Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order

[Vlastimil Babka]

On 10/5/18 10:10 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>

[...]

> @@ -655,26 +655,44 @@ 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);

This is now not called anymore, although the xen/hv variants still do
it. The function seems empty these days, maybe remove it as a followup
cleanup?

> -	__online_page_increment_counters(page);
> -	__online_page_free(page);
> +	__free_pages_core(page, order);
> +	totalram_pages += (1UL << order);
> +#ifdef CONFIG_HIGHMEM
> +	if (PageHighMem(page))
> +		totalhigh_pages += (1UL << order);
> +#endif

__online_page_increment_counters() would have used
adjust_managed_page_count() which would do the changes under
managed_page_count_lock. Are we safe without the lock? If yes, there
should perhaps be a comment explaining why.