> One of the biggest issues with reference counting, from a performance perspective, is that it turns reads into writes: if you read a heap-object out of a data structure, you have to increment the object's reference count.

You have to do this if you want deterministic deallocation, because your holding a read-only reference to that object might be exactly what keeps it around for longer. So you need to track that.

(Deterministic deallocation also means having to recursively free unreachable objects. That's often described as an arbitrary "pause" behavior in RC systems, but it's actually inherent in the requirement for deterministic behavior. If you don't care about determinism for some class of objects, you can amortize that pause by sending them to a separate cleanup thread.)