bug#17535: 24.3.91; Problems with profiling memory

[Stefan Monnier]

> If we don't count free as a negative allocation, can you envision a
> situation for which the memory profile, as we have it now, would be a
> useful tool?  Because I can't.

Beside a crutch for timer-less situations, this was also meant to help
debug high memory use by providing a profile of where memory allocation
tends to take place.

Counting freeing as 0 would make sense in this context.

Counting freeing as negative allocation is more tricky since it goes
towards trying to track "memory use" rather than "memory allocation",
but attributing memory use to particular code locations (or backtraces)
is often somewhere between hard and meaningless.

This said, "memory profiling" is a very hard subject, and I don't think
there's an approach that will always work better than another (or maybe
there is one, but it'd have to be tremendously more complex and costly
than the simplistic profiler we have), depending on the particulars of
the bug you're tracking.  So we should probably provide both options.


        Stefan