blk_attempt_plug_merge - try to merge with current's plugged list
bool blk_attempt_plug_merge(struct request_queue * q, struct bio * bio, unsigned int * request_count, struct request ** same_queue_rq);
Determine whether bio being queued on q can be merged with a request on current's plugged list. Returns true if merge was successful, otherwise false.
Plugging coalesces IOs from the same issuer for the same purpose without going through q->queue_lock. As such it's more of an issuing mechanism than scheduling, and the request, while may have elvpriv data, is not added on the elevator at this point. In addition, we don't have reliable access to the elevator outside queue lock. Only check basic merging parameters without querying the elevator.
Caller must ensure !blk_queue_nomerges(q) beforehand.
|January 2017||Kernel Hackers Manual 4.8.|