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Date: Sat, 5 Sep 2026 18:42:29 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Hui Zhu" <hui.zhu@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
 Roman Gushchin <roman.gushchin@linux.dev>, Shakeel Butt
 <shakeel.butt@linux.dev>, Muchun Song <muchun.song@linux.dev>, David
 Hildenbrand <david@kernel.org>, Qi Zheng <qi.zheng@linux.dev>, Lorenzo
 Stoakes <ljs@kernel.org>, Kairui Song <kasong@tencent.com>, Barry Song
 <baohua@kernel.org>, Axel Rasmussen <axelrasmussen@google.com>, Yuanchu Xie
 <yuanchu@google.com>, Wei Xu <weixugc@google.com>, cgroups@vger.kernel.org,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Zhu
 <zhuhui@kylinos.cn>, stable@vger.kernel.org
Subject: Re: [PATCH v3 2/3] mm: workingset: use lruvec_page_state_local() to
 count lru pages
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On Fri,  4 Sep 2026 17:45:55 +0800 "Hui Zhu" <hui.zhu@linux.dev> wrote:

> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> Commit 7404bd37cfbe ("mm: workingset: use lruvec_lru_size() to get the
> number of lru pages") switched count_shadow_nodes() to lruvec_lru_size().
> With CONFIG_MEMCG enabled, lruvec_lru_size() reads mz->lru_zone_size,
> which only the classic LRU paths maintain.  MGLRU accounts its pages
> through __update_lru_size(), which skips that array, so with MGLRU on the
> four evictable LRU lists are always seen as empty.  The shadow node budget
> (pages >> 3) then collapses to slab plus unevictable pages, and the
> workingset shadow shrinker reclaims eviction tokens almost as fast as they
> are created, losing thrashing protection.
> 
> lruvec_page_state_local() reads lruvec_stats->state_local instead, which
> both classic LRU and MGLRU maintain.  Switch back to it.  The reparenting
> race this re-exposes on cgroup v2 is closed by the follow-up patch that
> redirects dying-memcg stat updates for all hierarchies.

The follow-up patch is "mm: memcg: skip the RCU lock when the memcg is
not dying"?  But that's an optimization so I'm confused.

If we're re-exposing a race, the fix for that race should have the same
Fixes: and cc:stable as the commit which did the reexposure?

It isn't clear why any of these patches is cc:stable.  The overall
effect is a tiny performance improvement?  Very clear descriptions of
end-user effects are always helpful.

So at this time I'll schedule the whole series for 7.4-rc1.  If there's
some reason why some/all of these should be backported then please lmk.