I have described an alternate method using the Proc::Process module at Determining memory usage of a process... - This module gives access to the process table in a consistent fashion, hiding the vagarities of different /proc implementations.

With regard to the question at hand, the following code incorporating Proc::ProcessTable may be of use:

use strict;

print join("\n", &usage("jvm")), "\n";

#   this subroutine takes only one parameter, the process name
#   to return memory usage information on
#
#   Returns array of two values, raw process memory size and 
#   percentage memory utilisation, in this order.  Returns 
#   undefined if these values cannot be determined.

sub usage {
    use Proc::ProcessTable;
    my @usage;
    my $proc = Proc::ProcessTable->new;
    my %fields = map { $_ => 1 } $proc->fields;
    return undef unless exists $fields{'cmnd'};
    foreach (@{$proc->table}) {
        if ($_->cmnd =~ /$_[0]/) {
            my @proc;
            push (@proc, $_->size) if exists $fields{'size'};
            push (@proc, $_->pctmem) if exists $fields{'pctmem'};
            push @usage, \@proc;
        }
    }
    return @usage;
}
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