linux-kernel - Re: [PATCH 1/2] cgroup: Add generation number with cgroup id

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Date:   Sat, 26 Oct 2019 20:32:42 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Song Liu <liu.song.a23@...il.com>
Subject: Re: [PATCH 1/2] cgroup: Add generation number with cgroup id

Hi Tejun,

On Fri, Oct 25, 2019 at 7:57 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Fri, Oct 25, 2019 at 06:38:00PM +0900, Namhyung Kim wrote:
> > On Fri, Oct 25, 2019 at 5:30 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > > >  /*
> > > > >   * A cgroup_root represents the root of a cgroup hierarchy, and may be
> > > > >   * associated with a kernfs_root to form an active hierarchy.  This is
> > > > > @@ -521,7 +529,7 @@ struct cgroup_root {
> > > > >       unsigned int flags;
> > > > >
> > > > >       /* IDs for cgroups in this hierarchy */
> > > > > -     struct idr cgroup_idr;
> > > > > +     struct cgroup_idr cgroup_idr;
> > > >
> > > > Given that there's cgroup->self css, can we get rid of the above?
> > >
> > > I don't follow.  Do you want to remove cgroup_idr and share the
> > > css_idr for cgroup id?
>
> Yeah, so, each cgroup has its own css at cgroup->self which has css id
> and everything, so I was wondering whether it'd make sense to get rid
> of the cgroup id and use cgroup->self.id in its place.

I think it's possible to use self.id as cgroup id.  But css->id is managed
for each subsys, so it still needs to have an idr in cgroup_root for
cgroup->self.id, right?

Or do you want to get rid of subsys->idr and use a single idr for both
cgroup and css?

Thanks
Namhyung