That is the crux of the issue. I think the interesting thing about this benchmark is the degree to which different GCs assume the weak generational hypothesis t

That is the crux of the issue. I think the interesting thing about this benchmark is the degree to which different GCs assume the weak generational hypothesis to be true. For example, the Haskell/GHC GC seems to very much assume it, with its STW copying collector for all generations. On the other hand you have languages like Ocaml and Go which still have a lot of pointer chasing to do in the old generation, but have optimisations (concurrent/incremental GC) which prevent the pauses getting too long in the case that the hypothesis is broken. It's interesting to hear about the Python results. Ref counting makes absolute sense in this case!