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

Yin, Fengwei
2024-04-19T02:30:00Z

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;
> }