[merged mm-stable] mm-clarify-the-folio_free_swap-for-do_swap_page.patch removed from -mm tree

The quilt patch titled
     Subject: mm: clarify the folio_free_swap() for do_swap_page()
has been removed from the -mm tree.  Its filename was
     mm-clarify-the-folio_free_swap-for-do_swap_page.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Barry Song (Xiaomi)" <[email protected]>
Subject: mm: clarify the folio_free_swap() for do_swap_page()
Date: Thu, 2 Jul 2026 07:59:55 +0800

Since commit 4b34f1d82c654 ("mm, swap: free the swap cache after folio is
mapped"), we have relied on do_wp_page() to handle the non-exclusive case,
where the folio may either be reused or require CoW.

As a result, using the refcount in do_swap_page() to decide when to free
the swap cache is no longer necessary, since do_wp_page() can handle this
more cleanly and consistently.

We can now simply use FAULT_FLAG_WRITE together with exclusivity to decide
when to free the swap cache in do_swap_page().

Link: https://lore.kernel.org/[email protected]
Signed-off-by: Barry Song (Xiaomi) <[email protected]>
Suggested-by: David Hildenbrand (Arm) <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Usama Arif <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 mm/memory.c |   20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

--- a/mm/memory.c~mm-clarify-the-folio_free_swap-for-do_swap_page
+++ a/mm/memory.c
@@ -4509,7 +4509,7 @@ static vm_fault_t remove_device_exclusiv
 static inline bool should_try_to_free_swap(struct swap_info_struct *si,
 					   struct folio *folio,
 					   struct vm_area_struct *vma,
-					   unsigned int extra_refs,
+					   bool exclusive,
 					   unsigned int fault_flags)
 {
 	if (!folio_test_swapcache(folio))
@@ -4525,14 +4525,12 @@ static inline bool should_try_to_free_sw
 	if (mem_cgroup_swap_full(folio) || (vma->vm_flags & VM_LOCKED) ||
 	    folio_test_mlocked(folio))
 		return true;
+
 	/*
-	 * If we want to map a page that's in the swapcache writable, we
-	 * have to detect via the refcount if we're really the exclusive
-	 * user. Try freeing the swapcache to get rid of the swapcache
-	 * reference only in case it's likely that we'll be the exclusive user.
+	 * Free the swapcache only if we are the exclusive user and
+	 * this is a write fault.
 	 */
-	return (fault_flags & FAULT_FLAG_WRITE) && !folio_test_ksm(folio) &&
-		folio_ref_count(folio) == (extra_refs + folio_nr_pages(folio));
+	return (fault_flags & FAULT_FLAG_WRITE) && exclusive;
 }
 
 static vm_fault_t pte_marker_clear(struct vm_fault *vmf)
@@ -5036,10 +5034,8 @@ check_folio:
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
 		    !pte_needs_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
-			if (vmf->flags & FAULT_FLAG_WRITE) {
+			if (vmf->flags & FAULT_FLAG_WRITE)
 				pte = pte_mkdirty(pte);
-				vmf->flags &= ~FAULT_FLAG_WRITE;
-			}
 		}
 		rmap_flags |= RMAP_EXCLUSIVE;
 	}
@@ -5079,7 +5075,7 @@ check_folio:
 	 * Do it after mapping, so raced page faults will likely see the folio
 	 * in swap cache and wait on the folio lock.
 	 */
-	if (should_try_to_free_swap(si, folio, vma, nr_pages, vmf->flags))
+	if (should_try_to_free_swap(si, folio, vma, exclusive, vmf->flags))
 		folio_free_swap(folio);
 
 	folio_unlock(folio);
@@ -5096,7 +5092,7 @@ check_folio:
 		folio_put(swapcache);
 	}
 
-	if (vmf->flags & FAULT_FLAG_WRITE) {
+	if ((vmf->flags & FAULT_FLAG_WRITE) && !pte_write(pte)) {
 		ret |= do_wp_page(vmf);
 		if (ret & VM_FAULT_ERROR)
 			ret &= VM_FAULT_ERROR;
_

Patches currently in -mm which might be from [email protected] are

arm64-hugetlb-extend-batching-of-multiple-cont_pte-in-a-single-pte-setup.patch
arm64-vmalloc-allow-arch_vmap_pte_range_map_size-to-batch-multiple-cont_pte.patch
mm-vmalloc-extend-page-table-walk-to-support-larger-page_shift-sizes-and-eliminate-page-table-rewalk.patch
mm-vmalloc-map-contiguous-pages-in-batches-for-vmap-if-possible.patch
mm-vmalloc-align-vm_area-so-vmap-can-batch-mappings.patch