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

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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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