Re: [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag

Michael S. Tsirkin
2013-04-09T20:08:55Z

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@linux.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