On Mon, Dec 11, 2023 at 8:46 PM Liang Chen <liangchen.linux@xxxxxxxxx> wrote: > > To support multiple users referencing the same fragment, > 'pp_frag_count' is renamed to 'pp_ref_count', transitioning pp pages > from fragment management to reference count management after draining > based on the suggestion from [1]. > > The idea is that the concept of fragmenting exists before the page is > drained, and all related functions retain their current names. > However, once the page is drained, its management shifts to being > governed by 'pp_ref_count'. Therefore, all functions associated with > that lifecycle stage of a pp page are renamed. > > [1] > http://lore.kernel.org/netdev/f71d9448-70c8-8793-dc9a-0eb48a570300@xxxxxxxxxx > > Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx> > Reviewed-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> > Reviewed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> FWIW, Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx> > --- > .../net/ethernet/mellanox/mlx5/core/en_rx.c | 4 +- > include/linux/mm_types.h | 2 +- > include/net/page_pool/helpers.h | 60 +++++++++++-------- > include/net/page_pool/types.h | 6 +- > net/core/page_pool.c | 12 ++-- > 5 files changed, 46 insertions(+), 38 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > index 8d9743a5e42c..98d33ac7ec64 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > @@ -298,8 +298,8 @@ static void mlx5e_page_release_fragmented(struct mlx5e_rq *rq, > u16 drain_count = MLX5E_PAGECNT_BIAS_MAX - frag_page->frags; > struct page *page = frag_page->page; > > - if (page_pool_defrag_page(page, drain_count) == 0) > - page_pool_put_defragged_page(rq->page_pool, page, -1, true); > + if (page_pool_unref_page(page, drain_count) == 0) > + page_pool_put_unrefed_page(rq->page_pool, page, -1, true); > } > > static inline int mlx5e_get_rx_frag(struct mlx5e_rq *rq, > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 957ce38768b2..64e4572ef06d 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -125,7 +125,7 @@ struct page { > struct page_pool *pp; > unsigned long _pp_mapping_pad; > unsigned long dma_addr; > - atomic_long_t pp_frag_count; > + 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/page_pool/helpers.h b/include/net/page_pool/helpers.h > index 4ebd544ae977..d0c5e7e6857a 100644 > --- a/include/net/page_pool/helpers.h > +++ b/include/net/page_pool/helpers.h > @@ -29,7 +29,7 @@ > * 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. > + * 'struct page' and atomic operation for page->pp_ref_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 > @@ -214,69 +214,77 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool) > return pool->p.dma_dir; > } > > -/* pp_frag_count represents the number of writers who can update the page > - * either by updating skb->data or via DMA mappings for the device. > - * We can't rely on the page refcnt for that as we don't know who might be > - * holding page references and we can't reliably destroy or sync DMA mappings > - * of the fragments. > +/** > + * page_pool_fragment_page() - split a fresh page into fragments > + * @page: page to split > + * @nr: references to set > + * > + * pp_ref_count represents the number of outstanding references to the page, > + * which will be freed using page_pool APIs (rather than page allocator APIs > + * like put_page()). Such references are usually held by page_pool-aware > + * objects like skbs marked for page pool recycling. > * > - * When pp_frag_count reaches 0 we can either recycle the page if the page > - * refcnt is 1 or return it back to the memory allocator and destroy any > - * mappings we have. > + * This helper allows the caller to take (set) multiple references to a > + * freshly allocated page. The page must be freshly allocated (have a > + * pp_ref_count of 1). This is commonly done by drivers and > + * "fragment allocators" to save atomic operations - either when they know > + * upfront how many references they will need; or to take MAX references and > + * return the unused ones with a single atomic dec(), instead of performing > + * multiple atomic inc() operations. > */ > static inline void page_pool_fragment_page(struct page *page, long nr) > { > - atomic_long_set(&page->pp_frag_count, nr); > + atomic_long_set(&page->pp_ref_count, nr); > } > > -static inline long page_pool_defrag_page(struct page *page, long nr) > +static inline long page_pool_unref_page(struct page *page, long nr) > { > long ret; > > - /* If nr == pp_frag_count then we have cleared all remaining > + /* If nr == pp_ref_count then we have cleared all remaining > * references to the page: > * 1. 'n == 1': no need to actually overwrite it. > * 2. 'n != 1': overwrite it with one, which is the rare case > - * for pp_frag_count draining. > + * for pp_ref_count draining. > * > * The main advantage to doing this is that not only we avoid a atomic > * update, as an atomic_read is generally a much cheaper operation than > * an atomic update, especially when dealing with a page that may be > - * partitioned into only 2 or 3 pieces; but also unify the pp_frag_count > + * referenced by only 2 or 3 users; but also unify the pp_ref_count > * handling by ensuring all pages have partitioned into only 1 piece > * initially, and only overwrite it when the page is partitioned into > * more than one piece. > */ > - if (atomic_long_read(&page->pp_frag_count) == nr) { > + if (atomic_long_read(&page->pp_ref_count) == nr) { > /* As we have ensured nr is always one for constant case using > * the BUILD_BUG_ON(), only need to handle the non-constant case > - * here for pp_frag_count draining, which is a rare case. > + * here for pp_ref_count draining, which is a rare case. > */ > BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1); > if (!__builtin_constant_p(nr)) > - atomic_long_set(&page->pp_frag_count, 1); > + atomic_long_set(&page->pp_ref_count, 1); > > return 0; > } > > - ret = atomic_long_sub_return(nr, &page->pp_frag_count); > + ret = atomic_long_sub_return(nr, &page->pp_ref_count); > WARN_ON(ret < 0); > > - /* We are the last user here too, reset pp_frag_count back to 1 to > + /* We are the last user here too, reset pp_ref_count back to 1 to > * ensure all pages have been partitioned into 1 piece initially, > * this should be the rare case when the last two fragment users call > - * page_pool_defrag_page() currently. > + * page_pool_unref_page() currently. > */ > if (unlikely(!ret)) > - atomic_long_set(&page->pp_frag_count, 1); > + atomic_long_set(&page->pp_ref_count, 1); > > return ret; > } > > -static inline bool page_pool_is_last_frag(struct page *page) > +static inline bool page_pool_is_last_ref(struct page *page) > { > - /* If page_pool_defrag_page() returns 0, we were the last user */ > - return page_pool_defrag_page(page, 1) == 0; > + /* If page_pool_unref_page() returns 0, we were the last user */ > + return page_pool_unref_page(page, 1) == 0; > } > > /** > @@ -301,10 +309,10 @@ static inline void page_pool_put_page(struct page_pool *pool, > * allow registering MEM_TYPE_PAGE_POOL, but shield linker. > */ > #ifdef CONFIG_PAGE_POOL > - if (!page_pool_is_last_frag(page)) > + if (!page_pool_is_last_ref(page)) > return; > > - page_pool_put_defragged_page(pool, page, dma_sync_size, allow_direct); > + page_pool_put_unrefed_page(pool, page, dma_sync_size, allow_direct); > #endif > } > > diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h > index e1bb92c192de..6a5323619f6e 100644 > --- a/include/net/page_pool/types.h > +++ b/include/net/page_pool/types.h > @@ -224,9 +224,9 @@ static inline void page_pool_put_page_bulk(struct page_pool *pool, void **data, > } > #endif > > -void page_pool_put_defragged_page(struct page_pool *pool, struct page *page, > - unsigned int dma_sync_size, > - bool allow_direct); > +void page_pool_put_unrefed_page(struct page_pool *pool, struct page *page, > + unsigned int dma_sync_size, > + bool allow_direct); > > static inline bool is_page_pool_compiled_in(void) > { > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index df2a06d7da52..106220b1f89c 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -650,8 +650,8 @@ __page_pool_put_page(struct page_pool *pool, struct page *page, > return NULL; > } > > -void page_pool_put_defragged_page(struct page_pool *pool, struct page *page, > - unsigned int dma_sync_size, bool allow_direct) > +void page_pool_put_unrefed_page(struct page_pool *pool, struct page *page, > + unsigned int dma_sync_size, bool allow_direct) > { > page = __page_pool_put_page(pool, page, dma_sync_size, allow_direct); > if (page && !page_pool_recycle_in_ring(pool, page)) { > @@ -660,7 +660,7 @@ void page_pool_put_defragged_page(struct page_pool *pool, struct page *page, > page_pool_return_page(pool, page); > } > } > -EXPORT_SYMBOL(page_pool_put_defragged_page); > +EXPORT_SYMBOL(page_pool_put_unrefed_page); > > /** > * page_pool_put_page_bulk() - release references on multiple pages > @@ -687,7 +687,7 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data, > struct page *page = virt_to_head_page(data[i]); > > /* It is not the last user for the page frag case */ > - if (!page_pool_is_last_frag(page)) > + if (!page_pool_is_last_ref(page)) > continue; > > page = __page_pool_put_page(pool, page, -1, false); > @@ -729,7 +729,7 @@ static struct page *page_pool_drain_frag(struct page_pool *pool, > long drain_count = BIAS_MAX - pool->frag_users; > > /* Some user is still using the page frag */ > - if (likely(page_pool_defrag_page(page, drain_count))) > + if (likely(page_pool_unref_page(page, drain_count))) > return NULL; > > if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) { > @@ -750,7 +750,7 @@ static void page_pool_free_frag(struct page_pool *pool) > > pool->frag_page = NULL; > > - if (!page || page_pool_defrag_page(page, drain_count)) > + if (!page || page_pool_unref_page(page, drain_count)) > return; > > page_pool_return_page(pool, page); > -- > 2.31.1 > > -- Thanks, Mina
