docs/66621: Document fix for "kmem_map too small panics"

[Stefan Bethke]

>Number:         66621
>Category:       docs
>Synopsis:       Document fix for "kmem_map too small panics"
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          update
>Submitter-Id:   current-users
>Arrival-Date:   Thu May 13 14:10:21 PDT 2004
>Closed-Date:
>Last-Modified:
>Originator:     Stefan Bethke
>Release:        5-current
>Organization:
>Environment:
FreeBSD majestix.tallence.de 5.2-CURRENT FreeBSD 5.2-CURRENT #5: Wed May 12 12:47:06 GMT 2004     root at majestix.tallence.de:/usr/obj/usr/src/sys/MAJESTIX  i386
>Description:
solution to "kmem_map too small" panics have been requested at least 5 times on -current in the past two months; fix is simple to implement, but hard to find :-)

Kris Kennaway graciously provided advice to limit VM_KMEM_SIZE_MAX to 400 MB; that seems to be working for everybody who enquired.
>How-To-Repeat:
      
>Fix:
Index: book.sgml
===================================================================
RCS file: /home/ncvs/doc/en_US.ISO8859-1/books/faq/book.sgml,v
retrieving revision 1.618
diff -u -C10 -r1.618 book.sgml
cvs diff: conflicting specifications of output style
*** book.sgml   11 May 2004 13:29:47 -0000      1.618
--- book.sgml   13 May 2004 20:55:09 -0000
***************
*** 3082,3101 ****
--- 3082,3125 ----
          <question id="asusk7v-boot-failure">
            <para>The boot floppy hangs on a system with an ASUS K7V
              motherboard.  How do I fix this?</para>
          </question>
  
          <answer>
            <para>Go into the BIOS setup and disable the <quote>boot virus
              protection</quote>.</para>
          </answer>
        </qandaentry>
+ 
+       <qandaentry>
+         <question id="kmem-map-too-small">
+           <para>My system has more than 1 GB of RAM, and I'm getting panics
+             with <quote>kmem_map too small</quote> messages. What is
+             wrong?</para>
+         </question>
+ 
+         <answer>
+           <para>Normally, FreeBSD determines a number of kernel parameters,
+             such as the maximum number of open files that can be opened
+             concurrently, from the amount of memory installed in the
+             system.  On systems with one gigabyte of RAM or more, this
+             <quote>auto-sizing</quote> mechanism may choose values that are
+             too large, leading to poor performance, or even to
+             panics.</para>
+           <para>In this particular case, the kernel memory allocation map
+             is too small for the amount of memory the kernel believes it
+             should be able to allocate, hence the panic. Compile your own
+             kernel, and add the <option>VM_KMEM_SIZE_MAX</option> to your
+             kernel configuration file. Limiting the maximum size to 400 MB
+             (<option>VM_KMEM_SIZE_MAX 419430400</option>).  </para>
+         </answer>
+       </qandaentry>
      </qandaset>
    </chapter>
  
    <chapter id="troubleshoot">
      <title>Troubleshooting</title>
  
      <qandaset>
        <qandaentry>
          <question id="awre">
            <para>What do I do when I have bad blocks on my hard drive?</para>

>Release-Note:
>Audit-Trail:
>Unformatted: