+ mm-mglru-restore-accidentally-removed-seq-max_seq-check.patch added to mm-new branch

+ mm-mglru-restore-accidentally-removed-seq-max_seq-check.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/mglru: restore accidentally removed seq < max_seq check
has been added to the -mm mm-new branch.  Its filename is
     mm-mglru-restore-accidentally-removed-seq-max_seq-check.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-restore-accidentally-removed-seq-max_seq-check.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Barry Song (Xiaomi)" <baohua@kernel.org>
Subject: mm/mglru: restore accidentally removed seq < max_seq check
Date: Tue, 15 Sep 2026 18:15:56 +0800

Since commit 798c0330c2ca ("mm/mglru: rework aging feedback"), the
following sanity check was accidentally removed:

       if (seq < max_seq)
               return 0;

That means we can perform aging for any value less than or equal to
max_gen_nr.

This has been inconsistent with
Documentation/admin-guide/mm/multigen_lru.rst, which states:

 Users can write the following command to ``lru_gen`` to create a new
 generation ``max_gen_nr+1``:

     ``+ memcg_id node_id max_gen_nr [can_swap [force_scan]]``

The correct semantics are that writing a value smaller than max_gen_nr
should return 0, since the requested generation already exists.

Link: https://lore.kernel.org/20260915101556.50467-1-baohua@kernel.org
Fixes: 798c0330c2ca ("mm/mglru: rework aging feedback")
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Chuanhua Han <hanchuanhua802@gmail.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
---

 mm/vmscan.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/vmscan.c~mm-mglru-restore-accidentally-removed-seq-max_seq-check
+++ a/mm/vmscan.c
@@ -5837,6 +5837,9 @@ static int run_aging(struct lruvec *lruv
 {
 	DEFINE_MAX_SEQ(lruvec);
 
+	if (seq < max_seq)
+		return 0;
+
 	if (seq > max_seq)
 		return -EINVAL;
 
_

Patches currently in -mm which might be from baohua@kernel.org are

mm-mglru-make-retry-logic-explicit-in-isolate_folios.patch
mm-mglru-make-retry-logic-explicit-in-isolate_folios-fix.patch
mm-vmscan-avoid-pointless-large-folio-splits-without-swap.patch
mm-mglru-separate-folio-generation-update-from-lru-accounting.patch
mm-mglru-batch-update-lrugen-nr_pages-in-inc_min_seq.patch
mm-mglru-enhance-cold-hot-inversion-handling-in-inc_min_seq.patch
mm-mglru-exclude-folios-promoted-by-aging-from-protected-in-inc_min_seq.patch
mm-mglru-make-lru-folio-prefetch-helper-an-inline-function.patch
mm-mglru-move-folios-from-oldest-gen-to-second-oldest-gen-from-head-to-tail.patch
mm-mglru-batch-move-folios-to-the-second-oldest-gens-lru.patch
mm-mglru-restore-accidentally-removed-seq-max_seq-check.patch