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imf06.hostedemail.com; dkim=none; spf=pass (imf06.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1752448941; a=rsa-sha256; cv=none; b=opfAkveLUpPoNFN134onQAUG7PGY16IZAjJTboeENzEXBw/LfTpQA9wvikMaK5Mi17qg+6 2FBvGTam+0njsDbyLMn/kUItu4JCqhqgwt7jPNpMJJQdolng8HsgXYoukll3q8Kdp90UBN Jqpem0w9miSwL0Xx2VR9RDGuGgo/ZzA= X-AuditID: a67dfc5b-669ff7000002311f-d1-68743fab9764 Date: Mon, 14 Jul 2025 08:22:14 +0900 From: Byungchul Park To: Pavel Begunkov Cc: David Hildenbrand , Mina Almasry , "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, 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 Subject: Re: [PATCH net-next v9 3/8] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp() Message-ID: <20250713232214.GA13576@system.software.com> References: <20250710082807.27402-1-byungchul@sk.com> <20250710082807.27402-4-byungchul@sk.com> <20250711011435.GC40145@system.software.com> <582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com> <3acd967e-30b3-4e76-9e1b-41c1e19d4f31@redhat.com> <7c8b9d7f-545c-4e37-8d0e-39b1d525a949@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; 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> > > > > > + > > > > > > + return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > > > > > > +} > > > > > > > > > > pages can be pp pages (where they have pp fields inside of them) or > > > > > non-pp pages (where they don't have pp fields inside them, because > > > > > they were never allocated from the page_pool). > > > > > > > > > > Casting a page to a netmem_desc, and then checking if the page was a > > > > > pp page doesn't makes sense to me on a fundamental level. The > > > > > netmem_desc is only valid if the page was a pp page in the first > > > > > place. Maybe page_to_nmdesc should reject the cast if the page is not > > > > > a pp page or something. > > > > > > > > Right, as you already know, the current mainline code already has the > > > > same problem but we've been using the werid way so far, in other words, > > > > mm code is checking if it's a pp page or not by using ->pp_magic, but > > > > it's ->lur, ->buddy_list, or ->pcp_list if it's not a pp page. > > > > > > > > Both the mainline code and this patch can make sense *only if* it's > > > > actually a pp page. It's unevitable until mm provides a way to identify > > > > the type of page for page pool. Thoughts? > > > Question to mm folks, can we add a new PGTY for page pool and use > > > that to filter page pool originated pages? Like in the incomplete > > > and untested diff below? > > > > https://lore.kernel.org/all/77c6a6dd-0e03-4b81-a9c7-eaecaa4ebc0b@redhat.com/ > > Great, then it'll be the right thing to do here. I somehow missed > the post, will add your suggested-by. It'd be the ideal. I will wait and work on top of your patch then. Byungchul > > -- > Pavel Begunkov