On 19.04.24 04:29, Yin, Fengwei wrote:
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.
folio_entire_mapcount() does not apply to small folios, so we must not call that for small folios.
Regarding hugetlb, subpage mapcounts are completely unused, except subpage 0 mapcount, which is now *always* negative (storing a page type) -- so there is no trusting on that value at all.
So in the end, it all looked cleanest when only special-casing on partially-mappable folios where we know the entire mapcount exists and we know that subapge mapcount 0 actually stores something reasonable (not a type).
Thanks! -- Cheers, David / dhildenb
