Another thing big programs have is a huge ramp-up phase where they construct the main guts of their massive heap. Splay, for example, benefits from have an enor

Another thing big programs have is a huge ramp-up phase where they construct the main guts of their massive heap. Splay, for example, benefits from have an enormous nursery in the beginning because for the startup phase the generational hypothesis doesn't really hold; most objects survive. So the first copy or couple of copies are a waste. V8 had at one time a "high promotion mode" that would kick in for such programs at the start, using various heuristics. In high promotion mode, entire pages are simply promoted en masse to the old gen, and nursery size gets quickly enlarged.