docs/80267: Add information on tuning kern.maxvnodes

[Brad Davis]

>Number:         80267
>Category:       docs
>Synopsis:       Add information on tuning kern.maxvnodes
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          update
>Submitter-Id:   current-users
>Arrival-Date:   Fri Apr 22 22:40:16 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Brad Davis
>Release:        FreeBSD 5.4-STABLE i386
>Organization:
>Environment:
System: FreeBSD mccaffrey.house.so14k.com 5.4-STABLE FreeBSD 5.4-STABLE #0: Wed Apr 20 22:22:19 MDT 2005 root at mccaffrey.house.so14k.com:/usr/obj/usr/src/sys/SMP i386
>Description:
	Add information on tuning kern.maxvnodes.
>How-To-Repeat:
>Fix:

--- doc-ori/en_US.ISO8859-1/books/handbook/config/chapter.sgml	Fri Apr 22 11:51:50 2005
+++ doc/en_US.ISO8859-1/books/handbook/config/chapter.sgml	Fri Apr 22 15:58:09 2005
@@ -2228,6 +2228,42 @@
 	</note>
       </sect3>
     </sect2>
+
+    <sect2>
+      <title>Virtual Memory</title>
+
+      <sect3>
+        <title><varname>kern.maxvnodes</varname></title>
+
+        <para>A vnode is the internal representation of a file or
+          directory.  So increasing the number of vnodes avaliable to
+          the operating system cuts down on disk I/O.  Normally this
+          is handled by the operating system and does not need to be
+          changed.  In some cases where disk I/O is a bottleneck and
+          the system is running out of vnodes, this setting will need
+          to be increased.  The amount of inactive and free RAM will
+          need to be taken into account.</para>
+
+        <para>To see the current number of vnodes in use:</para>
+
+        <programlisting>&prompt.root; sysctl vfs.numvnodes
+vfs.numvnodes: 91349</programlisting>
+
+        <para>To see the maximum vnodes:</para>
+
+        <programlisting>&prompt.root; sysctl kern.maxvnodes
+kern.maxvnodes: 100000</programlisting>
+
+        <para>If the current vnode usage is near the maximum, upping
+          <varname>kern.maxvnodes</varname> by a 1,000 is probably a
+          good idea.  Keep an eye on the number of
+          <varname>vfs.numvnodes</varname>.  If it climbs up to the
+          maximum again, <varname>kern.maxvnodes</varname> will need to
+          be increased further.  A shift in your memory usage as
+          reported by &man.top.1; should be visable.  More memory should
+          be active.</para>
+      </sect3>
+    </sect2>
   </sect1>
 
   <sect1 id="adding-swap-space">
>Release-Note:
>Audit-Trail:
>Unformatted: