I developed that tweak for Python 2.7 and I am running in production with Python 3.6. I tested with later Python versions, too.
Do you have some pointers about arenas always using mmap? I'd like to know how that trick can work if that was the case.
It doesn't work, that's their point. With modern python versions those env variables do next to nothing. It won't crash your python but it also won't help you.
My point is that it does work. I tested with Python 2.7 and Python 3.6+.