I think you're still working under the assumption that the GC is keeping up with the allocation rate, which if you have a small allocation in a hot loop will largely not be true. Typically GC'd languages rely on escape analysis to handle this and not the generational GC at all, but if that fails then you're SOL because the generational GC is unable to keep up and unable to keep things in the fast path.
No, they don't. Most GC'd languages rely on generational GC, because escape analysis on its own doesn't directly provide a lot of performance benefits once you have a generational GC.
> if that fails then you're SOL because the generational GC is unable to keep up and unable to keep things in the fast path.
No, you aren't. Cleaning up dead objects (for example, temporaries created in a hot loop) in a nursery is extremely fast. The entire nursery semispace is typically in L1.
The entire nursery semispace is typically in L1.
If you read a bunch of data before making an object, I could see you easily evicting your nursery from L1 into L2, but then you only have about 4x as much space.
GCs are expensive relative to not doing anything, but minor GCs are very fast.
> The problem with modern generation GC langauges is they tend to be designed assuming that allocation is always cheap/free and it just isn't. That's a fairytale. It's just not true.
I'm not making an argument about language design here. Obviously value types are a good thing.
> Reusing the same memory address range is critical to getting maximum performance, and modern generational GCs are miserably bad at that.
Not at all. The nursery is usually in cache, just as the stack is. Nurseries are usually implemented as two space copying collectors with small spaces, which are excellent for cache locality (arguably even better than stacks, because stacks can grow deep).