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From: Yunsheng Lin <linyunsheng@huawei.com>
To: Jesper Dangaard Brouer <jbrouer@redhat.com>,
	<davem@davemloft.net>, <kuba@kernel.org>
Cc: <brouer@redhat.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <linuxarm@openeuler.org>,
	<hawk@kernel.org>, <ilias.apalodimas@linaro.org>,
	<jonathan.lemon@gmail.com>, <alobakin@pm.me>,
	<willemb@google.com>, <cong.wang@bytedance.com>,
	<pabeni@redhat.com>, <haokexin@gmail.com>, <nogikh@google.com>,
	<elver@google.com>, <memxor@gmail.com>, <edumazet@google.com>,
	<alexander.duyck@gmail.com>, <dsahern@gmail.com>
Subject: Re: [PATCH net-next 2/7] page_pool: support non-split page with PP_FLAG_PAGE_FRAG
Date: Fri, 24 Sep 2021 15:23:16 +0800	[thread overview]
Message-ID: <2f5a4b07-7acf-1838-cb42-fd8b5d4ba4c6@huawei.com> (raw)
In-Reply-To: <c85a4ecc-80bb-d78f-d72a-0f820fb02eb9@redhat.com>

On 2021/9/23 20:08, Jesper Dangaard Brouer wrote:
> 
> 
> On 22/09/2021 11.41, Yunsheng Lin wrote:
>> Currently when PP_FLAG_PAGE_FRAG is set, the caller is not
>> expected to call page_pool_alloc_pages() directly because of
>> the PP_FLAG_PAGE_FRAG checking in __page_pool_put_page().
>>
>> The patch removes the above checking to enable non-split page
>> support when PP_FLAG_PAGE_FRAG is set.
>>
>> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> ---
>>   net/core/page_pool.c | 12 +++++++-----
>>   1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>> index a65bd7972e37..f7e71dcb6a2e 100644
>> --- a/net/core/page_pool.c
>> +++ b/net/core/page_pool.c
>> @@ -315,11 +315,14 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
>>         /* Fast-path: Get a page from cache */
>>       page = __page_pool_get_cached(pool);
>> -    if (page)
>> -        return page;
>>         /* Slow-path: cache empty, do real allocation */
>> -    page = __page_pool_alloc_pages_slow(pool, gfp);
>> +    if (!page)
>> +        page = __page_pool_alloc_pages_slow(pool, gfp);
>> +
>> +    if (likely(page))
>> +        page_pool_set_frag_count(page, 1);
>> +
> 
> I really don't like that you add one atomic_long_set operation per page alloc call.
> This is a fast-path for XDP use-cases, which you are ignoring as you drivers doesn't implement XDP.
> 
> As I cannot ask you to run XDP benchmarks, I fortunately have some page_pool specific microbenchmarks you can run instead.
> 
> I will ask you to provide before and after results from running these benchmarks [1] and [2].
> 
>  [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c
> 
>  [2] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_cross_cpu.c
> 
> How to use these module is documented here[3]:
>  [3] https://prototype-kernel.readthedocs.io/en/latest/prototype-kernel/build-process.html

Will running these benchmarks to see if any performance overhead noticable here,
thanks for the benchmarks.

> 
>>       return page;
>>   }
>>   EXPORT_SYMBOL(page_pool_alloc_pages);
>> @@ -428,8 +431,7 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
>>                unsigned int dma_sync_size, bool allow_direct)
>>   {
>>       /* It is not the last user for the page frag case */
>> -    if (pool->p.flags & PP_FLAG_PAGE_FRAG &&
>> -        page_pool_atomic_sub_frag_count_return(page, 1))
>> +    if (page_pool_atomic_sub_frag_count_return(page, 1))
>>           return NULL;
> 
> This adds an atomic_long_read, even when PP_FLAG_PAGE_FRAG is not set.

The point here is to have consistent handling for both PP_FLAG_PAGE_FRAG
and non-PP_FLAG_PAGE_FRAG case in the following patch.

As the page->_refcount is accessed in "page_ref_count(page) == 1" checking
in __page_pool_put_page(), and page->pp_frag_count is most likely in the
same cache line as the page->_refcount, So I am not expecting a noticable
overhead here.

Anyway, will use the above benchmarks as an example to verify it.


> 
>>         /* This allocator is optimized for the XDP mode that uses
>>
> 
> .
> 

  reply	other threads:[~2021-09-24  7:23 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-22  9:41 [PATCH net-next 0/7] some optimization for page pool Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 1/7] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA Yunsheng Lin
2021-09-23  9:10   ` Ilias Apalodimas
2021-09-23  9:33   ` Jesper Dangaard Brouer
2021-09-23 10:02     ` Ilias Apalodimas
2021-09-23 11:13       ` Yunsheng Lin
2021-09-23 13:07         ` Ilias Apalodimas
2021-09-24  7:04           ` Yunsheng Lin
2021-09-24  7:25             ` Ilias Apalodimas
2021-09-24  8:01               ` Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 2/7] page_pool: support non-split page with PP_FLAG_PAGE_FRAG Yunsheng Lin
2021-09-23 12:08   ` Jesper Dangaard Brouer
2021-09-24  7:23     ` Yunsheng Lin [this message]
2021-09-30  7:28       ` [Linuxarm] " Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 3/7] pool_pool: avoid calling compound_head() for skb frag page Yunsheng Lin
2021-09-23  8:33   ` Ilias Apalodimas
2021-09-23 11:24     ` Yunsheng Lin
2021-09-23 11:47       ` Ilias Apalodimas
2021-09-24  7:33         ` Yunsheng Lin
2021-09-24  7:44           ` Ilias Apalodimas
2021-09-22  9:41 ` [PATCH net-next 4/7] page_pool: change BIAS_MAX to support incrementing Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 5/7] skbuff: keep track of pp page when __skb_frag_ref() is called Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 6/7] skbuff: only use pp_magic identifier for a skb' head page Yunsheng Lin
2021-09-22  9:41 ` [PATCH net-next 7/7] skbuff: remove unused skb->pp_recycle Yunsheng Lin
2021-09-23  7:07 ` [PATCH net-next 0/7] some optimization for page pool Ilias Apalodimas
2021-09-23 11:12   ` Yunsheng Lin

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