* Add information about NMBCLUSTERS/mbufs

* Add another item to the standard sypnosis

en_US.ISO8859-1/books/handbook/config/chapter.sgml

@@ -1,7 +1,7 @@
 <!--
      The FreeBSD Documentation Project
 
-     $FreeBSD: doc/en_US.ISO8859-1/books/handbook/config/chapter.sgml,v 1.21 2001/08/19 23:43:57 dd Exp $
+     $FreeBSD: doc/en_US.ISO8859-1/books/handbook/config/chapter.sgml,v 1.22 2001/08/22 05:37:48 murray Exp $
 -->
 
 <chapter id="config-tuning">
@@ -79,7 +79,13 @@
 	<para>Understand the basics of Unix and FreeBSD (<xref
 	    linkend="basics">).</para>
       </listitem>
-      </itemizedlist>
+      <listitem>
+	<para>Be familiar with keeping FreeBSD sources up to date
+	  (<xref linkend="cutting-edge">), and
+	  the basics of kernel configuration/compilation
+	  (<xref linkend="kernelconfig">).</para>
+      </listitem>
+    </itemizedlist>
   </sect1>
 
   <sect1 id="configtuning-initial">
@@ -922,9 +928,32 @@ kern.maxfiles: 2088 -> 5000</screen>
 	<para><varname>kern.maxfile</varname>'s default value is
 	  dictated by the <option>maxusers</option> option in your
 	  kernel configuration file.  <varname>kern.maxfiles</varname> grows
-	  proportionally to the value of <option>maxusers</option>.</para>
+	  proportionally to the value of <option>maxusers</option>.
+	  When compiling a custom kernel, it is a good idea to
+	  set this kernel configuration option according to
+	  the uses of your system.  From this number, the kernel
+	  is given most of its pre-defined limits.  Even though
+	  a production machine may not actually have 256 users
+	  connected as once, the resources needed may be similar to
+	  a high-scale webserver.</para>
       </sect3>
     </sect2>
+    <sect2>
+      <title>Network Limits</title>
+
+      <para>The <varname>NMBCLUSTERS</varname> kernel configuration
+	option dictate the amount of network mbufs available to the
+	system.  A heavily-trafficked server with a low number of MBUFs
+	will hinder FreeBSD's ability.  Each cluster represents
+	approximately 2K of memory, so a value of 1024 represents 2
+	megabytes of kernel memory reserved for network buffers.  A
+	simple calculation can be done to figure out how many are
+	needed. If you have a web server which maxes out at 1000
+	simultaneous connections, and each connection eats a 16K receive
+	and 16K send buffer, you need approximately 32MB worth of
+	network buffers to cover the webserver.  A good rule of thumb is
+	to multiply by 2, so 32MBx2 = 64MB/2K = 32768.</para>
+    </sect2>
   </sect1>
 </chapter>