Date: Fri, 22 Dec 2023 14:42:23 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Mina Almasry <almasrymina@...gle.com>
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Subject: Re: [RFC PATCH net-next v1 4/4] net: page_pool: use netmem_t instead
 of struct page in API

On 2023/12/22 5:22, Mina Almasry wrote:
> On Thu, Dec 21, 2023 at 3:32 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>>
>> On 2023/12/20 11:01, Mina Almasry wrote:
>>
>> ...
>>
>>>>>> Perhaps we should aim to not export netmem_to_page(),
>>>>>> prevent modules from accessing it directly.
>>>>>
>>>>> +1.
>>>>
>>>
>>> I looked into this, but it turns out it's a slightly bigger change
>>> that needs some refactoring to make it work. There are few places
>>> where I believe I need to add netmem_to_page() that are exposed to the
>>> drivers via inline helpers, these are:
>>>
>>> - skb_frag_page(), which returns NULL if the netmem is not a page, but
>>> needs to do a netmem_to_page() to return the page otherwise.
>>
>> Is it possible to introduce something like skb_frag_netmem() for
>> netmem? so that we can keep most existing users of skb_frag_page()
>> unchanged and avoid adding additional checking overhead for existing
>> users.
>>
> 
> In my experience most current skb_frag_page() users need specifically
> the struct page*. Example is illegal_highdma() which
> PageHighMem(skb_frag_page())

For illegal_highdma() case, is it possible to use something like
skb_readabe_frag() checking to avoid calling skb_frag_page() for netmem?

> 
> But RFC v5 adds skb_frag_netmem() for callsites that want a netmem and
> don't care about specifically a page:
> 
> https://patchwork.kernel.org/project/netdevbpf/patch/20231218024024.3516870-10-almasrymina@google.com/
> 
>>> - The helpers inside skb_add_rx_frag(), which needs to do a
>>> netmem_to_page() to set skb->pfmemalloc.
>>
>> Similar as above, perhaps introduce something like skb_add_rx_netmem_frag()?
>>
> 
> Yes, v3 of this series adds skb_add_rx_frag_netmem():
> 
> https://patchwork.kernel.org/project/netdevbpf/patch/20231220214505.2303297-4-almasrymina@google.com/

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