There's several situations that need to be addressed in every VMM:

Cold pages - not being used

Warm/normal pages - average use pages

Hot pages - being used a lot

1. LRU/histogramming cold RO-code/RO-data pages to be paged out (dropped) or compressed when other pages are hotter and there's memory pressure.

2. Compressing or paging out to disk volatile RW-data when cold and other pages are hotter and there's memory pressure.

3. Pinning in memory (compressed and/or uncompressed) pages that are hot for performance reasons, unlocking them when they become less hot or others become hotter.

4. Having the ability (like on macOS) to signal applications that the system is under severe memory pressure (say "SIGMEM", "SIGLOWMEM" or "SIGOOM"), and to drop volatile data that can regenerated or is ephemeral.