* chattr +c file
* chattr +c dir; touch dir/file
* mount w/ -o compress_extension=ext; touch file.ext
+ * mount w/ -o compress_extension=*; touch any_file
+
+- At this point, compression feature doesn't expose compressed space to user
+ directly in order to guarantee potential data updates later to the space.
+ Instead, the main goal is to reduce data writes to flash disk as much as
+ possible, resulting in extending disk life time as well as relaxing IO
+ congestion. Alternatively, we've added ioctl interface to reclaim compressed
+ space and show it to user after putting the immutable bit.
Compress metadata layout::