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); |
qrequest_queue new bio is being queued at
bionew bio being queued
request_countout parameter for number of traversed plugged requests
same_queue_rq
pointer to struct request that gets filled in when
another request associated with q is found on the plug list
(optional, may be NULL)
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.