On Linux, I use the data found in /proc/$$/status. I just insert a call to the following function right before the exit. As far as I know Perl does not release the memeory it uses, so this is the maximum size used by the process.

sub total_size
  { open( STATUS, "/proc/$$/status") or die "cannot find status info i
+n /proc/$$/status: $!";
    my( $size)= map { m{^VmData:\s+(\d+\s+[\w+])} } <STATUS>;
    close STATUS;
    return $size;
  }
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