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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vrlJH-00000001duk-2IlM; Sun, 15 Feb 2026 23:13:51 +0000 Date: Sun, 15 Feb 2026 23:13:51 +0000 From: Matthew Wilcox To: Kiryl Shutsemau Cc: Andrew Morton , Muchun Song , David Hildenbrand , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Huacai Chen , WANG Xuerui , Palmer Dabbelt , Paul Walmsley , Albert Ou , Alexandre Ghiti , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org Subject: Re: [PATCHv6 08/17] mm: Make page_zonenum() use head page Message-ID: References: <20260202155634.650837-1-kas@kernel.org> <20260202155634.650837-9-kas@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260202155634.650837-9-kas@kernel.org> X-Stat-Signature: qkxs9m584hwp1qwoe1py13p5epuyozrt X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 72BB620005 X-HE-Tag: 1771197252-258153 X-HE-Meta: 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 wcFNBlaa CxTL+4XCVNWuhumN2kBEqh7h6myonepMaDAm1qxafmROSkxZhySqi2uhZERaRyJl2cM0zIRxuq7Dg7CL7WJ/bSy12TSlKZHl6PX9jriFp1TirE44y+W8UMu7Bz6E93GTGceLNlqaFHEQ8j+7+UkFwxdbAi32u7lePVIWt1GbQ6w5d+iWyxzB4pNMRpP8uwaMnaOsH3xOPkZxmQ4tkEh/ikwhY7aXNU23Ikdn/JOVjjtTHxJCNg86RmU+nqKfZZOU9dJLNDZqcj8Z4dtAn5TAWd7kGokAa9OUYbys0K7AeC72kqxw= 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 Mon, Feb 02, 2026 at 03:56:24PM +0000, Kiryl Shutsemau wrote: > With the upcoming changes to HVO, a single page of tail struct pages > will be shared across all huge pages of the same order on a node. Since > huge pages on the same node may belong to different zones, the zone > information stored in shared tail page flags would be incorrect. > > Always fetch zone information from the head page, which has unique and > correct zone flags for each compound page. You're right that different pages in the same folio can have different zone number. But does it matter ... or to put it another way, why is returning the zone number of the head page the correct way to resolve this? Arguably, the caller is asking for the zone number of _this page_, and does not care about the zone number of the head page. It would be good to have a short discussion of this in the commit message (but probably not worth putting this in a comment).