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

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Message-ID: <15c404e4-8efa-cc1c-174f-0752005b6755@huawei.com>
Date:   Thu, 16 Nov 2023 19:12:33 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     David Ahern <dsahern@...nel.org>, 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 2023/11/16 1:57, David Ahern wrote:
> 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.

Yes, I am agreed the ultimate goal is to move away from struct page
references. But I am not sure if we can do it right away as there
still are different types of existing 'struct page' in the netstack,
see:

https://lore.kernel.org/all/8b7d25eb-1f10-3e37-8753-92b42da3fb34@huawei.com/

> 
> 
> .
>