[PATCH] mm: Introduce a pageflag for partially mapped folios fix

[Usama Arif <usamaarif642@xxxxxxxxx>]

Test partially_mapped flag before clearing it. This should
avoid unnecessary writes and will be needed in the nr_split_deferred
series.
Also no need to clear partially_mapped prepping compound head, as it
should start with already being cleared.

Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
---
 include/linux/page-flags.h | 2 +-
 mm/huge_memory.c           | 9 ++++++---
 mm/internal.h              | 4 +---
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index c3bb0e0da581..f1602695daf2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1182,7 +1182,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
  */
 #define PAGE_FLAGS_SECOND						\
 	(0xffUL /* order */		| 1UL << PG_has_hwpoisoned |	\
-	 1UL << PG_large_rmappable)
+	 1UL << PG_large_rmappable	| 1UL << PG_partially_mapped)
 
 #define PAGE_FLAGS_PRIVATE				\
 	(1UL << PG_private | 1UL << PG_private_2)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5d67d3b3c1b2..402b9d933de0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3422,7 +3422,8 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 			 * page_deferred_list.
 			 */
 			list_del_init(&folio->_deferred_list);
-			__folio_clear_partially_mapped(folio);
+			if (folio_test_partially_mapped(folio))
+				__folio_clear_partially_mapped(folio);
 		}
 		spin_unlock(&ds_queue->split_queue_lock);
 		if (mapping) {
@@ -3479,7 +3480,8 @@ void __folio_undo_large_rmappable(struct folio *folio)
 	if (!list_empty(&folio->_deferred_list)) {
 		ds_queue->split_queue_len--;
 		list_del_init(&folio->_deferred_list);
-		__folio_clear_partially_mapped(folio);
+		if (folio_test_partially_mapped(folio))
+			__folio_clear_partially_mapped(folio);
 	}
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 }
@@ -3610,7 +3612,8 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		} else {
 			/* We lost race with folio_put() */
 			list_del_init(&folio->_deferred_list);
-			__folio_clear_partially_mapped(folio);
+			if (folio_test_partially_mapped(folio))
+				__folio_clear_partially_mapped(folio);
 			ds_queue->split_queue_len--;
 		}
 		if (!--sc->nr_to_scan)
diff --git a/mm/internal.h b/mm/internal.h
index 27cbb5365841..52f7fc4e8ac3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -662,10 +662,8 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
 	atomic_set(&folio->_entire_mapcount, -1);
 	atomic_set(&folio->_nr_pages_mapped, 0);
 	atomic_set(&folio->_pincount, 0);
-	if (order > 1) {
+	if (order > 1)
 		INIT_LIST_HEAD(&folio->_deferred_list);
-		__folio_clear_partially_mapped(folio);
-	}
 }
 
 static inline void prep_compound_tail(struct page *head, int tail_idx)
-- 
2.43.5