[RFC PATCH 01/57] mm: add pte_folio()

[Kiryl Shutsemau <kirill@shutemov.name>]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Callers that want the folio behind a present PTE spell it out as
page_folio(pte_page(pte)).

Add pte_folio() as the folio companion to pte_page(), and convert the
callers in fs/proc/task_mmu.c and mm/hugetlb.c.

Preparation for the anonymous collapse engine, which reads the folio
behind a PTE in several places.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 fs/proc/task_mmu.c |  4 ++--
 include/linux/mm.h | 14 ++++++++++++++
 mm/hugetlb.c       |  8 ++++----
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5c54aebe2118..459c779b8141 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1277,7 +1277,7 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
 	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
 	ptent = huge_ptep_get(walk->mm, addr, pte);
 	if (pte_present(ptent)) {
-		folio = page_folio(pte_page(ptent));
+		folio = pte_folio(ptent);
 		present = true;
 	} else {
 		const softleaf_t entry = softleaf_from_pte(ptent);
@@ -2227,7 +2227,7 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask,
 	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, ptep);
 	pte = huge_ptep_get(walk->mm, addr, ptep);
 	if (pte_present(pte)) {
-		struct folio *folio = page_folio(pte_page(pte));
+		struct folio *folio = pte_folio(pte);
 
 		if (!folio_test_anon(folio))
 			flags |= PM_FILE;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0829e0d3b2d1..eb44e3dfee09 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2681,6 +2681,20 @@ static inline pte_t mk_pte(const struct page *page, pgprot_t pgprot)
 	return pfn_pte(page_to_pfn(page), pgprot);
 }
 
+/**
+ * pte_folio - Return the folio mapped by a present PTE.
+ * @pte: A present page table entry.
+ *
+ * The folio companion to pte_page(); only meaningful for a present PTE
+ * that maps a struct-page-backed folio.
+ *
+ * Return: The folio containing the page @pte maps.
+ */
+static inline struct folio *pte_folio(pte_t pte)
+{
+	return page_folio(pte_page(pte));
+}
+
 /**
  * folio_mk_pte - Create a PTE for this folio
  * @folio: The folio to create a PTE for
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dded1768193a..bceab8e14118 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5280,7 +5280,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		 * are about to unmap is the actual folio of interest.
 		 */
 		if (folio_provided) {
-			if (folio != page_folio(pte_page(pte))) {
+			if (folio != pte_folio(pte)) {
 				spin_unlock(ptl);
 				continue;
 			}
@@ -5291,7 +5291,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 			 */
 			set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
 		} else {
-			folio = page_folio(pte_page(pte));
+			folio = pte_folio(pte);
 		}
 
 		pte = huge_ptep_get_and_clear(mm, address, ptep, sz);
@@ -5514,7 +5514,7 @@ static vm_fault_t hugetlb_wp(struct vm_fault *vmf)
 		return 0;
 	}
 
-	old_folio = page_folio(pte_page(pte));
+	old_folio = pte_folio(pte);
 
 	delayacct_wpcopy_start();
 
@@ -6189,7 +6189,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			 * checks whether we can re-use the folio exclusively
 			 * for us in case we are the only user of it.
 			 */
-			folio = page_folio(pte_page(vmf.orig_pte));
+			folio = pte_folio(vmf.orig_pte);
 			if (folio_test_anon(folio) && !folio_trylock(folio)) {
 				need_wait_lock = true;
 				goto out_ptl;
-- 
2.54.0