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(cpe5c7695f3aee0-cm5c7695f3aede.cpe.net.cable.rogers.com. [99.254.144.39]) by smtp.gmail.com with ESMTPSA id p3-20020a0cfac3000000b00631fea4d5bcsm6277797qvo.95.2023.06.28.14.53.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jun 2023 14:53:13 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: David Hildenbrand , "Kirill A . Shutemov" , Andrew Morton , Andrea Arcangeli , Mike Rapoport , John Hubbard , Matthew Wilcox , Mike Kravetz , Vlastimil Babka , Yang Shi , James Houghton , Jason Gunthorpe , Lorenzo Stoakes , Hugh Dickins , peterx@redhat.com Subject: [PATCH v4 1/8] mm/hugetlb: Handle FOLL_DUMP well in follow_page_mask() Date: Wed, 28 Jun 2023 17:53:03 -0400 Message-ID: <20230628215310.73782-2-peterx@redhat.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230628215310.73782-1-peterx@redhat.com> References: <20230628215310.73782-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Firstly, the no_page_table() is meaningless for hugetlb which is a no-op there, because a hugetlb page always satisfies: - vma_is_anonymous() =3D=3D false - vma->vm_ops->fault !=3D NULL So we can already safely remove it in hugetlb_follow_page_mask(), alongside with the page* variable. Meanwhile, what we do in follow_hugetlb_page() actually makes sense for a dump: we try to fault in the page only if the page cache is already allocated. Let's do the same here for follow_page_mask() on hugetlb. It should so far has zero effect on real dumps, because that still goes into follow_hugetlb_page(). But this may start to influence a bit on follow_page() users who mimics a "dump page" scenario, but hopefully in a good way. This also paves way for unifying the hugetlb gup-slow. Reviewed-by: Mike Kravetz Reviewed-by: David Hildenbrand Signed-off-by: Peter Xu --- mm/gup.c | 9 ++------- mm/hugetlb.c | 9 +++++++++ 2 files changed, 11 insertions(+), 7 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index a8336b39d6b5..06bc2e31f209 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -767,7 +767,6 @@ static struct page *follow_page_mask(struct vm_area_str= uct *vma, struct follow_page_context *ctx) { pgd_t *pgd; - struct page *page; struct mm_struct *mm =3D vma->vm_mm; =20 ctx->page_mask =3D 0; @@ -780,12 +779,8 @@ static struct page *follow_page_mask(struct vm_area_st= ruct *vma, * hugetlb_follow_page_mask is only for follow_page() handling here. * Ordinary GUP uses follow_hugetlb_page for hugetlb processing. */ - if (is_vm_hugetlb_page(vma)) { - page =3D hugetlb_follow_page_mask(vma, address, flags); - if (!page) - page =3D no_page_table(vma, flags); - return page; - } + if (is_vm_hugetlb_page(vma)) + return hugetlb_follow_page_mask(vma, address, flags); =20 pgd =3D pgd_offset(mm, address); =20 diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bce28cca73a1..d04ba5782fdd 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6498,6 +6498,15 @@ struct page *hugetlb_follow_page_mask(struct vm_area= _struct *vma, spin_unlock(ptl); out_unlock: hugetlb_vma_unlock_read(vma); + + /* + * Fixup retval for dump requests: if pagecache doesn't exist, + * don't try to allocate a new page but just skip it. + */ + if (!page && (flags & FOLL_DUMP) && + !hugetlbfs_pagecache_present(h, vma, address)) + page =3D ERR_PTR(-EFAULT); + return page; } =20 --=20 2.41.0