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Add a Q&A about 'kmem_map too small' panics on machines with large

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amounts of memory.

PR:		66621
Submitted by:	Stefan Bethke <stb@lassitu.de>
Discussed with:	des, kris
This commit is contained in:
Peter Pentchev 2005-02-27 13:55:36 +00:00
parent 3697fca7df
commit e89885f1d1
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=23930
1 changed files with 33 additions and 4 deletions
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37
en_US.ISO8859-1/books/faq/book.sgml
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@ -3580,10 +3580,39 @@ quit</programlisting>
</qandaentry>
<qandaentry>
<question id="panic-kmemmap-too-small">
<para>Why does FreeBSD panic with
<errorname>kmem_map too small!</errorname>?</para>
</question>
<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 as the maximum number of files that can be open
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 high: while starting up, the kernel allocates various tables
and other structures that fill up most of the available kernel
memory. Later on, while the system is running, the kernel has no
more space left for dynamic memory allocations, and
panics.</para>
<para>Compile your own kernel, and add the
<option>VM_KMEM_SIZE_MAX</option> to your kernel configuration
file, increasing the maximum size to 400&nbsp;MB
(<option>options VM_KMEM_SIZE_MAX=419430400</option>).
400&nbsp;MB appears to be sufficient for machines with up to
6&nbsp;GB of memory.</para>
</answer>
</qandaentry>
<qandaentry>
<question id="panic-kmemmap-too-small">
<para>My system does not have 1 GB of RAM, and FreeBSD still
panics with <errorname>kmem_map too small!</errorname>
</para>
</question>
<answer>
<para>The panic indicates that the system ran out of virtual