netdev - [RFC PATCH v2 04/11] memory-provider: updates to core provider API for devmem TCP

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Date: Wed,  9 Aug 2023 18:57:40 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: netdev@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org
Cc: Mina Almasry <almasrymina@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Sumit Semwal <sumit.semwal@...aro.org>, 
	"Christian König" <christian.koenig@....com>, Jason Gunthorpe <jgg@...pe.ca>, 
	Hari Ramakrishnan <rharix@...gle.com>, Dan Williams <dan.j.williams@...el.com>, 
	Andy Lutomirski <luto@...nel.org>, stephen@...workplumber.org, sdf@...gle.com
Subject: [RFC PATCH v2 04/11] memory-provider: updates to core provider API
 for devmem TCP

Implement a few updates to Jakub's RFC memory provider[1] API to make it
suitable for device memory TCP:

1. Currently for devmem TCP the driver's netdev_rx_queue holds a
reference to the netdev_dmabuf_binding struct and needs to pass that to
the page_pool's memory provider somehow. For PoC purposes, create a
pp->mp_priv field that is set by the driver. Likely needs a better API
(likely dependent on the general memory provider API).

2. The current memory_provider API gives the memory_provider the option
to override put_page(), but tries page_pool_clear_pp_info() after the
memory provider has released the page. IMO if the page freeing is
delegated to the provider then the page_pool should not modify the
page after release_page() has been called.

[1]: https://lore.kernel.org/netdev/20230707183935.997267-1-kuba@kernel.org/

Signed-off-by: Mina Almasry <almasrymina@...gle.com>
---
 include/net/page_pool.h | 1 +
 net/core/page_pool.c    | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 13ae7f668c9e..e395f82e182b 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -78,6 +78,7 @@ struct page_pool_params {
 	struct device	*dev; /* device, for DMA pre-mapping purposes */
 	struct napi_struct *napi; /* Sole consumer of pages, otherwise NULL */
 	u8		memory_provider; /* haaacks! should be user-facing */
+	void		*mp_priv; /* argument to pass to the memory provider */
 	enum dma_data_direction dma_dir; /* DMA mapping direction */
 	unsigned int	max_len; /* max DMA sync memory size */
 	unsigned int	offset;  /* DMA addr offset */
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index d50f6728e4f6..df3f431fcff3 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -241,6 +241,7 @@ static int page_pool_init(struct page_pool *pool,
 		goto free_ptr_ring;
 	}

+	pool->mp_priv = pool->p.mp_priv;
 	if (pool->mp_ops) {
 		err = pool->mp_ops->init(pool);
 		if (err) {
@@ -564,16 +565,16 @@ void page_pool_return_page(struct page_pool *pool, struct page *page)
 	else
 		__page_pool_release_page_dma(pool, page);

-	page_pool_clear_pp_info(page);
-
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
 	 */
 	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
 	trace_page_pool_state_release(pool, page, count);

-	if (put)
+	if (put) {
+		page_pool_clear_pp_info(page);
 		put_page(page);
+	}
 	/* An optimization would be to call __free_pages(page, pool->p.order)
 	 * knowing page is not part of page-cache (thus avoiding a
 	 * __page_cache_release() call).
--
2.41.0.640.ga95def55d0-goog