a.pl

use strict;
use warnings;
use feature 'say';
use Memory::Stats;

sub multiplicador{ 
    my @ini = (100..999);
    my $fim = 999;
    my @memo;
    while ($fim != 100){
        foreach (@ini){
            my $m = $_ * $fim;
            push (@memo, $m);
        }
        $fim--;
    }

    scalar @memo;
}

my $stats = Memory::Stats->new;

$stats->start;
say multiplicador();
$stats->stop;
$stats->report;

output.txt

$ perl a.pl
809100
--- Memory Usage ---
start: 7151616
stop: 35123200 - delta: 27971584 - total: 27971584
--- Memory Usage ---