use strict; use warnings; use feature 'say';

my $free_space = {
    node1 => { cores => 12, mem => 200 },
    node2 => { cores => 12, mem => 500 },
    node3 => { cores => 10, mem => 600 },
    node4 => { cores => 11, mem => 500 },
    node5 => { cores => 16, mem => 800 },
    node6 => { cores => 16, mem => 800 },
};

for ( sort my_sort keys %{ $free_space } ) {
    say "$free_space->{$_}->{'cores'} $free_space->{$_}->{'mem'} $_";
}

sub my_sort {
    $free_space->{$b}->{'cores'} <=> $free_space->{$a}->{'cores'} ||
    $free_space->{$b}->{'mem'} <=> $free_space->{$a}->{'mem'} ||
    $a cmp $b
}

##</code><code>##

$ perl 1205589.pl

16  800 node5
16  800 node6
12  500 node2
12  200 node1
11  500 node4
10  600 node3