netdev - Re: [PATCH net-next] skbuff: Optimize SKB coalescing for page pool case

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Date: Tue, 4 Jul 2023 08:50:29 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Jakub Kicinski <kuba@...nel.org>, Liang Chen <liangchen.linux@...il.com>
CC: <ilias.apalodimas@...aro.org>, <hawk@...nel.org>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <pabeni@...hat.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] skbuff: Optimize SKB coalescing for page pool
 case

On 2023/7/4 2:53, Jakub Kicinski wrote:
> On Mon, 3 Jul 2023 17:12:46 +0800 Liang Chen wrote:
>> As for the "pp" reference, it has the test
>> page_pool_is_pp_page_frag(head_page) there. So for a non-frag pp page,
>> it will be a get_page call.
> 
> You don't understand - you can't put a page from a page pool in two
> skbs with pp_recycle set, unless the page is frag'ed.

Agreed. I think we should disallow skb coaleasing for non-frag pp page
instead of calling get_page(), as there is data race when calling
page_pool_return_skb_page() concurrently for the same non-frag pp page.

Even with my patchset, it may break the arch with
PAGE_POOL_DMA_USE_PP_FRAG_COUNT being true.

> .
>