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

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Date:	Fri, 11 Sep 2015 20:06:31 +0000
From:	"Hefty, Sean" <sean.hefty@...el.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.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

> > 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.

My point is that limiting the number of QPs that an app can allocate doesn't necessarily mean anything.  Is allocating 1000 QPs with 1 entry each better or worse than 1 QP with 10,000 entries?  Who knows?

> 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)

Yes - this makes more sense to me.

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