Re: Enabling balloon(4) in Xen dom0/domU kernels?

[Hugo Silva <hugo%barafranca.com@localhost>]

On 04/26/11 12:44, Jean-Yves Migeon wrote:
> On Tue, 26 Apr 2011 13:36:43 +0200, Manuel Bouyer
> <bouyer%antioche.eu.org@localhost> wrote:
>> On Mon, Apr 25, 2011 at 10:31:23PM +0200, Jean-Yves Migeon wrote:
>>> Dear all,
>>>
>>> I would like to know if it's acceptable to enable the balloon(4) driver
>>> by default for all NetBSD Xen kernels.
>>>
>>> I believe that it needs more coverage than the tests I ran. IMHO the
>>> easiest way to achieve that would to turn it on by default.
>>>
>>> FWIW, I tested the driver under "heavy" loads (mainly build.sh runs in
>>> domU), and it never appeared to cause issues, except the occasional
>>> swapping and delays due to balloon operations.
>>>
>>> Opinions?
>>
>> I think it can be turned on, yes.
> 
> Thanks Manuel, I will do it in a few days.
> 

Had it briefly enabled with a 5.99.49 box, but with ballooning enabled
it rebooted on its own 2 or 3 times.

I think the culprit might be swap on cgd though (or an interaction with
the ballooning code? I have no idea).

On several 5.1 domUs with very low memory (16-32M) I notice a hang where
the domU will be consuming 100% CPU (xm top from dom0) and xm console
seems to work but hangs right away, and ssh stops working too.

Notably, to be able to compile a kernel on these VMs, I had to disable
swap on cgd.

I'm not 100% sure it's 2 different problems, since the domU hangs at
100% and the dom0 just reboots. I have the dom0 running with swap on cgd
and 768M mem for a week now, no crashes (it did crash with ballooning).
There is that.


It's all a bit vague I know, but maybe someone else steps up with the
same problem and we might be able to track it down..

Hugo

Wish I had more precise information, I know it's a bit vague.