btrfs: Pack struct btrfs_device

Pack the structure btrfs_device in volumes.h to eliminate holes detected
by pahole, thus reducing binary memory footprint.
Signed-off-by: NDulshani Gunawardhana <dulshani.gunawardhana89@gmail.com>
Reviewed-by: NZach Brown <zab@redhat.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
Signed-off-by: NChris Mason <chris.mason@fusionio.com>

fs/btrfs/volumes.h

@@ -43,9 +43,8 @@ struct btrfs_device {
 	/* WRITE_SYNC bios */
 	struct btrfs_pending_bios pending_sync_bios;
 
-	int running_pending;
 	u64 generation;
-
+	int running_pending;
 	int writeable;
 	int in_fs_metadata;
 	int missing;
@@ -53,11 +52,11 @@ struct btrfs_device {
 	int is_tgtdev_for_dev_replace;
 
 	spinlock_t io_lock;
+	/* the mode sent to blkdev_get */
+	fmode_t mode;
 
 	struct block_device *bdev;
 
-	/* the mode sent to blkdev_get */
-	fmode_t mode;
 
 	struct rcu_string *name;
 
@@ -78,16 +77,21 @@ struct btrfs_device {
 
 	/* optimal io width for this device */
 	u32 io_width;
+	/* type and info about this device */
+	u64 type;
 
 	/* minimal io size for this device */
 	u32 sector_size;
 
-	/* type and info about this device */
-	u64 type;
 
 	/* physical drive uuid (or lvm uuid) */
 	u8 uuid[BTRFS_UUID_SIZE];
 
+	/* for sending down flush barriers */
+	int nobarriers;
+	struct bio *flush_bio;
+	struct completion flush_wait;
+
 	/* per-device scrub information */
 	struct scrub_ctx *scrub_device;
 
@@ -103,10 +107,6 @@ struct btrfs_device {
 	struct radix_tree_root reada_zones;
 	struct radix_tree_root reada_extents;
 
-	/* for sending down flush barriers */
-	struct bio *flush_bio;
-	struct completion flush_wait;
-	int nobarriers;
 
 	/* disk I/O failure stats. For detailed description refer to
 	 * enum btrfs_dev_stat_values in ioctl.h */