Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios
From: Yin, Fengwei <hidden>
Date: 2024-04-19 02:30:00
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On 4/10/2024 3:22 AM, David Hildenbrand wrote:
quoted hunk ↗ jump to hunk
@@ -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; }