netdev - Re: Device mem changes vs pinning/zerocopy changes

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Message-ID: <CAHS8izPOonh6E3B+xHRSsfXpo_jHXymVyNOZOUc_1LjOtT9wow@mail.gmail.com>
Date: Thu, 5 Jun 2025 12:30:26 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: David Howells <dhowells@...hat.com>
Cc: willy@...radead.org, hch@...radead.org, Jakub Kicinski <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: Device mem changes vs pinning/zerocopy changes

On Wed, Jun 4, 2025 at 8:59 AM David Howells <dhowells@...hat.com> wrote:
>
> (Apologies, I accidentally sent the incomplete email)
>
> > I think you need to modify the existing sk_buff. I think adding
> > a new struct and migrating the entire net stack to use that is a bit
> > too ambitious. But up to you. Just my 2 cents here.
>
> It may come down to that, and if it does, we'll need to handle frags
> differently.  Basically, for zerocopy, the following will all apply or come to
> apply sometime in the future:
>
>  (1) We're going to be getting arrays of {physaddr,len} from the higher
>      layers.  I think Christoph's idea is that this makes DMA mapping easier.
>      We will need to retain this.
>

I would punt this to a follow up project. Currently the net stack uses
pages extensively; replacing them with scatterlist-like {physaddr,
len} sounds like a huge undertaking. Especially with the conversion to
netmem_desc happening in parallel with Byungchul's series. Just my 2
cents.

-- 
Thanks,
Mina