linux-kernel - Re: [PATCH v3 cgroup/for-5.20] cgroup: Replace cgroup->ancestor

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Date:   Wed, 21 Sep 2022 21:05:20 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     cgroups <cgroups@...r.kernel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Michal Koutný <mkoutny@...e.com>,
        Christian Brauner <brauner@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v3 cgroup/for-5.20] cgroup: Replace cgroup->ancestor_ids[]
 with ->ancestors[]

Hi Tejun,

On Mon, Aug 15, 2022 at 2:17 PM Tejun Heo <tj@...nel.org> wrote:
>
> On Fri, Jul 29, 2022 at 01:10:16PM -1000, Tejun Heo wrote:
> > Every cgroup knows all its ancestors through its ->ancestor_ids[]. There's
> > no advantage to remembering the IDs instead of the pointers directly and
> > this makes the array useless for finding an actual ancestor cgroup forcing
> > cgroup_ancestor() to iteratively walk up the hierarchy instead. Let's
> > replace cgroup->ancestor_ids[] with ->ancestors[] and remove the walking-up
> > from cgroup_ancestor().
> >
> > While at it, improve comments around cgroup_root->cgrp_ancestor_storage.
> >
> > This patch shouldn't cause user-visible behavior differences.
> >
> > v2: Update cgroup_ancestor() to use ->ancestors[].
> >
> > v3: cgroup_root->cgrp_ancestor_storage's type is updated to match
> >     cgroup->ancestors[]. Better comments.
> >
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Acked-by: Namhyung Kim <namhyung@...nel.org>
>
> Applied to cgroup/for-6.1.

I've realized that perf stat change needs backward compatibility.
Will send a fix soon.

Thanks,
Namhyung