linux-kernel - Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect subtraction after reparent

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Message-ID: <20230324171114.32oru5sdubfsfvgi@blackpad>
Date:   Fri, 24 Mar 2023 18:11:14 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Cai Xinchen <caixinchen1@...wei.com>
Cc:     songmuchun@...edance.com, akpm@...ux-foundation.org,
        hannes@...xchg.org, longman@...hat.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        cgroups@...r.kernel.org, duanxiongchun@...edance.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        yosryahmed@...gle.com, mpenttil@...hat.com
Subject: Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect
 subtraction after reparent

Hello.

On Mon, Mar 20, 2023 at 03:06:48AM +0000, Cai Xinchen <caixinchen1@...wei.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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