Btrfs: fix autodefrag with compression

The autodefrag code skips defrag when two extents are adjacent.  But one
big advantage for autodefrag is cutting down on the number of small
extents, even when they are adjacent.  This commit changes it to defrag
all small extents.

Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -1019,8 +1019,10 @@ static bool defrag_check_next_extent(struct inode *inode, struct extent_map *em)
 		return false;
 
 	next = defrag_lookup_extent(inode, em->start + em->len);
-	if (!next || next->block_start >= EXTENT_MAP_LAST_BYTE ||
-	    (em->block_start + em->block_len == next->block_start))
+	if (!next || next->block_start >= EXTENT_MAP_LAST_BYTE)
+		ret = false;
+	else if ((em->block_start + em->block_len == next->block_start) &&
+		 (em->block_len > 128 * 1024 && next->block_len > 128 * 1024))
 		ret = false;
 
 	free_extent_map(next);
@@ -1055,7 +1057,6 @@ static int should_defrag_range(struct inode *inode, u64 start, int thresh,
 	}
 
 	next_mergeable = defrag_check_next_extent(inode, em);
-
 	/*
 	 * we hit a real extent, if it is big or the next extent is not a
 	 * real extent, don't bother defragging it