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man page for balloon driver from Cherry

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christos 2010-07-08 20:00:24 +00:00
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share/man/man4/Makefile
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# $NetBSD: Makefile,v 1.521 2010/07/04 15:21:58 tsutsui Exp $
# $NetBSD: Makefile,v 1.522 2010/07/08 20:00:24 christos Exp $
# @(#)Makefile 8.1 (Berkeley) 6/18/93
MAN= aac.4 ac97.4 acardide.4 aceride.4 acphy.4 \
@ -213,7 +213,7 @@ SUBDIR= man4.acorn26 man4.acorn32 man4.alpha man4.amiga man4.arc man4.atari \
man4.hp300 man4.hp700 man4.hpcarm man4.hpcmips man4.hpcsh man4.i386 \
man4.mac68k man4.macppc man4.mvme68k man4.pmax man4.prep \
man4.sgimips man4.sparc man4.sparc64 man4.sun2 man4.sun3 man4.vax \
man4.x68k
man4.x68k man4.x86
.include <bsd.man.mk>
.include <bsd.subdir.mk>

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share/man/man4/man4.x86/Makefile Normal file
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# $NetBSD: Makefile,v 1.1 2010/07/08 20:00:24 christos Exp $
MAN= balloon.4
MANSUBDIR=/x86
.include <bsd.man.mk>

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share/man/man4/man4.x86/balloon.4 Normal file
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.\" $NetBSD: balloon.4,v 1.1 2010/07/08 20:00:24 christos Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Cherry G. Mathew <cherry@zyx.in> and
.\" Jean-Yves Migeon <jym@NetBSD.org>
.\"
.\" 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
.\"
.Dd July 06, 2010
.Dt BALLOON 4 xen
.Os
.Sh NAME
.Nm balloon
.Nd Xen hypervisor dynamic memory resize helper
.Sh SYNOPSIS
.Cd "options XEN_BALLOON"
.Sh DESCRIPTION
The Xen
.Nm
driver can be enabled to allow the Xen hypervisor to dynamically
resize the amount of RAM a
.Nx
VM is allowed to use. This allows the hypervisor to manage RAM more
efficiently, similar in spirit to how the
.Nx
kernel would manage RAM wrt processes, with
.Xr uvm 9 .
.Pp
The
.Nm
driver negotiates domain VM memory allocation change requests from
the Xen hypervisor, by reserving "pinned" memory for itself from the
NetBSD
.Xr uvm 9
subsystem.
.Pp
There are two methods to notify the
.Nm
driver of memory allocation change requests.
.Bl -tag -width "Xr sysctl 3" -offset indent
.It xenbus
In the xenbus method, the change notification originates outside the
VM, presumable from the Hypervisor, and is communicated over the
xenbus interface.
.It Xr sysctl 3
In the
.Xr sysctl 3
method, the change notification originates from within the VM. Two
.Xr sysctl 7
nodes are provided:
.Bl -ohang -width kern.xen.balloon.current
.It Va kern.xen.balloon.current
This node is read-only and returns the number of memory pages
currently allocated to the VM.
.It Va kern.xen.balloon.target
This node can be written to, and sets a new target memory reservation,
in pages. Note that targets set this way from within the VM do not
reflect in the hypervisor. This is therefore a less preferred way to
use the
.Nm
.El
.El
.Pp
In either case, once a new allocation target is set, the balloon
driver thread asynchronously attempts to reach this target in discrete
steps. Every step, if it fails, is tried more than once. When the
target is reached, the thread goes back to sleep, waiting for a new
incoming target. If it is not reached, the target is updated to
reflect the value after the last successful step.
.Sh EXAMPLES
.Bd -literal
# # Have a look at the current reservations.
# sysctl -a|grep balloon
kern.xen.balloon.current = 32512
kern.xen.balloon.target = 32512
#
# # Change the current target to 30000 kernel pages.
# sysctl -w kern.xen.balloon.target=30000
kern.xen.balloon.target: 32512 -> 30000
#
.Ed
.Sh SEE ALSO
.Xr uvm 9
.Rs
.%A Carl A. Waldspurger
.%T Memory Resource Management in VMware ESX Server
.%U http://www.usenix.org/events/osdi02/tech/waldspurger/waldspurger_html/node6.html
.Re
.\"
.Sh AUTHORS
.An Cherry G. Mathew Aq cherry@zyx.in
.An Jean-Yves Migeon Aq jym@NetBSD.org
.Sh CAVEATS
VMs can be inadvertently crashed/panic()ed by over expanding the
balloon allocation, creating extreme OS memory pressure.
.Sh BUGS
.Fn xenmem_get_maxreservation
is currently hard-coded to return nkmempages.
This driver is still regarded as EXPERIMENTAL.