[CentOS-virt] xen_balloon: reserve_additional_memory: add_memory() Errors

Fri Jan 10 12:36:18 UTC 2014
David Vrabel <david.vrabel at citrix.com>

On 10/01/14 12:17, Johnny Hughes wrote:
> On 01/08/2014 08:05 AM, David Vrabel wrote:
>> On 08/01/14 13:59, Chris Elliott wrote:
>>> At the moment we are using dom0_mem=3G,max:3G for example (where
>>> dom0 mem and max values are the same). So we just need to allow a slightly
>>> higher max value to leave some ballooned pages?
>> Yes.
>>> The Xen4centos documentation also says to use the same value for
>>> dom0_mem and max.
>> That should be updated with the workaround.
>> David
> For completeness on this issue, here are the current kernel settings for
> all XEN kernel variables:
> As can be seen, CONFIG_XEN_SELFBALLOONING is not set  ... is this a
> problem?  (That option was decided during the beginning of the
> Xen4CentOS process and I'm not sure if it is still valid).

XEN_SELFBALLOONING enables automatic adjustment of the guest's own
target based on memory usage.  I don't think this a good idea,
especially for a dom0.

> If the kernel config option is still correct and if the Xen4CentOS Docs
> need changing then I will make that happen.


I would suggest that approx. 16 MB per VM is a reasonable amount of
pre-ballooned memory.

e.g., dom0_mem=3G,max:4G would allow for approx. 64 VMs.