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

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag
Date: Wed, 10 Apr 2013 18:05:39 +0300

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 ...

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