Like I said, the system will be almost completely unresponsive due to disk access being several orders of magnitude lower than RAM and allocation thrashing… you won’t be able to do much, the mouse, keyboard and display will react extremely slowly. There may be situations where you’d prefer this to an OOM kill, for example if you’re running a test or experiment where you’d rather have it finish even if it takes a very long time rather than lose the data. But if you’re a regular desktop user or server admin you’ll probably just reboot.