Re: [PATCH v7 4/4] mm/vmscan: avoid split lazyfree THP during shrink_folio_list()

[Lance Yang]

Hi Andrew,

I'd like to fix the bug[1] I mentioned previously. Could you please fold the
following changes into this patch? 

[1] https://lore.kernel.org/linux-mm/20240613065521.15960-1-ioworker0@xxxxxxxxx/

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f409ea9fcc18..425374ae06ed 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2707,10 +2707,8 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma,
 	if (unlikely(page_folio(page) != folio))
 		return false;
 
-	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) {
-		folio_set_swapbacked(folio);
+	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd))
 		return false;
-	}
 
 	orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp);
 
@@ -2737,10 +2735,8 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma,
 	 *
 	 * The only folio refs must be one from isolation plus the rmap(s).
 	 */
-	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd))
-		folio_set_swapbacked(folio);
-
-	if (folio_test_swapbacked(folio) || ref_count != map_count + 1) {
+	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) ||
+	    ref_count != map_count + 1) {
 		set_pmd_at(mm, addr, pmdp, orig_pmd);
 		return false;
 	}
diff --git a/mm/rmap.c b/mm/rmap.c
index b9e5943c8349..393e2c11c44c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1824,12 +1824,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			if (unlikely(folio_test_swapbacked(folio) !=
 					folio_test_swapcache(folio))) {
-				/*
-				 * unmap_huge_pmd_locked() will unmark a
-				 * PMD-mapped folio as lazyfree if the folio or
-				 * its PMD was redirtied.
-				 */
-				WARN_ON_ONCE(!pmd_mapped);
+				WARN_ON_ONCE(1);
 				goto walk_done_err;
 			}
 
-- 

Thanks,
Lance