Why not use Proc::ProcessTable:

$ cat mem.pl
use 5.12.1;
use warnings;
use Data::Peek;
use Proc::ProcessTable;

my $s;
$s += $_->{size} for grep { $_->cmndline =~ /java/ } @{Proc::ProcessTa
+ble->new->table};
say $s;
$ perl mem.pl
27656867840
[download]