Re: [openib-general] Re: RDMA memory registration

[David Addison <addy@quadrics.com>]

Grant Grundler wrote:
> On Fri, Apr 29, 2005 at 08:22:24PM +0200, Brice Goglin wrote:
> > For instance, instead of adding PROT_DONT/ALWAYSCOPY, you may use
> > an ioproc hook in the fork path. This hook (a function in your driver)
> > would be called for each registered page. It will decide whether
> > the page should be pre-copied or not and update the registration
> > table (or whatever stores address translations in the NIC).
> > In addition, the driver would probably pre-copy cow pages when
> > registering them.
>
> 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. And for processes/VMAs where there
are no registrations the overhead is very low.

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.

Cheers
Addy.
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