linux-kernel - Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

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Message-ID: <ee10d050-ef24-49b2-8712-c9bc8a911c2a@kernel.org>
Date:   Wed, 15 Nov 2023 10:57:30 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mina Almasry <almasrymina@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Willem de Bruijn <willemb@...gle.com>,
        Kaiyuan Zhang <kaiyuanz@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Christian König <christian.koenig@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

On 11/15/23 2:21 AM, Yunsheng Lin wrote:
> On 2023/11/14 21:16, Jason Gunthorpe wrote:
>> On Tue, Nov 14, 2023 at 04:21:26AM -0800, Mina Almasry wrote:
>>
>>> Actually because you put the 'strtuct page for devmem' in
>>> skb->bv_frag, the net stack will grab the 'struct page' for devmem
>>> using skb_frag_page() then call things like page_address(), kmap,
>>> get_page, put_page, etc, etc, etc.
>>
>> Yikes, please no. If net has its own struct page look alike it has to
>> stay entirely inside net. A non-mm owned struct page should not be
>> passed into mm calls. It is just way too hacky to be seriously
>> considered :(
> 
> Yes, that is something this patchset is trying to do, defining its own
> struct page look alike for page pool to support devmem.
> 

Networking needs to be able to move away from struct page references.
The devmem and host memory for Rx use cases do not need to be page based.