If you don't need exact size (that is, you only want to track the memory perl uses, and not the memory used by XS modules loaded, or libraries those modules use, and don't mind a little slop on top of that) you can use Devel::Size, hand it your top-level namespace pointer, and let it rip. It will use a pretty massive amount of memory itself as it runs, so don't be too surprised.
in reply to Tracking memory of a running application
use Devel::Size qw(total_size);
print total_size(*::), "\n";