[PATCH v2 1/7] mm/mglru: separate folio generation update from LRU accounting

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

folio_inc_gen() currently updates both the folio's generation and the
LRU size accounting. This makes it difficult to batch the LRU size updates
when moving multiple folios.

Extract the generation update into __folio_inc_gen(), which only updates
the folio's generation and reports whether the generation was actually
increased. Keep folio_inc_gen() as the wrapper that performs the LRU size
accounting when needed.

This separates the per-folio generation update from LRU accounting and
allows the latter to be batched by subsequent changes.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Tested-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
---
 mm/vmscan.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index fdd13299a04a..8f187d296b8e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3296,20 +3296,21 @@ static int folio_update_gen(struct folio *folio, int gen, const vma_flags_t *vma
 }
 
 /* protect pages accessed multiple times through file descriptors */
-static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio)
+static int __folio_inc_gen(struct folio *folio, int old_gen, bool *increased)
 {
-	int type = folio_is_file_lru(folio);
-	struct lru_gen_folio *lrugen = &lruvec->lrugen;
-	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
 	unsigned long new_flags, old_flags = READ_ONCE(folio->flags.f);
+	int new_gen;
 
 	VM_WARN_ON_ONCE_FOLIO(!(old_flags & LRU_GEN_MASK), folio);
 
 	do {
 		new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
 		/* folio_update_gen() has promoted this page? */
-		if (new_gen >= 0 && new_gen != old_gen)
+		if (new_gen >= 0 && new_gen != old_gen) {
+			if (increased)
+				*increased = false;
 			return new_gen;
+		}
 
 		new_gen = (old_gen + 1) % MAX_NR_GENS;
 
@@ -3317,8 +3318,21 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio)
 		new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
 	} while (!try_cmpxchg(&folio->flags.f, &old_flags, new_flags));
 
-	lru_gen_update_size(lruvec, folio, old_gen, new_gen);
+	if (increased)
+		*increased = true;
+	return new_gen;
+}
+
+static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio)
+{
+	int type = folio_is_file_lru(folio);
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
+	bool gen_increased;
 
+	new_gen = __folio_inc_gen(folio, old_gen, &gen_increased);
+	if (gen_increased)
+		lru_gen_update_size(lruvec, folio, old_gen, new_gen);
 	return new_gen;
 }
 
-- 
2.34.1