[PATCH v3 2/4] mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic

[Barry Song (Xiaomi)]

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.

[1] https://lore.kernel.org/all/20251220-swap-table-p2-v5-0-8862a265a033@xxxxxxxxxxx/

Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>
Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
---
 mm/memory.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 87da78eb1abd..71e9d394816b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5046,13 +5046,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		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 not because the swap entry indicates exclusivity.
 	 */
-	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);
-- 
2.39.3 (Apple Git-146)