linux-kernel - [PATCH v1 09/15] mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively

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Date:   Tue,  8 Mar 2022 15:14:31 +0100
From:   David Hildenbrand <david@...hat.com>
To:     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>,
        Vlastimil Babka <vbabka@...e.cz>, 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,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH v1 09/15] mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively

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.

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>
---
 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 c1f7eaba23ff..0b6fb409b9e4 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 00c45b3a9576..7b32f422798d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3307,6 +3307,7 @@ 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;
-- 
2.35.1