RE: [PATCH 06/10] xen: replace order with nr_pfns in assign_pages for better compatibility

[Penny Zheng <Penny.Zheng@arm.com>]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: Tuesday, May 18, 2021 6:21 PM
> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org;
> sstabellini@kernel.org
> Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>; Wei Chen
> <Wei.Chen@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH 06/10] xen: replace order with nr_pfns in assign_pages
> for better compatibility
> 
> Hi Penny,
> 
> On 18/05/2021 06:21, Penny Zheng wrote:
> > Function parameter order in assign_pages is always used as 1ul <<
> > order, referring to 2@order pages.
> >
> > Now, for better compatibility with new static memory, order shall be
> > replaced with nr_pfns pointing to page count with no constraint, like
> > 250MB.
> 
> We have similar requirements for LiveUpdate because are preserving the
> memory with a number of pages (rather than a power-of-two). With the
> current interface would be need to split the range in a power of 2 which is a
> bit of pain.
> 
> However, I think I would prefer if we introduce a new interface (maybe
> assign_pages_nr()) rather than change the meaning of the field. This is for
> two reasons:
>    1) We limit the risk to make mistake when backporting a patch touch
> assign_pages().
>    2) Adding (1UL << order) for pretty much all the caller is not nice.
> 

Ok. I will create a new interface assign_pages_nr(), and let assign_pages to call it with
2@order.

> Cheers,
> 
> --
> Julien Grall

Cheers

Penny Zheng