Check perldoc perlvar for $^M

Yes, and? $^M only has a use after running out of memory, a situation that the OP wants to avoid. Furthermore, use of $^M only means you will run out of memory quicker, and Perl will just allocate a chunk of memory when $^M is assigned to.

ask your sysadmin to configure more swap

This was already dismissed by the OP, saying 2 Gb is enough.

Abigail