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

[Yunsheng Lin]

On 2023/6/13 21:11, Alexander Lobakin wrote:
> 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? :)

No, I wouldn't mind. I am glad that if using the new API can both save memory
and improve performance for your case:)

>>
>> 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
> 
> .
>