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>>> */ >>> static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags) >>> { >>> - bool reject_file_backed = false; >>> struct address_space *mapping; >>> unsigned long mapping_flags; >>> >>> - /* >>> - * If we aren't pinning then no problematic write can occur. A long term >>> - * pin is the most egregious case so this is the one we disallow. >>> - */ >>> - if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) == >>> - (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) >>> - reject_file_backed = true; >>> - >>> /* We hold a folio reference, so we can safely access folio fields. */ >>> if (WARN_ON_ONCE(folio_test_slab(folio))) >>> return false; >>> @@ -2793,8 +2784,18 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags) >>> */ >>> if (secretmem_mapping(mapping)) >>> return false; >>> - /* The only remaining allowed file system is shmem. */ >>> - return !reject_file_backed || shmem_mapping(mapping); >>> + >>> + /* >>> + * If we aren't pinning then no problematic write can occur. A writable >>> + * long term pin is the most egregious case, so this is the one we >>> + * allow only for ... >>> + */ >>> + if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) != >>> + (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) >>> + return true; >>> + >>> + /* ... hugetlb (which we allowed above already) and shared memory. */ >>> + return shmem_mapping(mapping); >> >> Acked-by: David Hildenbrand (Arm) >> >> I'm wondering if it would be a good idea to check for a hugetlb mapping >> here instead of having the folio_test_hugetlb() check above. >> > > I think it's nice that hugetlb folios are determined immediately to be > eligible for GUP-fast regardless of whether the folio is file-backed or > not. Ok, I'll leave it as is for now. > >> Something to ponder about :) >> >> -- >> Cheers, >> >> David