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Tue, 10 Feb 2026 15:57:55 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id LAOiOINVi2liEwAAD6G6ig (envelope-from ); Tue, 10 Feb 2026 15:57:55 +0000 Message-ID: <6afd7334-82e8-4f87-8ed3-6448e89328c2@suse.cz> Date: Tue, 10 Feb 2026 16:57:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 08/17] mm: Make page_zonenum() use head page Content-Language: en-US To: Kiryl Shutsemau , "David Hildenbrand (Arm)" Cc: Andrew Morton , Muchun Song , Matthew Wilcox , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , 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 References: <20260202155634.650837-1-kas@kernel.org> <20260202155634.650837-9-kas@kernel.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam12 X-Stat-Signature: ftfeu5h4kx1ohsxiy91o7bg7wo54ficp X-Rspamd-Queue-Id: 16A89180013 X-Rspam-User: X-HE-Tag: 1770739077-302589 X-HE-Meta: U2FsdGVkX18BHIYyq3qSuy4FsTHmS8fb4AANfKi4W7xoKND7s4y68I77R99MHoDFk8vx3L2277oJEftz0QUqwBnb2xUqri4PvV3eeZnlXGBU32hBPiuB9yskCl1pm5IwNXu9ht2pz5kgJ0JZCK1+lkhkHWVk6yzkNjf7c5ERoy0AuqEAZVaCOl6B/mwS5AOOjVJr7uX72cw6LW5vTD/3/1EXUJbI2hYbcJZcVn/nft7hj54X2uqFLxdHDChpmnRSVt2MBaQMnKXwvzUvEo9KB2w9/qy/p5czm8/Mw73du3Y8xi+gxHUg93kmBUPXBZ3i78DIW5kqbmJ7Z1120XMt1KQte9IfXpgaUYyObwyDqxV+k7IHPAXFXszw6i89O5WAtTTwbzUz5sD5qO64vKixsHS8r4wBonfeYXVXXoBdjaDFG0d4j+koSYZwO7SQTTe/YE2c5wD5qMBAqXchoRJG7yOf5AFht4Ejn2nxjMPLHqMrtPMqqGYS+5ElPCBXerihj28s2DrRwSjMYOxgPqY64mV/XzenLgdBw+3v4JexfsQpWcw1upPqfBd+chVdtMsXDpoPVg+AdOJ7BjNPp+H4YrPiAuq8jh76miSdQGUa3hCjKZgoahCj5KBwluGrL9RjMygreYzgJ6cB4+aLi+5XP16GVWACu5E5EpWW2vmpRtTBQSWPXus+/2QZSpdKvNSzozb9If0kwt7VFA2B2fZoJnxNCRSUSq6KhvvyRfrO+KpRfwlsmZjJKkCwlzd2/OznJXz+hYHXi7hRvln1iclSZzhRZHwZhuZr1au1DcBz3wsAnyWwcoN/YjvoKCbMm7I79abwcejJd4W8RfwRnG0ahuNkwnENtiZtk5wB4iIdzbmYdyCuOli65h6tzp4jlM9HXOuhNE+k2pj1Tw1bmV5snlAyYM4OQx3ElfnCNCRh+wy7qBtrk/b+zYQ1aX0eJ6z9AGrWmTD1L6ZwwCk9qT0 mSCERaiO 3sYIIx5TRgVqygWDVbMNvQb7SyXNxZzuZTH4MA17s1bjH11wt2iDUcCHVO4YeVx3TVEl033p1/rCcidm2sk53Es+Hs03cf0pBNmFPFNRJMo6u1ESWyh2bsozQd59gXd5cKiQCUi6rHhO90p4du+hHCAnCZHJy0YJ6bVG3qW6+nBkbEVWO6r5M22yLkxBsqhBKPiGCC6kGN2GFkkpJft4+d3BJ6uq6e+3s3hh+Sj6NJiFmg9kZtFZPljsSBVEkan5igQJIDkDV7j8YU1q0VO2VESOoaLMuyaAvu0tKmKAh/Z0rND4Jb1W1+QAtF44YiwTFVffMRJq1B0MQzGkf3LTY0iwvYlyFZEhO5MSH6NySsU0jbGdz6jCY7zS7nUsR2yalI71W 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 2/9/26 12:52, Kiryl Shutsemau wrote: > 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. Not thrilled by this indeed. Would it be a problem to have the shared tail pages per node+zone instead of just per node?