On Tue, Aug 30, 2011 at 03:30:46PM +0200, Dennis Jacobfeuerborn wrote:
> On 08/27/2011 09:12 PM, sylvan.dcunha@xxxxxxxxx wrote:
> > Dear Dennis,
> >
> > Thanks a lot for the wise reply.. really did boost my knowledge..
> > honestly was unware of the fact that dom0 is just like another VM ...
> > Anyway I had never restricted dom0 mem and since my 4 vms were working fine
> > with no issues
> > i never bothered much.
>
> Yes, this is different from KVM where the VMs really are just normal
> processes on the host system and the host system itself isn't a VM.
>
> On a Xen system if you look at /etc/grub.conf you'll notice that it looks
> slightly different than on a non-virtualized system. Specifically you'll
> find the following line:
> kernel /xen.gz-2.6.18-164.el5
>
> That's the actual hypervisor and really the host system and once started it
> will basically start dom0 and give it special privileges. So Dom0 and the
> DomU's all run on top of the actual hypervisor.
>
> > It was only after I added more 32 gb to existing 32 gb i did realise the
> > above issue..
>
> Apparently dom0 has a 32G limit but that shouldn't be an issue unless you
> actually really require more than 32G specifically for dom0 and not the VMs.
>
> > anyway I will try to restrict my dom0 to 1 GB ... and check it out.
>
> Remember that the problems with the dynamic memory management are most
> likely fixed nowadays so the limitation is not strictly necessary. But then
> 1G will probably be more than enough for dom0 so it doesn't really hurt either.
>
Still today you should dedicate a fixed amount of memory for dom0!
say, 1GB, or so.
It's because of how Linux kernel allocates (and wastes) page struct memory:
http://wiki.xen.org/xenwiki/XenBestPractices
-- Pasi
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