balloon manipulation within a domU?

["Aaron J. Grier" <agrier%poofygoof.com@localhost>]

most of my VMs sit idle, so trading off memory between them depending on
load with the balloon driver so I can overcommit seems like a good idea.

manipulating a NetBSD domU's memory seems to work fine with "xl
mem-set", but trying to manipulate this within the domU with "sysctl -w
machdep.xen.balloon.target=XXXX" yields "error 13, couldn't write xenbus
target node".

is there something I need to enable in my xen configuration to allow a
domU to do its own balloon requests?

-- 
  Aaron J. Grier | "Not your ordinary poofy goof." | 
agrier%poofygoof.com@localhost