use Devel::Size 'total_size';
my @foo;
print total_size(\@foo), "\n";    # prints 64
$foo[100_000_000] = 'x';
print total_size(\@foo), "\n";    # prints 800000114
$foo[200_000_000] = 'x';
print total_size(\@foo), "\n";    # prints 1760000156