I don't know the specific characteristics of Kiji, but I know that it is not a real generational GC. A generational GC that doesn't break every C extension is i

I don't know the specific characteristics of Kiji, but I know that it is not a real generational GC. A generational GC that doesn't break every C extension is impossible because Ruby passes around direct pointers, so Ruby objects can't be moved in memory. That being said, I'm not a language or VM guy, so take what I say with a grain of salt.