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

Commit Message

David Hildenbrand March 8, 2022, 2:14 p.m. UTC

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 <[e-mail]>
---
 mm/huge_memory.c | 2 ++
 mm/memory.c      | 1 +
 2 files changed, 3 insertions(+)

Patch

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;