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s=arc-20220608; d=hostedemail.com; t=1748226992; a=rsa-sha256; cv=none; b=QZDuaA7TmHqvPFKXbPBCXgXlvp/bGgAKKQD/oUAM1zsoBceACum1jeRCilicNf3EMc8bfV p7FVVtxnvis9zvgOFftbDvrQbVvBpanm4cD0e1J4XSQo7ksIfelFl8NxPfcc3gFNFIsbIP F/9/Q7bA/nTy1OKxdc4j5fOfoD8eh0M= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf23.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com X-AuditID: a67dfc5b-681ff7000002311f-fe-6833d3ade381 Date: Mon, 26 May 2025 11:36:24 +0900 From: Byungchul Park To: Mina Almasry Cc: willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, 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, 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, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com Subject: Re: [PATCH 12/18] page_pool: use netmem APIs to access page->pp_magic in page_pool_page_is_pp() Message-ID: <20250526023624.GB27145@system.software.com> References: <20250523032609.16334-1-byungchul@sk.com> <20250523032609.16334-13-byungchul@sk.com> <20250526022307.GA27145@system.software.com> MIME-Version: 1.0 Content-Type: text/plain; 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> > > #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; > > > -} > > > > I vote for keeping this function as-is (do not convert it to netmem), > > and instead modify it to access page->netmem_desc->pp_magic. > > Once the page pool fields are removed from struct page, struct page will > have neither struct netmem_desc nor the fields.. > > So it's unevitable to cast it to netmem_desc in order to refer to > pp_magic. Again, pp_magic is no longer associated to struct page. Options that come across my mind are: 1. use lru field of struct page instead, with appropriate comment but looks so ugly. 2. instead of a full word for the magic, use a bit of flags or use the private field for that purpose. 3. do not check magic number for page pool. 4. more? Byungchul > > Thoughts? > > Byungchul > > > The reason is that page_pool_is_pp() is today only called from code > > paths we have a page and not a netmem. Casting the page to a netmem > > which will cast it back to a page pretty much is a waste of cpu > > cycles. The page_pool is a place where we count cycles and we have > > benchmarks to verify performance (I pointed you to > > page_pool_bench_simple on the RFC). > > > > So lets avoid the cpu cycles if possible. > > > > -- > > Thanks, > > Mina