Re: [Qemu-devel] [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag

[Michael R. Hines]

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.