Subject: Re: [PATCH net-next 3/4] net: page_pool: hide page_pool_release_page()

From: Ilias Apalodimas <[email-masked]>
Date: Mon, 24 Jul 2023 13:36:18 +0300

Hi Jakub,

Apologies for being late, I was on vacation and will now slowly go through
the pile of patches

On Wed, Jul 19, 2023 at 06:04:08PM -0700, Jakub Kicinski wrote:
> There seems to be no user calling page_pool_release_page()
> for legit reasons, all the users simply haven't been converted
> to skb-based recycling, yet. Previous changes converted them.
> Update the docs, and unexport the function.
>
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
> CC: [email-masked]
> CC: [email-masked]
> ---
>  Documentation/networking/page_pool.rst | 11 ++++-------
>  include/net/page_pool.h                | 10 ++--------
>  net/core/page_pool.c                   |  3 +--
>  3 files changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/networking/page_pool.rst b/Documentation/networking/page_pool.rst
> index 873efd97f822..0aa850cf4447 100644
> --- a/Documentation/networking/page_pool.rst
> +++ b/Documentation/networking/page_pool.rst
> @@ -13,9 +13,9 @@ replacing dev_alloc_pages().
>
>  API keeps track of in-flight pages, in order to let API user know
>  when it is safe to free a page_pool object.  Thus, API users
> -must run page_pool_release_page() when a page is leaving the page_pool or
> -call page_pool_put_page() where appropriate in order to maintain correct
> -accounting.
> +must call page_pool_put_page() to free the page, or attach
> +the page to a page_pool-aware objects like skbs marked with
> +skb_mark_for_recycle().
>
>  API user must call page_pool_put_page() once on a page, as it
>  will either recycle the page, or in case of refcnt > 1, it will
> @@ -87,9 +87,6 @@ a page will cause no race conditions is enough.
>    must guarantee safe context (e.g NAPI), since it will recycle the page
>    directly into the pool fast cache.
>
> -* page_pool_release_page(): Unmap the page (if mapped) and account for it on
> -  in-flight counters.
> -
>  * page_pool_dev_alloc_pages(): Get a page from the page allocator or page_pool
>    caches.
>
> @@ -194,7 +191,7 @@ NAPI poller
>              if XDP_DROP:
>                  page_pool_recycle_direct(page_pool, page);
>          } else (packet_is_skb) {
> -            page_pool_release_page(page_pool, page);
> +            skb_mark_for_recycle(skb);
>              new_page = page_pool_dev_alloc_pages(page_pool);
>          }
>      }
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 126f9e294389..f1d5cc1fa13b 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -18,9 +18,8 @@
>   *
>   * API keeps track of in-flight pages, in-order to let API user know
>   * when it is safe to dealloactor page_pool object.  Thus, API users
> - * must make sure to call page_pool_release_page() when a page is
> - * "leaving" the page_pool.  Or call page_pool_put_page() where
> - * appropiate.  For maintaining correct accounting.
> + * must call page_pool_put_page() where appropriate and only attach
> + * the page to a page_pool-aware objects, like skbs marked for recycling.
>   *
>   * API user must only call page_pool_put_page() once on a page, as it
>   * will either recycle the page, or in case of elevated refcnt, it
> @@ -251,7 +250,6 @@ void page_pool_unlink_napi(struct page_pool *pool);
>  void page_pool_destroy(struct page_pool *pool);
>  void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
>  			   struct xdp_mem_info *mem);
> -void page_pool_release_page(struct page_pool *pool, struct page *page);
>  void page_pool_put_page_bulk(struct page_pool *pool, void **data,
>  			     int count);
>  #else
> @@ -268,10 +266,6 @@ static inline void page_pool_use_xdp_mem(struct page_pool *pool,
>  					 struct xdp_mem_info *mem)
>  {
>  }
> -static inline void page_pool_release_page(struct page_pool *pool,
> -					  struct page *page)
> -{
> -}
>
>  static inline void page_pool_put_page_bulk(struct page_pool *pool, void **data,
>  					   int count)
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index a3e12a61d456..2c7cf5f2bcb8 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -492,7 +492,7 @@ static s32 page_pool_inflight(struct page_pool *pool)
>   * a regular page (that will eventually be returned to the normal
>   * page-allocator via put_page).
>   */
> -void page_pool_release_page(struct page_pool *pool, struct page *page)
> +static void page_pool_release_page(struct page_pool *pool, struct page *page)
>  {
>  	dma_addr_t dma;
>  	int count;
> @@ -519,7 +519,6 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
>  	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
>  	trace_page_pool_state_release(pool, page, count);
>  }
> -EXPORT_SYMBOL(page_pool_release_page);
>
>  /* Return a page to the page allocator, cleaning up our state */
>  static void page_pool_return_page(struct page_pool *pool, struct page *page)
> --
> 2.41.0
>

Reviewed-by: Ilias Apalodimas <[email-masked]>