Hm. Vague memories from when I created a better version of Devel::Size.

If you print the keys of the default stash %{main::} and filter it for those that keys that end in '::', it gives you a list of all the stashes (codespaces) in your program at that point:

[0]{} Perl> print for grep /::$/,
version::
Tie::
Devel::
Cwd::
Regexp::
UNIVERSAL::
overload::
File::
feature::
ActivePerl::
Config::
warnings::
Time::
EPOC::
Win32CORE::
attributes::
vars::
subs::
XSLoader::
main::
AutoLoader::
Carp::
Win32::
Used::
threads::
MIME::
ActiveState::
utf8::
constant::
re::
mro::
DynaLoader::
strict::
Term::
Sub::
used::
Dos::
Data::
List::
IO::
Exporter::
Internals::
DB::
CORE::
Scalar::
VMS::
PerlIO::
Benchmark::
c::
[download]

If you use Devel::Size total_size() against each of those stashes, it gives you a number that (more or less) represents the size of those stashes:

[0]{} Perl> print "$_: ", total_size( \%{$_} ) for grep /::$/, keys %{
+main::};;
version:::  8400
Tie:::  4339
Devel:::  25803
Cwd:::  118168
Regexp:::  1599
UNIVERSAL:::  1967
overload:::  54595
File:::  80032
feature:::  20416
ActivePerl:::  139164
Config:::  84324
warnings:::  84493
Time:::  39560
EPOC:::  481
Win32CORE:::  657
attributes:::  658
vars:::  14306
subs:::  4786
XSLoader:::  26283
main:::  1194552
AutoLoader:::  38435
Carp:::  39827
Win32:::  9600
Used:::  1872
threads:::  52381
MIME:::  914
ActiveState:::  74236
utf8:::  3147
constant:::  28102
re:::  40244
mro:::  3242
DynaLoader:::  59460
strict:::  8389
Term:::  685
Sub:::  1784
used:::  490
Dos:::  480
Data:::  163029
List:::  20470
IO:::  685
Exporter:::  119426
Internals:::  2469
DB:::  541
CORE:::  672
Scalar:::  38034
VMS:::  1579
PerlIO:::  1833
Benchmark:::  197989
c:::  203
[download]

You can take that one stage further, and iterate the keys of those stashes and you get a list of subs (and other assorted entities) which you can run total_size() against.

(The output shown is a partial list of the stuff loaded into my REPL environment; the full thing runs to well over 1000 lines):

for my $stash ( grep /::$/, keys %{main::} ) { 
    print "$stash ", total_size \%{$stash}; 
    for my $func ( keys %{$stash} ){ 
        print "${stash}${func}:", total_size( $func ); 
    } 
};;


version::  8400
version::normal: 80
version::vcmp: 78
version::parse: 79
version::boolean: 81
version::stringify: 83
version::AUTOLOAD: 82
version::qv: 76
version::("": 77
version::(<=>: 78
version::new: 77
version::(cmp: 78
version::(0+: 77
version::DESTROY: 81
version::noop: 78
version::(): 76
version::declare: 81
version::(nomethod: 83
version::(bool: 79
version::is_qv: 79
version::numify: 80
version::is_alpha: 82
Tie::  4339
Tie::Hash::: 80
Devel::  25803
Devel::Size::: 80
Cwd::  118168
Cwd::__ANON__: 82
Cwd::sys_abspath: 85
Cwd::_epoc_cwd: 83
Cwd::sys_cwd: 81
Cwd::_perl_abs_path: 88
Cwd::cwd: 77
Cwd::_dos_cwd: 82
Cwd::_vms_abs_path: 87
Cwd::_backtick_pwd: 87
Cwd::_carp: 79
Cwd::chdir_init: 84
Cwd::getcwd: 80
Cwd::_win32_cwd: 84
Cwd::fastcwd_: 82
Cwd::EXPORT_OK: 83
Cwd::_NT_cwd: 81
Cwd::_os2_cwd: 82
Cwd::ISA: 77
Cwd::fastcwd: 81
Cwd::_croak: 80
Cwd::REALPATH: 82
Cwd::DIR: 77
Cwd::fast_abs_path: 87
Cwd::_qnx_cwd: 82
Cwd::bootstrap: 83
Cwd::fastgetcwd: 84
Cwd::BEGIN: 79
Cwd::PARENT: 80
Cwd::fast_realpath: 87
Cwd::_vms_cwd: 82
Cwd::_perl_getcwd: 86
Cwd::realpath: 82
Cwd::EXPORT: 80
Cwd::getdcwd: 81
Cwd::chdir: 79
Cwd::VERSION: 81
Cwd::_qnx_abs_path: 87
Cwd::abs_path: 82
Regexp::  1599
Regexp::DESTROY: 81
UNIVERSAL::  1967
UNIVERSAL::isa: 77
UNIVERSAL::VERSION: 81
UNIVERSAL::can: 77
UNIVERSAL::DOES: 78
overload::  54595
overload::ops: 77
overload::mycan: 79
overload::unimport: 82
overload::BEGIN: 79
overload::remove_constant: 89
overload::OVERLOAD: 82
overload::nil: 77
overload::Method: 80
overload::AddrRef: 81
overload::Overloaded: 84
overload::StrVal: 80
overload::constant: 82
overload::OverloadedStringify: 93
overload::package: 81
overload::import: 80
overload::ov_method: 83
overload::constants: 83
overload::VERSION: 81
File::  80032
File::Spec::: 80
File::Basename::: 84
feature::  20416
feature::unknown_feature_bundle: 96
feature::unimport: 82
feature::VERSION: 81
feature::croak: 79
feature::import: 80
feature::unknown_feature: 89
ActivePerl::  139164
ActivePerl::BUILD: 79
ActivePerl::PRODUCT: 81
ActivePerl::CHANGELIST: 84
ActivePerl::_CONFIG_HEAVY: 87
ActivePerl::Config::: 82
ActivePerl::VERSION: 81
Config::  84324
Config::TIEHASH: 81
Config::config_vars: 85
Config::CLEAR: 79
Config::launcher: 82
Config::Config: 80
Config::NEXTKEY: 81
Config::fetch_string: 86
Config::summary: 81
Config::AUTOLOAD: 82
Config::byteorder: 83
Config::config_sh: 83
Config::BEGIN: 79
Config::EXISTS: 80
Config::myconfig: 82

...

used::  490
used::VERSION: 81
Dos::  480
Dos::GetCwd: 80
Data::  163029
Data::Dump::: 80
List::  20470
List::Util::: 80
IO::  685
IO::Handle::: 82
Exporter::  119426
Exporter::export_fail: 85
Exporter::__ANON__: 82
Exporter::export_tags: 85
Exporter::Cache: 79
Exporter::Heavy::: 81
Exporter::Verbose: 81
Exporter::export_ok_tags: 88
Exporter::Debug: 79
Exporter::export: 80
Exporter::ExportLevel: 85
Exporter::EXPORT: 80
Exporter::import: 80
Exporter::EXPORT_FAIL: 85
Exporter::as_heavy: 82
Exporter::require_version: 89
Exporter::FailCache: 83
Exporter::VERSION: 81
Exporter::export_to_level: 89
Internals::  2469
Internals::SvREFCNT: 82
Internals::hv_clear_placeholders: 95
Internals::hash_seed: 83
Internals::SvREADONLY: 84
Internals::HvREHASH: 82
Internals::rehash_seed: 85
DB::  541
DB::args: 78
CORE::  672
CORE::GLOBAL::: 82
Scalar::  38034
Scalar::Util::: 80
VMS::  1579
VMS::Filespec::: 84
PerlIO::  1833
PerlIO::get_layers: 84
PerlIO::Layer::: 81
Benchmark::  197989
Benchmark::timesum: 81
Benchmark::__ANON__: 82
Benchmark::cpu_a: 79
Benchmark::a: 75
Benchmark::n_to_for: 82
Benchmark::_doeval: 81
Benchmark::iters: 79
Benchmark::_Usage: 80
Benchmark::Min_CPU: 81
Benchmark::init: 78
Benchmark::cmpthese: 82
Benchmark::debug: 79
Benchmark::export: 80
Benchmark::new: 77
Benchmark::timestr: 81
Benchmark::EXPORT_TAGS: 85
Benchmark::timethis: 82
Benchmark::countit: 81
Benchmark::EXPORT_OK: 83
Benchmark::confess: 81
Benchmark::EXPORT_FAIL: 85
Benchmark::timediff: 82
Benchmark::cpu_c: 79
Benchmark::b: 75
Benchmark::ISA: 77
Benchmark::export_to_level: 89
Benchmark::Default_Style: 87
Benchmark::timethese: 83
Benchmark::time: 78
Benchmark::Cache: 79
Benchmark::cpu_p: 79
Benchmark::Debug: 79
Benchmark::clearcache: 84
Benchmark::BEGIN: 79
Benchmark::Do_Cache: 82
Benchmark::runloop: 81
Benchmark::timedebug: 83
Benchmark::real: 78
Benchmark::usage: 79
Benchmark::clearallcache: 87
Benchmark::timeit: 80
Benchmark::EXPORT: 80
Benchmark::croak: 79
Benchmark::import: 80
Benchmark::disablecache: 86
Benchmark::enablecache: 85
Benchmark::Min_Count: 83
Benchmark::carp: 78
Benchmark::Default_Format: 88
Benchmark::VERSION: 81
Benchmark::timethis::: 84
Benchmark::mytime: 80
c::  203
[download]

I make no guess as to the absolute accuracy of the numbers, but they ought to reflect changes fairly well.

As all the best lazy authors say; turning that into a module is left as an exercise :)

Note: I eliminated a bunch "Devel::Size: Calculated sizes for compiled regexes are incompatible, and probably always will be" warnings, as I don't think they are produced by newer versions of DEvel::Size (though the situation they document hasn't change AFAIK.).