[PATCH 1/7] mm: Set the pte dirty if the folio is already dirty

[Matthew Wilcox (Oracle)]

If the first access to a folio is a read that is then followed by a
write, we can save a page fault.  s390 implemented this in their
mk_pte() in commit abf09bed3cce ("s390/mm: implement software dirty
bits"), but other architectures can also benefit from this.

Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
---
 arch/s390/include/asm/pgtable.h | 7 +------
 mm/memory.c                     | 2 ++
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 3ca5af4cfe43..3ee495b5171e 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1451,12 +1451,7 @@ static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
 
 static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
 {
-	unsigned long physpage = page_to_phys(page);
-	pte_t __pte = mk_pte_phys(physpage, pgprot);
-
-	if (pte_write(__pte) && PageDirty(page))
-		__pte = pte_mkdirty(__pte);
-	return __pte;
+	return mk_pte_phys(page_to_phys(page), pgprot);
 }
 
 #define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
diff --git a/mm/memory.c b/mm/memory.c
index 539c0f7c6d54..4330560eee55 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5124,6 +5124,8 @@ void set_pte_range(struct vm_fault *vmf, struct folio *folio,
 
 	if (write)
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	else if (pte_write(entry) && folio_test_dirty(folio))
+		entry = pte_mkdirty(entry);
 	if (unlikely(vmf_orig_pte_uffd_wp(vmf)))
 		entry = pte_mkuffd_wp(entry);
 	/* copy-on-write page */
-- 
2.47.2