Re: [Xen-devel] initial ballooning amount on HVM+PoD

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.01.14 at 16:31, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
>> >>>> Question now is: Considering that (a) is broken (and hard to fix)
>> >>>> and (b) is in presumably a large part of practical cases leading to
>> >>>> too much ballooning down, shouldn't we open up
>> >>>> XENMEM_get_pod_target for domains to query on themselves?
>> >>>> Alternatively, can anyone see another way to calculate a
>> >>>> reasonably precise value?
>> >>> I think hypervisor query is a good thing although I don't know whether
>> >>> exposing PoD-specific data (count and entry_count) to the guest is
>> >>> necessary. It's probably OK (or we can set these fields to zero for
>> >>> non-privileged domains).
>> >> That's pointless then - if no useful data is provided through the
>> >> call to non-privileged domains, we can as well keep it erroring for
>> >> them.
>> >>
>> > 
>> > I thought that are after d->tot_pages, no?
>> 
>> That can be obtained through another XENMEM_ operation. No,
>> what is needed is the difference between PoD entries and PoD
>> cache (which then needs to be added to tot_pages).
> 
> Won't that be racy? Meaning the moment you get that information and
> kick of the balloon worker, said value might be different already?

There's a small risk for that, yes (albeit said difference ought to be
stable, and I don't immediately see how tot_pages would change
underneath the balloon driver initializing), but I am still awaiting
alternative suggestions...

Jan


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