> If it's easy to set up, it might be interesting to see if there's a difference if (e.g.) all interned strings are marked as immortal, or all small ints. Or type objects. Maybe set a flag during initialization and treat everything created before that as immortal.

I can look into it, the main problem is that every run of the pyperformance test suite takes several hours, even more with --full-pgo :(  I will try to set up some automation for that when I have some free cycles