Memory providers multiplexing (Was: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE_FRAG flag)

[Mina Almasry]

On Tue, Jul 11, 2023 at 9:32 AM Jakub Kicinski <kuba at kernel.org> wrote:
>
> On Tue, 11 Jul 2023 10:20:58 -0600 David Ahern wrote:
> > On 7/11/23 10:00 AM, Jakub Kicinski wrote:
> > >> RDMA works with the AMD and Intel intree drivers using DMABUF without
> > >> requiring struct pages using the DRM hacky scatterlist approach.
> > > I see, thanks. We need pages primarily for refcounting. Avoiding all
> > > the infamous problems with memory pins. Oh well.
> >
> > io_uring for example already manages the page pinning. An skb flag was
> > added for ZC Tx API to avoid refcounting in the core networking layer.
>
> Right, we can refcount in similar fashion. Still tracking explicitly
> when buffers are handed over to the NIC.
>
> > Any reason not to allow an alternative representation for skb frags than
> > struct page?
>
> I don't think there's a hard technical reason. We can make it work.

I also think we can switch the representation for skb frags to
something else. However - please do correct me if I'm wrong - I don't
think that is sufficient for device memory TCP. My understanding is
that we also need to modify any NIC drivers that want to use device
memory TCP to understand a new memory type, and the page pool as well
if that's involved. I think in particular modifying the memory type in
all the NIC drivers that want to do device memory TCP is difficult. Do
you think this is feasible?

--
Thanks,
Mina