linux-kernel - Re: [PATCH 0/7] devcg: device cgroup extension for rdma resource

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Message-ID: <55EED87E.3000408@mellanox.com>
Date:	Tue, 8 Sep 2015 15:45:50 +0300
From:	Haggai Eran <haggaie@...lanox.com>
To:	Parav Pandit <pandit.parav@...il.com>, <cgroups@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-rdma@...r.kernel.org>, <tj@...nel.org>,
	<lizefan@...wei.com>, <hannes@...xchg.org>, <dledford@...hat.com>
CC:	<corbet@....net>, <james.l.morris@...cle.com>, <serge@...lyn.com>,
	<ogerlitz@...lanox.com>, <matanb@...lanox.com>,
	<raindel@...lanox.com>, <akpm@...ux-foundation.org>,
	<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 0/7] devcg: device cgroup extension for rdma resource

On 07/09/2015 23:38, Parav Pandit wrote:
> Currently user space applications can easily take away all the rdma
> device specific resources such as AH, CQ, QP, MR etc. Due to which other
> applications in other cgroup or kernel space ULPs may not even get chance
> to allocate any rdma resources.
> 
> This patch-set allows limiting rdma resources to set of processes.
> It extend device cgroup controller for limiting rdma device limits.
I don't think extending the device cgroup is the right place for these
limits. It is currently a very generic controller and adding various
RDMA resources to it looks out of place. Why not create a new controller
for rdma?

Another thing I noticed is that all limits in this cgroup are global,
while the resources they control are hardware device specific.
I think it would be better if the cgroup controlled the limits of each
device separately.

> With this patch, user verbs module queries rdma device cgroup controller
> to query process's limit to consume such resource. It uncharge resource 
> counter after resource is being freed.
This is another reason why per-device limits would be better. Since
limits are reflected to user-space when querying a specific device, it
will show the same maximum limit on every device opened. If the user
opens 3 devices they might expect to be able to open 3 times the number
of the resources they actually can.

Regards,
Haggai
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