I think it's part bug and part having a GC with only two generations (old and young). When you have to choose between putting these tweener objects somewhere, you have to be more conservative and move them to the old generation. Once a third generation is added (Ruby 2.2?) this will be much smoother.
> For an app like Discourse 3-10% of request time is occupied looking up methods, due to cache inefficiency.
Hmmm, I thought Ruby 2.1 already had a per-class method cache, or maybe it was just a per-class method cache invalidation, but I don't know how you coud have one without the other. I'll have to reinvestigate this.
> That's amazing, and demonstrates that there's probably still quite a lot of low-hanging performance fruit that Ruby can look to exploit.
I'm not sure I share as much of a positive outlook. Short of adding JIT compilation, I think the gains from here on out will start to get smaller and smaller. The performance gains of RGenGC were very impressive, though.
> For an app like Discourse 3-10% of request time is occupied looking up methods, due to cache inefficiency.
Hmmm, I thought Ruby 2.1 already had a per-class method cache, or maybe it was just a per-class method cache invalidation, but I don't know how you coud have one without the other. I'll have to reinvestigate this.
> That's amazing, and demonstrates that there's probably still quite a lot of low-hanging performance fruit that Ruby can look to exploit.
I'm not sure I share as much of a positive outlook. Short of adding JIT compilation, I think the gains from here on out will start to get smaller and smaller. The performance gains of RGenGC were very impressive, though.