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Date:   Wed, 12 Jul 2023 15:35:14 +0200
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Subject: Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5]
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To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     Mina Almasry <almasrymina@google.com>,
        David Ahern <dsahern@kernel.org>,
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        Lorenzo Bianconi <lorenzo@kernel.org>,
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        Salil Mehta <salil.mehta@huawei.com>,
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From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Am 12.07.23 um 15:03 schrieb Jason Gunthorpe:
> On Wed, Jul 12, 2023 at 09:55:51AM +0200, Christian König wrote:
>
>>> Anyone see any glaring issues with this approach? I plan on trying to
>>> implement a PoC and sending an RFC v2.
>> Well we already have DMA-buf as user API for this use case, which is
>> perfectly supported by RDMA if I'm not completely mistaken.
>>
>> So what problem do you try to solve here actually?
> In a nutshell, netdev's design currently needs struct pages to do DMA
> to it's packet buffers.
>
> So it cannot consume the scatterlist that dmabuf puts out
>
> RDMA doesn't need struct pages at all, so it is fine.
>
> If Mina can go down the path of changing netdev to avoid needing
> struct pages then no changes to DRM side things.
>
> Otherwise a P2P struct page and a co-existance with netmem on a
> ZONE_DEVICE page would be required. :\

Uff, depending on why netdev needs struct page (I think I have a good 
idea why) this isn't really going to work generically either way.

What we maybe able to do is to allow copy_file_range() between DMA-buf 
file descriptor and a TCP socket.

If I'm not completely mistaken that should then end up in DMA-bufs 
file_operations->copy_file_range callback (maybe with some minor change 
to allows this).

The DMA-buf framework could then forward this to the exporter of the 
memory which owns the backing memory could then do the necessary steps.

Regards,
Christian.

>
> Jason