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 19:34:34 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
        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

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.

> +}
> +#else
> +static inline void obj_cgroup_release_bytes(struct obj_cgroup *objcg)
> +{
> +}
> +#endif

This empty body is for !CONFIG_MEMCG_KMEM, however, the subsequent use for LRU
pages makes no use of these, so it's warranted.

Altogether, I find this correct, hence
Reviewed-by: Michal Koutný <mkoutny@...e.com>