[RFC PATCH v3 1/4] RDMA/umem: Support importing dma-buf as user memory region

[Daniel Vetter]

On Tue, Oct 06, 2020 at 12:49:56PM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 06, 2020 at 11:22:14AM +0200, Daniel Vetter wrote:
> > 
> > For reinstanting the pages you need:
> > 
> > - dma_resv_lock, this prevents anyone else from issuing new moves or
> >   anything like that
> > - dma_resv_get_excl + dma_fence_wait to wait for any pending moves to
> >   finish. gpus generally don't wait on the cpu, but block the dependent
> >   dma operations from being scheduled until that fence fired. But for rdma
> >   odp I think you need the cpu wait in your worker here.
> 
> Reinstating is not really any different that the first insertion, so
> then all this should be needed in every case?

Yes. Without move_notify we pin the dma-buf into system memory, so it
can't move, and hence you also don't have to chase it. But with
move_notify this all becomes possible.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch