There are two problems, here:
- if the data is unavailable, better return nil than 0.
- we now have 2 ways to get the data, neither of which gives it all:
garbage-collect returns details data but misses the new vector-bytes
and bytes-free, whereas memory-free includes those 2 but only provides
the combined value.
The first problem is obviously a detail, but the second problem needs to
be fixed. The way I see it, it should be fixed by improving
garbage-collect's return value. The only problem with that is backward
compatibility, but AFAIK there are only 2 users of that data:
memory-usage and chart.el, which we can both fix easily.
I suggest we make garbage-collect return its data in a new format
that is more self-descriptive, like an alist where each entry takes the
form (CATEGORY SIZE USED FREE), where CATEGORY would be a symbol (like
`cons') and SIZE is the size of each element in bytes.
gc.patch