[CentOS-virt] Xen Balloon Driver on PVHVM CentOS6

Wed Jul 17 12:12:49 UTC 2013
David Vrabel <david.vrabel at citrix.com>

On 16/07/13 14:18, Rushikesh Jadhav wrote:
> On Tue, Jul 16, 2013 at 3:26 PM, David Vrabel <david.vrabel at citrix.com
> <mailto:david.vrabel at citrix.com>> wrote:
>     On 15/07/13 20:44, Rushikesh Jadhav wrote:
>     > Hi List,
>     >
>     > It seems that the xen balloon functionality for guest is not
>     enabled in
>     > CentOS 3.4.50-8.el6 xen kernel by default via
>     centos-release-xen.x86_64
>     > repo. I think this should have been present since this extra Xen repo
>     > needs to support as both Guest and Host (Dom0).
>     The kernel is only intended for use as a dom0 kernel.  We recommend the
>     use of the existing 2.6.32 kernel for guests.
> Any idea for not using 3.4.50 as guest kernel ?

The specific 3.4 kernel provided as part of the Xen4CentOS project as a
configuration selected for use as a dom0 kernel and thus it may not have
guest-centric options (like ballooning) correctly configured.

> Problem may be with CONFIG_XEN_BALLOON_MEMORY_HOTPLUG=y as well. What do
> you think ?

CONFIG_XEN_BALLOON_MEMORY_HOTPLUG=y is required to allow most Linux PV
guests to balloon above their initial allocation.  However, it is broken
in some cases when enabled in a dom0 kernel and has been disabled.

As a workaround I would suggest starting all guests with an initial
allocation that corresponds to the maximum they may ever use.  You can
then immediately balloon them down.