Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for custom page providers

[Pavel Begunkov]

On 6/10/24 16:16, David Ahern wrote:
> On 6/10/24 6:16 AM, Jason Gunthorpe wrote:
> > On Mon, Jun 10, 2024 at 02:07:01AM +0100, Pavel Begunkov wrote:
> > > On 6/10/24 01:37, David Wei wrote:
> > > > On 2024-06-07 17:52, Jason Gunthorpe wrote:
> > > > > IMHO it seems to compose poorly if you can only use the io_uring
> > > > > lifecycle model with io_uring registered memory, and not with DMABUF
> > > > > memory registered through Mina's mechanism.
> > > >
> > > > By this, do you mean io_uring must be exclusively used to use this
> > > > feature?
> > > >
> > > > And you'd rather see the two decoupled, so userspace can register w/ say
> > > > dmabuf then pass it to io_uring?
> > >
> > > Personally, I have no clue what Jason means. You can just as
> > > well say that it's poorly composable that write(2) to a disk
> > > cannot post a completion into a XDP ring, or a netlink socket,
> > > or io_uring's main completion queue, or name any other API.
> >
> > There is no reason you shouldn't be able to use your fast io_uring
> > completion and lifecycle flow with DMABUF backed memory. Those are not
> > widly different things and there is good reason they should work
> > together.

Let's not mix up devmem TCP and dmabuf specifically, as I see it
your question was concerning the latter: "... DMABUF memory registered
through Mina's mechanism". io_uring's zcrx can trivially get dmabuf
support in future, as mentioned it's mostly the setup side. ABI,
buffer workflow and some details is a separate issue, and I don't
see how further integration aside from what we're already sharing
is beneficial, on opposite it'll complicate things.

> > Pretending they are totally different just because two different
> > people wrote them is a very siloed view.
io_uring zcrx and devmem? They are not, nobody is saying otherwise,
_very_ similar approaches if anything but with different API, which
is the reason we already use common infra.

> > > The devmem TCP callback can implement it in a way feasible to
> > > the project, but it cannot directly post events to an unrelated
> > > API like io_uring. And devmem attaches buffers to a socket,
> > > for which a ring for returning buffers might even be a nuisance.
> >
> > If you can't compose your io_uring completion mechanism with a DMABUF
> > provided backing store then I think it needs more work.

As per above, it conflates devmem TCP with dmabuf.

> exactly. io_uring, page_pool, dmabuf - all kernel building blocks for
> solutions. This why I was pushing for Mina's set not to be using the
> name `devmem` - it is but one type of memory and with dmabuf it should
> not matter if it is gpu or host (or something else later on - cxl?).

--
Pavel Begunkov