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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762481294; bh=krN2HbEAPJ9LZ7iRNlMAlG+UbT7YoouhmyVRCR+YH4U=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=NCm/SkLf0sDAsmYdC0ji01eys0nbyjJVvHg3S7lgfslaEnD9BVkC/1GHvsGoJdtcD 6aFFfWl+eRdUa2P1IoiFv7Dm4LKqOdxkMEjcj0D7G9kE/QdBQjWl01CAqqMZlLk9gU OEKganv0Zc9V1YeZc8eewaAHC8E6S3BmHqVXJEkNXfY4ZohJUOvegj8GstXxpWV+dS bH8w8zRnLdd3MBCHEQhkcLSEgwh0QK8DGVApLdJqeFVKnO8+KZWlbOHbJo4Z8UCy0l q3fLPgBC9KjsOaNAodtNomC/uutUVR/IkxCfXaDgb5L4m5cwdnNmIfHePUsmOlTYTk t9ibqp7zouV1Q== Date: Thu, 6 Nov 2025 18:08:10 -0800 From: Jakub Kicinski To: Byungchul Park 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, 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, 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: [RFC mm v5 1/2] page_pool: check nmdesc->pp to see its usage as page pool for net_iov not page-backed Message-ID: <20251106180810.6b06f71a@kernel.org> In-Reply-To: <20251107015902.GA3021@system.software.com> References: <20251103075108.26437-1-byungchul@sk.com> <20251103075108.26437-2-byungchul@sk.com> <20251106173320.2f8e683a@kernel.org> <20251107015902.GA3021@system.software.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4CA494000C X-Rspamd-Server: rspam07 X-Stat-Signature: u5hxd8jw9xcsup1r9rsu1fe5t3hsnwob X-Rspam-User: X-HE-Tag: 1762481295-693311 X-HE-Meta: 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 6Aem7IEE 797VExKAu/P8oujzk/ABEQHxyk5mGLQK8sdHDFisxpcPeph4wGhKI0yM1kiUH3C8NuKlSwtmx/Y1VNKgo/pjjQBnl5kEpNOj0HnpM6TFvPvTLJAMqZ/ZFlK7Ll3TDB9+9Gp3gAhZtNgjFEw8gleaA45ePW8CRKCiSek+B4Hp8HFJDcHZruzksYvXEVJMgcGEphcE4h4bGID9KSswVmWfCZ0/0COXcXsUlcRd65XEjS9C3DfOmVgsi7SqMMAGf0LXMmHR/3yTm3babTvLuCFEcxLDUAX49niXqv99VBh3s2imekH8BHG9ki+5nDBrdNdBdMIJ1zXtWcB0+682sAWQr+96FmRp5AoKTFfBv2f99loccDqqT2OrmWn3HtIcnGagORgDA X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 7 Nov 2025 10:59:02 +0900 Byungchul Park wrote: > > > page-backed, the identification cannot be based on the page_type. > > > Instead, nmdesc->pp can be used to see if it belongs to a page pool, by > > > making sure nmdesc->pp is NULL otherwise. > > > > Please explain why. Isn't the type just a value in a field? > > Which net_iov could also set accordingly.. ? > > page_type field is in 'struct page', so 'struct page' can check the type. > > However, the field is not in 'struct net_iov', so 'struct net_iov' that > is not backed by page, cannot use the type checking to see if it's page > pool'ed instance. > > I'm afraid I didn't get your questions. I will try to explain again > properly if you give me more detail and example about your questions or > requirement. net_iov has members in the same place as page. page_type is just a field right now. static __always_inline int Page##uname(const struct page *page) \ { \ return data_race(page->page_type >> 24) == PGTY_##lname; \ } \ The whole thing works right now by overlaying one struct on top of another, and shared members being in the same places. Is this clear enough?