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

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Date:	Fri, 11 Sep 2015 13:43:11 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	"Hefty, Sean" <sean.hefty@...el.com>
Cc:	Tejun Heo <tj@...nel.org>, Doug Ledford <dledford@...hat.com>,
	Parav Pandit <pandit.parav@...il.com>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Jonathan Corbet <corbet@....net>,
	"james.l.morris@...cle.com" <james.l.morris@...cle.com>,
	"serge@...lyn.com" <serge@...lyn.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Matan Barak <matanb@...lanox.com>,
	"raindel@...lanox.com" <raindel@...lanox.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 0/7] devcg: device cgroup extension for rdma resource

On Fri, Sep 11, 2015 at 07:22:56PM +0000, Hefty, Sean wrote:
 
> Trying to limit the number of QPs that an app can allocate,
> therefore, just limits how much of the address space an app can use.
> There's no clear link between QP limits and HW resource limits,
> unless you assume a very specific underlying implementation.

Isn't that the point though? We have several vendors with hardware
that does impose hard limits on specific resources. There is no way to
avoid that, and ultimately, those exact HW resources need to be
limited.

If we want to talk about abstraction, then I'd suggest something very
general and simple - two limits:
 '% of the RDMA hardware resource pool' (per device or per ep?)
 'bytes of kernel memory for RDMA structures' (all devices)

That comfortably covers all the various kinds of hardware we support
in a reasonable fashion.

Unless there really is a reason why we need to constrain exactly
and precisely PD/QP/MR/AH (I can't think of one off hand)

The 'RDMA hardware resource pool' is a vendor-driver-device specific
thing, with no generic definition beyond something that doesn't fit in
the other limit.

Jason
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