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: <d143b16a-feda-4307-9e06-6232ecd08a88@kernel.org>
Date: Wed, 12 Mar 2025 12:48:56 -0600
From: shuah <shuah@...nel.org>
To: Yunsheng Lin <linyunsheng@...wei.com>,
 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 3/12/25 12:35, Shuah wrote:
> On 3/12/25 06:05, Yunsheng Lin wrote:
>> 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.
> 
> You can't point to talk given on the concept - people don't have to go
> find your talks to understand the concept. You are expected to answer
> the question and explain it to us here in this thread.
> 
> But
>>> sure, you're a special fucking snowflake and deserve your own unique
>>> explanation.

Mathew,

This message is a rude personal attack. This isn't the way to treat your
peers in the community. Apology is warranted.

> 
> Yunsheng Lin, This message is a rude personal attack. This isn't the
> way to treat your peers in the community. Apology is warranted.
> 

Yunsheng Lin, I am so sorry I got it wrong. Apologies for the mistake.

thanks,
-- Shuah (on behalf of the CoC committee)