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

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Date: Wed, 12 Jul 2023 20:57:35 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mina Almasry <almasrymina@...gle.com>
Cc: 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>,
	Eric Dumazet <edumazet@...gle.com>,
	Sunil Goutham <sgoutham@...vell.com>,
	Geetha sowjanya <gakula@...vell.com>,
	Subbaraya Sundeep <sbhatta@...vell.com>,
	hariprasad <hkelam@...vell.com>, Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leon@...nel.org>, Felix Fietkau <nbd@....name>,
	Ryder Lee <ryder.lee@...iatek.com>,
	Shayne Chen <shayne.chen@...iatek.com>,
	Sean Wang <sean.wang@...iatek.com>, Kalle Valo <kvalo@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	linux-rdma@...r.kernel.org, linux-wireless@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Jonathan Lemon <jonathan.lemon@...il.com>,
	Christian König <christian.koenig@....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 Wed, Jul 12, 2023 at 01:16:00PM -0700, Mina Almasry wrote:

> The proposal was that the uapi in step #1 allocates a region of GPU
> memory, and sets up a p2pdma provider for this region of memory.

Honestly that feels too hacky, which is why I've said a few times
you'd actually need to integrate p2p pages into a DRM driver properly.

> 2. The p2pdma semantics seem to be global to the pci device. I.e., 1
> GPU can export 1 p2pdma resource at a time (the way I'm reading the
> API).

All of this is just a reflection that you are trying to use it in a
wrong hacky way. The driver is supposed to create a p2p registration
for its entire BAR at startup. Not on demand and not in fragments.

Jason