A user-level program, whether written in Perl or any language, should not cause the operating system to leak memory after it exits. I'd speculate that something your program is doing is triggering a kernel bug, or, more likely, a kernel module bug.

Sound OS primitives (e.g. file handles) should automatically be cleaned up by the OS after the program exits (even if it crashes). Admittedly, there may be a few unsound OS primitives (e.g. the horrible old System V semaphores) that don't get automatically cleaned up on program exit.

Update: if you're able to run your program on a local disk (rather than NFS) that would be useful in that if it does not leak with local files only, that would suggest a fault with your NFS system software.