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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.


Julien Grall



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