Messages in this thread | | | Date | Wed, 3 Apr 2024 09:37:03 +0200 | Subject | Re: [PATCH 1/3] mm: Allow anon exclusive check over hugetlb tail pages | From | David Hildenbrand <> |
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On 03.04.24 03:32, peterx@redhat.com wrote: > From: Peter Xu <peterx@redhat.com> > > PageAnonExclusive() used to forbid tail pages for hugetlbfs, as that used > to be called mostly in hugetlb specific paths and the head page was > guaranteed. > > As we move forward towards merging hugetlb paths into generic mm, we may > start to pass in tail hugetlb pages (when with cont-pte/cont-pmd huge > pages) for such check. Allow it to properly fetch the head, in which case > the anon-exclusiveness of the head will always represents the tail page. > > There's already a sign of it when we look at the fast-gup which already
"GUP-fast" ;)
> contain the hugetlb processing altogether: we used to have a specific > commit 5805192c7b72 ("mm/gup: handle cont-PTE hugetlb pages correctly in > gup_must_unshare() via GUP-fast") covering that area. Now with this more > generic change, that can also go away. > > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > include/linux/page-flags.h | 8 +++++++- > mm/internal.h | 10 ---------- > 2 files changed, 7 insertions(+), 11 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 888353c209c0..225357f48a79 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -1095,7 +1095,13 @@ PAGEFLAG(Isolated, isolated, PF_ANY); > static __always_inline int PageAnonExclusive(const struct page *page) > { > VM_BUG_ON_PGFLAGS(!PageAnon(page), page); > - VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page); > + /* > + * Allow the anon-exclusive check to work on hugetlb tail pages. > + * Here hugetlb pages will always guarantee the anon-exclusiveness > + * of the head page represents the tail pages. > + */ > + if (PageHuge(page) && !PageHead(page)) > + page = compound_head(page); > return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags); > } > > diff --git a/mm/internal.h b/mm/internal.h > index 9512de7398d5..87f6e4fd56a5 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1259,16 +1259,6 @@ static inline bool gup_must_unshare(struct vm_area_struct *vma, > if (IS_ENABLED(CONFIG_HAVE_FAST_GUP)) > smp_rmb(); > > - /* > - * During GUP-fast we might not get called on the head page for a > - * hugetlb page that is mapped using cont-PTE, because GUP-fast does > - * not work with the abstracted hugetlb PTEs that always point at the > - * head page. For hugetlb, PageAnonExclusive only applies on the head > - * page (as it cannot be partially COW-shared), so lookup the head page. > - */ > - if (unlikely(!PageHead(page) && PageHuge(page))) > - page = compound_head(page); > - > /* > * Note that PageKsm() pages cannot be exclusive, and consequently, > * cannot get pinned.
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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