"David Hildenbrand (Arm)" <[email protected]> writes: > On 3/17/26 15:11, Kalyazin, Nikita wrote: >> From: Nikita Kalyazin <[email protected]> >> >> Move the check for pinning closer to where the result is used. >> No functional changes. >> >> Signed-off-by: Nikita Kalyazin <[email protected]> >> --- >> mm/gup.c | 23 ++++++++++++----------- >> 1 file changed, 12 insertions(+), 11 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index 5856d35be385..869d79c8daa4 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -2737,18 +2737,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked); >> */ >> 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) <[email protected]> > > 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. > Something to ponder about :) > > -- > Cheers, > > David
