netdev - Re: [RFC PATCH net-next] page_pool: Track DMA-mapped pages and unmap them when destroying the pool

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Message-ID: <8fa8f430-5740-42e8-b720-618811fabb22@huawei.com>
Date: Wed, 12 Mar 2025 20:05:22 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Matthew Wilcox <willy@...radead.org>
CC: Toke Høiland-Jørgensen <toke@...hat.com>, Yunsheng
 Lin <yunshenglin0825@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas
	<ilias.apalodimas@...aro.org>, "David S. Miller" <davem@...emloft.net>,
	Yonglong Liu <liuyonglong@...wei.com>, Mina Almasry <almasrymina@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<linux-mm@...ck.org>, <netdev@...r.kernel.org>, <conduct@...nel.org>
Subject: Re: [RFC PATCH net-next] page_pool: Track DMA-mapped pages and unmap
 them when destroying the pool

On 2025/3/11 23:11, Matthew Wilcox wrote:
> On Tue, Mar 11, 2025 at 08:25:25PM +0800, Yunsheng Lin wrote:
>>> struct page {
>>> 	unsigned long flags;
>>> 	unsigned long memdesc;
>>
>> It seems there may be memory behind the above 'memdesc' with different size
>> and layout for different subsystem?
> 
> Yes.
> 
>> I am not sure if I understand the case of the same page might be handle in
>> two subsystems concurrently or a page is allocated in one subsystem and
>> then passed to be handled in other subsystem, for examlpe:
>> page_pool owned page is mmap'ed into user space through tcp zero copy,
>> see tcp_zerocopy_vm_insert_batch(), it seems the same page is handled in
>> both networking/page_pool and vm subsystem?
> 
> It's not that arbitrary.  I mean, you could read all the documentation
> I've written about this concept, listen to the talks I've given.  But
> sure, you're a special fucking snowflake and deserve your own unique
> explanation.

If you don't like responding to the above question/comment, I would rather
you strip out them like the other question/comment or just ignore it:(

I am not sure how to interpret the comment, but I am sure it is not a kind
one, so CC 'Code of Conduct Committee' in case there is more coming.

> 
>