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

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Message-ID: <rpr65jo6oa6aismuhkhimj5ne3gquvo7rpok5qnd5jif5iqbya@uar7qwaox7fc>
Date: Thu, 18 Dec 2025 16:39:42 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com, 
	roman.gushchin@...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: Shakeel Butt <shakeel.butt@...ux.dev>