Btrfs: Limit btree writeback to prevent seeks

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index 24ddc8c..13c562f 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -113,6 +113,9 @@
 int __init extent_map_init(void);
 void __exit extent_map_exit(void);
 
+u64 count_range_bits(struct extent_map_tree *tree,
+		     u64 *start, u64 max_bytes, unsigned long bits);
+
 int test_range_bit(struct extent_map_tree *tree, u64 start, u64 end,
 		   int bits, int filled);
 int clear_extent_bits(struct extent_map_tree *tree, u64 start, u64 end,