[bug#39734] [PATCH] scripts: Emit GC hint if free space is lower than absolute and relative threshold.

[Ludovic Courtès]

Hello!

Pierre Neidhardt <address@hidden> skribis:

> Ludovic Courtès <address@hidden> writes:
>
>> Hi!
>>
>> Pierre Neidhardt <address@hidden> skribis:
>>
>>> * guix/scripts.scm (%disk-space-warning-absolute): New variable.
>>> (warn-about-disk-space): Test against %disk-space-warning-absolute.
>>> Fix error in display-hint due to extraneous 'profile' argument.
>>
>> [...]
>>
>>> +(define %disk-space-warning-absolute
>>> +  ;; The decimal number of GiB of free disk space below which a warning is
>>> +  ;; emitted.
>>> +  (make-parameter (match (and=> (getenv "GUIX_DISK_SPACE_WARNING_ABSOLUTE")
>>> +                                string->number)
>>> +                    (#f        17.0)
>>> +                    (threshold threshold))))
>>
>> Perhaps we should arrange for ‘GUIX_DISK_SPACE_WARNING’ to handle both
>> cases?
>>
>> That is, we’d first try to convert it with ‘size->number’; if that
>> works, it’s an absolute measure, and if it returns #f, then pass the
>> string to ‘string->number’ and assume it’s a fraction.
>
> I thought of something similar too, but this needs discussion:
>
> - If we change the meaning of a value like "1", we are breaking backward 
> compatibility.

We can assume values <= 100 are a percentage.

> - GUIX_DISK_SPACE_WARNING is currently undocumented, so I guess it's OK
>   to break backward compatibility.  However, it'd be nice to document it :)

Yup.

> - Currently (size->number "1.MiB") "leaves" the Guile instance on error.  
> Which
>   I find quite weird, I'd expect it to return #f when it cannot parse
>   the input.

Fixed.

> - Currently (size->number "0.8") returns 1.  If we want to use your
>   suggestion, we would need to change the behaviour so that it returns
>   #f.

Hmm.

> - Alternatively, since we are breaking backward compatibility anyways,
>   we could parse a trailing percent sign "%" to decide whether the value
>   is relative or absolute.

Right.

> Anyways, the issue was originally about dealing with both small and big
> partitions, and for this we need both a default absolute threshold and a
> default relative threshold.  Does that make sense?

It does!

So how about this:

  We check for a trailing “%”, and if there’s one, assume it’s a percentage.

  Else, call ‘size->number’.  If we get an integer < 100, assume it’s a
  percentage, otherwise assume it’s an absolute size in bytes.

How does that sound?

Thanks!

Ludo’.