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

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

On 04/11/2013 11:58 AM, Michael S. Tsirkin wrote:
> On Thu, Apr 11, 2013 at 05:47:53PM +0200, Paolo Bonzini wrote:
>> Il 11/04/2013 17:46, Michael S. Tsirkin ha scritto:
>>>> Ok, let's keep it simple.  The only two things we need are:
>>>>
>>>> 1) remove the patch to disable is_dup_page
>>>>
>>>> 2) rename the transport to "x-rdma" (just in migration.c)
>>>>
>>>> Both things together let us keep it safe for a release or two.  Let's
>>>> merge this thing.
>>> I would drop the chunk based thing too.  Besides being slow, it turns
>>> out that it pins all memory anyway. So no memory overcommit.
>> It doesn't pin zero pages.  Those are never transmitted (it's a recent
>> change).  So pages that are ballooned at the beginning of migration, and
>> remain ballooned throughout, will never be pinned.
>>
>> Paolo
> Of course Michael says it's slow unless you disable zero page detection,
> and then I'm guessing it does?
>
Only during the bulk phase round, and even then, as Paolo described,
zero pages do not get pinned on the destination.

Chunk registration is still very valuable when zero page detection is
activated.

The realization is that chunk registration (and zero page scanning) have
very little effect whatsoever on performance *after* the bulk phase 
round because
pages have already been mapped and already pinned in memory for life.

- Michael