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[2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453646fd816sm104134785e9.24.2025.06.23.02.16.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 02:16:44 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 11:16:43 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v6 9/9] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp() To: Byungchul Park , willy@infradead.org, netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, almasrymina@google.com, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, hawk@kernel.org, akpm@linux-foundation.org, davem@davemloft.net, john.fastabend@gmail.com, andrew+netdev@lunn.ch, asml.silence@gmail.com, toke@redhat.com, tariqt@nvidia.com, edumazet@google.com, pabeni@redhat.com, saeedm@nvidia.com, leon@kernel.org, ast@kernel.org, daniel@iogearbox.net, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com, hannes@cmpxchg.org, ziy@nvidia.com, jackmanb@google.com References: <20250620041224.46646-1-byungchul@sk.com> <20250620041224.46646-10-byungchul@sk.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 20.06.25 06:12, Byungchul Park wrote: > To simplify struct page, the effort to separate its own descriptor from > struct page is required and the work for page pool is on going. > > To achieve that, all the code should avoid directly accessing page pool > members of struct page. > > Access ->pp_magic through struct netmem_desc instead of directly > accessing it through struct page in page_pool_page_is_pp(). Plus, move > page_pool_page_is_pp() from mm.h to netmem.h to use struct netmem_desc > without header dependency issue. > > Signed-off-by: Byungchul Park > Reviewed-by: Toke Høiland-Jørgensen > Reviewed-by: Mina Almasry > Reviewed-by: Pavel Begunkov > Reviewed-by: Vlastimil Babka > Acked-by: Harry Yoo > --- > include/linux/mm.h | 12 ------------ > include/net/netmem.h | 14 ++++++++++++++ > mm/page_alloc.c | 1 + > 3 files changed, 15 insertions(+), 12 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0ef2ba0c667a..0b7f7f998085 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4172,16 +4172,4 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > */ > #define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL) > > -#ifdef CONFIG_PAGE_POOL > -static inline bool page_pool_page_is_pp(struct page *page) > -{ > - return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > -} > -#else > -static inline bool page_pool_page_is_pp(struct page *page) > -{ > - return false; > -} > -#endif > - > #endif /* _LINUX_MM_H */ > diff --git a/include/net/netmem.h b/include/net/netmem.h > index d49ed49d250b..3d1b1dfc9ba5 100644 > --- a/include/net/netmem.h > +++ b/include/net/netmem.h > @@ -56,6 +56,20 @@ NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count); > */ > static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount)); > > +#ifdef CONFIG_PAGE_POOL > +static inline bool page_pool_page_is_pp(struct page *page) > +{ > + struct netmem_desc *desc = (struct netmem_desc *)page; > + > + return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > +} > +#else > +static inline bool page_pool_page_is_pp(struct page *page) > +{ > + return false; > +} > +#endif I wonder how helpful this cleanup is long-term. page_pool_page_is_pp() is only called from mm/page_alloc.c, right? There, we want to make sure that no pagepool page is ever returned to the buddy. How reasonable is this sanity check to have long-term? Wouldn't we be able to check that on some higher-level freeing path? The reason I am commenting is that once we decouple "struct page" from "struct netmem_desc", we'd have to lookup here the corresponding "struct netmem_desc". ... but at that point here (when we free the actual pages), the "struct netmem_desc" would likely already have been freed separately (remember: it will be dynamically allocated). With that in mind: 1) Is there a higher level "struct netmem_desc" freeing path where we could check that instead, so we don't have to cast from pages to netmem_desc at all. 2) How valuable are these sanity checks deep in the buddy? -- Cheers, David / dhildenb