[PATCH v16 0/4] RDMA: Add dma-buf support

[Alex Deucher]

On Thu, Feb 4, 2021 at 2:48 AM John Hubbard <jhubbard at nvidia.com> wrote:
>
> On 12/15/20 1:27 PM, Jianxin Xiong wrote:
> > This patch series adds dma-buf importer role to the RDMA driver in
> > attempt to support RDMA using device memory such as GPU VRAM. Dma-buf is
> > chosen for a few reasons: first, the API is relatively simple and allows
> > a lot of flexibility in implementing the buffer manipulation ops.
> > Second, it doesn't require page structure. Third, dma-buf is already
> > supported in many GPU drivers. However, we are aware that existing GPU
> > drivers don't allow pinning device memory via the dma-buf interface.
> > Pinning would simply cause the backing storage to migrate to system RAM.
> > True peer-to-peer access is only possible using dynamic attach, which
> > requires on-demand paging support from the NIC to work. For this reason,
> > this series only works with ODP capable NICs.
>
> Hi,
>
> Looking ahead to after this patchset is merged...
>
> Are there design thoughts out there, about the future of pinning to vidmem,
> for this? It would allow a huge group of older GPUs and NICs and such to
> do p2p with this approach, and it seems like a natural next step, right?

The argument is that vram is a scarce resource, but I don't know if
that is really the case these days.  At this point, we often have as
much vram as system ram if not more.

Alex