Ah, that makes things clearer - thanks.

> What I'd like to know is how you can guarantee that all garbage is eventually collected in a system like this.

Me too. If you can't guarantee that, it seems that when you unmap a page of virtual memory, you'd have to make sure never to use that page again. You'd also have to keep around your table of "mappings from old pointers to new pointers" forever, just in case you encounter a lingering bad pointer and need to correct it.