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

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Date:	Tue, 09 Apr 2013 13:56:00 -0400
From:	"Michael R. Hines" <mrhines@...ux.vnet.ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Roland Dreier <roland@...nel.org>, qemu-devel@...gnu.org,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Yishai Hadas <yishaih@...lanox.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag

On 04/09/2013 12:39 PM, Michael S. Tsirkin wrote:
> On Fri, Apr 05, 2013 at 04:54:39PM -0400, Michael R. Hines wrote:
>> To be more specific, here's what I did:
>>
>> 1. apply kernel module patch - re-insert module
>> 1. QEMU does: ibv_reg_mr(........IBV_ACCESS_GIFT | IBV_ACCESS_REMOTE_READ)
>> 2. Start the RDMA migration
>> 3. Migration completes without any errors
>>
>> This test does *not* work with a cgroup swap limit, however. The
>> process gets killed. (Both with and without GIFT)
>>
>> - Michael
> Try to attach a debugger and see where it is when it gets killed?
>

It's killed by cgroups - not a CPU exception.

The same test works fine using TCP migration with cgroups - everything 
is fine there.

The memory that RDMA attempted to register hits some kind of cgroups policy
which results in a kernel message saying that the cgroup swap limit was hit
and then it goes ahead and kills the process altogether.

It's not a QEMU problem - it seems to be a kernel bug.

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