Comment by rescbr

I know how mmap works. The JVM is/was terrible on freeing allocated memory though.

If the program is actively using that allocation, that's fine. My problem is with the runtime hoarding RAM when it should have been freed after GC back to the OS.

Then there's also the JVM not handling peaks well because it hit the max heap size, while you still could rely on the OS doing its job to shuffle stuff to swap temporarily. I still see JVM OOMs in my $dayjob's product while the OS has plenty of free physical memory. It is stupid.

I mean, we have malloc() and free(), they are in the stdlib for a reason :)

The JVM seems to follow a philosophy where it assumes it is the only process running besides PID 1, which is valid for some scenarios, but not for others.