I second space_monk's suggestion of using hashes keyed on the location_id. The following uses two hashes of arrays of hashes to handle multiple 'records' having the same location_id:

use strict;
use warnings;
use Benchmark qw(cmpthese);

my %subnets;
my %filers_info;

my @subnets = (
    {
        'id'          => '1',
        'location_id' => '30',
        'subnet'      => '255.255.255.0'
    },
    {
        'id'          => '2',
        'location_id' => '13',
        'subnet'      => '255.255.254.0'
    },
    {
        'id'          => '3',
        'location_id' => '19',
        'subnet'      => '255.255.0.0'
    },
);

my @filers_info = (
    {
        'id'          => '1',
        'location_id' => '19',
        'info'        => 'blah1',
    },
    {
        'id'          => '2',
        'location_id' => '30',
        'info'        => 'blah1',
    },
    {
        'id'          => '3',
        'location_id' => '30',
        'info'        => 'blah1',
    },
);

push @{ $subnets{ $_->{'location_id'} } },     $_ for @subnets;
push @{ $filers_info{ $_->{'location_id'} } }, $_ for @filers_info;

sub original {
    my @total_filers;
    foreach my $subnet (@subnets) {
        my @found_filers =
          grep { $_->{'location_id'} == $subnet->{'location_id'} } @fi
+lers_info;
        push @total_filers, @found_filers;
    }
}

sub hashed {
    my @total_filers;
    exists $subnets{$_} and push @total_filers, @{ $filers_info{$_} }
      for keys %filers_info;
}

cmpthese(
    -5,
    {
        original => sub { original() },
        hashed   => sub { hashed() },
    }
);
[download]

Dumper output of @total_filers from sub hashed { ...:

$VAR1 = [
          {
            'info' => 'blah1',
            'location_id' => '30',
            'id' => '2'
          },
          {
            'info' => 'blah1',
            'location_id' => '30',
            'id' => '3'
          },
          {
            'info' => 'blah1',
            'location_id' => '19',
            'id' => '1'
          }
        ];
[download]

Benchmark results:

             Rate original   hashed
original 282623/s       --     -64%
hashed   780346/s     176%       --
[download]

Hope this helps!