my %set;
my $how_many = 10_000_000;
for( my $i = 0; $i < $how_many; $i++ ) {
    $set{$i} = undef;
}

print 'mem usage: ', my_mem(), "\n";

sub my_mem {
    my ($proc_info)
        = grep { $_->[2] == $$ } map { [ split ] } `ps l | tail -n +2`;
    return $proc_info->[6];
}
__END__
mem usage: 1323312