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@xxxxxxxxxx>
CC: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
CC: Alexander Duyck <alexander.duyck@xxxxxxxxx>
CC: Liang Chen <liangchen.linux@xxxxxxxxx>
CC: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
CC: Dima Tisnek <dimaqq@xxxxxxxxx>
---
Documentation/networking/page_pool.rst | 4 +-
include/net/page_pool/helpers.h | 91 ++++++++++++++++++++++----
2 files changed, 81 insertions(+), 14 deletions(-)
diff --git a/Documentation/networking/page_pool.rst b/Documentation/networking/page_pool.rst
index 215ebc92752c..0c0705994f51 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_cache_free
+ page_pool_dev_alloc_pages page_pool_dev_alloc_frag
+ page_pool_dev_alloc page_pool_dev_cache_alloc
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 251c075084b8..017d1568af77 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 napi_alloc_frag() and alloc_pages() calls with
+ * page_pool_cache_alloc() and page_pool_alloc(), which allocate memory with or
+ * without page splitting depending on the requested memory size.
*
- * 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 call page_pool_put_page() to free the page, or attach
- * the page to a page_pool-aware objects 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.
+ *
+ * API keeps track of in-flight pages, in order to let API user know when it is
+ * safe to free a page_pool object, the API users must call page_pool_put_page()
+ * or page_pool_cache_free() to free the pp page or the pp buffer, or attach the
+ * pp page or the pp buffer 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
- * 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)
@@ -133,6 +180,16 @@ static inline void *page_pool_cache_alloc(struct page_pool *pool,
return page_address(page) + offset;
}
+/**
+ * page_pool_dev_cache_alloc() - allocate a cache.
+ * @pool: pool from which to allocate
+ * @size: in as the requested size, out as the allocated size
+ *
+ * Get a cache from the page allocator or page_pool caches.
+ *
+ * Return:
+ * Return the addr for the allocated cache, otherwise return NULL.
+ */
static inline void *page_pool_dev_cache_alloc(struct page_pool *pool,
unsigned int *size)
{
@@ -280,6 +337,14 @@ 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_cache_free() - free a cache into the page_pool
+ * @pool: pool from which cache was allocated
+ * @data: addr of cache to be free
+ * @allow_direct: freed by the consumer, allow lockless caching
+ *
+ * Free a cache allocated from page_pool_dev_cache_alloc().
+ */
static inline void page_pool_cache_free(struct page_pool *pool, void *data,
bool allow_direct)
{
--
2.33.0
