Re: [PATCH net-next v4 3/5] page_pool: introduce page_pool_alloc() API

[Alexander Lobakin]

From: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Date: Tue, 13 Jun 2023 15:08:41 +0200

> From: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
> Date: Mon, 12 Jun 2023 21:02:54 +0800
> 
>> Currently page pool supports the below use cases:
>> use case 1: allocate page without page splitting using
>>             page_pool_alloc_pages() API if the driver knows
>>             that the memory it need is always bigger than
>>             half of the page allocated from page pool.
>> use case 2: allocate page frag with page splitting using
>>             page_pool_alloc_frag() API if the driver knows
>>             that the memory it need is always smaller than
>>             or equal to the half of the page allocated from
>>             page pool.
>>
>> There is emerging use case [1] & [2] that is a mix of the
>> above two case: the driver doesn't know the size of memory it
>> need beforehand, so the driver may use something like below to
>> allocate memory with least memory utilization and performance
>> penalty:
>>
>> if (size << 1 > max_size)
>> 	page = page_pool_alloc_pages();
>> else
>> 	page = page_pool_alloc_frag();
>>
>> To avoid the driver doing something like above, add the
>> page_pool_alloc() API to support the above use case, and update
>> the true size of memory that is acctually allocated by updating
>> '*size' back to the driver in order to avoid the truesize
>> underestimate problem.
>>
>> 1. https://lore.kernel.org/all/d3ae6bd3537fbce379382ac6a42f67e22f27ece2.1683896626.git.lorenzo@xxxxxxxxxx/
>> 2. https://lore.kernel.org/all/20230526054621.18371-3-liangchen.linux@xxxxxxxxx/
>>
>> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
>> CC: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
>> CC: Alexander Duyck <alexander.duyck@xxxxxxxxx>
>> ---
>>  include/net/page_pool.h | 43 +++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 43 insertions(+)
>>
>> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
>> index 0b8cd2acc1d7..c135cd157cea 100644
>> --- a/include/net/page_pool.h
>> +++ b/include/net/page_pool.h
>> @@ -260,6 +260,49 @@ static inline struct page *page_pool_dev_alloc_frag(struct page_pool *pool,
>>  	return page_pool_alloc_frag(pool, offset, size, gfp);
>>  }
>>  
>> +static inline struct page *page_pool_alloc(struct page_pool *pool,
>> +					   unsigned int *offset,
>> +					   unsigned int *size, gfp_t gfp)
> 
> Oh, really nice. Wouldn't you mind if I base my series on top of this? :)
> 
> Also, with %PAGE_SIZE of 32k+ and default MTU, there is truesize
> underestimation. I haven't looked at the latest conversations as I had a
> small vacation, sowwy :s What's the current opinion on this?

Please ignore this, seems like I didn't manage to read 2 lines below,
you explicitly mention in the comment that you already handle this >_<

Thanks,
Olek