netdev - Re: [RFC PATCH net-next v1 4/4] net: page_pool: use netmem

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Date: Thu, 21 Dec 2023 19:32:07 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Mina Almasry <almasrymina@...gle.com>, Shakeel Butt <shakeelb@...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 2023/12/20 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.

> - 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()?

> - Some of the page_pool APIs are exposed to the drivers as static
> inline helpers, and if I want the page_pool to use netmem internally
> the page_pool needs to do a netmem_to_page() in these helpers.
> 
> The refactor is not an issue, but I was wondering if not exporting
> netmem_to_page() was worth moving the code around. I was thinking in
> the interim until netmem is adopted and has actual driver users we may
> prefer to just add a comment on the netmem_to_page() helper that says
> 'try not to use this directly and use the netmem helpers instead'.
>