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Message-ID: <ee10d050-ef24-49b2-8712-c9bc8a911c2a@kernel.org>
Date:   Wed, 15 Nov 2023 10:57:30 -0700
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Subject: Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider
Content-Language: en-US
To:     Yunsheng Lin <linyunsheng@huawei.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mina Almasry <almasrymina@google.com>
Cc:     Jakub Kicinski <kuba@kernel.org>, davem@davemloft.net,
        pabeni@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Willem de Bruijn <willemb@google.com>,
        Kaiyuan Zhang <kaiyuanz@google.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Eric Dumazet <edumazet@google.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Matthew Wilcox <willy@infradead.org>,
        Linux-MM <linux-mm@kvack.org>
References: <20231113130041.58124-1-linyunsheng@huawei.com>
 <20231113130041.58124-4-linyunsheng@huawei.com>
 <CAHS8izMjmj0DRT_vjzVq5HMQyXtZdVK=o4OP0gzbaN=aJdQ3ig@mail.gmail.com>
 <20231113180554.1d1c6b1a@kernel.org>
 <0c39bd57-5d67-3255-9da2-3f3194ee5a66@huawei.com>
 <CAHS8izNxkqiNbTA1y+BjQPAber4Dks3zVFNYo4Bnwc=0JLustA@mail.gmail.com>
 <ZVNzS2EA4zQRwIQ7@nvidia.com>
 <ed875644-95e8-629a-4c28-bf42329efa56@huawei.com>
From:   David Ahern <dsahern@kernel.org>
In-Reply-To: <ed875644-95e8-629a-4c28-bf42329efa56@huawei.com>
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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.