compsize takes a list of files (given as arguments) on a btrfs filesystem
and measures used compression types and effective compression ratio,
producing a report such as:

[~]$ compsize /usr/share
Processed 120101 files.
Type       Perc     Disk Usage   Uncompressed
Data        58%      1.1G         1.9G
none       100%      351M         351M
zlib        29%       41M         137M
lzo         51%      776M         1.4G