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

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Message-ID: <ZK6ktnwIjXIobFIM@ziepe.ca>
Date:   Wed, 12 Jul 2023 10:03:50 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christian König <christian.koenig@....com>
Cc:     Mina Almasry <almasrymina@...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>,
        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>, 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 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. :\

Jason