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S1932jSJN9mI7/XGIhxH33aHqP1QTmCT7sQe6OQHTIZITDFZIV9oUK9bdvu0vg16+2ZrAdeBDS0YR5XGAU5M1qdCgI0FgKuR6+/9arDmQOIOjetEW5J100ByyxfJYM/kBnN7xGw3JPVG3NdkvnKWo2lT8Lr2fo9DXrQaMW4F9Y5oLTV3x6h+ScTezCs9I5UvGMaHZphhqWvkln5UBmol5yjKoWmmezHGeu6X/gu5p8kKZ8b2RuPvuvXbeq+pGzBklluFeDKVUpQj8GAVrSPcg00i0RnRdGyHsYboQUmw4/iEOueiH+rli1AOkAMp0m4jHZaPUAaWLcPcenbvo7aMqPAb8JMydfxh/FL3siqmEY7xtUIEx34QPxnwbhSQmfOk7gPWhxPm/Sf/u8GE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/19/2024 5:19 PM, David Hildenbrand wrote: > 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. Right. I missed this part. Thanks for clarification. Regards Yin, Fengwei > > 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! >