linux-kernel - Re: [PATCH net-next] page_pool: Rename frag_users to frag

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Date: Thu, 21 Dec 2023 10:07:26 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Ilias Apalodimas <ilias.apalodimas@...aro.org>
CC: <netdev@...r.kernel.org>, Jesper Dangaard Brouer <hawk@...nel.org>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] page_pool: Rename frag_users to frag_cnt

On 2023/12/20 15:56, Ilias Apalodimas wrote:
> Hi Yunsheng,
>>>>>  #ifdef CONFIG_PAGE_POOL_STATS
>>>>>       /* these stats are incremented while in softirq context */
>>>>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>>>>> index 9b203d8660e4..19a56a52ac8f 100644
>>>>> --- a/net/core/page_pool.c
>>>>> +++ b/net/core/page_pool.c
>>>>> @@ -659,7 +659,7 @@ EXPORT_SYMBOL(page_pool_put_page_bulk);
>>>>>  static struct page *page_pool_drain_frag(struct page_pool *pool,
>>>>>                                        struct page *page)
>>>>>  {
>>>>> -     long drain_count = BIAS_MAX - pool->frag_users;
>>>>> +     long drain_count = BIAS_MAX - pool->frag_cnt;
>>>>
>>>> drain_count = pool->refcnt_bais;
>>>
>>> I think this is a typo right? This still remains
>>
>> It would be better to invert logic too, as it is mirroring:
>>
>> https://elixir.bootlin.com/linux/v6.7-rc5/source/mm/page_alloc.c#L4745
> 
> This is still a bit confusing for me since the actual bias is the
> number of fragments that you initially split the page. But I am fine
Acctually there are two bais numbers for a page used by
page_pool_alloc_frag().
the one for page->pp_ref_count, which already use the BIAS_MAX, which
indicates the initial bais number:
https://elixir.bootlin.com/linux/latest/source/net/core/page_pool.c#L779

Another one for pool->frag_users indicating the runtime bais number, which
need changing when a page is split into more fragments:
https://elixir.bootlin.com/linux/latest/source/net/core/page_pool.c#L776
https://elixir.bootlin.com/linux/latest/source/net/core/page_pool.c#L783

> with having a common approach. I'll send the rename again shortly, and
> I can send the logic invert a bit later (or feel free to send it,
> since it was your idea).
> 
> Thanks
> /Ilias
> .
>