linux-kernel - Re: [PATCH v5 03/11] mm: memcontrol: prepare objcg API for non-kmem usage

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Date:   Wed, 1 Jun 2022 11:33:46 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Muchun Song <songmuchun@...edance.com>, hannes@...xchg.org,
        mhocko@...nel.org, shakeelb@...gle.com, akpm@...ux-foundation.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        longman@...hat.com
Subject: Re: [PATCH v5 03/11] mm: memcontrol: prepare objcg API for non-kmem
 usage

On Wed, Jun 01, 2022 at 07:34:34PM +0200, Michal Koutny wrote:
> Hello.
> 
> On Mon, May 30, 2022 at 03:49:11PM +0800, Muchun Song <songmuchun@...edance.com> wrote:
> > So we also allocate an object cgroup for the root_mem_cgroup.
> 
> This change made me wary that this patch also kmem charging in the
> root_mem_cgroup. Fortunately, get_obj_cgroup_from_current won't return
> this objcg so all is fine.

Yes, I had the same experience here :)

Overall I feel like the handling of the root memcg and objcg are begging
for a cleanup, but it's really far from being trivial.

Maybe starting with documenting how it works now is a good idea...