linux-kernel - Re: [RFC 01/19] netmem: rename struct net_iov to struct netmem

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Message-ID: <d08b9abf-9b42-47ae-9ec7-36b59931ffb5@gmail.com>
Date: Tue, 13 May 2025 13:58:10 +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, ast@...nel.org,
 daniel@...earbox.net, davem@...emloft.net, john.fastabend@...il.com,
 andrew+netdev@...n.ch, edumazet@...gle.com, pabeni@...hat.com,
 vishal.moola@...il.com
Subject: Re: [RFC 01/19] netmem: rename struct net_iov to struct netmem_desc

On 5/13/25 03:00, Byungchul Park wrote:
> On Mon, May 12, 2025 at 12:14:13PM -0700, Mina Almasry wrote:
>> On Mon, May 12, 2025 at 6:29 AM Byungchul Park <byungchul@...com> wrote:
>>>
>>> On Mon, May 12, 2025 at 02:11:13PM +0100, Pavel Begunkov wrote:
>>>> On 5/9/25 12:51, Byungchul Park wrote:
>>>>> To simplify struct page, the page pool members of struct page should be
>>>>> moved to other, allowing these members to be removed from struct page.
>>>>>
>>>>> Reuse struct net_iov for also system memory, that already mirrored the
>>>>> page pool members.
>>>>>
>>>>> Signed-off-by: Byungchul Park <byungchul@...com>
>>>>> ---
>>>>>    include/linux/skbuff.h                  |  4 +--
>>>>>    include/net/netmem.h                    | 20 ++++++------
>>>>>    include/net/page_pool/memory_provider.h |  6 ++--
>>>>>    io_uring/zcrx.c                         | 42 ++++++++++++-------------
>>>>
>>>> You're unnecessarily complicating it for yourself. It'll certainly
>>>> conflict with changes in the io_uring tree, and hence it can't
>>>> be taken normally through the net tree.
>>>>
>>>> Why are you renaming it in the first place? If there are good
>>>
>>> It's because the struct should be used for not only io vetor things but
>>> also system memory.  Current network code uses struct page as system
>>> memory descriptor but struct page fields for page pool will be gone.
>>>
>>> So I had to reuse struct net_iov and I thought renaming it made more
>>> sense.  It'd be welcome if you have better idea.
>>>
>>
>> As I said in another thread, struct page should not embed struct
> 
> I don't understand here.  Can you explain more?  Do you mean do not use
> place holder?

I assume this:

struct netmem_desc {
	...
};

struct net_iov {
	netmem_desc desc;
};

struct page {
	union {
		// eventually will go away
		netmem_desc desc;
		...	
	};
};


And to avoid conflicts with io_uring, you can send something like the
following to the net tree, and finish the io_uring conversion later.

struct net_iov {
	struct_group_tagged(netmem_desc, desc,
		...
	);
};

-- 
Pavel Begunkov