[PATCH v2 2/7] mm/mglru: batch update lrugen->nr_pages in inc_min_seq()

["Barry Song (Xiaomi)" <baohua@kernel.org>]

Currently, folio_inc_gen() updates lrugen->nr_pages for every folio
as it advances generations. Instead, accumulate the size changes
and update lrugen->nr_pages in a batch after scanning the entire
oldest generation, or when the scan stops because remaining reaches
zero.

Since we only move folios from the oldest generation to the second
oldest generation, the active/inactive state cannot change. We can
therefore skip __lru_update_size().

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Tested-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
---
 mm/vmscan.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8f187d296b8e..07c22d51debd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3918,6 +3918,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int hist = lru_hist_from_seq(lrugen->min_seq[type]);
 	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
+	int target_gen = (old_gen + 1) % MAX_NR_GENS;
 
 	/* For file type, skip the check if swappiness is anon only */
 	if (type && (swappiness == SWAPPINESS_ANON_ONLY))
@@ -3927,35 +3928,47 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 	if (!type && !swappiness)
 		goto done;
 
+	VM_WARN_ON_ONCE(get_nr_gens(lruvec, type) != MAX_NR_GENS);
+	VM_WARN_ON_ONCE(lru_gen_is_active(lruvec, old_gen) !=
+			lru_gen_is_active(lruvec, target_gen));
 	/* prevent cold/hot inversion if the type is evictable */
 	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
 		struct list_head *head = &lrugen->folios[old_gen][type][zone];
+		long delta = 0;
 
 		while (!list_empty(head)) {
 			struct folio *folio = lru_to_folio(head);
+			long nr_pages = folio_nr_pages(folio);
 			int refs = folio_lru_refs(folio);
 			bool workingset = folio_test_workingset(folio);
+			bool gen_increased;
 
 			VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
 
-			new_gen = folio_inc_gen(lruvec, folio);
+			new_gen = __folio_inc_gen(folio, old_gen, &gen_increased);
 			list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
-
+			if (gen_increased)
+				delta += nr_pages;
 			/* don't count the workingset being lazily promoted */
 			if (refs + workingset != BIT(LRU_REFS_WIDTH) + 1) {
 				int tier = lru_tier_from_refs(refs, workingset);
-				int delta = folio_nr_pages(folio);
 
 				WRITE_ONCE(lrugen->protected[hist][type][tier],
-					   lrugen->protected[hist][type][tier] + delta);
+					   lrugen->protected[hist][type][tier] + nr_pages);
 			}
 
 			if (!--remaining)
-				return false;
+				break;
 		}
+		WRITE_ONCE(lrugen->nr_pages[old_gen][type][zone],
+			   lrugen->nr_pages[old_gen][type][zone] - delta);
+		WRITE_ONCE(lrugen->nr_pages[target_gen][type][zone],
+			   lrugen->nr_pages[target_gen][type][zone] + delta);
+		if (!remaining)
+			return false;
 	}
 done:
 	reset_ctrl_pos(lruvec, type, true);
-- 
2.34.1