Re: [Xen-devel] [PATCH v2 16/17] libxc/xc_dom_arm: Copy ACPI tables to guest space

[Shannon Zhao <zhaoshenglong@xxxxxxxxxx>]

On 2016/7/19 18:38, Wei Liu wrote:
> On Fri, Jul 15, 2016 at 05:39:32PM +0800, Shannon Zhao wrote:
> [...]
>>> > > 
>>> > > It would be trivial to have another option in xl.cfg to allow MB
>>> > > granularity. But I don't think that's a good idea. Asking for more
>>> > > memory when you don't really know how much is enough is not very useful.
>>> > > If an admin can know how much is needed, surely the library can be
>>> > > taught to obtain that knowledge, too.
>>> > > 
>>> > > We need to decide which model we should go with. And, if we decide to
>>> > > diverge, document the difference between x86 and ARM model.
>>> > > 
>> > Hi Wei,
>> > 
>> > Do you decide how to add the size of ACPI blob to max_memkb?
>> > 
> AFAICT ARM and x86 maintainers hold different opinions on how memory
> should be accounted.
> 
> I would like to have a unified memory accounting model. But if we can't
> have that at the moment, I'm fine with divergence, but please document
> it somewhere (comment near code snippet, in header, or a file under docs
> etc). And the amount added to max_memkb needs to be properly calculated,
> not some magic number, so that we have a chance in the future to
> confidently change how we do thing.
If it's only allowed to add the size to max_memkb in
libxl__domain_build_info_setdefault(), it only can use a const number
since the tables are not generted and we don;t know the size. But the
const number could be chosen properly since we could know the maximum
ACPI tables size of current ARM approach.

But maybe in the future, if we add some new ACPI tables, it should
increase the size as well. So I think this should be documented.

As I asked before, is it ok to add the size to max_memkb after
generating the ACPI tables and before loading the tables to guest space?

Thanks,
-- 
Shannon


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