The patch titled
Subject: mm/gup: use gup_can_follow_protnone() also in GUP-fast
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-use-gup_can_follow_protnone-also-in-gup-fast.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-use-gup_can_follow_protnone-also-in-gup-fast.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/gup: use gup_can_follow_protnone() also in GUP-fast
Date: Thu, 25 Aug 2022 18:46:58 +0200
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Note that the comment regarding THP migration is outdated: commit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and drop the somewhat outdated comments.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@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
--- a/mm/gup.c~mm-gup-use-gup_can_follow_protnone-also-in-gup-fast
+++ a/mm/gup.c
@@ -2367,11 +2367,7 @@ static int gup_pte_range(pmd_t pmd, unsi
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))
@@ -2753,12 +2749,8 @@ static int gup_pmd_range(pud_t *pudp, pu
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,
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-gup-replace-foll_numa-by-gup_can_follow_protnone.patch
mm-gup-use-gup_can_follow_protnone-also-in-gup-fast.patch
mm-fixup-documentation-regarding-pte_numa-and-prot_numa.patch
