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Date: Mon, 10 Jun 2024 14:38:18 +0200
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Subject: Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for
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To: Jason Gunthorpe <jgg@ziepe.ca>, Pavel Begunkov <asml.silence@gmail.com>
Cc: David Wei <dw@davidwei.uk>, David Ahern <dsahern@kernel.org>,
 Mina Almasry <almasrymina@google.com>, Christoph Hellwig
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 Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>,
 Martin KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman
 <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
 Yonghong Song <yonghong.song@linux.dev>,
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 Shakeel Butt <shakeel.butt@linux.dev>, Jeroen de Borst
 <jeroendb@google.com>, Praveen Kaligineedi <pkaligineedi@google.com>
References: <20240530201616.1316526-3-almasrymina@google.com>
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 <eb237e6e-3626-4435-8af5-11ed3931b0ac@gmail.com>
 <be2d140f-db0f-4d15-967c-972ea6586b5c@kernel.org>
 <20240607145247.GG791043@ziepe.ca>
 <45803740-442c-4298-b47e-2d87ae5a6012@davidwei.uk>
 <54975459-7a5a-46ff-a9ae-dc16ceffbab4@gmail.com>
 <20240610121625.GI791043@ziepe.ca>
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Am 10.06.24 um 14:16 schrieb Jason Gunthorpe:
> 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.

Well there is the fundamental problem that you can't use io_uring to 
implement the semantics necessary for a dma_fence.

That's why we had to reject the io_uring work on DMA-buf sharing from 
Google a few years ago.

But this only affects the dma_fence synchronization part of DMA-buf, but 
*not* the general buffer sharing.

Regards,
Christian.

>
> 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