linux-kernel - Re: [Patch v3 0/2] cgroup: New misc cgroup controller

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Date:   Thu, 11 Mar 2021 14:39:36 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Vipin Sharma <vipinsh@...gle.com>, rdunlap@...radead.org,
        thomas.lendacky@....com, brijesh.singh@....com, jon.grimm@....com,
        eric.vantassell@....com, pbonzini@...hat.com, hannes@...xchg.org,
        frankja@...ux.ibm.com, borntraeger@...ibm.com, corbet@....net,
        seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, gingell@...gle.com,
        rientjes@...gle.com, dionnaglaze@...gle.com, kvm@...r.kernel.org,
        x86@...nel.org, cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v3 0/2] cgroup: New misc cgroup controller

Hello,

On Thu, Mar 11, 2021 at 07:58:19PM +0100, Michal Koutný wrote:
> > Michal, as you've been reviewing the series, can you please take
> > another look and ack them if you don't find anything objectionable?
> Honestly, I'm still sitting on the fence whether this needs a new
> controller and whether the miscontroller (:-p) is a good approach in the
> long term [1].

Yeah, it's a bit of cop-out. My take is that the underlying hardware feature
isn't mature enough to have reasonable abstraction built on top of them.
Given time, maybe future iterations will get there or maybe it's a passing
fad and people will mostly forget about these.

In the meantime, keeping them out of cgroup is one direction, a relatively
high friction one but still viable. Or we can provide something of a halfway
house so that people who have immediate needs can still leverage the
existing infrastructure while controlling the amount of time, energy and
future lock-ins they take. So, that's misc controller.

I'm somewhat ambivalent but we've had multiple of these things popping up in
the past several years and containment seems to be a reasonable approach at
this point.

> [1] Currently, only one thing comes to my mind -- the delegation via
> cgroup.subtree_control. The miscontroller may add possibly further
> resources whose delegation granularity is bunched up under one entry.

Controller enabling and delegation in themselves aren't supposed to have
resource or security implications, so I don't think it's a practical
problem.

Thanks.

-- 
tejun