[PATCH net-next v8 0/5] Split netmem from struct page

[PATCH net-next v8 0/5] Split netmem from struct page

[Byungchul Park]

Hi all,

In this version, I'm posting non-controversial patches first since there
are pending works that should be based on this series so that those can
be started shortly.  I will post the rest later.

The MM subsystem is trying to reduce struct page to a single pointer.
The first step towards that is splitting struct page by its individual
users, as has already been done with folio and slab.  This patchset does
that for netmem which is used for page pools.

Matthew Wilcox tried and stopped the same work, you can see in:

   https://lore.kernel.org/linux-mm/20230111042214.907030-1-willy@infradead.org/

Mina Almasry already has done a lot fo prerequisite works by luck.  I
stacked my patches on the top of his work e.i. netmem.

I focused on removing the page pool members in struct page this time,
not moving the allocation code of page pool from net to mm.  It can be
done later if needed.

The final patch removing the page pool fields will be submitted once
all the converting work of page to netmem are done:

   1. converting of libeth_fqe by Tony Nguyen.
   2. converting of mlx5 by Tariq Toukan.
   3. converting of prueth_swdata.
   4. converting of freescale driver.

For our discussion, I'm sharing what the final patch looks like the
following.

	Byungchul
--8<--
commit 1847d9890f798456b21ccb27aac7545303048492
Author: Byungchul Park <byungchul@sk.com>
Date:   Wed May 28 20:44:55 2025 +0900

    mm, netmem: remove the page pool members in struct page
    
    Now that all the users of the page pool members in struct page have been
    gone, the members can be removed from struct page.
    
    However, since struct netmem_desc still uses the space in struct page,
    the important offsets should be checked properly, until struct
    netmem_desc has its own instance from slab.
    
    Remove the page pool members in struct page and modify static checkers
    for the offsets.
    
    Signed-off-by: Byungchul Park <byungchul@sk.com>

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 32ba5126e221..db2fe0d0ebbf 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -120,17 +120,6 @@ struct page {
 			 */
 			unsigned long private;
 		};
-		struct {	/* page_pool used by netstack */
-			/**
-			 * @pp_magic: magic value to avoid recycling non
-			 * page_pool allocated pages.
-			 */
-			unsigned long pp_magic;
-			struct page_pool *pp;
-			unsigned long _pp_mapping_pad;
-			unsigned long dma_addr;
-			atomic_long_t pp_ref_count;
-		};
 		struct {	/* Tail pages of compound page */
 			unsigned long compound_head;	/* Bit zero is set */
 		};
diff --git a/include/net/netmem.h b/include/net/netmem.h
index 8f354ae7d5c3..3414f184d018 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -42,11 +42,8 @@ struct netmem_desc {
 	static_assert(offsetof(struct page, pg) == \
 		      offsetof(struct netmem_desc, desc))
 NETMEM_DESC_ASSERT_OFFSET(flags, _flags);
-NETMEM_DESC_ASSERT_OFFSET(pp_magic, pp_magic);
-NETMEM_DESC_ASSERT_OFFSET(pp, pp);
-NETMEM_DESC_ASSERT_OFFSET(_pp_mapping_pad, _pp_mapping_pad);
-NETMEM_DESC_ASSERT_OFFSET(dma_addr, dma_addr);
-NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
+NETMEM_DESC_ASSERT_OFFSET(lru, pp_magic);
+NETMEM_DESC_ASSERT_OFFSET(mapping, _pp_mapping_pad);
 #undef NETMEM_DESC_ASSERT_OFFSET
 
 /*
---
Changes from v7 (no actual updates):
	1. Exclude "netmem: introduce struct netmem_desc mirroring
	   struct page" that might be controversial.
	2. Exclude "netmem: introduce a netmem API,
	   virt_to_head_netmem()" since there are no users.

Changes from v6 (no actual updates):
	1. Rebase on net-next/main as of Jun 25.
	2. Supplement a comment describing struct net_iov.
	3. Exclude a controversial patch, "page_pool: access ->pp_magic
	   through struct netmem_desc in page_pool_page_is_pp()".
	4. Exclude "netmem: remove __netmem_get_pp()" since the API
	   started to be used again by libeth.

Changes from v5 (no actual updates):
	1. Rebase on net-next/main as of Jun 20.
	2. Add given 'Reviewed-by's and 'Acked-by's, thanks to all.
	3. Add missing cc's.

Changes from v4:
	1. Add given 'Reviewed-by's, thanks to all.
	2. Exclude potentially controversial patches.

Changes from v3:
	1. Relocates ->owner and ->type of net_iov out of netmem_desc
	   and make them be net_iov specific.
	2. Remove __force when casting struct page to struct netmem_desc.

Changes from v2:
	1. Introduce a netmem API, virt_to_head_netmem(), and use it
	   when it's needed.
	2. Introduce struct netmem_desc as a new struct and union'ed
	   with the existing fields in struct net_iov.
	3. Make page_pool_page_is_pp() access ->pp_magic through struct
	   netmem_desc instead of struct page.
	4. Move netmem alloc APIs from include/net/netmem.h to
	   net/core/netmem_priv.h.
	5. Apply trivial feedbacks, thanks to Mina, Pavel, and Toke.
	6. Add given 'Reviewed-by's, thanks to Mina.

Changes from v1:
	1. Rebase on net-next's main as of May 26.
	2. Check checkpatch.pl, feedbacked by SJ Park.
	3. Add converting of page to netmem in mt76.
	4. Revert 'mlx5: use netmem descriptor and APIs for page pool'
	   since it's on-going by Tariq Toukan.  I will wait for his
	   work to be done.
	5. Revert 'page_pool: use netmem APIs to access page->pp_magic
	   in page_pool_page_is_pp()' since we need more discussion.
	6. Revert 'mm, netmem: remove the page pool members in struct
	   page' since there are some prerequisite works to remove the
	   page pool fields from struct page.  I can submit this patch
	   separatedly later.
	7. Cancel relocating a page pool member in struct page.
	8. Modify static assert for offests and size of struct
	   netmem_desc.

Changes from rfc:
	1. Rebase on net-next's main branch.
	   https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/
	2. Fix a build error reported by kernel test robot.
	   https://lore.kernel.org/all/202505100932.uzAMBW1y-lkp@intel.com/
	3. Add given 'Reviewed-by's, thanks to Mina and Ilias.
	4. Do static_assert() on the size of struct netmem_desc instead
	   of placing place-holder in struct page, feedbacked by
	   Matthew.
	5. Do struct_group_tagged(netmem_desc) on struct net_iov instead
	   of wholly renaming it to strcut netmem_desc, feedbacked by
	   Mina and Pavel.

Byungchul Park (5):
  page_pool: rename page_pool_return_page() to page_pool_return_netmem()
  page_pool: rename __page_pool_release_page_dma() to
    __page_pool_release_netmem_dma()
  page_pool: rename __page_pool_alloc_pages_slow() to
    __page_pool_alloc_netmems_slow()
  netmem: use _Generic to cover const casting for page_to_netmem()
  page_pool: make page_pool_get_dma_addr() just wrap
    page_pool_get_dma_addr_netmem()

 include/net/netmem.h            |  7 +++----
 include/net/page_pool/helpers.h |  7 +------
 net/core/page_pool.c            | 36 ++++++++++++++++-----------------
 3 files changed, 22 insertions(+), 28 deletions(-)


base-commit: 8dacfd92dbefee829ca555a860e86108fdd1d55b
-- 
2.17.1

[PATCH net-next v8 1/5] page_pool: rename page_pool_return_page() to page_pool_return_netmem()

[Byungchul Park]

Now that page_pool_return_page() is for returning netmem, not struct
page, rename it to page_pool_return_netmem() to reflect what it does.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 net/core/page_pool.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index ba7cf3e3c32f..3bf25e554f96 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -371,7 +371,7 @@ struct page_pool *page_pool_create(const struct page_pool_params *params)
 }
 EXPORT_SYMBOL(page_pool_create);
 
-static void page_pool_return_page(struct page_pool *pool, netmem_ref netmem);
+static void page_pool_return_netmem(struct page_pool *pool, netmem_ref netmem);
 
 static noinline netmem_ref page_pool_refill_alloc_cache(struct page_pool *pool)
 {
@@ -409,7 +409,7 @@ static noinline netmem_ref page_pool_refill_alloc_cache(struct page_pool *pool)
 			 * (2) break out to fallthrough to alloc_pages_node.
 			 * This limit stress on page buddy alloactor.
 			 */
-			page_pool_return_page(pool, netmem);
+			page_pool_return_netmem(pool, netmem);
 			alloc_stat_inc(pool, waive);
 			netmem = 0;
 			break;
@@ -712,7 +712,7 @@ static __always_inline void __page_pool_release_page_dma(struct page_pool *pool,
  * a regular page (that will eventually be returned to the normal
  * page-allocator via put_page).
  */
-void page_pool_return_page(struct page_pool *pool, netmem_ref netmem)
+static void page_pool_return_netmem(struct page_pool *pool, netmem_ref netmem)
 {
 	int count;
 	bool put;
@@ -826,7 +826,7 @@ __page_pool_put_page(struct page_pool *pool, netmem_ref netmem,
 	 * will be invoking put_page.
 	 */
 	recycle_stat_inc(pool, released_refcnt);
-	page_pool_return_page(pool, netmem);
+	page_pool_return_netmem(pool, netmem);
 
 	return 0;
 }
@@ -869,7 +869,7 @@ void page_pool_put_unrefed_netmem(struct page_pool *pool, netmem_ref netmem,
 	if (netmem && !page_pool_recycle_in_ring(pool, netmem)) {
 		/* Cache full, fallback to free pages */
 		recycle_stat_inc(pool, ring_full);
-		page_pool_return_page(pool, netmem);
+		page_pool_return_netmem(pool, netmem);
 	}
 }
 EXPORT_SYMBOL(page_pool_put_unrefed_netmem);
@@ -912,7 +912,7 @@ static void page_pool_recycle_ring_bulk(struct page_pool *pool,
 	 * since put_page() with refcnt == 1 can be an expensive operation.
 	 */
 	for (; i < bulk_len; i++)
-		page_pool_return_page(pool, bulk[i]);
+		page_pool_return_netmem(pool, bulk[i]);
 }
 
 /**
@@ -995,7 +995,7 @@ static netmem_ref page_pool_drain_frag(struct page_pool *pool,
 		return netmem;
 	}
 
-	page_pool_return_page(pool, netmem);
+	page_pool_return_netmem(pool, netmem);
 	return 0;
 }
 
@@ -1009,7 +1009,7 @@ static void page_pool_free_frag(struct page_pool *pool)
 	if (!netmem || page_pool_unref_netmem(netmem, drain_count))
 		return;
 
-	page_pool_return_page(pool, netmem);
+	page_pool_return_netmem(pool, netmem);
 }
 
 netmem_ref page_pool_alloc_frag_netmem(struct page_pool *pool,
@@ -1076,7 +1076,7 @@ static void page_pool_empty_ring(struct page_pool *pool)
 			pr_crit("%s() page_pool refcnt %d violation\n",
 				__func__, netmem_ref_count(netmem));
 
-		page_pool_return_page(pool, netmem);
+		page_pool_return_netmem(pool, netmem);
 	}
 }
 
@@ -1109,7 +1109,7 @@ static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
 	 */
 	while (pool->alloc.count) {
 		netmem = pool->alloc.cache[--pool->alloc.count];
-		page_pool_return_page(pool, netmem);
+		page_pool_return_netmem(pool, netmem);
 	}
 }
 
@@ -1253,7 +1253,7 @@ void page_pool_update_nid(struct page_pool *pool, int new_nid)
 	/* Flush pool alloc cache, as refill will check NUMA node */
 	while (pool->alloc.count) {
 		netmem = pool->alloc.cache[--pool->alloc.count];
-		page_pool_return_page(pool, netmem);
+		page_pool_return_netmem(pool, netmem);
 	}
 }
 EXPORT_SYMBOL(page_pool_update_nid);
-- 
2.17.1

Re: [PATCH net-next v8 1/5] page_pool: rename page_pool_return_page() to page_pool_return_netmem()

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  2 Jul 2025 14:32:52 +0900 you wrote:
> Now that page_pool_return_page() is for returning netmem, not struct
> page, rename it to page_pool_return_netmem() to reflect what it does.
> 
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Reviewed-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> 
> [...]

Here is the summary with links:
  - [net-next,v8,1/5] page_pool: rename page_pool_return_page() to page_pool_return_netmem()
    https://git.kernel.org/netdev/net-next/c/61a332475334
  - [net-next,v8,2/5] page_pool: rename __page_pool_release_page_dma() to __page_pool_release_netmem_dma()
    https://git.kernel.org/netdev/net-next/c/4ad125ae380b
  - [net-next,v8,3/5] page_pool: rename __page_pool_alloc_pages_slow() to __page_pool_alloc_netmems_slow()
    https://git.kernel.org/netdev/net-next/c/b56ce8684622
  - [net-next,v8,4/5] netmem: use _Generic to cover const casting for page_to_netmem()
    https://git.kernel.org/netdev/net-next/c/4369d40da2f2
  - [net-next,v8,5/5] page_pool: make page_pool_get_dma_addr() just wrap page_pool_get_dma_addr_netmem()
    https://git.kernel.org/netdev/net-next/c/d8bf56a0ca10

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[PATCH net-next v8 2/5] page_pool: rename __page_pool_release_page_dma() to __page_pool_release_netmem_dma()

[Byungchul Park]

Now that __page_pool_release_page_dma() is for releasing netmem, not
struct page, rename it to __page_pool_release_netmem_dma() to reflect
what it does.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 net/core/page_pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 3bf25e554f96..95ffa48c7c67 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -673,8 +673,8 @@ void page_pool_clear_pp_info(netmem_ref netmem)
 	netmem_set_pp(netmem, NULL);
 }
 
-static __always_inline void __page_pool_release_page_dma(struct page_pool *pool,
-							 netmem_ref netmem)
+static __always_inline void __page_pool_release_netmem_dma(struct page_pool *pool,
+							   netmem_ref netmem)
 {
 	struct page *old, *page = netmem_to_page(netmem);
 	unsigned long id;
@@ -721,7 +721,7 @@ static void page_pool_return_netmem(struct page_pool *pool, netmem_ref netmem)
 	if (static_branch_unlikely(&page_pool_mem_providers) && pool->mp_ops)
 		put = pool->mp_ops->release_netmem(pool, netmem);
 	else
-		__page_pool_release_page_dma(pool, netmem);
+		__page_pool_release_netmem_dma(pool, netmem);
 
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
@@ -1136,7 +1136,7 @@ static void page_pool_scrub(struct page_pool *pool)
 		}
 
 		xa_for_each(&pool->dma_mapped, id, ptr)
-			__page_pool_release_page_dma(pool, page_to_netmem(ptr));
+			__page_pool_release_netmem_dma(pool, page_to_netmem((struct page *)ptr));
 	}
 
 	/* No more consumers should exist, but producers could still
-- 
2.17.1

[PATCH net-next v8 3/5] page_pool: rename __page_pool_alloc_pages_slow() to __page_pool_alloc_netmems_slow()

[Byungchul Park]

Now that __page_pool_alloc_pages_slow() is for allocating netmem, not
struct page, rename it to __page_pool_alloc_netmems_slow() to reflect
what it does.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 net/core/page_pool.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 95ffa48c7c67..05e2e22a8f7c 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -544,8 +544,8 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
 }
 
 /* slow path */
-static noinline netmem_ref __page_pool_alloc_pages_slow(struct page_pool *pool,
-							gfp_t gfp)
+static noinline netmem_ref __page_pool_alloc_netmems_slow(struct page_pool *pool,
+							  gfp_t gfp)
 {
 	const int bulk = PP_ALLOC_CACHE_REFILL;
 	unsigned int pp_order = pool->p.order;
@@ -615,7 +615,7 @@ netmem_ref page_pool_alloc_netmems(struct page_pool *pool, gfp_t gfp)
 	if (static_branch_unlikely(&page_pool_mem_providers) && pool->mp_ops)
 		netmem = pool->mp_ops->alloc_netmems(pool, gfp);
 	else
-		netmem = __page_pool_alloc_pages_slow(pool, gfp);
+		netmem = __page_pool_alloc_netmems_slow(pool, gfp);
 	return netmem;
 }
 EXPORT_SYMBOL(page_pool_alloc_netmems);
-- 
2.17.1

Re: [PATCH net-next v8 3/5] page_pool: rename __page_pool_alloc_pages_slow() to __page_pool_alloc_netmems_slow()

[Ilias Apalodimas]

On Wed, 2 Jul 2025 at 08:33, Byungchul Park <byungchul@sk.com> wrote:
>
> Now that __page_pool_alloc_pages_slow() is for allocating netmem, not
> struct page, rename it to __page_pool_alloc_netmems_slow() to reflect
> what it does.
>
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Reviewed-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

>  net/core/page_pool.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 95ffa48c7c67..05e2e22a8f7c 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -544,8 +544,8 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
>  }
>
>  /* slow path */
> -static noinline netmem_ref __page_pool_alloc_pages_slow(struct page_pool *pool,
> -                                                       gfp_t gfp)
> +static noinline netmem_ref __page_pool_alloc_netmems_slow(struct page_pool *pool,
> +                                                         gfp_t gfp)
>  {
>         const int bulk = PP_ALLOC_CACHE_REFILL;
>         unsigned int pp_order = pool->p.order;
> @@ -615,7 +615,7 @@ netmem_ref page_pool_alloc_netmems(struct page_pool *pool, gfp_t gfp)
>         if (static_branch_unlikely(&page_pool_mem_providers) && pool->mp_ops)
>                 netmem = pool->mp_ops->alloc_netmems(pool, gfp);
>         else
> -               netmem = __page_pool_alloc_pages_slow(pool, gfp);
> +               netmem = __page_pool_alloc_netmems_slow(pool, gfp);
>         return netmem;
>  }
>  EXPORT_SYMBOL(page_pool_alloc_netmems);
> --
> 2.17.1
>

[PATCH net-next v8 4/5] netmem: use _Generic to cover const casting for page_to_netmem()

[Byungchul Park]

The current page_to_netmem() doesn't cover const casting resulting in
trying to cast const struct page * to const netmem_ref fails.

To cover the case, change page_to_netmem() to use macro and _Generic.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/net/netmem.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 7a1dafa3f080..de1d95f04076 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -139,10 +139,9 @@ static inline netmem_ref net_iov_to_netmem(struct net_iov *niov)
 	return (__force netmem_ref)((unsigned long)niov | NET_IOV);
 }
 
-static inline netmem_ref page_to_netmem(const struct page *page)
-{
-	return (__force netmem_ref)page;
-}
+#define page_to_netmem(p)	(_Generic((p),			\
+	const struct page * :	(__force const netmem_ref)(p),	\
+	struct page * :		(__force netmem_ref)(p)))
 
 /**
  * virt_to_netmem - convert virtual memory pointer to a netmem reference
-- 
2.17.1

[PATCH net-next v8 5/5] page_pool: make page_pool_get_dma_addr() just wrap page_pool_get_dma_addr_netmem()

[Byungchul Park]

The page pool members in struct page cannot be removed unless it's not
allowed to access any of them via struct page.

Do not access 'page->dma_addr' directly in page_pool_get_dma_addr() but
just wrap page_pool_get_dma_addr_netmem() safely.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/net/page_pool/helpers.h | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 773fc65780b5..db180626be06 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -444,12 +444,7 @@ static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
  */
 static inline dma_addr_t page_pool_get_dma_addr(const struct page *page)
 {
-	dma_addr_t ret = page->dma_addr;
-
-	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
-		ret <<= PAGE_SHIFT;
-
-	return ret;
+	return page_pool_get_dma_addr_netmem(page_to_netmem(page));
 }
 
 static inline void __page_pool_dma_sync_for_cpu(const struct page_pool *pool,
-- 
2.17.1

Re: [PATCH net-next v8 5/5] page_pool: make page_pool_get_dma_addr() just wrap page_pool_get_dma_addr_netmem()

[Jesper Dangaard Brouer]

On 02/07/2025 07.32, Byungchul Park wrote:
> The page pool members in struct page cannot be removed unless it's not
> allowed to access any of them via struct page.
> 
> Do not access 'page->dma_addr' directly in page_pool_get_dma_addr() but
> just wrap page_pool_get_dma_addr_netmem() safely.
> 
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Reviewed-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>   include/net/page_pool/helpers.h | 7 +------
>   1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
> index 773fc65780b5..db180626be06 100644
> --- a/include/net/page_pool/helpers.h
> +++ b/include/net/page_pool/helpers.h
> @@ -444,12 +444,7 @@ static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
>    */
>   static inline dma_addr_t page_pool_get_dma_addr(const struct page *page)
>   {
> -	dma_addr_t ret = page->dma_addr;
> -
> -	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
> -		ret <<= PAGE_SHIFT;
> -
> -	return ret;
> +	return page_pool_get_dma_addr_netmem(page_to_netmem(page));

Wow - the amount of type casting shenanigans going on here make the code
hard to follow.

This code changes adds an extra "AND" operation, but we don't have a
micro-benchmark that tests the performance of a DMA enabled page_pool,
so I cannot tell if this add any overhead.  My experience tells me that
this extra AND-operation will not be measurable.

I see a lot of reviewed-by from people I trust, so you also get my 
page_pool maintainer ack.

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>

--Jesper

Re: [PATCH net-next v8 0/5] Split netmem from struct page

[Jesper Dangaard Brouer]

On 02/07/2025 07.32, Byungchul Park wrote:
> Hi all,
> 
> In this version, I'm posting non-controversial patches first since there
> are pending works that should be based on this series so that those can
> be started shortly.  I will post the rest later.
> 
> The MM subsystem is trying to reduce struct page to a single pointer.
> The first step towards that is splitting struct page by its individual
> users, as has already been done with folio and slab.  This patchset does
> that for netmem which is used for page pools.
> 
[...]
> 
> Byungchul Park (5):
>    page_pool: rename page_pool_return_page() to page_pool_return_netmem()
>    page_pool: rename __page_pool_release_page_dma() to
>      __page_pool_release_netmem_dma()
>    page_pool: rename __page_pool_alloc_pages_slow() to
>      __page_pool_alloc_netmems_slow()
>    netmem: use _Generic to cover const casting for page_to_netmem()
>    page_pool: make page_pool_get_dma_addr() just wrap
>      page_pool_get_dma_addr_netmem()
> 
>   include/net/netmem.h            |  7 +++----
>   include/net/page_pool/helpers.h |  7 +------
>   net/core/page_pool.c            | 36 ++++++++++++++++-----------------
>   3 files changed, 22 insertions(+), 28 deletions(-)

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>