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Tue, 17 Mar 2026 07:28:38 -0400 (EDT) Date: Tue, 17 Mar 2026 11:28:34 +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: [PATCHv7 09/18] mm/hugetlb: Defer vmemmap population for bootmem hugepages Message-ID: References: <20260227194302.274384-1-kas@kernel.org> <20260227194302.274384-10-kas@kernel.org> <4e52f70d-e0c3-471f-8073-68c0e9bc94ca@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4e52f70d-e0c3-471f-8073-68c0e9bc94ca@kernel.org> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AF2721C0003 X-Stat-Signature: w9drryst8phzp7jikpnignt3pwaern5q X-Rspam-User: X-HE-Tag: 1773746923-280448 X-HE-Meta: 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 v1ubNk51 gMb7umiZV6P7CSMA6LWHHWYaT04MyBK0HXMVhZXmZJuTws56plIKsRrJpzf54jipXWN2at65Ot/EaHyvb7/Bm+MohInKlcVHwG0IZJKxhQ7AynflUROESIxEfWSLKbRNavq6idE4kUs1pPSeTKtCnFYLdbybuit/r51UFoaJWHnEsPAOrNUdrYxud7jGDa/N/NiG2PVznTJ0Xp/bhEhyxQnYGdcS1lpA4j7Iu0TyRw3IgVrk2Vxt3vk6LvEphFytNAxDRWeoONP0HhEACtxJUJQY1iyBzgR1HNZnY10/N1AUAzBk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 16, 2026 at 05:48:24PM +0100, David Hildenbrand (Arm) wrote: > On 2/27/26 20:42, Kiryl Shutsemau (Meta) wrote: > > Currently, the vmemmap for bootmem-allocated gigantic pages is populated > > early in hugetlb_vmemmap_init_early(). However, the zone information is > > only available after zones are initialized. If it is later discovered > > that a page spans multiple zones, the HVO mapping must be undone and > > replaced with a normal mapping using vmemmap_undo_hvo(). > > > > Defer the actual vmemmap population to hugetlb_vmemmap_init_late(). At > > this stage, zones are already initialized, so it can be checked if the > > page is valid for HVO before deciding how to populate the vmemmap. > > > > This allows us to remove vmemmap_undo_hvo() and the complex logic > > required to rollback HVO mappings. > > > > In hugetlb_vmemmap_init_late(), if HVO population fails or if the zones > > are invalid, fall back to a normal vmemmap population. > > > > Postponing population until hugetlb_vmemmap_init_late() also makes zone > > information available from within vmemmap_populate_hvo(). > > So we'll keep marking the sections as SECTION_IS_VMEMMAP_PREINIT such > that sparse_init_nid() will still properly skip it and leave population > to hugetlb_vmemmap_init_late(). > > Should we clear SECTION_IS_VMEMMAP_PREINIT in case we run into the > hugetlb_bootmem_page_zones_valid() scenario? > > I suspect we don't care about SECTION_IS_VMEMMAP_PREINIT after boot and > can just leave the flag set. (maybe we wan to add a comment in the code? > above the vmemmap_populate() ?) I think keeping the flag is right thing to do. SECTION_IS_VMEMMAP_PREINIT indicates to core-sparse that the section should not be populated and it will be initialized elsewhere. Even in !hugetlb_bootmem_page_zones_valid() we take care of it in hugetlb_vmemmap_init_late(). And, as you mentioned, nobody looks at the flag after boot. > Nothing else jumped at me > > Acked-by: David Hildenbrand (Arm) > > -- > Cheers, > > David -- Kiryl Shutsemau / Kirill A. Shutemov