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RE: [PATCH 06/10] xen: replace order with nr_pfns in assign_pages for better compatibility
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>
- From: Penny Zheng <Penny.Zheng@xxxxxxx>
- Date: Wed, 19 May 2021 05:35:26 +0000
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- Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, nd <nd@xxxxxxx>
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- Thread-topic: [PATCH 06/10] xen: replace order with nr_pfns in assign_pages for better compatibility
Hi Julien
> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: Tuesday, May 18, 2021 6:21 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>
> 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
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