netdev - Re: [RFC PATCH v2 00/11] Device Memory TCP

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Message-ID: <ZNULIDzuVVyfyMq2@ziepe.ca>
Date: Thu, 10 Aug 2023 13:06:56 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Christian König <christian.koenig@....com>
Cc: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Hari Ramakrishnan <rharix@...gle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy Lutomirski <luto@...nel.org>, stephen@...workplumber.org,
	sdf@...gle.com
Subject: Re: [RFC PATCH v2 00/11] Device Memory TCP

On Thu, Aug 10, 2023 at 12:29:08PM +0200, Christian König wrote:
> Am 10.08.23 um 03:57 schrieb Mina Almasry:
> > Changes in RFC v2:
> > ------------------
> > 
> > The sticking point in RFC v1[1] was the dma-buf pages approach we used to
> > deliver the device memory to the TCP stack. RFC v2 is a proof-of-concept
> > that attempts to resolve this by implementing scatterlist support in the
> > networking stack, such that we can import the dma-buf scatterlist
> > directly.
> 
> Impressive work, I didn't thought that this would be possible that "easily".
> 
> Please note that we have considered replacing scatterlists with simple
> arrays of DMA-addresses in the DMA-buf framework to avoid people trying to
> access the struct page inside the scatterlist.
> 
> It might be a good idea to push for that first before this here is finally
> implemented.
> 
> GPU drivers already convert the scatterlist used to arrays of DMA-addresses
> as soon as they get them. This leaves RDMA and V4L as the other two main
> users which would need to be converted.

Oh that would be a nightmare for RDMA.

We need a standard based way to have scalable lists of DMA addresses :(

> > 2. Netlink API (Patch 1 & 2).
> 
> How does netlink manage the lifetime of objects?

And access control..

Jason