#!/usr/bin/perl
use strict;
...etc...
...initiate variables...
...HTML::Template setup...

my $AoH = &largesub($a, $b, $c, $d) if $run_large_sub;

$template -> param( todisplay => $AoH );
print $template->output();	
exit();

sub largesub {
	my ($e, $f, $g, $h) = @_;
	
	my $foo = &smallsub($e);	
	
	...process...
	return \@AoH;
}
	
sub smallsub {
...process...
}