[ofa-general] Re: Demand paging for memory regions

[Christoph Lameter]

On Tue, 12 Feb 2008, Roland Dreier wrote:

> I don't know anything about the T3 internals, but it's not clear that
> you could do this without a new chip design in general.  Lot's of RDMA
> devices were designed expecting that when a packet arrives, the HW can
> look up the bus address for a given memory region/offset and place the
> packet immediately.  It seems like a major change to be able to
> generate a "page fault" interrupt when a page isn't present, or even
> just wait to scatter some data until the host finishes updating page
> tables when the HW needs the translation.

Well if the VM wants to invalidate a page then the remote end first has to 
remove its mapping. 

If a page has been removed then the remote end would encounter a fault and 
then would have to wait for the local end to reestablish its mapping 
before proceeding.

So the packet would only be generated when both ends are in sync.