From 0cf459866a91c741eb14a92f3633638d1dd9db59 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Thu, 25 Aug 2022 18:46:58 +0200 Subject: [PATCH] mm/gup: use gup_can_follow_protnone() also in GUP-fast 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 Note that the comment regarding THP migration is outdated: commit 2b4847e73004 ("mm: numa: serialise parallel get_user_page against THP migration") described that this was required for THP due to lack of PMD migration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 So let's just reuse gup_can_follow_protnone() here to make it consistent and drop the somewhat outdated comments. Link: https://lkml.kernel.org/r/20220825164659.89824-3-david@redhat.com Signed-off-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: John Hubbard Cc: Matthew Wilcox Cc: Mel Gorman Cc: Peter Xu Signed-off-by: Andrew Morton --- mm/gup.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index f06770e03549..ce00a4c40da8 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2420,11 +2420,7 @@ static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, 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)) @@ -2808,12 +2804,8 @@ 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,