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

Michael S. Tsirkin
2013-04-10T16:10:31Z

On Wed, Apr 10, 2013 at 11:48:24AM -0400, Michael R. Hines wrote:
>
> There's a very nice, simple client/server RDMA application on the
> internet you can use to test your patch.
>
> http://thegeekinthecorner.wordpress.com/2010/09/28/
> rdma-read-and-write-with-ib-verbs/
>
> This guy provides the source code which dumps several gigabytes over RDMA
> to the other side.
>
> There's no need to run QEMU to test your patch,
> assuming you have access to infiniband hardware.
>
> - Michael

Does this app have any COW pages?

> On 04/10/2013 01:32 AM, Michael S. Tsirkin wrote:
>
> On Wed, Apr 10, 2013 at 12:32:31AM -0400, Michael R. Hines wrote:
>
> 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
>
> Okay, but GIFT is supposed to be used on send side: it's only allowed
> with local/remote read access, and serves to reduce memory usage
> on send side.
> For example, disable zero page detection and look at memory usage
> on send side before and after migration.
> Dynamic registration on the receive side is nice but seems
> completely unrelated ...
>
>
>