blk-mq: get rid of ->cmd_size in the hardware queue

We store it in the tag set, we don't need it in the hardware queue.
While removing cmd_size, place ->queue_num further down to avoid
a hole on 64-bit archs. It's not used in any fast paths, so we
can safely move it.
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -1615,7 +1615,6 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	hctx->queue = q;
 	hctx->queue_num = hctx_idx;
 	hctx->flags = set->flags;
-	hctx->cmd_size = set->cmd_size;
 
 	blk_mq_init_cpu_notifier(&hctx->cpu_notifier,
 					blk_mq_hctx_notify, hctx);

include/linux/blk-mq.h

@@ -34,7 +34,6 @@ struct blk_mq_hw_ctx {
 	unsigned long		flags;		/* BLK_MQ_F_* flags */
 
 	struct request_queue	*queue;
-	unsigned int		queue_num;
 	struct blk_flush_queue	*fq;
 
 	void			*driver_data;
@@ -54,7 +53,7 @@ struct blk_mq_hw_ctx {
 	unsigned long		dispatched[BLK_MQ_MAX_DISPATCH_ORDER];
 
 	unsigned int		numa_node;
-	unsigned int		cmd_size;	/* per-request extra data */
+	unsigned int		queue_num;
 
 	atomic_t		nr_active;