If I'm reading the article correctly, they do fix up all the pointers on the next gc run. For every scanned pointer just check first whether it points to a stale page (and update it), then do the liveness marking. btw, they're using 2mb pages to cut down on page faulting overhead. And they're talking about terabytes of allocations per second (because they're compacting the first gc generation with this scheme, too), so virtual memory deallocation needs to happen somewhat timely. Furthermore at least the linux kernel never deallocates page tables, so no longer used virtual memory is definitely not free.