linux-kernel - Re: [PATCHv10 1/3] rdmacg: Added rdma cgroup controller

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Date:	Tue, 5 Apr 2016 05:55:26 -0700
From:	Parav Pandit <pandit.parav@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org, lizefan@...wei.com,
	Johannes Weiner <hannes@...xchg.org>,
	Doug Ledford <dledford@...hat.com>,
	Liran Liss <liranl@...lanox.com>,
	"Hefty, Sean" <sean.hefty@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Jonathan Corbet <corbet@....net>, james.l.morris@...cle.com,
	serge@...lyn.com, Or Gerlitz <ogerlitz@...lanox.com>,
	Matan Barak <matanb@...lanox.com>, akpm@...ux-foundation.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCHv10 1/3] rdmacg: Added rdma cgroup controller

Hi Christoph,

On Tue, Apr 5, 2016 at 5:42 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Tue, Apr 05, 2016 at 05:39:21AM -0700, Parav Pandit wrote:
>> I am not really trying to address OFED issues here. I am sure you
>> understand that if ib_core.ko kernel module is in-kernel module than,
>> for all the fixes/enhancements that goes to it would require people to
>> upgrade to newer kernel, instead of just modules upgrade. Such heavy
>> weight upgrade slows down the adoption which i am trying to avoid here
>> by placing knobs in right kernel module's hand.
>
> What a load of rubbish.  The Linux kernel is one program and should be
> upgraded together.

Just because we add one more rdma resource, we need to ask someone to
upgrade kernel?

Flexibility is coming at very minimal cost, so what exactly is the
issue in having that instead of forcing architecture to give away
that? Whole code is hardly 700 odd lines.

>
>> Its like making ib_core.ko from module to in kernel component, if I
>> understand correctly nobody wants to do that.
>
> We allow splitting subsystems out where it's easily doable to avoid the
> resources consumption if they're all built in.  For cgroups it's not
> really practical, but that doesn't mean you can upgrade invidual parts
> of a complex program without a lot of precaution.