Re: [Qemu-devel] [RFC PATCH RDMA support v4: 03/10] more verbose documentation of the RDMA transport

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

FYI, I used the following redhat cgroups instructions, to test if 
overcommit + RDMA was working:

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/sec-memory.html

- Michael

On 03/21/2013 02:11 AM, Michael S. Tsirkin wrote:
> On Tue, Mar 19, 2013 at 01:49:34PM -0400, Michael R. Hines wrote:
>> I also did a test using RDMA + cgroup, and the kernel killed my QEMU :)
>>
>> So, infiniband is not smart enough to know how to avoid pinning a
>> zero page, I guess.
>>
>> - Michael
>>
>> On 03/19/2013 01:14 PM, Paolo Bonzini wrote:
>>> Il 19/03/2013 18:09, Michael R. Hines ha scritto:
>>>> Allowing QEMU to swap due to a cgroup limit during migration is a viable
>>>> overcommit option?
>>>>
>>>> I'm trying to keep an open mind, but that would kill the migration
>>>> time.....
>>> Would it swap?  Doesn't the kernel back all zero pages with a single
>>> copy-on-write page?  If that still accounts towards cgroup limits, it
>>> would be a bug.
>>>
>>> Old kernels do not have a shared zero hugepage, and that includes some
>>> distro kernels.  Perhaps that's the problem.
>>>
>>> Paolo
>>>
> I really shouldn't break COW if you don't request LOCAL_WRITE.
> I think it's a kernel bug, and apparently has been there in the code since the
> first version: get_user_pages parameters swapped.
>
> I'll send a patch. If it's applied, you should also
> change your code from
>
> +                                IBV_ACCESS_LOCAL_WRITE |
> +                                IBV_ACCESS_REMOTE_WRITE |
> +                                IBV_ACCESS_REMOTE_READ);
>
> to
>
> +                                IBV_ACCESS_REMOTE_READ);
>
> on send side.
> Then, each time we detect a page has changed we must make sure to
> unregister and re-register it. Or if you want to be very
> smart, check that the PFN didn't change and reregister
> if it did.
>
> This will make overcommit work.
>