think we want to traverse the whole plug list each time we are
> adding a request to it. We have just recently managed to avoid that at
> least for single-device cases and apparently it was a win for fast devices
> (see commit d38a9c04c0d5 ("block: only check previous entry for plug merge
> attempt")).
REQ_OP_WRITE request for zoned devices are never added to the plug
list, so all of this actually is dead (and probably untested?) code.
See blk_mq_plug() and bdev_op_is_zoned_write().
