Re: [Xen-devel] [PATCH v2] memory_hotplug: Free pages as higher order

[Vlastimil Babka <vbabka@xxxxxxx>]

On 9/25/18 7:42 AM, Arun KS wrote:
> When free pages are done with higher order, time spend on
> coalescing pages by buddy allocator can be reduced. With
> section size of 256MB, hot add latency of a single section
> shows improvement from 50-60 ms to less than 1 ms, hence
> improving the hot add latency by 60%.
> 
> Modify external providers of online callback to align with
> the change.
> 
> Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>

Hi,

> @@ -655,26 +655,53 @@ void __online_page_free(struct page *page)
>  }
>  EXPORT_SYMBOL_GPL(__online_page_free);
>  
> -static void generic_online_page(struct page *page)
> +static int generic_online_page(struct page *page, unsigned int order)
>  {
> -     __online_page_set_limits(page);
> -     __online_page_increment_counters(page);
> -     __online_page_free(page);
> +     unsigned long nr_pages = 1 << order;
> +     struct page *p = page;
> +     unsigned int loop;
> +
> +     for (loop = 0 ; loop < nr_pages ; loop++, p++) {
> +             __ClearPageReserved(p);
> +             set_page_count(p, 0);
> +     }
> +
> +     adjust_managed_page_count(page, nr_pages);
> +     set_page_refcounted(page);
> +     __free_pages(page, order);
> +
> +     return 0;

This seems like almost complete copy of __free_pages_boot_core(), could
you do some code reuse instead? I think Michal Hocko also suggested that.

Thanks,
Vlastimil

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