my $bytes_used = 0;

foreach my $key ( @{ $response->{keys} } ) {
  $bytes_used += $key->{size};
}

my $num_keys = commify($#{ $response->{keys} });
$bytes_used  = commify($bytes_used);
...

##</code><code>##

29,118            keys in bucket bla.
98,524,002,052    total bytes used in bucket bla.

##</code><code>##

 > dprofpp
Total Elapsed Time =   2111.4 Seconds
  User+System Time =  2029.76 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 48.6   987.9 987.94 469469   0.0021 0.0021  XML::LibXML::NodeList::new
 48.2   979.3 979.37 469402   0.0021 0.0021  XML::LibXML::Literal::new
 0.75   15.27 15.270 469402   0.0000 0.0000  XML::LibXML::XPathContext::_find
 0.50   10.25 29.390 469536   0.0000 0.0001  XML::LibXML::XPathContext::_guarde
                                             d_find_call
 0.42   8.430 992.83 469402   0.0000 0.0021  XML::LibXML::NodeList::to_literal
 0.35   7.130 1024.0 469402   0.0000 0.0022  XML::LibXML::XPathContext::find
 0.34   6.820 2026.5 469402   0.0000 0.0043  XML::LibXML::XPathContext::findval
                  10                         ue
 0.25   5.030  5.030 335335   0.0000 0.0000  XML::LibXML::Node::string_value
 0.24   4.840 2034.3     68   0.0712 29.916  Net::Amazon::S3::list_bucket
 0.14   2.820  2.820 469402   0.0000 0.0000  XML::LibXML::Literal::value
 0.07   1.420  1.420 469000   0.0000 0.0000  XML::LibXML::XPathContext::getCont
                                             extNode
 0.06   1.310  1.310 938000   0.0000 0.0000  XML::LibXML::XPathContext::setCont
                                             extNode
 0.05   0.930  0.930 402402   0.0000 0.0000  XML::LibXML::Node::DESTROY
 0.04   0.890  0.890 469536   0.0000 0.0000  XML::LibXML::XPathContext::_free_n
                                             ode_pool
 0.02   0.360  0.360     68   0.0053 0.0053  XML::LibXML::_parse_string

##</code><code>##

:2: parser error : xmlParseCharRef: invalid xmlChar value 8