netdev - Re: [PATCH 04/10 net-next] page_pool: Add API to update numa node and flush page caches

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Date:   Fri, 18 Oct 2019 16:38:54 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Saeed Mahameed" <saeedm@...lanox.com>
Cc:     ilias.apalodimas@...aro.org, kernel-team@...com,
        netdev@...r.kernel.org, "Tariq Toukan" <tariqt@...lanox.com>,
        brouer@...hat.com
Subject: Re: [PATCH 04/10 net-next] page_pool: Add API to update numa node and
 flush page caches



On 18 Oct 2019, at 14:07, Saeed Mahameed wrote:

> On Thu, 2019-10-17 at 15:06 +0300, Ilias Apalodimas wrote:
>> Hi Saeed,
>>
>> On Wed, Oct 16, 2019 at 03:50:22PM -0700, Jonathan Lemon wrote:
>>> From: Saeed Mahameed <saeedm@...lanox.com>
>>>
>>> Add page_pool_update_nid() to be called from drivers when they
>>> detect
>>> numa node changes.
>>>
>>> It will do:
>>> 1) Flush the pool's page cache and ptr_ring.
>>> 2) Update page pool nid value to start allocating from the new numa
>>> node.
>>>
>>> Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
>>> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
>>> ---
>>>  include/net/page_pool.h | 10 ++++++++++
>>>  net/core/page_pool.c    | 16 +++++++++++-----
>>>  2 files changed, 21 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
>>> index 2cbcdbdec254..fb13cf6055ff 100644
>>> --- a/include/net/page_pool.h
>>> +++ b/include/net/page_pool.h
>>> @@ -226,4 +226,14 @@ static inline bool page_pool_put(struct
>>> page_pool *pool)
>>>  	return refcount_dec_and_test(&pool->user_cnt);
>>>  }
>>>
>>> +/* Only safe from napi context or when user guarantees it is
>>> thread safe */
>>> +void __page_pool_flush(struct page_pool *pool);
>>
>> This should be called per packet right? Any noticeable impact on
>> performance?
>>
> no, once per napi and only if a change in numa node is detected, so
> very very rare !
>
>>> +static inline void page_pool_update_nid(struct page_pool *pool,
>>> int new_nid)
>>> +{
>>> +	if (unlikely(pool->p.nid != new_nid)) {
>>> +		/* TODO: Add statistics/trace */
>>> +		__page_pool_flush(pool);
>>> +		pool->p.nid = new_nid;
>>> +	}
>>> +}
>>>  #endif /* _NET_PAGE_POOL_H */
>>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>>> index 5bc65587f1c4..678cf85f273a 100644
>>> --- a/net/core/page_pool.c
>>> +++ b/net/core/page_pool.c
>>> @@ -373,16 +373,13 @@ void __page_pool_free(struct page_pool *pool)
>>>  }
>>>  EXPORT_SYMBOL(__page_pool_free);
>>>
>>> -/* Request to shutdown: release pages cached by page_pool, and
>>> check
>>> - * for in-flight pages
>>> - */
>>> -bool __page_pool_request_shutdown(struct page_pool *pool)
>>> +void __page_pool_flush(struct page_pool *pool)
>>>  {
>>>  	struct page *page;
>>>
>>>  	/* Empty alloc cache, assume caller made sure this is
>>>  	 * no-longer in use, and page_pool_alloc_pages() cannot be
>>> -	 * call concurrently.
>>> +	 * called concurrently.
>>>  	 */
>>>  	while (pool->alloc.count) {
>>>  		page = pool->alloc.cache[--pool->alloc.count];
>>> @@ -393,6 +390,15 @@ bool __page_pool_request_shutdown(struct
>>> page_pool *pool)
>>>  	 * be in-flight.
>>>  	 */
>>>  	__page_pool_empty_ring(pool);
>>> +}
>>> +EXPORT_SYMBOL(__page_pool_flush);
>>
>> A later patch removes this, do we actually need it here?
>
> I agree, Jonathan changed the design of my last patch in this series
> and this became redundant as he is going to do lazy release of unwanted
> pages, rather than flushing the cache.

Yeah - I didn't want to take the latency hit when the node changed,
and would prefer to just amortize the cost over time.
-- 
Jonathan


>
>>
>>> +
>>> +/* Request to shutdown: release pages cached by page_pool, and
>>> check
>>> + * for in-flight pages
>>> + */
>>> +bool __page_pool_request_shutdown(struct page_pool *pool)
>>> +{
>>> +	__page_pool_flush(pool);
>>>
>>>  	return __page_pool_safe_to_destroy(pool);
>>>  }
>>> -- 
>>> 2.17.1
>>>
>>
>> Thanks
>> /Ilias