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Wed, 09 Sep 2026 11:28:40 -0700 (PDT) Date: Wed, 9 Sep 2026 14:28:39 -0400 From: Johannes Weiner To: Qinyun Tan Cc: Andrew Morton , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Michal =?iso-8859-1?Q?Koutn=FD?= , David Hildenbrand , Zi Yan , Baolin Wang , Usama Arif , Dave Chinner , Qi Zheng , Yosry Ahmed , Nhat Pham , Chengming Zhou , Xunlei Pang , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/4] mm: thp: restore SHRINKER_NONSLAB on the deferred split shrinker Message-ID: References: <20260907110111.2286932-1-qinyuntan@linux.alibaba.com> <20260907110111.2286932-4-qinyuntan@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260907110111.2286932-4-qinyuntan@linux.alibaba.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: AD28414000F X-Stat-Signature: g3ju8tfos1uzeiy54rzsrxfqczmri35j X-Rspam-User: X-HE-Tag: 1788978522-414647 X-HE-Meta: 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 G2K0/BoN 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 07:01:10PM +0800, Qinyun Tan wrote: > 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. Here is the reason why it was dropped: https://lore.kernel.org/all/ah9PGv12mqai84ES@cmpxchg.org/ After your patch to make list_lru expand for NONSLAB shrinkers, it can be restored. > 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. > > [1] https://lore.kernel.org/lkml/697713c4-0857-485b-aba7-c74f37a3c8b4@linux.alibaba.com/ > > Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru") > Suggested-by: Michal Koutný > Signed-off-by: Qinyun Tan > Acked-by: Zi Yan > Acked-by: David Hildenbrand (Arm) > Acked-by: Usama Arif > Reviewed-by: Baolin Wang Reviewed-by: Johannes Weiner