Currently we do a OOL VMCall when arena is empty. This happens in raytrace 1 out of 62 times. We could add an ool path (not vm) to pull a new arena in GC's freelists. Than we can stay in jitcode, except in cases where there are no arenas available at all, and we need to GC or allocate a new chunk. Currently the time spend in the OOL VMCall is 3% of raytrace. The OOL path will probably be much faster and almost remove the total time.

This has the potential to be quite hard because of the background sweep thread, but would be a nice stopgap until we get Generational GC. And even with a fully-tuned GGC, this will still be useful for shapes and anything else we can't nursery allocate.