[PATCH 3/9] blk-mq: don't predicate last flag in blk_mq_dispatch_rq_list

[Ming Lei <ming.lei@redhat.com>]

.commit_rqs() is supposed to handle partial dispatch when driver may not
see .last of flag passed to .queue_rq().

We have added .commit_rqs() in case of partial dispatch and all consumers
of bd->last have implemented .commit_rqs() callback, so it is perfect to
pass real .last flag of the request list to .queue_rq() instead of faking
it by trying to allocate driver tag for next request in the batching list.

Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Baolin Wang <baolin.wang7@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f064e7923ea5..f8c4b59022d7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1169,16 +1169,6 @@ static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
 static void blk_mq_handle_dev_resource(struct request *rq,
 				       struct list_head *list)
 {
-	struct request *next =
-		list_first_entry_or_null(list, struct request, queuelist);
-
-	/*
-	 * If an I/O scheduler has been configured and we got a driver tag for
-	 * the next request already, free it.
-	 */
-	if (next)
-		blk_mq_put_driver_tag(next);
-
 	list_add(&rq->queuelist, list);
 	__blk_mq_requeue_request(rq);
 }
@@ -1203,7 +1193,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 			     bool got_budget)
 {
 	struct request_queue *q = hctx->queue;
-	struct request *rq, *nxt;
+	struct request *rq;
 	bool no_tag = false;
 	int errors, queued;
 	blk_status_t ret = BLK_STS_OK;
@@ -1254,17 +1244,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		list_del_init(&rq->queuelist);
 
 		bd.rq = rq;
-
-		/*
-		 * Flag last if we have no more requests, or if we have more
-		 * but can't assign a driver tag to it.
-		 */
-		if (list_empty(list))
-			bd.last = true;
-		else {
-			nxt = list_first_entry(list, struct request, queuelist);
-			bd.last = !blk_mq_get_driver_tag(nxt);
-		}
+		bd.last = !!list_empty(list);
 
 		ret = q->mq_ops->queue_rq(hctx, &bd);
 		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
-- 
2.25.2