rbd: set blk_queue request sizes to object size

This improves performance since more requests can be merged.
Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>

drivers/block/rbd.c

@@ -629,6 +629,14 @@ static int rbd_get_num_segments(struct rbd_image_header *header,
 	return end_seg - start_seg + 1;
 }
 
+/*
+ * returns the size of an object in the image
+ */
+static u64 rbd_obj_bytes(struct rbd_image_header *header)
+{
+	return 1 << header->obj_order;
+}
+
 /*
  * bio helpers
  */
@@ -1765,6 +1773,13 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 	q = blk_init_queue(rbd_rq_fn, &rbd_dev->lock);
 	if (!q)
 		goto out_disk;
+
+	/* set io sizes to object size */
+	blk_queue_max_hw_sectors(q, rbd_obj_bytes(&rbd_dev->header) / 512ULL);
+	blk_queue_max_segment_size(q, rbd_obj_bytes(&rbd_dev->header));
+	blk_queue_io_min(q, rbd_obj_bytes(&rbd_dev->header));
+	blk_queue_io_opt(q, rbd_obj_bytes(&rbd_dev->header));
+
 	blk_queue_merge_bvec(q, rbd_merge_bvec);
 	disk->queue = q;