Messages in this thread | | | Date | Mon, 14 Aug 2023 15:42:34 -0700 | Subject | Re: [PATCH net-next v6 5/6] page_pool: update document about frag API | From | Randy Dunlap <> |
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Hi--
On 8/14/23 05:56, Yunsheng Lin wrote: > As more drivers begin to use the frag 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> > --- > Documentation/networking/page_pool.rst | 4 +- > include/net/page_pool/helpers.h | 58 +++++++++++++++++++++++--- > 2 files changed, 55 insertions(+), 7 deletions(-) >
> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h > index b920224f6584..0f1eaa2986f9 100644 > --- a/include/net/page_pool/helpers.h > +++ b/include/net/page_pool/helpers.h > @@ -8,13 +8,28 @@ > /** > * 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 frag 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. > + * > + * If the driver knows that it always requires full pages or its allocates are
allocations
> + * 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 > + * avoid TLB/cache miss for data access, but there also is some cost to
avoids
> + * 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. Thus, API users > @@ -100,6 +115,14 @@ static inline struct page *page_pool_alloc_frag(struct page_pool *pool, > return __page_pool_alloc_frag(pool, offset, size, gfp); > } > > +/** > + * page_pool_dev_alloc_frag() - allocate a page frag. > + * @pool[in] pool from which to allocate > + * @offset[out] offset to the allocated page > + * @size[in] requested size
Please use kernel-doc syntax/notation here.
> + * > + * Get a page frag from the page allocator or page_pool caches. > + */ > static inline struct page *page_pool_dev_alloc_frag(struct page_pool *pool, > unsigned int *offset, > unsigned int size) > @@ -143,6 +166,14 @@ static inline struct page *page_pool_alloc(struct page_pool *pool, > return page; > } > > +/** > + * page_pool_dev_alloc() - allocate a page or a page frag. > + * @pool[in]: pool from which to allocate > + * @offset[out]: offset to the allocated page > + * @size[in, out]: in as the requested size, out as the allocated size
and here.
> + * > + * Get a page or a page frag from the page allocator or page_pool caches. > + */ > static inline struct page *page_pool_dev_alloc(struct page_pool *pool, > unsigned int *offset, > unsigned int *size) > @@ -165,6 +196,13 @@ 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[in]: pool from which to allocate > + * @size[in, out]: in as the requested size, out as the allocated size
and here.
> + * > + * Get a cache from the page allocator or page_pool caches. > + */ > static inline void *page_pool_dev_cache_alloc(struct page_pool *pool, > unsigned int *size) > { > @@ -316,6 +354,14 @@ static inline void page_pool_recycle_direct(struct page_pool *pool, > page_pool_put_full_page(pool, page, true); > } > > +/** > + * page_pool_cache_free() - free a cache into the page_pool > + * @pool[in]: pool from which cache was allocated > + * @data[in]: cache to free > + * @allow_direct[in]: freed by the consumer, allow lockless caching
and here.
> + * > + * 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) > {
Thanks.
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