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: <20230711093224.1bf30ed5@kernel.org>
Date:   Tue, 11 Jul 2023 09:32:24 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Ahern <dsahern@...nel.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Christoph Hellwig <hch@....de>,
        Mina Almasry <almasrymina@...gle.com>,
        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>
Subject: Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5]
 page_pool: remove PP_FLAG_PAGE_FRAG flag)

On Tue, 11 Jul 2023 10:20:58 -0600 David Ahern wrote:
> On 7/11/23 10:00 AM, Jakub Kicinski wrote:
> >> RDMA works with the AMD and Intel intree drivers using DMABUF without
> >> requiring struct pages using the DRM hacky scatterlist approach.  
> > I see, thanks. We need pages primarily for refcounting. Avoiding all
> > the infamous problems with memory pins. Oh well.  
> 
> io_uring for example already manages the page pinning. An skb flag was
> added for ZC Tx API to avoid refcounting in the core networking layer.

Right, we can refcount in similar fashion. Still tracking explicitly
when buffers are handed over to the NIC.

> Any reason not to allow an alternative representation for skb frags than
> struct page?

I don't think there's a hard technical reason. We can make it work.