Optimization category 8 tweaks

- Document cost of the category in shorewall.conf(5)
- Omit DONT_DELETE chains from consideration right off the bat

Signed-off-by: Tom Eastep <teastep@shorewall.net>

Shorewall/Perl/Shorewall/Chains.pm

@@ -3857,7 +3857,10 @@ sub optimize_level8( $$$ ) {
     %renamed = ();
 
     while ( $progress ) {
-	my @chains   = ( sort { level8_compare($a, $b) } ( grep $_->{referenced} && ! $_->{builtin}, values %{$tableref} ) );
+	my @chains   = ( sort { level8_compare($a, $b) } ( grep $_->{referenced} &&
+							   @{$_->{rules}}        &&
+							   ! $_->{builtin},
+							   values %{$tableref} ) );
 	my @chains1  = @chains;
 	my $chains   = @chains;
 	my %rename;
@@ -3877,12 +3880,15 @@ sub optimize_level8( $$$ ) {
 	    # Shift the current $chainref off of @chains1
 	    #
 	    shift @chains1;
-	    #
+
-	    # Skip empty chains
-	    #
 	    for my $chainref1 ( @chains1 ) {
-		next unless @{$chainref1->{rules}};
+		#
+		# Skip chain if it can't be deleted
+		#
 		next if $chainref1->{optflags} & DONT_DELETE;
+		#
+		# Chains identical?
+		#
 		if ( $chainref->{digest} eq $chainref1->{digest} ) {
 		    progress_message "  Chain $chainref1->{name} combined with $chainref->{name}";
 		    $progress = 1;

Shorewall/manpages/shorewall.conf.xml

@@ -2147,6 +2147,14 @@ LOG:info:,bar                        net                    fw</programlisting>
               <para>Optimization category 8 - Added in Shorewall 4.4.9. When
               set, causes chains with identical rules to be collapsed into a
               single chain.</para>
+
+              <warning>
+                <para>While Optimization category 8 can significantly reduce
+                the size of the generated iptables ruleset, it can also take
+                significant system resources during compilation. If you find
+                that compilation takes an unreasonably long time, try
+                disabling this category by setting OPTIMIZE=23.</para>
+              </warning>
             </listitem>
 
             <listitem>
@@ -2219,7 +2227,8 @@ LOG:info:,bar                        net                    fw</programlisting>
 
           <para>In versions prior to 5.1.0, the default value is zero which
           disables all optimizations. Beginning with Shorewall 5.1.0, the
-          default value is All which enables all optimizations.</para>
+          default value is <emphasis role="bold">All</emphasis> which enables
+          all optimizations.</para>
         </listitem>
       </varlistentry>