Btrfs: Replace extent tree preallocation code with some bit radix magic.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 8b2714e..65a395e 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -39,6 +39,8 @@
 	unsigned long blocks_used;
 	struct btrfs_transaction *transaction;
 	struct btrfs_block_group_cache *block_group;
+	u64 alloc_exclude_start;
+	u64 alloc_exclude_nr;
 };