Btrfs: allocator and tuning

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 086e7de..cdb7c23 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -255,6 +255,7 @@
 struct btrfs_block_group_cache {
 	struct btrfs_key key;
 	struct btrfs_block_group_item item;
+	struct radix_tree_root *radix;
 	u64 first_free;
 	u64 last_alloc;
 	u64 pinned;