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

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Date:   Thu, 17 Oct 2019 15:06:17 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     brouer@...hat.com, saeedm@...lanox.com, tariqt@...lanox.com,
        netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 04/10 net-next] page_pool: Add API to update numa node
 and flush page caches

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?

> +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?

> +
> +/* 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