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Subject: Re: [PATCH] mm/memcg: remove definition of MEM_CGROUP_ID_MAX when
 !CONFIG_MEMCG
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From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20230706112820.2393447-1-linmiaohe@huawei.com>
Date:   Fri, 7 Jul 2023 09:47:46 +0800
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>, cgroups@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>
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References: <20230706112820.2393447-1-linmiaohe@huawei.com>
To:     Miaohe Lin <linmiaohe@huawei.com>
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> On Jul 6, 2023, at 19:28, Miaohe Lin <linmiaohe@huawei.com> wrote:
> 
> MEM_CGROUP_ID_MAX is only used when CONFIG_MEMCG is configured. Remove
> unneeded !CONFIG_MEMCG variant.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

MEM_CGROUP_ID_MAX is also only used in mem_cgroup_alloc(), maybe you also
could move it from memcontrol.h to memcontrol.c. And define it as:

#define MEM_CGROUP_ID_MAX ((1U << MEM_CGROUP_ID_SHIFT) - 1)

I am not suggesting defining it as USHRT_MAX, because if someone changes
MEM_CGROUP_ID_SHIFT in the future, then MEM_CGROUP_ID_MAX will not updated
accordingly.

For this patch, LGTM.

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.