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Date: Tue, 12 Apr 2022 11:26:44 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org Cc: Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, David Rientjes <rientjes@...gle.com>, Shakeel Butt <shakeelb@...gle.com>, John Hubbard <jhubbard@...dia.com>, Jason Gunthorpe <jgg@...dia.com>, Mike Kravetz <mike.kravetz@...cle.com>, Mike Rapoport <rppt@...ux.ibm.com>, Yang Shi <shy828301@...il.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Matthew Wilcox <willy@...radead.org>, Jann Horn <jannh@...gle.com>, Michal Hocko <mhocko@...nel.org>, Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>, Roman Gushchin <guro@...com>, Andrea Arcangeli <aarcange@...hat.com>, Peter Xu <peterx@...hat.com>, Donald Dutile <ddutile@...hat.com>, Christoph Hellwig <hch@....de>, Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>, Liang Zhang <zhangliang5@...wei.com>, Pedro Gomes <pedrodemargomes@...il.com>, Oded Gabbay <oded.gabbay@...il.com>, linux-mm@...ck.org Subject: Re: [PATCH v3 09/16] mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively On 3/29/22 18:04, David Hildenbrand wrote: > We want to mark anonymous pages exclusive, and when using > page_move_anon_rmap() we know that we are the exclusive user, as > properly documented. This is a preparation for marking anonymous pages > exclusive in page_move_anon_rmap(). > > In both instances, we're holding page lock and are sure that we're the > exclusive owner (page_count() == 1). hugetlb already properly uses > page_move_anon_rmap() in the write fault handler. Yeah, note that do_wp_page() used to call page_move_anon_rmap() always since the latter was introduced, until commit 09854ba94c6a ("mm: do_wp_page() simplification"). Probably not intended. > Note that in case of a PTE-mapped THP, we'll only end up calling this > function if the whole THP is only referenced by the single PTE mapping > a single subpage (page_count() == 1); consequently, it's fine to modify > the compound page mapping inside page_move_anon_rmap(). > > Signed-off-by: David Hildenbrand <david@...hat.com> Acked-by: Vlastimil Babka <vbabka@...e.cz> > --- > mm/huge_memory.c | 2 ++ > mm/memory.c | 1 + > 2 files changed, 3 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index c4526343565a..dd16819c5edc 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1317,6 +1317,8 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf) > try_to_free_swap(page); > if (page_count(page) == 1) { > pmd_t entry; > + > + page_move_anon_rmap(page, vma); > entry = pmd_mkyoung(orig_pmd); > entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); > if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry, 1)) > diff --git a/mm/memory.c b/mm/memory.c > index 03e29c9614e0..4303c0fdcf17 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3303,6 +3303,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) > * and the page is locked, it's dark out, and we're wearing > * sunglasses. Hit it. > */ > + page_move_anon_rmap(page, vma); > unlock_page(page); > wp_page_reuse(vmf); > return VM_FAULT_WRITE;
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