Update Question 18.16:

- Restrict the question and answer to i386
- Remove description of the original hack since changing the size of
  kernel address space is much easier these days (fortunately)
- Mention KVA value for PAE
- Add ZFS as a possible cause of doing this (stolen from the wiki)

Reviewed by:  trhodes
Approved by:  gabor

en_US.ISO8859-1/books/faq/book.sgml

@@ -10896,75 +10896,25 @@ panic: page fault</programlisting>
 
       <qandaentry>
         <question id="change-kernel-address-space">
-          <para>How can I increase or reduce the kernel address space?</para>
+          <para>How can I increase or reduce the kernel address space on i386?</para>
         </question>
 
         <answer>
-          <para>By default, the kernel address space is 256 MB on
-            FreeBSD 3.X and 1 GB on FreeBSD 4.X. If you run a
-            network-intensive server (e.g. a large FTP or HTTP server),
-            you might find that 256 MB is not enough.</para>
+	  <para>By default, the kernel address space is 1&nbsp;GB
+	    (2&nbsp;GB for PAE) for i386.  If you run a
+	    network-intensive server (e.g.  a large FTP or HTTP server),
+	    or you want to use ZFS, you might find that is not
+	    enough.</para>
 
-          <para>So how do you increase the address space? There are two
-            aspects to this. First, you need to tell the kernel to reserve
-            a larger portion of the address space for itself. Second, since
-            the kernel is loaded at the top of the address space, you need
-            to lower the load address so it does not bump its head against
-            the ceiling.</para>
+	  <para>Add the following line to your kernel configuration file
+	    to increase available space and rebuild your kernel:</para>
 
-          <para>The first goal is achieved by increasing the value of
-            <literal>NKPDE</literal> in
-            <filename>src/sys/i386/include/pmap.h</filename>. Here is what
-            it looks like for a 1 GB address space:</para>
+	  <programlisting>options KVA_PAGES=<replaceable>N</replaceable></programlisting>
 
-          <programlisting>#ifndef NKPDE
-#ifdef SMP
-#define NKPDE                   254     /* addressable number of page tables/pde's */
-#else
-#define NKPDE                   255     /* addressable number of page tables/pde's */
-#endif  /* SMP */
-#endif</programlisting>
-
-          <para>To find the correct value of <literal>NKPDE</literal>,
-            divide the desired address space size (in megabytes) by four,
-            then subtract one for UP and two for SMP.</para>
-
-          <para>To achieve the second goal, you need to compute the
-            correct load address: simply subtract the address space size
-            (in bytes) from 0x100100000; the result is 0xc0100000 for a 1
-            GB address space. Set <symbol>LOAD_ADDRESS</symbol> in
-            <filename>src/sys/i386/conf/Makefile.i386</filename> to that
-            value; then set the location counter in the beginning of the
-            section listing in
-            <filename>src/sys/i386/conf/kernel.script</filename> to the
-            same value, as follows:</para>
-
-          <programlisting>OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
-OUTPUT_ARCH(i386)
-ENTRY(btext)
-SEARCH_DIR(/usr/lib); SEARCH_DIR(/usr/obj/elf/home/src/tmp/usr/i386-unknown-freebsdelf/lib);
-SECTIONS
-{
-  /* Read-only sections, merged into text segment: */
-  . = 0xc0100000 + SIZEOF_HEADERS;
-  .interp     : { *(.interp)    }</programlisting>
-
-          <para>Then reconfig and rebuild your kernel. You will
-            probably have problems with &man.ps.1; &man.top.1; and the
-            like; <command>make world</command> should take care of it
-            (or a manual rebuild of <filename>libkvm</filename>,
-            &man.ps.1; and &man.top.1; after copying the patched
-            <filename>pmap.h</filename> to
-            <filename>/usr/include/vm/</filename>.</para>
-
-          <para>NOTE: the size of the kernel address space must be a
-            multiple of four megabytes.</para>
-
-          <para>[&a.dg; adds: <emphasis>I think the kernel address space
-            needs to be a power of two, but I am not certain about that. The
-          old(er) boot code used to monkey with the high order address bits
-          and I think expected at least 256MB
-          granularity.]</emphasis></para>
+	  <para>To find the correct value of
+	    <replaceable>N</replaceable>, divide the desired address
+	    space size (in megabytes) by four.  (For example, it is
+	    <literal>512</literal> for 2&nbsp;GB.)</para>
         </answer>
       </qandaentry>
     </qandaset>