void blk_attempt_remerge (request_queue_t * q, struct request * rq);
For head-active devices, the queue can easily be unplugged so quickly that proper merging is not done on the front request. This may hurt performance greatly for some devices. The block layer cannot safely do merging on that first request for these queues, but the driver can call this function and make it happen any way. Only the driver knows when it is safe to do so.