linux-kernel - Re: [PATCHv2] rdma: add a new IB_ACCESS

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Message-ID: <20130409190943.GC8212@redhat.com>
Date:	Tue, 9 Apr 2013 22:09:44 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Roland Dreier <roland@...nel.org>
Cc:	"Michael R. Hines" <mrhines@...ux.vnet.ibm.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Yishai Hadas <yishaih@...lanox.com>,
	Christoph Lameter <cl@...ux.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, qemu-devel@...gnu.org
Subject: Re: [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag

On Fri, Apr 05, 2013 at 02:03:33PM -0700, Roland Dreier wrote:
> On Fri, Apr 5, 2013 at 1:51 PM, Michael R. Hines
> <mrhines@...ux.vnet.ibm.com> wrote:
> > Sorry, I was wrong. ignore the comments about cgroups. That's still broken.
> > (i.e. trying to register RDMA memory while using a cgroup swap limit cause
> > the process get killed).
> >
> > But the GIFT flag patch works (my understanding is that GIFT flag allows the
> > adapter to transmit stale memory information, it does not have anything to
> > do with cgroups specifically).
> 
> The point of the GIFT patch is to avoid triggering copy-on-write so
> that memory doesn't blow up during migration.  If that doesn't work
> then there's no point to the patch.
> 
>  - R.

Absolutely. Checking whether an OOM gets triggered looks like a heavy
handed approach to testing the feature though.
It's relevant, but there could be many other reasons for it to trigger.
See Documentation/cgroups/memory.txt section "Troubleshooting".

It's easier to just check whether this patch reduces the memory consumption,
that's the point really.

-- 
MST
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