Re: [PATCH net-next RFC 1/2] page_pool: add page recycling support based on elevated refcnt

[Yunsheng Lin <linyunsheng@huawei.com>]

On 2021/7/2 17:42, Jesper Dangaard Brouer wrote:
> 
> On 30/06/2021 11.17, Yunsheng Lin wrote:
>> Currently page pool only support page recycling only when
>> refcnt of page is one, which means it can not support the
>> split page recycling implemented in the most ethernet driver.
> 
> Cc. Alex Duyck as I consider him an expert in this area.

Thanks.

> 
> 
>> So add elevated refcnt support in page pool, and support
>> allocating page frag to enable multi-frames-per-page based
>> on the elevated refcnt support.
>>
>> As the elevated refcnt is per page, and there is no space
>> for that in "struct page" now, so add a dynamically allocated
>> "struct page_pool_info" to record page pool ptr and refcnt
>> corrsponding to a page for now. Later, we can recycle the
>> "struct page_pool_info" too, or use part of page memory to
>> record pp_info.
> 
> I'm not happy with allocating a memory (slab) object "struct page_pool_info" per page.
> 
> This also gives us an extra level of indirection.

I'm not happy with that either, if there is better way to
avoid that, I will be happy to change it:)

> 
> 
> You are also adding a page "frag" API inside page pool, which I'm not 100% convinced belongs inside page_pool APIs.
> 
> Please notice the APIs that Alex Duyck added in mm/page_alloc.c:

Actually, that is where the idea of using "page frag" come from.

Aside from the performance improvement, there is memory usage
decrease for 64K page size kernel, which means a 64K page can
be used by 32 description with 2k buffer size, and that is a
lot of memory saving for 64 page size kernel comparing to the
current split page reusing implemented in the driver.


> 
>  __page_frag_cache_refill() + __page_frag_cache_drain() + page_frag_alloc_align()
> 
> 

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