[to-be-updated] mm-thp-restore-shrinker_nonslab-on-the-deferred-split-shrinker.patch removed from -mm tree

[to-be-updated] mm-thp-restore-shrinker_nonslab-on-the-deferred-split-shrinker.patch removed from -mm tree

[Andrew Morton]

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The quilt patch titled
     Subject: mm: thp: restore SHRINKER_NONSLAB on the deferred split shrinker
has been removed from the -mm tree.  Its filename was
     mm-thp-restore-shrinker_nonslab-on-the-deferred-split-shrinker.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------
From: Qinyun Tan <qinyuntan@linux.alibaba.com>
Subject: mm: thp: restore SHRINKER_NONSLAB on the deferred split shrinker
Date: Fri, 4 Sep 2026 11:35:02 +0800

Patch series "mm: restore SHRINKER_NONSLAB on THP and zswap shrinkers".

While reviewing the patch "mm/list_lru: don't copy stale shrinker id from
non-memcg-aware shrinkers" (now in mm-unstable), Michal noticed that the
two non-slab memcg-aware shrinkers, the THP deferred split shrinker and
the zswap shrinker, are registered without SHRINKER_NONSLAB [1].

Without that flag, booting with cgroup.memory=nokmem silently demotes both
shrinkers to non-memcg-aware ones: memcg (limit-induced) reclaim neither
splits partially unmapped THPs nor writes back zswapped pages of the
cgroup under pressure.

Patch 1 restores the flag on the deferred split shrinker; it was lost when
commit fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru")
re-registered the shrinker.

Patch 2 adds the flag to the zswap shrinker, which has never carried it
since its introduction in commit b5ba474f3f51 ("zswap: shrink zswap pool
based on memory pressure").


This patch (of 2):

On a system booted with cgroup.memory=nokmem, the deferred split shrinker
is quietly demoted to a non-memcg-aware one.  As a result, partially
unmapped THPs are only split under global reclaim; memcg (limit-induced)
reclaim never splits them, so a cgroup under memory pressure keeps its
underused THPs intact.

This is a regression from commit fafaeceb89a5 ("mm: switch deferred split
shrinker to list_lru"), which re-registered the shrinker without
SHRINKER_NONSLAB.  The shrinker had carried this flag since commit
0a432dcbeb32 ("mm: shrinker: make shrinker not depend on memcg kmem")
precisely so it would keep working with kmem accounting disabled.  Without
the flag, shrinker_memcg_alloc() fails with -ENOSYS under nokmem and the
shrinker loses its memcg awareness.

This was noticed by Michal during review of the patch "mm/list_lru: don't
copy stale shrinker id from non-memcg-aware shrinkers" [1].

Restore the flag.

Link: https://lore.kernel.org/20260904033503.4067283-1-qinyuntan@linux.alibaba.com
Link: https://lore.kernel.org/20260904033503.4067283-2-qinyuntan@linux.alibaba.com
Link: https://lore.kernel.org/lkml/697713c4-0857-485b-aba7-c74f37a3c8b4@linux.alibaba.com/ [1]
Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru")
Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Usama Arif <usama.arif@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Xunlei Pang <xlpang@linux.alibaba.com>
---

 mm/huge_memory.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/huge_memory.c~mm-thp-restore-shrinker_nonslab-on-the-deferred-split-shrinker
+++ a/mm/huge_memory.c
@@ -1064,7 +1064,8 @@ int folio_memcg_alloc_deferred(struct fo
 static int __init thp_shrinker_init(void)
 {
 	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
-						 SHRINKER_MEMCG_AWARE,
+						 SHRINKER_MEMCG_AWARE |
+						 SHRINKER_NONSLAB,
 						 "thp-deferred_split");
 	if (!deferred_split_shrinker)
 		return -ENOMEM;
_

Patches currently in -mm which might be from qinyuntan@linux.alibaba.com are

mm-list_lru-disable-memcg-awareness-under-cgroup_disable=memory.patch
mm-list_lru-dont-copy-stale-shrinker-id-from-non-memcg-aware-shrinkers.patch
mm-zswap-mark-the-zswap-shrinker-shrinker_nonslab.patch
mm-memcontrol-drop-kmemcg_id-and-use-mem_cgroup_id-for-list_lru-indexing.patch
mm-list_lru-keep-per-memcg-lists-with-nokmem-for-nonslab-backed-lrus.patch