> The OS should also allow marking pages as piority to stop them from being swapped out.

This is IIUC possible using the mlock(2) family of syscalls: https://man7.org/linux/man-pages/man2/mlock.2.html. (On Linux, though I'm guessing other UNIXen and operating systems have it or something equivalent.)

Cool. So this should be a bug ticket, not irrefutable proof that GCs suck :D