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b=Cr8uxAh+loQpjXmCoE2TaiGITt+TcZwPIbr+2RkfQvmH016d7LsS1fYXzAGa6tfaf 9aDJgI4NZQWIIfDBz/fxuLE/C3bF1QUfjJm+eaXZpA2bd1iUEfFaidDc9+2lnQk7Q3 fQJRqh1thkcoH/XcJKSphQ+kRTI9UCWbfmO7NEFJcIOb1DT9Y1d3+rxytyM6koiRnU o67Kghqz/3Sl1fwOV1noQq1Zz+1JhcTHzbgMwOwLPK3z3cP5r0vFt1ZXjSDshcLTta 3mJYS/6/YKEFhO2y4qtuIGDtUUcWsUjMz9l5ZpGFjeP+r/soM1XXNhz2++NoEly8au TOmcMnI67TGGw== Date: Wed, 13 May 2026 10:42:38 +0100 From: Lorenzo Stoakes To: Byungchul Park Cc: linux-mm@kvack.org, akpm@linux-foundation.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, david@kernel.org, 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, almasrymina@google.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, sfr@canb.auug.org.au, dw@davidwei.uk, ap420073@gmail.com, dtatulea@nvidia.com Subject: Re: [PATCH v4] mm: introduce a new page type for page pool in page type Message-ID: References: <20260224051347.19621-1-byungchul@sk.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260224051347.19621-1-byungchul@sk.com> X-Rspam-User: X-Rspamd-Queue-Id: AAFA780003 X-Rspamd-Server: rspam04 X-Stat-Signature: 1tfuyqkuops1m19q7egrnkfjjg34tus9 X-HE-Tag: 1778665362-687685 X-HE-Meta: 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 w5vSz9jv 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: -cc previous kernel mail address -cc David's very previous kernel mail address +cc David's current mail address Hi, Just an annoying reminder to please check people's addresses via get_maintainer.pl, as otherwise stuff might get missed! :) Cheers, Lorenzo On Tue, Feb 24, 2026 at 02:13:47PM +0900, Byungchul Park wrote: > Currently, the condition 'page->pp_magic == PP_SIGNATURE' is used to > determine if a page belongs to a page pool. However, with the planned > removal of @pp_magic, we should instead leverage the page_type in struct > page, such as PGTY_netpp, for this purpose. > > Introduce and 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(). > > Plus, add @page_type to struct net_iov at the same offset as struct page > so as to use the page_type APIs for struct net_iov as well. While at it, > reorder @type and @owner in struct net_iov to avoid a hole and > increasing the struct size. > > This work was inspired by the following link: > > https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/ > > While at it, move the sanity check for page pool to on the free path. > > Suggested-by: David Hildenbrand > Co-developed-by: Pavel Begunkov > Signed-off-by: Pavel Begunkov > Signed-off-by: Byungchul Park > Acked-by: David Hildenbrand > Acked-by: Zi Yan > Acked-by: Vlastimil Babka > Reviewed-by: Toke Høiland-Jørgensen > --- > The following 'Acked-by's were given only for mm part: > > Acked-by: David Hildenbrand > Acked-by: Zi Yan > Acked-by: Vlastimil Babka > > This patch changes both mm and page-pool, but I'm currently targetting > mm tree because Jakub asked and I also think it's more about mm change. > See the following link: > > https://lore.kernel.org/all/20250813075212.051b5178@kernel.org/ > > Changes from v3: > 1. Rebase on mm-new as of Feb 24, 2026. > 2. Fix an issue reported by kernel test robot due to incorrect > type. > 3. Add 'Acked-by: Vlastimil Babka '. Thanks. > > Changes from v2: > 1. Fix an issue reported by kernel test robot due to incorrect > type in argument of __netmem_to_page(). > > Changes from v1: > 1. Drop the finalizing patch removing the pp fields of struct > page since I found that there is still code accessing a pp > field via struct page. I will retry the finalizing patch > after resolving the issue. > --- > .../net/ethernet/mellanox/mlx5/core/en/xdp.c | 2 +- > include/linux/mm.h | 27 +++---------------- > include/linux/page-flags.h | 6 +++++ > include/net/netmem.h | 15 +++++++++-- > mm/page_alloc.c | 11 +++++--- > net/core/netmem_priv.h | 23 +++++++--------- > net/core/page_pool.c | 24 +++++++++++++++-- > 7 files changed, 62 insertions(+), 46 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c > index 80f9fc10877ad..7d90d2485c787 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 13336340612e2..0db764b3d6b84 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4824,10 +4824,9 @@ 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. > * > @@ -4862,26 +4861,6 @@ 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 > - > #define PAGE_SNAPSHOT_FAITHFUL (1 << 0) > #define PAGE_SNAPSHOT_PG_BUDDY (1 << 1) > #define PAGE_SNAPSHOT_PG_IDLE (1 << 2) > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 0426cac91c0bb..30c4eb24e4edf 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -939,6 +939,7 @@ enum pagetype { > PGTY_zsmalloc = 0xf6, > PGTY_unaccepted = 0xf7, > PGTY_large_kmalloc = 0xf8, > + PGTY_netpp = 0xf9, > > PGTY_mapcount_underflow = 0xff > }; > @@ -1071,6 +1072,11 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc) > PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted) > PAGE_TYPE_OPS(LargeKmalloc, 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 a96b3e5e5574c..85e3b26ec547f 100644 > --- a/include/net/netmem.h > +++ b/include/net/netmem.h > @@ -110,10 +110,21 @@ struct net_iov { > atomic_long_t pp_ref_count; > }; > }; > - struct net_iov_area *owner; > + > + unsigned int page_type; > enum net_iov_type type; > + struct net_iov_area *owner; > }; > > +/* Make sure 'the offset of page_type in struct page == the offset of > + * type in struct net_iov'. > + */ > +#define NET_IOV_ASSERT_OFFSET(pg, iov) \ > + static_assert(offsetof(struct page, pg) == \ > + offsetof(struct net_iov, iov)) > +NET_IOV_ASSERT_OFFSET(page_type, page_type); > +#undef NET_IOV_ASSERT_OFFSET > + > struct net_iov_area { > /* Array of net_iovs for this area. */ > struct net_iov *niovs; > @@ -256,7 +267,7 @@ static inline unsigned long netmem_pfn_trace(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 d88c8c67ac0b7..cae9f93271469 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1079,7 +1079,6 @@ static inline bool page_expected_state(struct page *page, > #ifdef CONFIG_MEMCG > page->memcg_data | > #endif > - page_pool_page_is_pp(page) | > (page->flags.f & check_flags))) > return false; > > @@ -1106,8 +1105,6 @@ 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))) > - bad_reason = "page_pool leak"; > return bad_reason; > } > > @@ -1416,9 +1413,15 @@ __always_inline bool __free_pages_prepare(struct page *page, > mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); > folio->mapping = NULL; > } > - if (unlikely(page_has_type(page))) > + if (unlikely(page_has_type(page))) { > + /* networking expects to clear its page type before releasing */ > + if (unlikely(PageNetpp(page))) { > + bad_page(page, "page_pool leak"); > + return false; > + } > /* Reset the page_type (which overlays _mapcount) */ > page->page_type = UINT_MAX; > + } > > if (is_check_pages_enabled()) { > if (free_page_is_bad(page)) > diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h > index 23175cb2bd866..3e6fde8f1726f 100644 > --- a/net/core/netmem_priv.h > +++ b/net/core/netmem_priv.h > @@ -8,21 +8,18 @@ static inline unsigned long netmem_get_pp_magic(netmem_ref netmem) > 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_to_nmdesc(netmem)->pp_magic |= pp_magic; > -} > - > -static inline void netmem_clear_pp_magic(netmem_ref netmem) > -{ > - WARN_ON_ONCE(netmem_to_nmdesc(netmem)->pp_magic & PP_DMA_INDEX_MASK); > - > - netmem_to_nmdesc(netmem)->pp_magic = 0; > -} > - > static inline bool netmem_is_pp(netmem_ref netmem) > { > - return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE; > + struct page *page; > + > + /* XXX: Now that the offset of page_type is shared between > + * struct page and net_iov, just cast the netmem to struct page > + * unconditionally by clearing NET_IOV if any, no matter whether > + * it comes from struct net_iov or struct page. This should be > + * adjusted once the offset is no longer shared. > + */ > + page = (struct page *)((__force unsigned long)netmem & ~NET_IOV); > + return PageNetpp(page); > } > > static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool) > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index 265a729431bb7..877bbf7a19389 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -702,8 +702,18 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict) > > void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) > { > + struct page *page; > + > netmem_set_pp(netmem, pool); > - netmem_or_pp_magic(netmem, PP_SIGNATURE); > + > + /* XXX: Now that the offset of page_type is shared between > + * struct page and net_iov, just cast the netmem to struct page > + * unconditionally by clearing NET_IOV if any, no matter whether > + * it comes from struct net_iov or struct page. This should be > + * adjusted once the offset is no longer shared. > + */ > + page = (struct page *)((__force unsigned long)netmem & ~NET_IOV); > + __SetPageNetpp(page); > > /* Ensuring all pages have been split into one fragment initially: > * page_pool_set_pp_info() is only called once for every page when it > @@ -718,7 +728,17 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) > > void page_pool_clear_pp_info(netmem_ref netmem) > { > - netmem_clear_pp_magic(netmem); > + struct page *page; > + > + /* XXX: Now that the offset of page_type is shared between > + * struct page and net_iov, just cast the netmem to struct page > + * unconditionally by clearing NET_IOV if any, no matter whether > + * it comes from struct net_iov or struct page. This should be > + * adjusted once the offset is no longer shared. > + */ > + page = (struct page *)((__force unsigned long)netmem & ~NET_IOV); > + __ClearPageNetpp(page); > + > netmem_set_pp(netmem, NULL); > } > > -- > 2.17.1 >