RE: [Xen-users] allocating memory to dom0

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Ulrich Windl
> Sent: 20 October 2006 07:52
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] allocating memory to dom0
> 
> On 19 Oct 2006 at 22:43, john maclean wrote:
> 
> > Hey chaps, having a minor dispute with a friend. According 
> the README
> > in the Xen sources....
> > "
> >    The Xen command line takes a number of optional 
> arguments described
> >    in the manual. The most common is 'dom0_mem=xxxM' which sets the
> >    amount of memory to allocate for use by your initial virtual
> >    machine (known as domain 0). Note that Xen itself reserves about
> >    32MB memory for internal use, which is not available for 
> allocation
> >    to virtual machines.
> > .."
> > 
> > I've taken this to mean that one allocates say, half of one's RAM to
> > dom0 with the command `dom0_mem=xxxM`. The domUs will then use up to
> > the other half of the box's RAM. Is this correct?
> > 
> > My buddy says that this is unnecessary as the dom0 only needs 32M of
> > ram. It will give the RAM away to the domU chaps until it 
> has no more
> > RAM to spare.
> > 
> 
> Hi,
> 
> let me add: I got the idea that all DomUs take their RAM from 
> the Dom0 RAM, so if 
> I limit the RAM of Dom0, will I waste RAM? Maybe some 
> documentation about memory 
> management should be added to the user manual...

Xen keeps track of ALL the memory in the system, and it's got two
different methods of allocating memory: From the "free memory" or "from
Dom0". That's listed in the order of priority, so if there's "free
memory", Xen will use that, and when that's exhausted, it will attempt
to use Dom0 memory until it reaches the minimum size for Dom0 (or
something goes wrong and the system crashes). If you know what size your
Dom0 will be able to operate under, you should set dom0_mem=<size> in
your boot configuration file (grub.conf/menu.lst or whatever it's called
in your system). 

--
Mats
> 
> Regards,
> Ulrich
> 
> 
> > -- 
> > John Maclean  - 07739 171 531
> > MSc (DIC)
> > 
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