linux-kernel - Re: [PATCHv1 3/6] rdmacg: implements rdma cgroup

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Date:	Fri, 8 Jan 2016 02:09:23 +0530
From:	Parav Pandit <pandit.parav@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	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>, raindel@...lanox.com,
	akpm@...ux-foundation.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCHv1 3/6] rdmacg: implements rdma cgroup

On Fri, Jan 8, 2016 at 1:58 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello, Parav.
>
> On Fri, Jan 08, 2016 at 01:55:09AM +0530, Parav Pandit wrote:
> ...
>> Above functionality is achieved, by maintaining the map this tgid and
>> associated original cgroup at try_charge(), uncharge() time.
>
> Hmmm, what happens after the following?
>
> 1. A process allocates some rdma resources and get registered on the
>    hash table.
>
> 2. The process gets migrated to a different cgroup.
>
> 3. The process allocates more rdma resources.
>
> Which cgroup would the resources from #3 be attributed to?

Since the pid/tgid of the process doesn't change in step_3, it
allocates from original cgroup of step_1.

However in next patch V2, as described below, since IB resource will
store rdma_cg pointer,
in step_3, new resource will be allocated from new cgroup.
old resource will be freed from older cgroup.
This is what you are expecting, right?


>
>> In alternate method,
>> Its simple to store the pointer of rdma_cgroup structure in the IB
>> resource structure and hold on reference count to rdma_cgroup.
>> so that when its freed, uncharge_resource can accept rdma_cgroup
>> structure pointer.
>
> That'd be a lot more in line with how other controllers behave.
>

> Thanks.
>
> --
> tejun