[merged mm-stable] mm-drop-stale-folio_ref_count==1-check-in-do_swap_page-reuse-logic.patch removed from -mm tree

[merged mm-stable] mm-drop-stale-folio_ref_count==1-check-in-do_swap_page-reuse-logic.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic
has been removed from the -mm tree.  Its filename was
     mm-drop-stale-folio_ref_count==1-check-in-do_swap_page-reuse-logic.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)" <baohua@kernel.org>
Subject: mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic
Date: Thu, 2 Jul 2026 07:59:53 +0800

The "we just allocated them without exposing them to the swapcache" case
no longer exists, as Kairui has routed synchronous I/O through the
swapcache as well in his series "unify swapin use swap cache and cleanup
flags"[1].  As a result, folio_ref_count() should never be 1 in this path,
since at least two references are held (base ref plus swapcache).  Remove
the folio_ref_count()==1 check and update the comment accordingly.

The ksm_might_need_to_copy() check may allocate a fresh folio with
folio_ref_count() == 1.  Along that path, exclusive has already been
set to true, so the folio can still be reused correctly.

[akpm@linux-foundation.org: update comment, per David]
  Link: https://lore.kernel.org/3a185a5d-2f2c-4e9d-9cd9-8bdb236dfc5c@kernel.org
Link: https://lore.kernel.org/20260701235955.36126-3-baohua@kernel.org
Link: https://lore.kernel.org/all/20251220-swap-table-p2-v5-0-8862a265a033@tencent.com/ [1]
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Acked-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/mm/memory.c~mm-drop-stale-folio_ref_count==1-check-in-do_swap_page-reuse-logic
+++ a/mm/memory.c
@@ -5039,13 +5039,10 @@ check_folio:
 		pte = pte_mkuffd_wp(pte);
 
 	/*
-	 * Same logic as in do_wp_page(); however, optimize for pages that are
-	 * certainly not shared either because we just allocated them without
-	 * exposing them to the swapcache or because the swap entry indicates
-	 * exclusivity.
+	 * Similar logic as in do_wp_page(); however, optimize for pages that
+	 * are certainly exclusive.
 	 */
-	if (!folio_test_ksm(folio) &&
-	    (exclusive || folio_ref_count(folio) == 1)) {
+	if (exclusive) {
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
 		    !pte_needs_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
_

Patches currently in -mm which might be from baohua@kernel.org 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