Yeah, Proc::ProcessTable is a big wasteful module, since it makes you load all process data to work with it. If you are on Linux, you can go directly to /proc and get your information. For example:

#!/usr/bin/perl
use warnings;
use strict;

my $pid = shift || $$;
print get_size($pid),"\n";

sub get_size{
    my $pid = shift;
    my @size = split "\n", `cat /proc/$pid/status`;
      (my $vmsize) = grep {/VmSize/} @size;
      my (undef,$size) = split '   ',$vmsize;
      return($size);
}
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