Re: [Qemu-devel] [RFC PATCH RDMA support v5: 03/12] comprehensive protocol documentation

["Michael R. Hines" <mrhines@linux.vnet.ibm.com>]

On 04/14/2013 04:28 AM, Michael S. Tsirkin wrote:
> On Fri, Apr 12, 2013 at 09:47:08AM -0400, Michael R. Hines wrote:
>> Second, as I've explained, I strongly, strongly disagree with unregistering
>> memory for all of the aforementioned reasons - workloads do not
>> operate in such a manner that they can tolerate memory to be
>> pulled out from underneath them at such fine-grained time scales
>> in the *middle* of a relocation and I will not commit to writing a solution
>> for a problem that doesn't exist.
> Exactly same thing happens with swap, doesn't it?
> You are saying workloads simply can not tolerate swap.
>
>> If you can prove (through some kind of anaylsis) that workloads
>> would benefit from this kind of fine-grained memory overcommit
>> by having cgroups swap out memory to disk underneath them
>> without their permission, I would happily reconsider my position.
>>
>> - Michael
> This has nothing to do with cgroups directly, it's just a way to
> demonstrate you have a bug.
>

If your datacenter or your cloud or your product does not want to
tolerate page registration, then don't use RDMA!

The bottom line is: RDMA is useless without page registration. Without
it, the performance of it will be crippled. If you define that as a bug,
then so be it.

- Michael