+ mm-mglru-lift-youngest-gen-protection-for-higher-priority.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mglru: lift youngest gen protection for higher priority
has been added to the -mm mm-new branch.  Its filename is
     mm-mglru-lift-youngest-gen-protection-for-higher-priority.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-lift-youngest-gen-protection-for-higher-priority.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: Kairui Song <kasong@tencent.com>
Subject: mm/mglru: lift youngest gen protection for higher priority
Date: Thu, 12 Nov 2026 07:25:55 +0800

The forced protection of younger generations contradicts the
goal of minimizing the I/O cost of reclaim. Under high memory
pressure, MGLRU can repeatedly trigger premature OOMs, while
the classic LRU does not.

The problem is that aging may fail to keep up with reclaim.
When this happens, reclaimers may all abort prematurely
because they see only empty generations or just two
generations remaining.

Proactive aging does not solve this problem either. The
number of threads performing proactive aging is limited,
while the number of concurrent reclaimers can be much
larger. This is a fundamental limitation of MGLRU. One
possible solution is to use an aging lock. However, the
aging lock introduces significant jitter under heavy memory
pressure and has been reported to cause noticeable lags
on Android.

Furthermore, the generation-based reclaim model can
conflict with the goal of swappiness, which is to minimize
I/O cost rather than blindly follow folio hotness.

The previous commit allowed reclaimers running at
non-default priorities to reclaim up to `lrugen->max_seq`,
while reclaimers at the default priority could reclaim only
up to `lrugen->min_seq`.

This patch further refines generation protection based on
reclaim priority. At the default priority, reclaimers can
reclaim generations down to `lrugen->min_seq - MIN_NR_GENS`.
As reclaim priority increases, reclaimers are progressively
allowed to reclaim younger generations.

With this graduated protection, premature OOMs are no
longer observed, while swappiness is also respected.

Link: https://lore.kernel.org/20261111232603.9934-9-baohua@kernel.org
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <hui.zhu@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: wang lian <lianux.mm@gmail.com>
Cc: <liuxiang.277@bytedance.com>
Cc: <lyugaofei@xiaomi.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Ridong Chen <ridong.chen@linux.dev>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: wangzicheng <wangzicheng@honor.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Bo Zhang <zhangbo56@xiaomi.com>
Cc: Hui Zhu <zhuhui@kylinos.cn>
Cc: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Cc: Kunwu Chan <chentao@kylinos.cn>
---

 mm/vmscan.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/mm/vmscan.c~mm-mglru-lift-youngest-gen-protection-for-higher-priority
+++ a/mm/vmscan.c
@@ -4774,12 +4774,14 @@ static int scan_folios(unsigned long nr_
 	VM_WARN_ON_ONCE(!list_empty(list));
 
 	/*
-	 * Respect the gen hotness distribution at low priority to avoid
-	 * aging and scan cost, but prefer to satisfy the reclaimers request
-	 * when under pressure to respect swappiness more and reduce IO cost.
+	 * Respect hotness at default priority, and only reach into the
+	 * newest generation when under severe pressure, so hot folios are
+	 * not evicted as soon as priority is raised.
 	 */
 	if (sc->priority == DEF_PRIORITY)
-		seq = lrugen->min_seq[type];
+		seq = lrugen->max_seq - MIN_NR_GENS;
+	else if (sc->priority > DEF_PRIORITY / 2)
+		seq = lrugen->max_seq - 1;
 	else
 		seq = lrugen->max_seq;
 
_

Patches currently in -mm which might be from kasong@tencent.com are

mm-mglru-report-evictable-sizes-per-type.patch
mm-mglru-extract-lruvec_populated_min_seq-helper.patch
mm-mglru-reclaim-from-the-oldest-populated-gen.patch
mm-mglru-lift-the-forced-protection-of-reclaimer.patch
mm-mglru-skip-zones-above-reclaim_idx-instead-of-rotating-them.patch
mm-mglru-return-for-unavailable-anon-reclaim-earlier.patch
mm-mglru-balance-anon-and-file-scan-budget-by-refault-rate.patch
mm-mglru-lift-youngest-gen-protection-for-higher-priority.patch