Re: PROBLEM: Xen ballon driver seems to be broken in 2.6.26

[Jeremy Fitzhardinge <jeremy@goop.org>]

Németh Tamás wrote:
> I use openSUSE 10.3 both for dom0 and domU, but the kernels and the entire Xen 
> system (hypervisor, tools and dom0 kernel) is replaced by the newest version 
> downloadable from xen.org. Every component is compiled from source. The 
> hypervisor is 64 bit, and the dom0 and domU systems are 32 bit, PAE. The domU 
> kernel is the vanilla 2.6.26. It's OK, that migration, save, restore, etc. 
> don't work, as you plan the support for these features to be included in 
> 2.6.27 AFAIK. (BTW, when will you include the domU support for x86_64 and CPU 
> hotplug?) But:
>
> The balloon driver also seems to be broken. If i decrease the amount of memory 
> in domU, it becomes immediately almost unresponsive. I can ping the domU, and 
> even Xvnc continues to operate (the "screen" of domU changes, the KDE clock 
> continues to count the seconds), but i cannot start new programs. Sadly it 
> includes the fact that i can't even run dmesg. Neither the output of 'xm 
> console'  gives any error message. When i destroy and restart the domU then, 
> i cannot find anything about the crash in /var/log/messages. When i try to 
> start a new program, then the domU totally hangs finally, the KDE clock 
> stops, and it cannot be shut down (only destroyed).
>   

So that's consistent with the balloon driver over-aggressively shrinking 
the domain, until there's no memory left to do anything.  The balloon 
driver has no safety checks to prevent that from happening.

What value are you setting the target size to?  Are you using the right 
units?

    J