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Date: Tue, 22 Sep 2026 06:30:52 +0200
From: "Oscar Salvador (SUSE)" <osalvador@kernel.org>
To: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Hongfu Li <hongfu.li@linux.dev>, Muchun Song <muchun.song@linux.dev>,
	Oscar Salvador <osalvador@suse.de>,
	David Hildenbrand <david@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shakeel Butt <shakeel.butt@linux.dev>,
	Michal Hocko <mhocko@suse.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Nhat Pham <nphamcs@gmail.com>, Chris Down <chris@chrisdown.name>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	Hongfu Li <lihongfu@kylinos.cn>, stable@vger.kernel.org
Subject: Re: [PATCH 2/2] mm/memcg: migrate per-node hugetlb lruvec stat
 together with hugetlb folio
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 <20260922042054.3264663-1-joshua.hahnjy@gmail.com>
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In-Reply-To: <20260922042054.3264663-1-joshua.hahnjy@gmail.com>

On Mon, Sep 21, 2026 at 09:20:53PM -0700, Joshua Hahn wrote:
> On Tue, 22 Sep 2026 06:15:07 +0200 "Oscar Salvador (SUSE)" <osalvador@kernel.org> wrote:

> > Why do we need the whole thing to be embraced by rcu?
> 
> Hi Oscar,

Hi Joshua,

> 
> I believe it's because now getting the memcg from the objcg requires
> an RCU lock to make sure it doesn't get removed while we work on the
> memcg. I think this is since Qi Zheng's "Eliminate Dying Memory
> Cgroup" series.

Yes, I understood that obj_cgroup_memcg might need the rcu-dance, but I was
unsure about the mod_memcg_lruvec_state() calls.


-- 
Oscar Salvador
SUSE Labs