Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios

[Yin, Fengwei]

On 4/10/2024 3:22 AM, David Hildenbrand wrote:
> @@ -2200,7 +2200,22 @@ static inline size_t folio_size(struct folio *folio)
>    */
>   static inline bool folio_likely_mapped_shared(struct folio *folio)
>   {
> -	return page_mapcount(folio_page(folio, 0)) > 1;
> +	int mapcount = folio_mapcount(folio);
> +
> +	/* Only partially-mappable folios require more care. */
> +	if (!folio_test_large(folio) || unlikely(folio_test_hugetlb(folio)))
> +		return mapcount > 1;
My understanding is that mapcount > folio_nr_pages(folio) can cover
order 0 folio. And also folio_entire_mapcount() can cover hugetlb (I am
not 100% sure for this one).  I am wondering whether we can drop above
two lines? Thanks.


Regards
Yin, Fengwei

> +
> +	/* A single mapping implies "mapped exclusively". */
> +	if (mapcount <= 1)
> +		return false;
> +
> +	/* If any page is mapped more than once we treat it "mapped shared". */
> +	if (folio_entire_mapcount(folio) || mapcount > folio_nr_pages(folio))
> +		return true;
> +
> +	/* Let's guess based on the first subpage. */
> +	return atomic_read(&folio->_mapcount) > 0;
>   }