linux-kernel - Re: [PATCH v2 07/28] mm: memcontrol: return root object cgroup for root memory cgroup

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Message-ID: <aUMgbirV5dNpuBoM@cmpxchg.org>
Date: Wed, 17 Dec 2025 16:28:14 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hughd@...gle.com, mhocko@...e.com, roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev, muchun.song@...ux.dev, david@...nel.org,
	lorenzo.stoakes@...cle.com, ziy@...dia.com, harry.yoo@...cle.com,
	imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
	axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
	chenridong@...weicloud.com, mkoutny@...e.com,
	akpm@...ux-foundation.org, hamzamahfooz@...ux.microsoft.com,
	apais@...ux.microsoft.com, lance.yang@...ux.dev, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Muchun Song <songmuchun@...edance.com>,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 07/28] mm: memcontrol: return root object cgroup for
 root memory cgroup

On Wed, Dec 17, 2025 at 03:27:31PM +0800, Qi Zheng wrote:
> From: Muchun Song <songmuchun@...edance.com>
> 
> Memory cgroup functions such as get_mem_cgroup_from_folio() and
> get_mem_cgroup_from_mm() return a valid memory cgroup pointer,
> even for the root memory cgroup. In contrast, the situation for
> object cgroups has been different.
> 
> Previously, the root object cgroup couldn't be returned because
> it didn't exist. Now that a valid root object cgroup exists, for
> the sake of consistency, it's necessary to align the behavior of
> object-cgroup-related operations with that of memory cgroup APIs.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>