[PATCH net-next v12 0/5] introduce page_pool_alloc() related API

[PATCH net-next v12 0/5] introduce page_pool_alloc() related API

[Yunsheng Lin]

In [1] & [2] & [3], there are usecases for veth and virtio_net
to use frag support in page pool to reduce memory usage, and it
may request different frag size depending on the head/tail
room space for xdp_frame/shinfo and mtu/packet size. When the
requested frag size is large enough that a single page can not
be split into more than one frag, using frag support only have
performance penalty because of the extra frag count handling
for frag support.

So this patchset provides a page pool API for the driver to
allocate memory with least memory utilization and performance
penalty when it doesn't know the size of memory it need
beforehand.

1. https://patchwork.kernel.org/project/netdevbpf/patch/d3ae6bd3537fbce379382ac6a42f67e22f27ece2.1683896626.git.lorenzo@kernel.org/
2. https://patchwork.kernel.org/project/netdevbpf/patch/20230526054621.18371-3-liangchen.linux@gmail.com/
3. https://github.com/alobakin/linux/tree/iavf-pp-frag

V12: Rename page_pool_cache_alloc() to page_pool_alloc_va()
     and mask off __GFP_HIGHMEM for page allocation.

V11: Repost based on the latest net-next branch and collect
     Tested-by Tag from Alexander.

V10: Use fragment instead of frag in English docs.
     Remove PP_FLAG_PAGE_FRAG usage in idpf driver.

V9: Update some performance info in patch 2.

V8: Store the dma addr on a shifted u32 instead of using
    dma_addr_t explicitly for 32-bit arch with 64-bit DMA.
    Update document according to discussion in v7.

V7: Fix a compile error, a few typo and use kernel-doc syntax.

V6: Add a PP_FLAG_PAGE_SPLIT_IN_DRIVER flag to fail the page_pool
    creation for 32-bit arch with 64-bit DMA when driver tries to
    do the page splitting itself, adjust the requested size to
    include head/tail room in veth, and rebased on the latest
    next-net.

v5 RFC: Add a new page_pool_cache_alloc() API, and other minor
        change as discussed in v4. As there seems to be three
        comsumers that might be made use of the new API, so
        repost it as RFC and CC the relevant authors to see
        if the new API fits their need.

V4. Fix a typo and add a patch to update document about frag
    API, PAGE_POOL_DMA_USE_PP_FRAG_COUNT is not renamed yet
    as we may need a different thread to discuss that.

V3: Incorporate changes from the disscusion with Alexander,
    mostly the inline wraper, PAGE_POOL_DMA_USE_PP_FRAG_COUNT
    change split to separate patch and comment change.

V2: Add patch to remove PP_FLAG_PAGE_FRAG flags and mention
    virtio_net usecase in the cover letter.

V1: Drop RFC tag and page_pool_frag patch.

Yunsheng Lin (5):
  page_pool: unify frag_count handling in page_pool_is_last_frag()
  page_pool: remove PP_FLAG_PAGE_FRAG
  page_pool: introduce page_pool_alloc() API
  page_pool: update document about fragment API
  net: veth: use newly added page pool API for veth with xdp

 Documentation/networking/page_pool.rst        |   4 +-
 drivers/net/ethernet/broadcom/bnxt/bnxt.c     |   2 -
 .../net/ethernet/hisilicon/hns3/hns3_enet.c   |   3 +-
 drivers/net/ethernet/intel/idpf/idpf_txrx.c   |   3 -
 .../marvell/octeontx2/nic/otx2_common.c       |   2 +-
 .../net/ethernet/mellanox/mlx5/core/en_main.c |   2 +-
 drivers/net/veth.c                            |  25 ++-
 drivers/net/wireless/mediatek/mt76/mac80211.c |   2 +-
 include/net/page_pool/helpers.h               | 210 +++++++++++++++---
 include/net/page_pool/types.h                 |   6 +-
 net/core/page_pool.c                          |  17 +-
 net/core/skbuff.c                             |   2 +-
 12 files changed, 220 insertions(+), 58 deletions(-)

-- 
2.33.0

[PATCH net-next v12 4/5] page_pool: update document about fragment API

[Yunsheng Lin]

As more drivers begin to use the fragment API, update the
document about how to decide which API to use for the
driver author.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
CC: Lorenzo Bianconi <lorenzo@kernel.org>
CC: Alexander Duyck <alexander.duyck@gmail.com>
CC: Liang Chen <liangchen.linux@gmail.com>
CC: Alexander Lobakin <aleksander.lobakin@intel.com>
CC: Dima Tisnek <dimaqq@gmail.com>
---
 Documentation/networking/page_pool.rst |  4 +-
 include/net/page_pool/helpers.h        | 93 ++++++++++++++++++++++----
 2 files changed, 83 insertions(+), 14 deletions(-)

diff --git a/Documentation/networking/page_pool.rst b/Documentation/networking/page_pool.rst
index 215ebc92752c..60993cb56b32 100644
--- a/Documentation/networking/page_pool.rst
+++ b/Documentation/networking/page_pool.rst
@@ -58,7 +58,9 @@ a page will cause no race conditions is enough.
 
 .. kernel-doc:: include/net/page_pool/helpers.h
    :identifiers: page_pool_put_page page_pool_put_full_page
-		 page_pool_recycle_direct page_pool_dev_alloc_pages
+		 page_pool_recycle_direct page_pool_free_va
+		 page_pool_dev_alloc_pages page_pool_dev_alloc_frag
+		 page_pool_dev_alloc page_pool_dev_alloc_va
 		 page_pool_get_dma_addr page_pool_get_dma_dir
 
 .. kernel-doc:: net/core/page_pool.c
diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 1b76e05dc4d2..4ebd544ae977 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -8,23 +8,46 @@
 /**
  * DOC: page_pool allocator
  *
- * The page_pool allocator is optimized for the XDP mode that
- * uses one frame per-page, but it can fallback on the
- * regular page allocator APIs.
+ * The page_pool allocator is optimized for recycling page or page fragment used
+ * by skb packet and xdp frame.
  *
- * Basic use involves replacing alloc_pages() calls with the
- * page_pool_alloc_pages() call.  Drivers should use
- * page_pool_dev_alloc_pages() replacing dev_alloc_pages().
+ * Basic use involves replacing and alloc_pages() calls with page_pool_alloc(),
+ * which allocate memory with or without page splitting depending on the
+ * requested memory size.
  *
- * The API keeps track of in-flight pages, in order to let API users know
- * when it is safe to free a page_pool object.  Thus, API users
- * must call page_pool_put_page() to free the page, or attach
- * the page to a page_pool-aware object like skbs marked with
+ * If the driver knows that it always requires full pages or its allocations are
+ * always smaller than half a page, it can use one of the more specific API
+ * calls:
+ *
+ * 1. page_pool_alloc_pages(): allocate memory without page splitting when
+ * driver knows that the memory it need is always bigger than half of the page
+ * allocated from page pool. There is no cache line dirtying for 'struct page'
+ * when a page is recycled back to the page pool.
+ *
+ * 2. page_pool_alloc_frag(): allocate memory with page splitting when driver
+ * knows that the memory it need is always smaller than or equal to half of the
+ * page allocated from page pool. Page splitting enables memory saving and thus
+ * avoids TLB/cache miss for data access, but there also is some cost to
+ * implement page splitting, mainly some cache line dirtying/bouncing for
+ * 'struct page' and atomic operation for page->pp_frag_count.
+ *
+ * The API keeps track of in-flight pages, in order to let API users know when
+ * it is safe to free a page_pool object, the API users must call
+ * page_pool_put_page() or page_pool_free_va() to free the page_pool object, or
+ * attach the page_pool object to a page_pool-aware object like skbs marked with
  * skb_mark_for_recycle().
  *
- * API users 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
- * release the DMA mapping and in-flight state accounting.
+ * page_pool_put_page() may be called multi times on the same page if a page is
+ * split into multi fragments. For the last fragment, it will either recycle the
+ * page, or in case of page->_refcount > 1, it will release the DMA mapping and
+ * in-flight state accounting.
+ *
+ * dma_sync_single_range_for_device() is only called for the last fragment when
+ * page_pool is created with PP_FLAG_DMA_SYNC_DEV flag, so it depends on the
+ * last freed fragment to do the sync_for_device operation for all fragments in
+ * the same page when a page is split, the API user must setup pool->p.max_len
+ * and pool->p.offset correctly and ensure that page_pool_put_page() is called
+ * with dma_sync_size being -1 for fragment API.
  */
 #ifndef _NET_PAGE_POOL_HELPERS_H
 #define _NET_PAGE_POOL_HELPERS_H
@@ -73,6 +96,17 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
 	return page_pool_alloc_pages(pool, gfp);
 }
 
+/**
+ * page_pool_dev_alloc_frag() - allocate a page fragment.
+ * @pool: pool from which to allocate
+ * @offset: offset to the allocated page
+ * @size: requested size
+ *
+ * Get a page fragment from the page allocator or page_pool caches.
+ *
+ * Return:
+ * Return allocated page fragment, otherwise return NULL.
+ */
 static inline struct page *page_pool_dev_alloc_frag(struct page_pool *pool,
 						    unsigned int *offset,
 						    unsigned int size)
@@ -111,6 +145,19 @@ static inline struct page *page_pool_alloc(struct page_pool *pool,
 	return page;
 }
 
+/**
+ * page_pool_dev_alloc() - allocate a page or a page fragment.
+ * @pool: pool from which to allocate
+ * @offset: offset to the allocated page
+ * @size: in as the requested size, out as the allocated size
+ *
+ * Get a page or a page fragment from the page allocator or page_pool caches
+ * depending on the requested size in order to allocate memory with least memory
+ * utilization and performance penalty.
+ *
+ * Return:
+ * Return allocated page or page fragment, otherwise return NULL.
+ */
 static inline struct page *page_pool_dev_alloc(struct page_pool *pool,
 					       unsigned int *offset,
 					       unsigned int *size)
@@ -134,6 +181,18 @@ static inline void *page_pool_alloc_va(struct page_pool *pool,
 	return page_address(page) + offset;
 }
 
+/**
+ * page_pool_dev_alloc_va() - allocate a page or a page fragment and return its
+ *			      va.
+ * @pool: pool from which to allocate
+ * @size: in as the requested size, out as the allocated size
+ *
+ * This is just a thin wrapper around the page_pool_alloc() API, and
+ * it returns va of the allocated page or page fragment.
+ *
+ * Return:
+ * Return the va for the allocated page or page fragment, otherwise return NULL.
+ */
 static inline void *page_pool_dev_alloc_va(struct page_pool *pool,
 					   unsigned int *size)
 {
@@ -281,6 +340,14 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 #define PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA	\
 		(sizeof(dma_addr_t) > sizeof(unsigned long))
 
+/**
+ * page_pool_free_va() - free a va into the page_pool
+ * @pool: pool from which va was allocated
+ * @va: va to be freed
+ * @allow_direct: freed by the consumer, allow lockless caching
+ *
+ * Free a va allocated from page_pool_allo_va().
+ */
 static inline void page_pool_free_va(struct page_pool *pool, void *va,
 				     bool allow_direct)
 {
-- 
2.33.0

[PATCH net-next v12 5/5] net: veth: use newly added page pool API for veth with xdp

[Yunsheng Lin]

Use page_pool_alloc() API to allocate memory with least
memory utilization and performance penalty.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
CC: Lorenzo Bianconi <lorenzo@kernel.org>
CC: Alexander Duyck <alexander.duyck@gmail.com>
CC: Liang Chen <liangchen.linux@gmail.com>
CC: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 drivers/net/veth.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 0deefd1573cf..9980517ed8b0 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -737,10 +737,11 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 	if (skb_shared(skb) || skb_head_is_locked(skb) ||
 	    skb_shinfo(skb)->nr_frags ||
 	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
-		u32 size, len, max_head_size, off;
+		u32 size, len, max_head_size, off, truesize, page_offset;
 		struct sk_buff *nskb;
 		struct page *page;
 		int i, head_off;
+		void *va;
 
 		/* We need a private copy of the skb and data buffers since
 		 * the ebpf program can modify it. We segment the original skb
@@ -753,14 +754,17 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 		if (skb->len > PAGE_SIZE * MAX_SKB_FRAGS + max_head_size)
 			goto drop;
 
+		size = min_t(u32, skb->len, max_head_size);
+		truesize = SKB_HEAD_ALIGN(size) + VETH_XDP_HEADROOM;
+
 		/* Allocate skb head */
-		page = page_pool_dev_alloc_pages(rq->page_pool);
-		if (!page)
+		va = page_pool_dev_alloc_va(rq->page_pool, &truesize);
+		if (!va)
 			goto drop;
 
-		nskb = napi_build_skb(page_address(page), PAGE_SIZE);
+		nskb = napi_build_skb(va, truesize);
 		if (!nskb) {
-			page_pool_put_full_page(rq->page_pool, page, true);
+			page_pool_free_va(rq->page_pool, va, true);
 			goto drop;
 		}
 
@@ -768,7 +772,6 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 		skb_copy_header(nskb, skb);
 		skb_mark_for_recycle(nskb);
 
-		size = min_t(u32, skb->len, max_head_size);
 		if (skb_copy_bits(skb, 0, nskb->data, size)) {
 			consume_skb(nskb);
 			goto drop;
@@ -783,14 +786,18 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 		len = skb->len - off;
 
 		for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
-			page = page_pool_dev_alloc_pages(rq->page_pool);
+			size = min_t(u32, len, PAGE_SIZE);
+			truesize = size;
+
+			page = page_pool_dev_alloc(rq->page_pool, &page_offset,
+						   &truesize);
 			if (!page) {
 				consume_skb(nskb);
 				goto drop;
 			}
 
-			size = min_t(u32, len, PAGE_SIZE);
-			skb_add_rx_frag(nskb, i, page, 0, size, PAGE_SIZE);
+			skb_add_rx_frag(nskb, i, page, page_offset, size,
+					truesize);
 			if (skb_copy_bits(skb, off, page_address(page),
 					  size)) {
 				consume_skb(nskb);
-- 
2.33.0

Re: [PATCH net-next v12 0/5] introduce page_pool_alloc() related API

[Jakub Kicinski]

On Fri, 20 Oct 2023 17:59:47 +0800 Yunsheng Lin wrote:
> In [1] & [2] & [3], there are usecases for veth and virtio_net
> to use frag support in page pool to reduce memory usage, and it
> may request different frag size depending on the head/tail
> room space for xdp_frame/shinfo and mtu/packet size. When the
> requested frag size is large enough that a single page can not
> be split into more than one frag, using frag support only have
> performance penalty because of the extra frag count handling
> for frag support.
> 
> So this patchset provides a page pool API for the driver to
> allocate memory with least memory utilization and performance
> penalty when it doesn't know the size of memory it need
> beforehand.

I don't mean to cut off the discussion, if any is still to happen.
But AFAIU we have a general agreement that this is a good direction,
we're at v12 already, and it's getting late in the release cycle.
To give this series a chance of making v6.7 I will apply it now.
If there are any unresolved concerns in a couple of days we can drop it.

Re: [PATCH net-next v12 0/5] introduce page_pool_alloc() related API

[patchwork-bot+netdevbpf]

Hello:

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

On Fri, 20 Oct 2023 17:59:47 +0800 you wrote:
> In [1] & [2] & [3], there are usecases for veth and virtio_net
> to use frag support in page pool to reduce memory usage, and it
> may request different frag size depending on the head/tail
> room space for xdp_frame/shinfo and mtu/packet size. When the
> requested frag size is large enough that a single page can not
> be split into more than one frag, using frag support only have
> performance penalty because of the extra frag count handling
> for frag support.
> 
> [...]

Here is the summary with links:
  - [net-next,v12,1/5] page_pool: unify frag_count handling in page_pool_is_last_frag()
    https://git.kernel.org/netdev/net-next/c/58d53d8f7da6
  - [net-next,v12,2/5] page_pool: remove PP_FLAG_PAGE_FRAG
    https://git.kernel.org/netdev/net-next/c/09d96ee5674a
  - [net-next,v12,3/5] page_pool: introduce page_pool_alloc() API
    https://git.kernel.org/netdev/net-next/c/de97502e16fc
  - [net-next,v12,4/5] page_pool: update document about fragment API
    https://git.kernel.org/netdev/net-next/c/8ab32fa1c794
  - [net-next,v12,5/5] net: veth: use newly added page pool API for veth with xdp
    https://git.kernel.org/netdev/net-next/c/2d0de67da51a

You are awesome, thank you!
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