# Belegung "anwärmen"
my $gtop = GTop->new;
my $x    = XML::LibXML->new; $x->parse_string('<root/>');
my @attr = qw(size vsize resident share rss rss_rlim);
say join "\t", map {substr $_, 0, 7} @attr;
my (%before, %after);

# kleinstmögliche Gültigkeitsbereiche, aber Berechnung im selben Bereich,
# ansonsten +4 KiB unnützer Stack
{
    $before{$_} = $gtop->proc_mem($$)->$_ for @attr;
    my $p1 = $x->parse_string($s1);
    $after{$_}  = $gtop->proc_mem($$)->$_ for @attr;
    say join "\t", map {$after{$_} - $before{$_}} @attr;
}

{
    $before{$_} = $gtop->proc_mem($$)->$_ for @attr;
    my $p2 = $x->parse_string($s2);
    $after{$_}  = $gtop->proc_mem($$)->$_ for @attr;
    say join "\t", map {$after{$_} - $before{$_}} @attr;
}
__END__
size    vsize   residen share   rss     rss_rli
0       0       57344   53248   57344   0
0       0       0       0       0       0