On Mon, Jul 14, 2025 at 12:30:12PM +0100, Pavel Begunkov wrote:
> On 7/14/25 05:23, Byungchul Park wrote:
> > On Sat, Jul 12, 2025 at 03:39:59PM +0100, Pavel Begunkov wrote:
> > > On 7/10/25 09:28, Byungchul Park wrote:
> > > > To simplify struct page, the page pool members of struct page should be
> > > > moved to other, allowing these members to be removed from struct page.
> > > >
> > > > Introduce a network memory descriptor to store the members, struct
> > > > netmem_desc, and make it union'ed with the existing fields in struct
> > > > net_iov, allowing to organize the fields of struct net_iov.
> > >
> > > FWIW, regardless of memdesc business, I think it'd be great to have
> > > this patch, as it'll help with some of the netmem casting ugliness and
> > > shed some cycles as well. For example, we have a bunch of
> > > niov -> netmem -> niov casts in various places.
> >
> > If Jakub agrees with this, I will re-post this as a separate patch so
> > that works that require this base can go ahead.
>
> I think it'd be a good idea. It's needed to clean up netmem handling,
> and I'll convert io_uring and get rid of the union in niov.
>
> The diff below should give a rough idea of what I want to use it for.
> It kills __netmem_clear_lsb() to avoid casting struct page * to niov.
> And saves some masking for zcrx, see page_pool_get_dma_addr_nmdesc(),
> and there are more places like that.
>
>
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 535cf17b9134..41f3a3fd6b6c 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -247,6 +247,8 @@ static inline unsigned long netmem_pfn_trace(netmem_ref netmem)
> return page_to_pfn(netmem_to_page(netmem));
> }
>
> +#define pp_page_to_nmdesc(page) ((struct netmem_desc *)(page))
> +
> /* __netmem_clear_lsb - convert netmem_ref to struct net_iov * for access to
> * common fields.
> * @netmem: netmem reference to extract as net_iov.
> @@ -262,11 +264,18 @@ static inline unsigned long netmem_pfn_trace(netmem_ref netmem)
> *
> * Return: the netmem_ref cast to net_iov* regardless of its underlying type.
> */
> -static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
> +static inline struct net_iov *__netmem_to_niov(netmem_ref netmem)
> {
> return (struct net_iov *)((__force unsigned long)netmem & ~NET_IOV);
> }
>
> +static inline struct netmem_desc *netmem_to_nmdesc(netmem_ref netmem)
I removed netmem_to_nmdesc() and its users, while I was working for v10.
However, You can add it if needed for your clean up.
I think I should share v10 now, to share the decision I made.
Byungchul
> +{
> + if (netmem_is_net_iov(netmem))
> + return &__netmem_to_niov(netmem)->desc;
> + return pp_page_to_nmdesc(__netmem_to_page(netmem));
> +}
> +
> /**
> * __netmem_get_pp - unsafely get pointer to the &page_pool backing @netmem
> * @netmem: netmem reference to get the pointer from
> @@ -280,17 +289,17 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
> */
> static inline struct page_pool *__netmem_get_pp(netmem_ref netmem)
> {
> - return __netmem_to_page(netmem)->pp;
> + return pp_page_to_nmdesc(__netmem_to_page(netmem))->pp;
> }
>
> static inline struct page_pool *netmem_get_pp(netmem_ref netmem)
> {
> - return __netmem_clear_lsb(netmem)->pp;
> + return netmem_to_nmdesc(netmem)->pp;
> }
>
> static inline atomic_long_t *netmem_get_pp_ref_count_ref(netmem_ref netmem)
> {
> - return &__netmem_clear_lsb(netmem)->pp_ref_count;
> + return &netmem_to_nmdesc(netmem)->pp_ref_count;
> }
>
> static inline bool netmem_is_pref_nid(netmem_ref netmem, int pref_nid)
> @@ -355,7 +364,7 @@ static inline bool netmem_is_pfmemalloc(netmem_ref netmem)
>
> static inline unsigned long netmem_get_dma_addr(netmem_ref netmem)
> {
> - return __netmem_clear_lsb(netmem)->dma_addr;
> + return netmem_to_nmdesc(netmem)->dma_addr;
> }
>
> void get_netmem(netmem_ref netmem);
> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
> index db180626be06..002858f3bcb3 100644
> --- a/include/net/page_pool/helpers.h
> +++ b/include/net/page_pool/helpers.h
> @@ -425,9 +425,9 @@ static inline void page_pool_free_va(struct page_pool *pool, void *va,
> page_pool_put_page(pool, virt_to_head_page(va), -1, allow_direct);
> }
>
> -static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
> +static inline dma_addr_t page_pool_get_dma_addr_nmdesc(struct netmem_desc *desc)
> {
> - dma_addr_t ret = netmem_get_dma_addr(netmem);
> + dma_addr_t ret = desc->dma_addr;
>
> if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
> ret <<= PAGE_SHIFT;
> @@ -435,6 +435,13 @@ static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
> return ret;
> }
>
> +static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
> +{
> + struct netmem_desc *desc = netmem_to_nmdesc(netmem);
> +
> + return page_pool_get_dma_addr_nmdesc(desc);
> +}
> +
> /**
> * page_pool_get_dma_addr() - Retrieve the stored DMA address.
> * @page: page allocated from a page pool
> diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
> index 085eeed8cd50..2e80692d9ee1 100644
> --- a/io_uring/zcrx.c
> +++ b/io_uring/zcrx.c
> @@ -290,7 +290,7 @@ static void io_zcrx_sync_for_device(const struct page_pool *pool,
> if (!dma_dev_need_sync(pool->p.dev))
> return;
>
> - dma_addr = page_pool_get_dma_addr_netmem(net_iov_to_netmem(niov));
> + dma_addr = page_pool_get_dma_addr_nmdesc(&niov->desc);
> __dma_sync_single_for_device(pool->p.dev, dma_addr + pool->p.offset,
> PAGE_SIZE, pool->p.dma_dir);
> #endif
> diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
> index cd95394399b4..97d4beda9174 100644
> --- a/net/core/netmem_priv.h
> +++ b/net/core/netmem_priv.h
> @@ -5,19 +5,21 @@
>
> static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
> {
> - return __netmem_clear_lsb(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
> + return netmem_to_nmdesc(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
> }
>
> static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
> {
> - __netmem_clear_lsb(netmem)->pp_magic |= pp_magic;
> + netmem_to_nmdesc(netmem)->pp_magic |= pp_magic;
> }
>
> static inline void netmem_clear_pp_magic(netmem_ref netmem)
> {
> - WARN_ON_ONCE(__netmem_clear_lsb(netmem)->pp_magic & PP_DMA_INDEX_MASK);
> + struct netmem_desc *desc = netmem_to_nmdesc(netmem);
>
> - __netmem_clear_lsb(netmem)->pp_magic = 0;
> + WARN_ON_ONCE(desc->pp_magic & PP_DMA_INDEX_MASK);
> +
> + desc->pp_magic = 0;
> }
>
> static inline bool netmem_is_pp(netmem_ref netmem)
> @@ -27,13 +29,13 @@ static inline bool netmem_is_pp(netmem_ref netmem)
>
> static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
> {
> - __netmem_clear_lsb(netmem)->pp = pool;
> + netmem_to_nmdesc(netmem)->pp = pool;
> }
>
> static inline void netmem_set_dma_addr(netmem_ref netmem,
> unsigned long dma_addr)
> {
> - __netmem_clear_lsb(netmem)->dma_addr = dma_addr;
> + netmem_to_nmdesc(netmem)->dma_addr = dma_addr;
> }
>
> static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
> @@ -43,7 +45,7 @@ static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
> if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
> return 0;
>
> - magic = __netmem_clear_lsb(netmem)->pp_magic;
> + magic = netmem_to_nmdesc(netmem)->pp_magic;
>
> return (magic & PP_DMA_INDEX_MASK) >> PP_DMA_INDEX_SHIFT;
> }
> @@ -51,12 +53,12 @@ static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
> static inline void netmem_set_dma_index(netmem_ref netmem,
> unsigned long id)
> {
> - unsigned long magic;
> + struct netmem_desc *desc;
>
> if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
> return;
>
> - magic = netmem_get_pp_magic(netmem) | (id << PP_DMA_INDEX_SHIFT);
> - __netmem_clear_lsb(netmem)->pp_magic = magic;
> + desc = netmem_to_nmdesc(netmem);
> + desc->pp_magic |= id << PP_DMA_INDEX_SHIFT;
> }
> #endif
