Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <f183b995-9ed1-db80-5f0a-493e77946886@huawei.com>
Date:   Mon, 27 Mar 2023 09:29:37 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.5.1
Subject: Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect
 subtraction after reparent
References: <20230320030648.50663-1-caixinchen1@huawei.com>
 <20230320030648.50663-2-caixinchen1@huawei.com>
 <20230324171114.32oru5sdubfsfvgi@blackpad>
To:     <mkoutny@suse.com>
From:   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>
In-Reply-To: <20230324171114.32oru5sdubfsfvgi@blackpad>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

Yes, only cgroup v1.

On 2023/3/25 1:11, Michal Koutný wrote:
> 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