124 lines
4.5 KiB
Groff
124 lines
4.5 KiB
Groff
.\"
|
|
.\" Copyright (c) 2003 Networks Associates Technology, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This software was developed for the FreeBSD Project by Jake Burkholder,
|
|
.\" Safeport Network Services, and Network Associates Laboratories, the
|
|
.\" Security Research Division of Network Associates, Inc. under
|
|
.\" DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the DARPA
|
|
.\" CHATS research program.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd April 8, 2003
|
|
.Dt PAE 4 i386
|
|
.Os
|
|
.Sh NAME
|
|
.Nm PAE
|
|
.Sh SYNOPSIS
|
|
.Cd "options PAE"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Dv PAE
|
|
option provides support for the physical address extensions capability
|
|
of the
|
|
.Tn Intel
|
|
.Tn Pentium Pro
|
|
and above CPUs,
|
|
and allows for up to 64 gigabytes of memory to be used in systems capable
|
|
of supporting it.
|
|
With the
|
|
.Dv PAE
|
|
option, memory above 4 gigabytes is simply added to the general page pool.
|
|
The system makes no distinction between memory above or below 4 gigabytes,
|
|
and no specific facility is provided for a process or the kernel to access
|
|
more memory than they would otherwise be able to access, through a sliding
|
|
window or otherwise.
|
|
.Sh SEE ALSO
|
|
.Xr smp 4 ,
|
|
.Xr tuning 7 ,
|
|
.Xr config 8
|
|
.Sh HISTORY
|
|
The
|
|
.Dv PAE
|
|
option first appeared in
|
|
.Fx 5.1 .
|
|
.Sh AUTHORS
|
|
.An Jake Burkholder Aq jake@FreeBSD.org
|
|
.Sh BUGS
|
|
Since KLD modules are not compiled with the same options headers that
|
|
the kernel is compiled with,
|
|
they must not be loaded into a kernel compiled with the
|
|
.Dv PAE
|
|
option.
|
|
.Pp
|
|
Many devices or their device drivers are not capable of direct memory access
|
|
to physical addresses above 4 gigabytes.
|
|
In order to make use of direct memory access IO in a system with more than
|
|
4 gigabytes of memory when the
|
|
.Dv PAE
|
|
option is used,
|
|
these drivers must use a facility for remapping or substituting physical
|
|
memory which is not accessible to the device.
|
|
One such facility is provided by the
|
|
.Nm busdma
|
|
interface.
|
|
Device drivers which do not account for such devices will not work reliably
|
|
in a system with more than 4 gigabytes of memory when the
|
|
.Dv PAE
|
|
option is used,
|
|
and may cause data corruption.
|
|
The
|
|
.Pa PAE
|
|
kernel configuration file includes the
|
|
.Dv PAE
|
|
option, and explicitly excludes all device drivers which are known to not work
|
|
or have not been tested in a system with the
|
|
.Dv PAE
|
|
option and more than 4 gigabytes of memory.
|
|
.Pp
|
|
Many parameters which determine how memory is used in the kernel are based on
|
|
the amount of physical memory.
|
|
The formulas used to determine the values of these paramters for specific
|
|
memory configurations may not take into account the fact there may be more
|
|
than 4 gigabytes of memory, and may not scale well to these memory
|
|
configurations.
|
|
In particular,
|
|
it may be necessary to increase the amount of virtual address space available
|
|
to the kernel,
|
|
or to reduce the amount of a specific resource that is heavily used,
|
|
in order to avoid running out of virtual address space.
|
|
The
|
|
.Dv KVA_PAGES
|
|
option may be used to increase the kernel virtual address space,
|
|
and the
|
|
.Va kern.maxvnodes
|
|
.Xr sysctl 8
|
|
may be used to decrease the number of vnodes allowed,
|
|
an example of a resource that the kernel is likely to overallocate in
|
|
large memory configurations.
|
|
For optimal performance and stability it may be necessary to consult the
|
|
.Xr tuning 7
|
|
manual page, and make adjustments to the parameters documented there.
|