Re: [Qemu-devel] [PATCH v2 repost 6/7] mm: add the related functions to get free page info

[Dave Hansen]

On 07/26/2016 06:23 PM, Liang Li wrote:
> +     for_each_migratetype_order(order, t) {
> +             list_for_each(curr, &zone->free_area[order].free_list[t]) {
> +                     pfn = page_to_pfn(list_entry(curr, struct page, lru));
> +                     if (pfn >= start_pfn && pfn <= end_pfn) {
> +                             page_num = 1UL << order;
> +                             if (pfn + page_num > end_pfn)
> +                                     page_num = end_pfn - pfn;
> +                             bitmap_set(bitmap, pfn - start_pfn, page_num);
> +                     }
> +             }
> +     }

Nit:  The 'page_num' nomenclature really confused me here.  It is the
number of bits being set in the bitmap.  Seems like calling it nr_pages
or num_pages would be more appropriate.

Isn't this bitmap out of date by the time it's send up to the
hypervisor?  Is there something that makes the inaccuracy OK here?