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

[Alexander Lobakin]

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?

[...]

Thanks,
Olek