I then jumped ship to OSRM, which did the same job in ~3GB of memory, AND several times faster, AND didn't return spurious routing results afterwards. (I was getting some routes with "hyperspace jumps" between points in the road network that weren't connected, and due to previous issues with memory I just decided to stop trying, so I didn't investigate the cause of those jumps.) So if you'll ever decide to do that again, just use OSRM. It "just works" (at least in my experience).