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Mon, 9 Feb 2026 06:52:16 -0500 (EST) Date: Mon, 9 Feb 2026 11:52:11 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Muchun Song , Matthew Wilcox , 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-Rspamd-Server: rspam11 X-Stat-Signature: su1qeyaq8nurawhnc5c98bkog8mwhckw X-Rspam-User: X-Rspamd-Queue-Id: 4A0104000B X-HE-Tag: 1770637942-451049 X-HE-Meta: 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 aWO7hy8b 9/hF0wEjCna7Vf/elUaiB0xQBtAOtNg64RpyBpwbGm/3KngqV3X13tj5Q7d9tG9NKiPn+N0UqxBMfA/fQH3jVVebiQJkFHtWqQgmWiS38YFUlmmdDZ5Zwp8eQEkJibggBe5dmNvOPtYRYUqjD+rrBWbs/1N3Z8nE7mnd+EizIvHkFaHqJOv+SsELtqNyBZxQf2TzlIHpG6c/J4SQxFPMJhcX6jbJJEaZ2ccj4Mbwt4nab3UdNbbjgqBNiK7My2FhgQ1o6BGvJDXoZqfCghNjtVb954CQB1Kcn37GtiPM21CrQxdyLjQ7LfDQqIih5q9VOM2TwDUrhd+Vtm8AnDQLid4ix4v8AsI+WDXOlKAiOaSJzfMA2peWCKoWSvQ== 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 Thu, Feb 05, 2026 at 02:10:40PM +0100, David Hildenbrand (Arm) wrote: > On 2/2/26 16:56, 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. > > > > Signed-off-by: Kiryl Shutsemau > > Acked-by: Zi Yan > > --- > > include/linux/mmzone.h | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index be8ce40b5638..192143b5cdc0 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -1219,6 +1219,7 @@ static inline enum zone_type memdesc_zonenum(memdesc_flags_t flags) > > static inline enum zone_type page_zonenum(const struct page *page) > > { > > + page = compound_head(page); > > return memdesc_zonenum(page->flags); > > We end up calling page_zonenum() without holding a reference. > > Given that _compound_head() does a READ_ONCE(), this should work even if we > see concurrent page freeing etc. > > However, this change implies that we now perform a compound page lookup for > every PageHighMem() [meh], page_zone() [quite some users in the buddy, > including for pageblock access and page freeing]. > > That's a nasty compromise for making HVO better? :) > > We should likely limit that special casing to kernels that really rquire it > (HVO). I will add compound_info_has_mask() check. -- Kiryl Shutsemau / Kirill A. Shutemov