linux-kernel - Re: [PATCH v5 RFC 2/6] page_pool: unify frag_count handling in page_pool_is_last

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Date:   Tue, 11 Jul 2023 19:47:48 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Liang Chen <liangchen.linux@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v5 RFC 2/6] page_pool: unify frag_count handling in
 page_pool_is_last_frag()

On 2023/7/10 22:39, Alexander Lobakin wrote:
> From: Yunsheng Lin <linyunsheng@...wei.com>
> Date: Thu, 29 Jun 2023 20:02:22 +0800
> 
>> Currently when page_pool_create() is called with
>> PP_FLAG_PAGE_FRAG flag, page_pool_alloc_pages() is only
>> allowed to be called under the below constraints:
>> 1. page_pool_fragment_page() need to be called to setup
>>    page->pp_frag_count immediately.
>> 2. page_pool_defrag_page() often need to be called to drain
>>    the page->pp_frag_count when there is no more user will
>>    be holding on to that page.
> 
> [...]
> 
>> @@ -352,12 +377,10 @@ static inline bool page_pool_is_last_frag(struct page_pool *pool,
>>  {
>>  	/* We assume we are the last frag user that is still holding
>>  	 * on to the page if:
>> -	 * 1. Fragments aren't enabled.
>> -	 * 2. We are running in 32-bit arch with 64-bit DMA.
>> -	 * 3. page_pool_defrag_page() indicate we are the last user.
>> +	 * 1. We are running in 32-bit arch with 64-bit DMA.
>> +	 * 2. page_pool_defrag_page() indicate we are the last user.
>>  	 */
>> -	return !(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
>> -	       PAGE_POOL_DMA_USE_PP_FRAG_COUNT ||
>> +	return PAGE_POOL_DMA_USE_PP_FRAG_COUNT ||
>>  	       (page_pool_defrag_page(page, 1) == 0);
> 
> Just noticed while developing: after this change, the first function
> argument, i.e. @pool, is not needed anymore and can be removed.

Yes, thanks.

>