net: page_pool: hide page_pool_release_page()

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.

Link: https://lore.kernel.org/r/20230720010409.1967072-4-kuba@kernel.org
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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);
         }
     }

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)

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 @@ skip_dma_unmap:
 	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)