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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vuaVP-0000000Et8q-2Mg0; Mon, 23 Feb 2026 18:18:03 +0000 Date: Mon, 23 Feb 2026 18:18:03 +0000 From: Matthew Wilcox To: "David Hildenbrand (Arm)" Cc: Kiryl Shutsemau , Andrew Morton , Muchun Song , 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: X-Rspam-User: X-Rspamd-Queue-Id: 9EBF140007 X-Rspamd-Server: rspam02 X-Stat-Signature: e1pnyqeg71d54wnzhd94e9pbcwie99dz X-HE-Tag: 1771870699-954388 X-HE-Meta: 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 GcLe1dnP UnbgoAF22v07HBgU/iQEzvwcl+fvJk0jH8V6Vy/gjUiYkH7hEjClwTxLKFE9fWktIVN897VDf4BcNe5PtTxW9NSaQm0jGgvKLvqXAMXjvn/5e8l590Ch0A1TrXhKqTE7xQtq/0SbTSeOZK8Xr8sDS3WsZ65HPuOc8C3JCaKnkBxmzNcIGtZ1GDbt0SCc6Ztb3/EN3ZARPGCR2yzwozlUYmiagPYVfx3XA+fjAyPVjD3HgsHCSqj1K6JnLmoNmd+f5d8in3Im4QSnobBFYTu8Vm+YJ3RsuapwW8YJLkpe1wgSErJM= 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 16, 2026 at 10:06:57AM +0100, David Hildenbrand (Arm) wrote: > On 2/16/26 00:13, Matthew Wilcox wrote: > > 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? > > How can a folio cross zones? I thought 1GB pages in hugetlb could cross zones? Maybe that used to be true and isn't any more, or maybe it was never true and I was just confused.