You don't mark pointers, you unmap a page of virtual memory. This instantly invalidates all pointers to that page without touching them, and allows you to immediately reuse that physical memory by mapping it to a new virtual address. When you eventually dereference a pointer to an unmapped page the processor's MMU throws a page fault. The VM catches the fault and fixes up the pointer on the spot.
What I'd like to know is how you can guarantee that all garbage is eventually collected in a system like this, and how you can guarantee that you've fixed up all pointers to an unmapped virtual page so you can reuse it.
What I'd like to know is how you can guarantee that all garbage is eventually collected in a system like this, and how you can guarantee that you've fixed up all pointers to an unmapped virtual page so you can reuse it.