block: don't call elevator callbacks for plug merges

[linux-flexiantxendom0-3.2.10.git] / block / blk-core.c

diff --git a/block/blk-core.c b/block/blk-core.c
index fa697bf..3a78b00 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1212,7 +1212,6 @@ static bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
        req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
 
        drive_stat_acct(req, 0);
-       elv_bio_merged(q, req, bio);
        return true;
 }
 
@@ -1243,7 +1242,6 @@ static bool bio_attempt_front_merge(struct request_queue *q,
        req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
 
        drive_stat_acct(req, 0);
-       elv_bio_merged(q, req, bio);
        return true;
 }
 
@@ -1257,13 +1255,12 @@ static bool bio_attempt_front_merge(struct request_queue *q,
  * on %current's plugged list.  Returns %true if merge was successful,
  * otherwise %false.
  *
- * This function is called without @q->queue_lock; however, elevator is
- * accessed iff there already are requests on the plugged list which in
- * turn guarantees validity of the elevator.
- *
- * Note that, on successful merge, elevator operation
- * elevator_bio_merged_fn() will be called without queue lock.  Elevator
- * must be ready for this.
+ * 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.
  */
 static bool attempt_plug_merge(struct request_queue *q, struct bio *bio,
                               unsigned int *request_count)
@@ -1282,7 +1279,7 @@ static bool attempt_plug_merge(struct request_queue *q, struct bio *bio,
 
                (*request_count)++;
 
-               if (rq->q != q || !elv_rq_merge_ok(rq, bio))
+               if (rq->q != q || !blk_rq_merge_ok(rq, bio))
                        continue;
 
                el_ret = blk_try_merge(rq, bio);
@@ -1347,12 +1344,14 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
        el_ret = elv_merge(q, &req, bio);
        if (el_ret == ELEVATOR_BACK_MERGE) {
                if (bio_attempt_back_merge(q, req, bio)) {
+                       elv_bio_merged(q, req, bio);
                        if (!attempt_back_merge(q, req))
                                elv_merged_request(q, req, el_ret);
                        goto out_unlock;
                }
        } else if (el_ret == ELEVATOR_FRONT_MERGE) {
                if (bio_attempt_front_merge(q, req, bio)) {
+                       elv_bio_merged(q, req, bio);
                        if (!attempt_front_merge(q, req))
                                elv_merged_request(q, req, el_ret);
                        goto out_unlock;