sub get_memory_used
{
  my $result;
  open STAT, "</proc/$$/status" or die "can't open ...: $!";
  while (<STAT>)
  {
    /^VmSize.*?(\d+) kB/ or next;
    $result = $1;
    last;
  }
  close STAT;
  defined($result) or die "can't find memory used";
  return $result * 1024;
}