netdev - Re: [PATCH net-next v5 3/5] page_pool: Allow drivers to hint on SKB recycling

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Date:   Mon, 17 May 2021 19:10:09 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
CC:     Matteo Croce <mcroce@...ux.microsoft.com>,
        <netdev@...r.kernel.org>, <linux-mm@...ck.org>,
        Ayush Sawal <ayush.sawal@...lsio.com>,
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        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v5 3/5] page_pool: Allow drivers to hint on SKB
 recycling

On 2021/5/17 17:36, Ilias Apalodimas wrote:
 >>
>> Even if when skb->pp_recycle is 1, pages allocated from page allocator directly
>> or page pool are both supported, so it seems page->signature need to be reliable
>> to indicate a page is indeed owned by a page pool, which means the skb->pp_recycle
>> is used mainly to short cut the code path for skb->pp_recycle is 0 case, so that
>> the page->signature does not need checking?
> 
> Yes, the idea for the recycling bit, is that you don't have to fetch the page
> in cache do do more processing (since freeing is asynchronous and we
> can't have any guarantees on what the cache will have at that point).  So we
> are trying to affect the existing release path a less as possible. However it's
> that new skb bit that triggers the whole path.
> 
> What you propose could still be doable though.  As you said we can add the
> page pointer to struct page when we allocate a page_pool page and never
> reset it when we recycle the buffer. But I don't think there will be any
> performance impact whatsoever. So I prefer the 'visible' approach, at least for

setting and unsetting the page_pool ptr every time the page is recycled may
cause a cache bouncing problem when rx cleaning and skb releasing is not
happening on the same cpu.

> the first iteration.
> 
> Thanks
> /Ilias
>  
> 
> .
>