+ mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.patch added to mm-new branch

+ mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/mglru: fix ineffective memory protection for non-kswapd reclaim
has been added to the -mm mm-new branch.  Its filename is
     mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.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: Ridong Chen <chenridong@xiaomi.com>
Subject: mm/mglru: fix ineffective memory protection for non-kswapd reclaim
Date: Mon, 7 Sep 2026 10:54:45 +0800

For MGLRU, memory.min/low is not honored during global proactive reclaim
(writing to the root memory.reclaim) and global direct reclaim, because
these paths shrink memcgs using stale protection (emin/elow).  It can be
reproduced as follows:

  # echo 7 > /sys/kernel/mm/lru_gen/enabled
  # cd /sys/fs/cgroup
  # mkdir -p a/b
  # echo 100M > a/memory.min
  # echo +memory > a/cgroup.subtree_control
  # echo 100M > a/b/memory.min
  # echo $$ > a/b/cgroup.procs
  # dd if=/dev/zero of=/tmp/testfile bs=1M count=200
  # cat a/b/memory.current
  222650368
  # echo 500M > memory.reclaim
  -bash: echo: write error: Resource temporarily unavailable
  # cat a/b/memory.current
  6070272

memory.min is 100M, yet reclaim drops a/b down to 6M, breaking the
protection.  The traditional LRU path is not affected because
shrink_node() calls mem_cgroup_calculate_protection() for each memcg it
visits during a top-down tree walk.

Commit 30d77b7eef01 ("mm/mglru: fix ineffective protection calculation")
moved the protection computation into lru_gen_age_node(), which only runs
for kswapd.  Non-kswapd global reclaim reaches shrink_one() through
lru_gen_shrink_node() -> shrink_many() without any protection computation,
so emin/elow are whatever a previous kswapd run left behind - or zero if
kswapd never ran on this node.  Relying on a prior kswapd pass is not
correct either: a memcg's emin/elow are derived from its ancestors'
memory.min/low settings and from children_min_usage, both of which change
over time, so emin/elow go stale even after kswapd has run and must be
recomputed at the point of reclaim.

Introduce mem_cgroup_calculate_protection_path() which computes emin/elow
along the root-to-target path only, by iterating through the cgroup
ancestors array top-down.  This avoids the full tree traversal that would
be needed with mem_cgroup_calculate_protection(), limiting the cost to
O(depth) per memcg - typically 3-5 levels.

Call it from shrink_one() for the non-kswapd path so that each memcg about
to be shrunk has correct protection values.

Link: https://lore.kernel.org/20260907025445.1836238-3-ridong.chen@linux.dev
Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: David Hildenbrand <david@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/memcontrol.h |   10 +++++++
 mm/memcontrol.c            |   45 +++++++++++++++++++++++++++++++++++
 mm/vmscan.c                |    8 +++++-
 3 files changed, 62 insertions(+), 1 deletion(-)

--- a/include/linux/memcontrol.h~mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim
+++ a/include/linux/memcontrol.h
@@ -1921,6 +1921,16 @@ static inline bool memcg_is_dying(struct
 }
 #endif /* CONFIG_MEMCG */
 
+#if defined(CONFIG_MEMCG) && defined(CONFIG_LRU_GEN)
+void mem_cgroup_calculate_protection_path(struct mem_cgroup *root,
+					  struct mem_cgroup *memcg);
+#else
+static inline void mem_cgroup_calculate_protection_path(struct mem_cgroup *root,
+							struct mem_cgroup *memcg)
+{
+}
+#endif
+
 #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
 bool obj_cgroup_may_zswap(struct obj_cgroup *objcg);
 void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size);
--- a/mm/memcontrol.c~mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim
+++ a/mm/memcontrol.c
@@ -5253,6 +5253,51 @@ void mem_cgroup_calculate_protection(str
 	page_counter_calculate_protection(&root->memory, &memcg->memory, recursive_protection);
 }
 
+#ifdef CONFIG_LRU_GEN
+/**
+ * mem_cgroup_calculate_protection_path - compute protection along a path
+ * @root: the top ancestor of the sub-tree being checked (NULL for root_mem_cgroup)
+ * @memcg: the target memory cgroup
+ *
+ * Walk the ancestor path from @root down to @memcg and compute the effective
+ * protection at each level.  This is safe for isolated queries because it
+ * ensures parents are computed before children.
+ */
+void mem_cgroup_calculate_protection_path(struct mem_cgroup *root,
+					  struct mem_cgroup *memcg)
+{
+	bool recursive_protection =
+		cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT;
+	struct cgroup *cg;
+	int root_level, i;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	if (!root)
+		root = root_mem_cgroup;
+
+	if (memcg == root)
+		return;
+
+	root_level = root->css.cgroup->level;
+	cg = memcg->css.cgroup;
+
+	rcu_read_lock();
+	for (i = root_level + 1; i <= cg->level; i++) {
+		struct mem_cgroup *cur;
+
+		cur = mem_cgroup_from_css(cgroup_css(cg->ancestors[i],
+						     &memory_cgrp_subsys));
+		if (cur)
+			page_counter_calculate_protection(&root->memory,
+							  &cur->memory,
+							  recursive_protection);
+	}
+	rcu_read_unlock();
+}
+#endif /* CONFIG_LRU_GEN */
+
 static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg,
 			gfp_t gfp)
 {
--- a/mm/vmscan.c~mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim
+++ a/mm/vmscan.c
@@ -5245,7 +5245,13 @@ static int shrink_one(struct lruvec *lru
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 
-	/* lru_gen_age_node() called mem_cgroup_calculate_protection() */
+	/*
+	 * For kswapd, mem_cgroup_calculate_protection() has already
+	 * been called during the top-down cgroup traversal.
+	 */
+	if (!current_is_kswapd())
+		mem_cgroup_calculate_protection_path(NULL, memcg);
+
 	if (mem_cgroup_below_min(NULL, memcg))
 		return MEMCG_LRU_YOUNG;
 
_

Patches currently in -mm which might be from chenridong@xiaomi.com are

mm-vmscan-drop-the-combined-limit-gate-in-__node_reclaim.patch
mm-mglru-preserve-inactive-placement-when-enabling-mglru.patch
mm-mglru-make-type-fallback-logic-explicit-in-isolate_folios.patch
memcg-acquire-peaks_lock-when-reading-memorypeak.patch
mm-memcg-fix-memorypeak-reset-clobbering-other-fds-watermark.patch
mm-page_counter-avoid-integer-overflow-in-effective_protection.patch
mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.patch