linux-kernel - Re: [PATCH 01/18] netmem: introduce struct netmem_desc struct_group_tagged()'ed on struct net

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Message-ID: <4d7a307f-d595-4020-8060-f3bc2f8f72ca@gmail.com>
Date: Wed, 28 May 2025 08:43:34 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Byungchul Park <byungchul@...com>, Mina Almasry <almasrymina@...gle.com>
Cc: willy@...radead.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel_team@...ynix.com,
 kuba@...nel.org, ilias.apalodimas@...aro.org, harry.yoo@...cle.com,
 hawk@...nel.org, akpm@...ux-foundation.org, davem@...emloft.net,
 john.fastabend@...il.com, andrew+netdev@...n.ch, toke@...hat.com,
 tariqt@...dia.com, edumazet@...gle.com, pabeni@...hat.com,
 saeedm@...dia.com, leon@...nel.org, ast@...nel.org, daniel@...earbox.net,
 david@...hat.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, mhocko@...e.com,
 horms@...nel.org, linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
 vishal.moola@...il.com
Subject: Re: [PATCH 01/18] netmem: introduce struct netmem_desc
 struct_group_tagged()'ed on struct net_iov

On 5/28/25 06:03, Byungchul Park wrote:
...>> Thus abstractly different things maybe should not share the same
>> in-kernel struct.
>>
>> One thing that maybe could work is if struct net_iov has a field in it
>> which tells us whether it's actually a struct page that can be passed
>> to mm apis, or not a struct page which cannot be passed to mm apis.
>>
>>> Or I should introduce another struct
>>
>> maybe introducing another struct is the answer. I'm not sure. The net
> 
> The final form should be like:
> 
>     struct netmem_desc {
>        struct page_pool *pp;
>        unsigned long dma_addr;
>        atomic_long_t ref_count;
>     };
> 
>     struct net_iov {
>        struct netmem_desc;
>        enum net_iov_type type;
>        struct net_iov_area *owner;
>        ...
>     };
> 
> However, now that overlaying on struct page is required, struct
> netmem_desc should be almost same as struct net_iov.  So I'm not sure if
> we should introduce struct netmem_desc as a new struct along with struct
> net_iov.

Yes, you should. Mina already explained that net_iov is not the same
thing as the net specific sub-struct of the page. They have common
fields, but there are also net_iov (memory provider) specific fields
as well.

-- 
Pavel Begunkov