There seems to be no reason why FOLL_FORCE during GUP-fast would have to
fallback to the slow path when stumbling over a PROT_NONE mapped page. We
only have to trigger hinting faults in case FOLL_FORCE is not set, and any
kind of fault handling naturally happens from the slow path -- where
NUMA hinting accounting/handling would be performed.
Note that the comment regarding THP migration is outdated:
commit 2b4847e73004 ("mm: numa: serialise parallel get_user_page against
THP migration") described that this was required for THP due to lack of PMD
migration entries. Nowadays, we do have proper PMD migration entries in
place -- see set_pmd_migration_entry(), which does a proper
pmdp_invalidate() when placing the migration entry.
So let's just reuse gup_can_follow_protnone() here to make it
consistent and drop the somewhat outdated comments.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/gup.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index a1355dbd848e..dfef23071dc8 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2350,11 +2350,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
struct page *page;
struct folio *folio;
- /*
- * Similar to the PMD case below, NUMA hinting must take slow
- * path using the pte_protnone check.
- */
- if (pte_protnone(pte))
+ if (pte_protnone(pte) && !gup_can_follow_protnone(flags))
goto pte_unmap;
if (!pte_access_permitted(pte, flags & FOLL_WRITE))
@@ -2736,12 +2732,8 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo
if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
pmd_devmap(pmd))) {
- /*
- * NUMA hinting faults need to be handled in the GUP
- * slowpath for accounting purposes and so that they
- * can be serialised against THP migration.
- */
- if (pmd_protnone(pmd))
+ if (pmd_protnone(pmd) &&
+ !gup_can_follow_protnone(flags))
return 0;
if (!gup_huge_pmd(pmd, pmdp, addr, next, flags,
--
2.37.1
