linux-kernel - Re: [PATCH -tip 26/32] sched: Add a second-level tag for nested CGroup usecase

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Message-ID: <X8fijKlASP4yo8kp@mtj.duckdns.org>
Date:   Wed, 2 Dec 2020 13:53:00 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Don <joshdon@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>, mingo@...nel.org,
        torvalds@...ux-foundation.org, fweisbec@...il.com,
        Kees Cook <keescook@...omium.org>,
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        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
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        Oleg Rombakh <olegrom@...gle.com>
Subject: Re: [PATCH -tip 26/32] sched: Add a second-level tag for nested
 CGroup usecase

Hello,

On Wed, Dec 02, 2020 at 09:02:11AM +0100, Peter Zijlstra wrote:
> > the user might only want subsets of {B, C, D, E} to share.  For
> > instance, the user might only want {B,C} and {D, E} to share.  One way
> > to solve this would be to allow the user to write the group cookie
> > directly.  However, this interface would need to be restricted to
> > privileged users, since otherwise the cookie could be configured to
> > share with any arbitrary cgroup.  The purpose of the 'color' field is
> > to expose a portion of the cookie that can be modified by a
> > non-privileged user in order to achieve this sharing goal.
> > 
> > If this doesn't seem like a useful case, I'm happy to drop this patch
> > from the series to unblock it.
> 
> Well, the traditional cgroup way of doing that would be to:
> 
>          A
> 	/ \
>        T1 T2
>       / \
>      B   C
> 
> And tag T1 if you want B,C to share.
> 
> So me the color thing reads like an end-run around the cgroup hierarchy.

+1

and please cc me on cgroup related changes.

Thanks.

-- 
tejun