block: remove struct request_queue queue_head

The dispatch list is not used any more, as the legacy block IO stack
has been removed.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -482,7 +482,6 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	if (!q)
 		return NULL;
 
-	INIT_LIST_HEAD(&q->queue_head);
 	q->last_merge = NULL;
 
 	q->id = ida_simple_get(&blk_queue_ida, 0, 0, gfp_mask);

include/linux/blkdev.h

@@ -391,10 +391,6 @@ static inline int blkdev_reset_zones_ioctl(struct block_device *bdev,
 #endif /* CONFIG_BLK_DEV_ZONED */
 
 struct request_queue {
-	/*
-	 * Together with queue_head for cacheline sharing
-	 */
-	struct list_head	queue_head;
 	struct request		*last_merge;
 	struct elevator_queue	*elevator;