[PATCH] mm: remove redundant page parameter from do_set_pmd()

[PATCH] mm: remove redundant page parameter from do_set_pmd()

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

The page parameter passed to do_set_pmd() was always overwritten with
&folio->page immediately upon function entry (line 5369 in memory.c),
making the parameter completely redundant. This confused callers who
computed different page values only to have them ignored.

Changes:
- Convert page from a function parameter to a local variable
- Update function signature in both implementations and stub
- Remove unnecessary folio_file_page() calculation in filemap.c
- Update all three call sites to remove the page argument

This simplifies the API since folio already contains all the page
information needed. The function still uses &folio->page internally
for cache flushing and rmap operations.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 include/linux/mm.h | 2 +-
 mm/filemap.c       | 3 +--
 mm/khugepaged.c    | 6 +++---
 mm/memory.c        | 7 ++++---
 4 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 710d20fc954b..cb1fe75575c3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1490,7 +1490,7 @@ 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 folio *folio, struct page *page);
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio);
 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 ebd75684cb0a..4be5f3f5b8d6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3678,8 +3678,7 @@ 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, folio, page);
+		vm_fault_t ret = do_set_pmd(vmf, folio);
 		if (!ret) {
 			/* The page is mapped successfully, reference consumed. */
 			folio_unlock(folio);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 9f790ec34400..2d7b23efa11b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1442,7 +1442,7 @@ static void collect_mm_slot(struct mm_slot *slot)
 
 /* folio must be locked, and mmap_lock must be held */
 static enum scan_result set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
-				     pmd_t *pmdp, struct folio *folio, struct page *page)
+				     pmd_t *pmdp, struct folio *folio)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct vm_fault vmf = {
@@ -1470,7 +1470,7 @@ static enum scan_result set_huge_pmd(struct vm_area_struct *vma, unsigned long a
 	}
 
 	vmf.pmd = pmdp;
-	if (do_set_pmd(&vmf, folio, page))
+	if (do_set_pmd(&vmf, folio))
 		return SCAN_FAIL;
 
 	folio_get(folio);
@@ -1678,7 +1678,7 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign
 maybe_install_pmd:
 	/* step 5: install pmd entry */
 	result = install_pmd
-			? set_huge_pmd(vma, haddr, pmd, folio, &folio->page)
+			? set_huge_pmd(vma, haddr, pmd, folio)
 			: SCAN_SUCCEED;
 	goto drop_folio;
 abort:
diff --git a/mm/memory.c b/mm/memory.c
index 30a897018482..8b29ecbfe7fa 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5342,8 +5342,9 @@ static void deposit_prealloc_pte(struct vm_fault *vmf)
 	vmf->prealloc_pte = NULL;
 }
 
-vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio)
 {
+	struct page *page;
 	struct vm_area_struct *vma = vmf->vma;
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
@@ -5418,7 +5419,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *pa
 	return ret;
 }
 #else
-vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *page)
+vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio)
 {
 	return VM_FAULT_FALLBACK;
 }
@@ -5542,7 +5543,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 
 	if (pmd_none(*vmf->pmd)) {
 		if (!needs_fallback && folio_test_pmd_mappable(folio)) {
-			ret = do_set_pmd(vmf, folio, page);
+			ret = do_set_pmd(vmf, folio);
 			if (ret != VM_FAULT_FALLBACK)
 				return ret;
 		}
-- 
2.43.0

Re: [PATCH] mm: remove redundant page parameter from do_set_pmd()

[Matthew Wilcox]

On Tue, Jan 13, 2026 at 09:41:29AM +0800, Ye Liu wrote:
> The page parameter passed to do_set_pmd() was always overwritten with
> &folio->page immediately upon function entry (line 5369 in memory.c),
> making the parameter completely redundant. This confused callers who
> computed different page values only to have them ignored.

No.  It's an accident of the implementation that we currently only
support folios up to the size of PMDs.  That is not the long-term plan.
We always want to specify exactly which pages of the folio to map.