Btrfs: allow compressed extents to be merged during defragment

The rule originally comes from nocow writing, but snapshot-aware
defrag is a different case, the extent has been writen and we're
not going to change the extent but add a reference on the data.

So we're able to allow such compressed extents to be merged into
one bigger extent if they're pointing to the same data.
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/inode.c

@@ -2212,16 +2212,18 @@ static noinline bool record_extent_backrefs(struct btrfs_path *path,
 
 static int relink_is_mergable(struct extent_buffer *leaf,
 			      struct btrfs_file_extent_item *fi,
-			      u64 disk_bytenr)
+			      struct new_sa_defrag_extent *new)
 {
-	if (btrfs_file_extent_disk_bytenr(leaf, fi) != disk_bytenr)
+	if (btrfs_file_extent_disk_bytenr(leaf, fi) != new->bytenr)
 		return 0;
 
 	if (btrfs_file_extent_type(leaf, fi) != BTRFS_FILE_EXTENT_REG)
 		return 0;
 
-	if (btrfs_file_extent_compression(leaf, fi) ||
-	    btrfs_file_extent_encryption(leaf, fi) ||
+	if (btrfs_file_extent_compression(leaf, fi) != new->compress_type)
+		return 0;
+
+	if (btrfs_file_extent_encryption(leaf, fi) ||
 	    btrfs_file_extent_other_encoding(leaf, fi))
 		return 0;
 
@@ -2365,8 +2367,8 @@ static noinline int relink_extent_backref(struct btrfs_path *path,
 				    struct btrfs_file_extent_item);
 		extent_len = btrfs_file_extent_num_bytes(leaf, fi);
 
-		if (relink_is_mergable(leaf, fi, new->bytenr) &&
-		    extent_len + found_key.offset == start) {
+		if (extent_len + found_key.offset == start &&
+		    relink_is_mergable(leaf, fi, new)) {
 			btrfs_set_file_extent_num_bytes(leaf, fi,
 							extent_len + len);
 			btrfs_mark_buffer_dirty(leaf);