you can use a glob for that, though usually it is a bad idea to do so:

sub check_limit (\*) {
  my $glob = shift;
  my $name = *{$glob};
  $name=~/^\*/%/;
  my $num = keys %{*$glob};  
  print "Hash: $name has $num keys\n";
}

our %foo = qw(q w e t y j f f);
check_limit(*foo);
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