On 23/03/2026 20:22, Ackerley Tng wrote:
"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.
Ok, I'll leave it as is for now.
Something to ponder about :)
--
Cheers,
David
