I'm not sure I understand the problem, but why are you using prototypes and taking a reference to the parameters? I think the following is more obvious:

my $big_text = get_big_text();
process_text(\$big_text, \$other_big_text);

sub process_text {
  my ($big_text_ref, $other_big_text_ref) = @_;
  # do something
  print ${$big_text_ref}, ${$other_big_text_ref};
}
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