On Tue, Aug 30, 2011 at 03:30:46PM +0200, Dennis Jacobfeuerborn wrote:
On 08/27/2011 09:12 PM, sylvan.dcunha@gmail.com 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