Profile gProfiler's memory utilization

The gProfiler Python process memory can grow beyond a few 10s of mbs which is what I'd say it should take at standard times (at least, when not doing any merging). This might be because we have a memory leak, and might be because AFAIK Python is unable to release memory to the OS.

I'd like us to have tools to investigate that (e.g: gProfiler could report every cycle what it's heap utilization, so we can see if there's a leak; each cache can report its total size so we see if resizes need to happen; etc). Eventually, I want to keep memory usage low.