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

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Date: Mon, 10 Jun 2024 09:16:25 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: David Wei <dw@...idwei.uk>, David Ahern <dsahern@...nel.org>,
	Mina Almasry <almasrymina@...gle.com>,
	Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org,
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	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	"David S. Miller" <davem@...emloft.net>,
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	Praveen Kaligineedi <pkaligineedi@...gle.com>
Subject: Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for
 custom page providers

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.

Pretending they are totally different just because two different
people wrote them is a very siloed view.

> 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.

Jason