Re: [PATCH v5 0/6] mm/mglru: clean up folio counters and flag usage

[Andrew Morton]

On Wed, 02 Sep 2026 17:50:53 +0800 Kairui Song via B4 Relay <devnull+kasong.tencent.com@xxxxxxxxxx> wrote:

> This is a cleanup series separated out from the MGLRU-FG series [1]. As
> that series is getting too long in following updates, seperate out the
> clean up part for easier review and merge.
> 
> No feature change is intended, except one bugfix. It mostly replaces
> the open-coded bit operations scattered throughout the MGLRU code with
> new helpers, with proper kdocs, sanity debug checks, and hardens a few
> MGLRU functions.
> 
> A subtle generation counter leak is also found during the refactoring
> and the fix is included.
> 
> Also collected review feedbacks on the cleanup part from the posted
> series.

Thanks.  I hit a non-trivial reject in [2/6] presumably thanks to
mm.git (mm-new) race conditions (appended).

The patchset comes nicely review by humans, but AI is less happy:
	https://sashiko.dev/#/patchset/20260902-mglru-flags-cleanup-v5-0-9db761d779ef@xxxxxxxxxxx

So please take a look at all that and retry in a few days?

Thanks.

--- mm/vmscan.c
+++ mm/vmscan.c
@@ -3307,21 +3313,20 @@ 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]);
-	unsigned long new_flags, old_flags = READ_ONCE(folio->flags.f);
-
-	VM_WARN_ON_ONCE_FOLIO(!(old_flags & LRU_GEN_MASK), folio);
+	unsigned long new_flags, old_flags = READ_ONCE(*folio_flags(folio, 0));
 
 	do {
-		new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+		new_gen = lru_get_gen_flags(old_flags);
+
 		/* folio_update_gen() has promoted this page? */
 		if (new_gen >= 0 && new_gen != old_gen)
 			return new_gen;
 
+		new_flags = old_flags;
 		new_gen = (old_gen + 1) % MAX_NR_GENS;
-
-		new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_FLAGS);
-		new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
-	} while (!try_cmpxchg(&folio->flags.f, &old_flags, new_flags));
+		lru_set_gen_flags(&new_flags, new_gen);
+		lru_set_refs_flags(&new_flags, 0);
+	} while (!try_cmpxchg(folio_flags(folio, 0), &old_flags, new_flags));
 
 	lru_gen_update_size(lruvec, folio, old_gen, new_gen);