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

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Message-ID: <0dfffe91-2bd4-2151-cf71-ef29bf562767@huawei.com>
Date: Thu, 21 Dec 2023 15:59:32 +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 2023/12/21 14:37, Ilias Apalodimas wrote:
> Hi Yunsheng,
> 
> On Thu, 21 Dec 2023 at 04:07, Yunsheng Lin <linyunsheng@...wei.com> wrote:
>>
>> 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
> 
> I know, and that's exactly what my commit message explains.  Also,
> that's the reason that the rename was 'frag_cnt' on v1.
> 

Yes, I think we do not need to invert logic when the naming is frag_users
or frag_cnt.

But if we use 'bias' as part of the name, isn't that more reasonable to set
both of the bias number to BIAS_MAX initially, and decrement the runtime
bais number every time the page is split to more fragmemts?

>