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Date:   Fri, 24 Mar 2023 18:11:14 +0100
From:   Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
To:     Cai Xinchen <caixinchen1@huawei.com>
Cc:     songmuchun@bytedance.com, akpm@linux-foundation.org,
        hannes@cmpxchg.org, longman@redhat.com, mhocko@kernel.org,
        roman.gushchin@linux.dev, shakeelb@google.com,
        cgroups@vger.kernel.org, duanxiongchun@bytedance.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        yosryahmed@google.com, mpenttil@redhat.com
Subject: Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect
 subtraction after reparent
Message-ID: <20230324171114.32oru5sdubfsfvgi@blackpad>
References: <20230320030648.50663-1-caixinchen1@huawei.com>
 <20230320030648.50663-2-caixinchen1@huawei.com>
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Hello.

On Mon, Mar 20, 2023 at 03:06:48AM +0000, Cai Xinchen <caixinchen1@huawei.com> wrote:
> When memcg C is offllined, its pages are reparented to memcg P,
> so far P->vmstats (hierarchical) have those pages, and
> P->vmstats_percpu (non-hierarchical) don't. When those pages get
> uncharged, P->vmstats (hierachical) decreases, which is correct,
> but P->vmstats_percpu (non-hierarchical) also decreases, which
> is wrong, as those stats were never added to P->vmstats_percpu to
> begin with.

I was wondering why ->vmstats_percpu matters (in the end all is summed
in ->vmstats) -- do you mean this is a cgroup v1 only issue? As only
that exposes the non-hieararchical stats.

Thanks,
Michal

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