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

[Michael R. Hines]

On 04/09/2013 11:24 PM, Michael S. Tsirkin wrote:
> Which mechanism do you refer to? You patches still seem to pin each 
> page in guest memory at some point, which will break all COW. In 
> particular any pagemap tricks to detect duplicates on source that I 
> suggested won't work. 

Sorry, I mispoke. I'm reffering to dynamic server page registration.

Of course it does not eliminate pinning - but it does mitigate the foot 
print of the VM as a feature that was requested.

I have implemented it and documented it.

- Michael

> > On 04/09/2013 03:03 PM, Michael S. Tsirkin wrote:
> > > presumably is_dup_page reads the page, so should not break COW ...
> > >
> > > I'm not sure about the cgroups swap limit - you might have
> > > too many non COW pages so attempting to fault them all in
> > > makes you exceed the limit. You really should look at
> > > what is going on in the pagemap, to see if there's
> > > measureable gain from the patch.
> > >
> > >
> > > On Fri, Apr 05, 2013 at 05:32:30PM -0400, Michael R. Hines wrote:
> > > > Well, I have the "is_dup_page()" commented out.......when RDMA is
> > > > activated.....
> > > >
> > > > Is there something else in QEMU that could be touching the page that
> > > > I don't know about?
> > > >
> > > > - Michael
> > > >
> > > >
> > > > On 04/05/2013 05:03 PM, Roland Dreier wrote:
> > > > > On Fri, Apr 5, 2013 at 1:51 PM, Michael R. Hines
> > > > > <mrhines@xxxxxxxxxxxxxxxxxx> 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.

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