[RFC PATCH 12/14] mm: Free folios directly in move_folios_to_lru()

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

The few folios which can't be moved to the LRU list (because their
refcount dropped to zero) used to be returned to the caller to dispose
of.  Make this simpler to call by freeing the folios directly through
free_unref_folios().

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/vmscan.c | 31 ++++++++++++-------------------
 1 file changed, 12 insertions(+), 19 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 965c429847fd..d5080510608e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2489,8 +2489,9 @@ static unsigned int move_folios_to_lru(struct lruvec *lruvec,
 		struct list_head *list)
 {
 	int nr_pages, nr_moved = 0;
-	LIST_HEAD(folios_to_free);
+	struct folio_batch free_folios;
 
+	folio_batch_init(&free_folios);
 	while (!list_empty(list)) {
 		struct folio *folio = lru_to_folio(list);
 
@@ -2519,12 +2520,12 @@ static unsigned int move_folios_to_lru(struct lruvec *lruvec,
 		if (unlikely(folio_put_testzero(folio))) {
 			__folio_clear_lru_flags(folio);
 
-			if (unlikely(folio_test_large(folio))) {
+			if (folio_batch_add(&free_folios, folio) == 0) {
 				spin_unlock_irq(&lruvec->lru_lock);
-				destroy_large_folio(folio);
+				mem_cgroup_uncharge_folios(&free_folios);
+				free_unref_folios(&free_folios);
 				spin_lock_irq(&lruvec->lru_lock);
-			} else
-				list_add(&folio->lru, &folios_to_free);
+			}
 
 			continue;
 		}
@@ -2541,10 +2542,12 @@ static unsigned int move_folios_to_lru(struct lruvec *lruvec,
 			workingset_age_nonresident(lruvec, nr_pages);
 	}
 
-	/*
-	 * To save our caller's stack, now use input list for pages to free.
-	 */
-	list_splice(&folios_to_free, list);
+	if (free_folios.nr) {
+		spin_unlock_irq(&lruvec->lru_lock);
+		mem_cgroup_uncharge_folios(&free_folios);
+		free_unref_folios(&free_folios);
+		spin_lock_irq(&lruvec->lru_lock);
+	}
 
 	return nr_moved;
 }
@@ -2623,8 +2626,6 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 	spin_unlock_irq(&lruvec->lru_lock);
 
 	lru_note_cost(lruvec, file, stat.nr_pageout, nr_scanned - nr_reclaimed);
-	mem_cgroup_uncharge_list(&folio_list);
-	free_unref_page_list(&folio_list);
 
 	/*
 	 * If dirty folios are scanned that are not queued for IO, it
@@ -2765,8 +2766,6 @@ static void shrink_active_list(unsigned long nr_to_scan,
 
 	nr_activate = move_folios_to_lru(lruvec, &l_active);
 	nr_deactivate = move_folios_to_lru(lruvec, &l_inactive);
-	/* Keep all free folios in l_active list */
-	list_splice(&l_inactive, &l_active);
 
 	__count_vm_events(PGDEACTIVATE, nr_deactivate);
 	__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
@@ -2776,8 +2775,6 @@ static void shrink_active_list(unsigned long nr_to_scan,
 
 	if (nr_rotated)
 		lru_note_cost(lruvec, file, 0, nr_rotated);
-	mem_cgroup_uncharge_list(&l_active);
-	free_unref_page_list(&l_active);
 	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
 			nr_deactivate, nr_rotated, sc->priority, file);
 }
@@ -5238,10 +5235,6 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
 
 	spin_unlock_irq(&lruvec->lru_lock);
 
-	mem_cgroup_uncharge_list(&list);
-	free_unref_page_list(&list);
-
-	INIT_LIST_HEAD(&list);
 	list_splice_init(&clean, &list);
 
 	if (!list_empty(&list)) {
-- 
2.40.1