[CentOS] new memory not getting regonized

[Dennis Jacobfeuerborn]

On 08/31/2011 05:38 PM, Pasi Kärkkäinen wrote:
> On Tue, Aug 30, 2011 at 03:30:46PM +0200, Dennis Jacobfeuerborn wrote:
>> On 08/27/2011 09:12 PM, sylvan.dcunha at 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

Very good to know. Thanks for the information!

Regards,
   Dennis