[openib-general] Re: RDMA memory registration

[Grant Grundler]

On Tue, May 03, 2005 at 09:42:12AM +0100, David Addison wrote:
> >This doesn't scale well as more cards are added to the box.
> >I think I understand why it's good for single cards though.
>
> With the IOPROC patch the device driver hooks are registered on a per 
> process or perhaps better still, a per VMA basis.

I was originally thinking the registrations are global (for all memory)
and not per process. Per process or per VMA seems reasonable to me.

> And for processes/VMAs where there are no registrations the overhead
> is very low.

Yes - thanks. I'm still reading the LKML thread you started:
	http://lkml.org/lkml/2005/4/26/198

In particular, the comments from Brice Goglin:
	http://lkml.org/lkml/2005/4/26/222

openib.org folks can find the IOPROC patch for 2.6.12-rc3 archived here:
	http://lkml.org/lkml/diff/2005/4/26/198/1

> With multiple cards in a box, all using different device drivers,
> I guess there could end up being multiple registrations per process/VMA.
> But I'm not sure this will be a common case for RDMA use in real life.

I agree. Gateways between fabrics is the only case I can think of.
This won't be a problem until someone at a large national lab tries
to connect two "legacy" fabrics together.

thanks,
grant