Great review, thanks you very much.  I'll apply all your suggestions.  Need to
discuss this one though:

> * In `disk-usage--list-recursively', you make a loop over
>
>              for attributes = (file-attributes name)
>
>   This is slow, at least on remote systems, because you apply
>   `file-attributes' on every file on a possibly large list. Maybe you
>   could call `directory-files-and-attributes' per directory, instead.

Hmmm, not sure about this, because walking a directory recursively with
directory-files-and-attributes is extremely slow, which is why I resorted to
using the `find' shell command instead.

Alternatively, I could mix-match both approaches:  run `find' to list all
directories recursively, then run `directory-files-and-attributes` on this result.

Does anyone have experience with that kind of performance issues?

The upside is that it would remove the need for custom `find' arguments since
the following is portable:

--8<---------------cut here---------------start------------->8---
  find DIR -type d
--8<---------------cut here---------------end--------------->8---

-- 
Pierre Neidhardt
https://ambrevar.xyz/