Hmm, maybe I'm misunderstanding? When you make a (single) patently large allocation, macOS will do nothing; it won't show up as used virtual memory and the swap size won't go up. As you write to the memory usage will go up ("Memory" in Activity Monitor) but then it will quickly start swapping out until the limits of your disk, at which point you'll get OOM'd (assuming that your memory doesn't compress well, that is…).
