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

[Christoph Lameter]

On Tue, 12 Feb 2008, Felix Marti 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.
> 
> That is correct, not a change we can make for T3. We could, in theory,
> deal with changing mappings though. The change would need to be
> synchronized though: the VM would need to tell us which mapping were
> about to change and the driver would then need to disable DMA to/from
> it, do the change and resume DMA.

Right. That is the intend of the patchset.