mm-mglru-fix-young-counter-undercount-for-large-folios.patch removed from -mm tree

The quilt patch titled
Subject: mm/mglru: fix young counter undercount for large folios
has been removed from the -mm tree. Its filename was
mm-mglru-fix-young-counter-undercount-for-large-folios.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Hui Zhu <[email protected]>
Subject: mm/mglru: fix young counter undercount for large folios
Date: Wed, 12 Aug 2026 14:59:33 +0800

lru_gen_look_around() feeds its local 'young' counter into suitable_to_scan(), which decides whether the current PMD is added to the bloom filter and checked again on the next aging round.

The folio triggering the look-around is processed at function entry:
test_and_clear_young_ptes_notify() clears the accessed bits of the nr PTEs it maps, and the function bails out if none of them is young. The loop that follows therefore never recounts this folio, since its accessed bits are already cleared. Every other young folio the loop finds is accounted as a batch (young += nr), where nr is the number of consecutive PTEs it maps. The triggering folio, however, still contributes a fixed young = 1 regardless of its size -- a leftover from before PTE batching. A large triggering folio is thus accounted inconsistently with the rest of the window.

Initialize young to nr so the triggering folio is accounted the same way as any other young folio batch in the loop.

Note this is a deliberate overestimate, not a measured value. The test-and-clear helper only reports whether any of the nr PTEs is young, not how many were accessed, so the true number of accessed PTEs in a large folio is unknown and can be smaller than nr. Counting the full batch is
intentional: the mm core tracks accessed/dirty state per folio, not per page, so a per-page count is neither obtainable nor meaningful. The only consumer is suitable_to_scan(), and the bloom filter it feeds tolerates error. Overestimating is also the safe direction: at worst a PMD that saw little access is rescanned, whereas underestimating could skip rescanning a PMD whose folios are still hot and reclaim them incorrectly. (nr here is the PTE batch size, not necessarily folio_nr_pages().)

---

 mm/vmscan.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -4261,7 +4261,7 @@ bool lru_gen_look_around(struct page_vma
 	unsigned long end;
 	struct lru_gen_mm_walk *walk;
 	struct folio *last = NULL;
-	int young = 1;
+	int young = nr;
 	pte_t *pte = pvmw->pte;
 	unsigned long addr = pvmw->address;
 	struct vm_area_struct *vma = pvmw->vma;

_

Patches currently in -mm which might be from [email protected] are