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s=arc-20220608; d=hostedemail.com; t=1753245980; a=rsa-sha256; cv=none; b=YQIS4pcv2tzb9ptdMvK4JPYX87YnV832sK2PzYNONEV4YWeJZh1HLamPKZPaWBC7GwXvAZ fDS3HsYliDcjKNtBNzjZBYLvhVbTb6WOIXG/O8KCnsFga6ga+MLTv8AdGaeaRiMk1wZRGo 1secwLM5jpFguBIvsI7aqWGCqFPRHyM= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com X-AuditID: a67dfc5b-669ff7000002311f-bd-68806918915e Date: Wed, 23 Jul 2025 13:46:10 +0900 From: Byungchul Park To: Mina Almasry Cc: linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel_team@skhynix.com, harry.yoo@oracle.com, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, andrew+netdev@lunn.ch, edumazet@google.com, pabeni@redhat.com, akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ilias.apalodimas@linaro.org, willy@infradead.org, brauner@kernel.org, kas@kernel.org, yuzhao@google.com, usamaarif642@gmail.com, baolin.wang@linux.alibaba.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org Subject: Re: [PATCH] mm, page_pool: introduce a new page type for page pool in page type Message-ID: <20250723044610.GA80428@system.software.com> References: <20250721054903.39833-1-byungchul@sk.com> MIME-Version: 1.0 Content-Type: text/plain; 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However, yes. Additional works would better be > > considered on top like: > > > > 1. Adjust how to store and retrieve dma index. Maybe network guys > > can work better on top. > > > > 2. Move the sanity check for page pool in mm/page_alloc.c to on free. > > > > Byungchul > > > > ---8<--- > > From 7d207a1b3e9f4ff2a72f5b54b09e3ed0c4aaaca3 Mon Sep 17 00:00:00 2001 > > From: Byungchul Park > > Date: Mon, 21 Jul 2025 14:05:20 +0900 > > Subject: [PATCH] mm, page_pool: introduce a new page type for page pool in page type > > > > ->pp_magic field in struct page is current used to identify if a page > > belongs to a page pool. However, page type e.i. PGTY_netpp can be used > > for that purpose. > > > > Use the page type APIs e.g. PageNetpp(), __SetPageNetpp(), and > > __ClearPageNetpp() instead, and remove the existing APIs accessing > > ->pp_magic e.g. page_pool_page_is_pp(), netmem_or_pp_magic(), and > > netmem_clear_pp_magic() since they are totally replaced. > > > > This work was inspired by the following link by Pavel: > > > > [1] https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/ > > > > Suggested-by: Pavel Begunkov > > Signed-off-by: Byungchul Park > > --- > > .../net/ethernet/mellanox/mlx5/core/en/xdp.c | 2 +- > > include/linux/mm.h | 28 ++----------------- > > include/linux/page-flags.h | 6 ++++ > > include/net/netmem.h | 2 +- > > mm/page_alloc.c | 4 +-- > > net/core/netmem_priv.h | 16 ++--------- > > net/core/page_pool.c | 10 +++++-- > > 7 files changed, 24 insertions(+), 44 deletions(-) > > > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c > > index 5d51600935a6..def274f5c1ca 100644 > > --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c > > @@ -707,7 +707,7 @@ static void mlx5e_free_xdpsq_desc(struct mlx5e_xdpsq *sq, > > xdpi = mlx5e_xdpi_fifo_pop(xdpi_fifo); > > page = xdpi.page.page; > > > > - /* No need to check page_pool_page_is_pp() as we > > + /* No need to check PageNetpp() as we > > * know this is a page_pool page. > > */ > > page_pool_recycle_direct(pp_page_to_nmdesc(page)->pp, > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index ae50c1641bed..736061749535 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -4135,10 +4135,9 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > > * DMA mapping IDs for page_pool > > * > > * When DMA-mapping a page, page_pool allocates an ID (from an xarray) and > > - * stashes it in the upper bits of page->pp_magic. We always want to be able to > > - * unambiguously identify page pool pages (using page_pool_page_is_pp()). Non-PP > > - * pages can have arbitrary kernel pointers stored in the same field as pp_magic > > - * (since it overlaps with page->lru.next), so we must ensure that we cannot > > + * stashes it in the upper bits of page->pp_magic. Non-PP pages can have > > + * arbitrary kernel pointers stored in the same field as pp_magic (since > > + * it overlaps with page->lru.next), so we must ensure that we cannot > > * mistake a valid kernel pointer with any of the values we write into this > > * field. > > * > > @@ -4168,25 +4167,4 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > > > > #define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \ > > PP_DMA_INDEX_SHIFT) > > - > > -/* Mask used for checking in page_pool_page_is_pp() below. page->pp_magic is > > - * OR'ed with PP_SIGNATURE after the allocation in order to preserve bit 0 for > > - * the head page of compound page and bit 1 for pfmemalloc page, as well as the > > - * bits used for the DMA index. page_is_pfmemalloc() is checked in > > - * __page_pool_put_page() to avoid recycling the pfmemalloc page. > > - */ > > -#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL) > > - > > -#ifdef CONFIG_PAGE_POOL > > -static inline bool page_pool_page_is_pp(const struct page *page) > > -{ > > - return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > > -} > > -#else > > -static inline bool page_pool_page_is_pp(const struct page *page) > > -{ > > - return false; > > -} > > -#endif > > - > > #endif /* _LINUX_MM_H */ > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > > index 4fe5ee67535b..906ba7c9e372 100644 > > --- a/include/linux/page-flags.h > > +++ b/include/linux/page-flags.h > > @@ -957,6 +957,7 @@ enum pagetype { > > PGTY_zsmalloc = 0xf6, > > PGTY_unaccepted = 0xf7, > > PGTY_large_kmalloc = 0xf8, > > + PGTY_netpp = 0xf9, > > > > PGTY_mapcount_underflow = 0xff > > }; > > @@ -1101,6 +1102,11 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc) > > PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted) > > FOLIO_TYPE_OPS(large_kmalloc, large_kmalloc) > > > > +/* > > + * Marks page_pool allocated pages. > > + */ > > +PAGE_TYPE_OPS(Netpp, netpp, netpp) > > + > > /** > > * PageHuge - Determine if the page belongs to hugetlbfs > > * @page: The page to test. > > diff --git a/include/net/netmem.h b/include/net/netmem.h > > index f7dacc9e75fd..3667334e16e7 100644 > > --- a/include/net/netmem.h > > +++ b/include/net/netmem.h > > @@ -298,7 +298,7 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem) > > */ > > #define pp_page_to_nmdesc(p) \ > > ({ \ > > - DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p)); \ > > + DEBUG_NET_WARN_ON_ONCE(!PageNetpp(p)); \ > > __pp_page_to_nmdesc(p); \ > > }) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 2ef3c07266b3..71c7666e48a9 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -898,7 +898,7 @@ static inline bool page_expected_state(struct page *page, > > #ifdef CONFIG_MEMCG > > page->memcg_data | > > #endif > > - page_pool_page_is_pp(page) | > > + PageNetpp(page) | > > (page->flags & check_flags))) > > return false; > > > > @@ -925,7 +925,7 @@ static const char *page_bad_reason(struct page *page, unsigned long flags) > > if (unlikely(page->memcg_data)) > > bad_reason = "page still charged to cgroup"; > > #endif > > - if (unlikely(page_pool_page_is_pp(page))) > > + if (unlikely(PageNetpp(page))) > > bad_reason = "page_pool leak"; > > return bad_reason; > > } > > diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h > > index cd95394399b4..39a97703d9ed 100644 > > --- a/net/core/netmem_priv.h > > +++ b/net/core/netmem_priv.h > > @@ -8,21 +8,11 @@ static inline unsigned long netmem_get_pp_magic(netmem_ref netmem) > > return __netmem_clear_lsb(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; > > -} > > - > > -static inline void netmem_clear_pp_magic(netmem_ref netmem) > > -{ > > - WARN_ON_ONCE(__netmem_clear_lsb(netmem)->pp_magic & PP_DMA_INDEX_MASK); > > - > > - __netmem_clear_lsb(netmem)->pp_magic = 0; > > -} > > - > > static inline bool netmem_is_pp(netmem_ref netmem) > > { > > - return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE; > > + if (netmem_is_net_iov(netmem)) > > + return true; > > As Pavel alludes, this is dubious, and at least it's difficult to > reason about it. > > There could be net_iovs that are not attached to pp, and should not be > treated as pp memory. These are in the devmem (and future net_iov) tx > paths. > > We need a way to tell if a net_iov is pp or not. A couple of options: > > 1. We could have it such that if net_iov->pp is set, then the > netmem_is_pp == true, otherwise false. > 2. We could implement a page-flags equivalent for net_iov. > > Option #1 is simpler and is my preferred. To do that properly, you need to: > > 1. Make sure everywhere net_iovs are allocated that pp=NULL in the > non-pp case and pp=non NULL in the pp case. those callsites are > net_devmem_bind_dmabuf (devmem rx & tx path), io_zcrx_create_area > (io_uring rx path). > > 2. Change netmem_is_pp to check net_iov->pp in the net_iov case. Good idea, but I'm not sure if I could work on it without consuming your additional review efforts. Can anyone add net_iov_is_pp() helper? Or use the page type, Netpp, as an additional way to identify if it's a pp page for system memory, keeping the current way using ->pp_magic. So the page type, Netpp, is used for system memory, and ->pp_magic is used for net_iov. The clean up for ->pp_magic can be done if needed. Byungchul > -- > Thanks, > Mina