One possible way to return memory to the system is starting a new process, using exec or Win32::Process. This is only valid if your program will be sleeping for long periods of time (at least maybe 5 minutes or more). This way you can upon finishing running, start a new process from the same executable, with a clean memory usage which will not expand until you require the desired modules. Make sure you do use require and not use so they won't be loaded at compile time. This probably isn't what you are looking for, but I thought I'd mention it anyway.