[tsimionescu]

> under memory pressure those pages are simply dropped, not swapped out

This is just semantics. The pages are evicted from memory, knowing that they are backed by the disk, and can be swapped back in from disk when needed - behavior that I called "swapping out" since it's pretty similar to what happens with other memory pages in the presence of swap.

Regardless of the naming, the important part is what happens when the page is needed again. If your code page was evicted, when your thread gets scheduled again, it will ask for the page to be read back into memory, requiring a disk read; this will cause some other code page to be evicted; then a new thread will be scheduled - worse case, one that uses the exact code page that just got evicted, repeating the process. And since the scheduler will generally try to execute the thread that has been waiting the most, while the VMM will prefer to evict the oldest read pages, there is actually a decent chance that this exact worse case will happen a lot. This whole thing will completely freeze the system to a degree that is extremely unlikely for a system with a decent amount of swap space.