[PATCH v2 2/2] mm: convert do_set_pmd() to take a folio

[Baolin Wang]

In do_set_pmd(), we always use the folio->page to build PMD mappings for
the entire folio. Since all callers of do_set_pmd() already hold a stable
folio, converting do_set_pmd() to take a folio is safe and more straightforward.

In addition, to ensure the extensibility of do_set_pmd() for supporting
larger folios beyond PMD size, we keep the 'page' parameter to specify
which page within the folio should be mapped.

No functional changes expected.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
Changes from v1:
 - Keep the 'page' parameter of the do_set_pmd().

Note: I did mm selftests and built kernel on tmpfs/xfs filesystems, and
did not find any regression.
---
 include/linux/mm.h |  2 +-
 mm/filemap.c       |  2 +-
 mm/khugepaged.c    |  2 +-
 mm/memory.c        | 11 +++++------
 4 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 43748c8f3454..d5f578c91e77 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1237,7 +1237,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 	return pte;
 }
 
-vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page);
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page);
 void set_pte_range(struct vm_fault *vmf, struct folio *folio,
 		struct page *page, unsigned int nr, unsigned long addr);
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 7b90cbeb4a1a..09d005848f0d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3533,7 +3533,7 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
 
 	if (pmd_none(*vmf->pmd) && folio_test_pmd_mappable(folio)) {
 		struct page *page = folio_file_page(folio, start);
-		vm_fault_t ret = do_set_pmd(vmf, page);
+		vm_fault_t ret = do_set_pmd(vmf, folio, page);
 		if (!ret) {
 			/* The page is mapped successfully, reference consumed. */
 			folio_unlock(folio);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index aca66e7f4fd9..c4b5031f3254 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1478,7 +1478,7 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
 
 	mmap_assert_locked(vma->vm_mm);
 
-	if (do_set_pmd(&vmf, &folio->page))
+	if (do_set_pmd(&vmf, folio, &folio->page))
 		return SCAN_FAIL;
 
 	folio_get(folio);
diff --git a/mm/memory.c b/mm/memory.c
index 68c1d962d0ad..9c202c32ca66 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5176,9 +5176,8 @@ static void deposit_prealloc_pte(struct vm_fault *vmf)
 	vmf->prealloc_pte = NULL;
 }
 
-vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
 {
-	struct folio *folio = page_folio(page);
 	struct vm_area_struct *vma = vmf->vma;
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
@@ -5251,7 +5250,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
 	return ret;
 }
 #else
-vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
 {
 	return VM_FAULT_FALLBACK;
 }
@@ -5345,6 +5344,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 	else
 		page = vmf->page;
 
+	folio = page_folio(page);
 	/*
 	 * check even for read faults because we might have lost our CoWed
 	 * page
@@ -5356,8 +5356,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 	}
 
 	if (pmd_none(*vmf->pmd)) {
-		if (PageTransCompound(page)) {
-			ret = do_set_pmd(vmf, page);
+		if (folio_test_pmd_mappable(folio)) {
+			ret = do_set_pmd(vmf, folio, page);
 			if (ret != VM_FAULT_FALLBACK)
 				return ret;
 		}
@@ -5368,7 +5368,6 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 			return VM_FAULT_OOM;
 	}
 
-	folio = page_folio(page);
 	nr_pages = folio_nr_pages(folio);
 
 	/*
-- 
2.43.5