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

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Message-ID: <20240610221500.GN791043@ziepe.ca>
Date: Mon, 10 Jun 2024 19:15:00 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: David Ahern <dsahern@...nel.org>, David Wei <dw@...idwei.uk>,
	Mina Almasry <almasrymina@...gle.com>,
	Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org,
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	"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 08:20:08PM +0100, Pavel Begunkov wrote:
> On 6/10/24 16:16, David Ahern wrote:

> > > 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.

Again, I am talking about composability here, duplicating the DMABUF
stuff into io_uring is not composable, it is just duplicating things.

It does not match the view that there should be two distinct layers
here, one that provides the pages and one that manages the
lifecycle. As HCH pushes for pages either come from the allocator and
get to use the struct folio or the come from a dmabuf and they
don't. That is it, the only two choices.

The iouring stuff is trying to confuse the source of the pages with
the lifecycle - which is surely convenient, but is why Christoph is
opposing it.

Jason