Re: kernel log flooded with: xen_balloon: reserve_additional_memory: add_memory() failed: -17

[David Vrabel <david.vrabel@citrix.com>]

On 28/01/13 16:36, Darren Shepherd wrote:
> biting this behavior.  The specific
> error I'm seeing is
> 
> xen_balloon: reserve_additional_memory: add_memory() failed: -17
> System RAM resource 88000000 - 8fffffff cannot be added

Inside dom0, yes?

Looking at the balloon driver, it doesn't seem to handle dom0 (or domUs
with PCI devices passed-through) very well because it doesn't check the
memory map before attempting to hotplug additional memory so it ends up
overlapping a region that is already reserved.  This is is particularly
common if you booted Xen with dom0_mem=max:MMM as the host's memory
beyond MMM is still in dom0's memory map (marked as UNUSABLE).

I suggest disabling CONFIG_XEN_BALLOON_MEMORY_HOTPLUG for now.

However, this only triggers if current_pages != target_pages and there
are no ballooned pages available.  This shouldn't happen unless the
target is explicitly adjusted upwards.

If you're seeing this with the beta 3.4.y kernel for CentOS 6, then it's
probably because I missed backporting 58b7b53a3 (xen/balloon: Subtract
from xen_released_pages the count that is populated).

David