block: shrink rq_map_data a bit

We don't need full ints for several of these members. Change the
page_order and nr_entries to unsigned shorts, and the true/false from_user
and null_mapped to booleans.

This shrinks the struct from 32 to 24 bytes on 64-bit archs.
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-map.c

@@ -158,7 +158,7 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data,
 	bio_init(bio, NULL, bio->bi_inline_vecs, nr_pages, req_op(rq));
 
 	if (map_data) {
-		nr_pages = 1 << map_data->page_order;
+		nr_pages = 1U << map_data->page_order;
 		i = map_data->offset / PAGE_SIZE;
 	}
 	while (len) {

include/linux/blk-mq.h

@@ -963,11 +963,11 @@ blk_status_t blk_insert_cloned_request(struct request *rq);
 
 struct rq_map_data {
 	struct page **pages;
-	int page_order;
-	int nr_entries;
 	unsigned long offset;
-	int null_mapped;
-	int from_user;
+	unsigned short page_order;
+	unsigned short nr_entries;
+	bool null_mapped;
+	bool from_user;
 };
 
 int blk_rq_map_user(struct request_queue *, struct request *,