Re: xl.cfg, memory options clarification

[Ian Campbell <Ian.Campbell@citrix.com>]

On Fri, 2012-03-09 at 09:45 -0500, Anthony PERARD wrote:
> I also try something else with the default qemu, having memory=128 and 
> maxmem=1024. The guest boot, but after using it a bit Xen print:
> 
> (XEN) p2m_pod_demand_populate: Out of populate-on-demand memory! 
> tot_pages 31733 pod_entries 231424
> (XEN) domain_crash called from p2m-pod.c:1076

This might just be because a 128:1024 ratio is too much for PoD to cope
with? Or is your guest not running a balloon driver perhaps?

Using maxmem>memory for an HVM guest requires that the balloon driver
gets starts pretty early on in the guest boot up.

> [...]
> (XEN) Panic on CPU 0:
> (XEN) Assertion 'lock->recurse_cnt < 0xfu' failed at spinlock.c:251

This seems like a bug to me -- running out of PoD memory shouldn't crash
the host...

> and reboot.
> 
> Is maxmem not suppose to be used with a guest ? Or is just broken.
> 
>  From all of that, I think I'll just make a change to the 
> build_dm_args_new and give "-m $((maxmem - videoram))" instead of targetmem.

I think the value is probably correct but I guess there ought to be a
libxl__ function to just give you the right amount rather than
calculating it yourself -- perhaps Stefano can advise?

Ian.