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

Wed Jan 8 13:59:59 UTC 2014
Chris Elliott <chris at chriselliott.info>

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?

The Xen4centos documentation also says to use the same value for dom0_mem and max.


From: David Vrabel [david.vrabel at citrix.com]
Sent: 08 January 2014 13:12
To: Discussion about the virtualization on CentOS
Cc: Chris Elliott
Subject: Re: [CentOS-virt] xen_balloon: reserve_additional_memory: add_memory() Errors

On 03/01/14 19:58, Chris Elliott wrote:
> Hi All
> Back in August there was a report of these errors popping up in dmesg,
> and as far as I can tell it’s still unresolved even in the latest kernel.
> System RAM resource [mem 0xc8000000-0xcfffffff] cannot be added
> xen_balloon: reserve_additional_memory: add_memory() failed: -17

Drivers (e.g., blkback) use ballooned pages for use for foreign
mappings.  Depending on dom0_mem options there may be no ballooned
memory available at boot and dom0's balloon is increased by allocating
pages.  This decreases current_kb.

The balloon driver then tries to decrease the balloon to match the
target but it can only do this by hotplugging new memory.  A bug in the
balloon driver means the location of this memory overlaps with an
address range that is already in use and the hotplug will fail.

As a workaround you can boot dom0 with a suitable amount of
pre-ballooned memory with:


You may need to experiment with the max: value.