netdev - Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE

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Message-ID: <ZLFv2PIgdeH8gKmh@ziepe.ca>
Date: Fri, 14 Jul 2023 12:55:04 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mina Almasry <almasrymina@...gle.com>
Cc: Christian König <christian.koenig@....com>,
	Hari Ramakrishnan <rharix@...gle.com>,
	David Ahern <dsahern@...nel.org>,
	Samiullah Khawaja <skhawaja@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Christoph Hellwig <hch@....de>,
	John Hubbard <jhubbard@...dia.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jesper Dangaard Brouer <jbrouer@...hat.com>, brouer@...hat.com,
	Alexander Duyck <alexander.duyck@...il.com>,
	Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
	pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lorenzo Bianconi <lorenzo@...nel.org>,
	Yisen Zhuang <yisen.zhuang@...wei.com>,
	Salil Mehta <salil.mehta@...wei.com>,
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	Ryder Lee <ryder.lee@...iatek.com>,
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	Jonathan Lemon <jonathan.lemon@...il.com>, logang@...tatee.com,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5]
 page_pool: remove PP_FLAG_PAGE_FRAG flag)

On Fri, Jul 14, 2023 at 07:55:15AM -0700, Mina Almasry wrote:

> Once the skb frags with struct new_abstraction are in the TCP stack,
> they will need some special handling in code accessing the frags. But
> my RFC already addressed that somewhat because the frags were
> inaccessible in that case. In this case the frags will be both
> inaccessible and will not be struct pages at all (things like
> get_page() will not work), so more special handling will be required,
> maybe.

It seems sort of reasonable, though there will be interesting concerns
about coherence and synchronization with generial purpose DMABUFs that
will need tackling.

Still it is such a lot of churn and weridness in the netdev side, I
think you'd do well to present an actual full application as
justification.

Yes, you showed you can stick unordered TCP data frags into GPU memory
sort of quickly, but have you gone further with this to actually show
it is useful for a real world GPU centric application?

BTW your cover letter said 96% utilization, the usual server
configuation is one NIC per GPU, so you were able to hit 1500Gb/sec of
TCP BW with this?

Jason