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b=Mmx0yAMPyaTi+W7LMOLMl9+7j+cgfxWgN+0e8+WOHglYQuD4eGL8x36KMvnKPf8pn wVn0efCAa7oEY8R0Id09hXCEmjRworf4hb93qMp5v/xMr+uwYeFP0hoPWqXx65PWUT 28MvJwArdGTlcRdzcbOVdEVX+vwzLSPskqz2CxbZWLn4w9Lf3/9wnOrQNGE78MhC1w 8HqKB40pzPWf8MIbg3kDKy+lOBM54cmDfPUaQ8Go8LlCRvyEMOBq2etcU5lk1GT0fs /+JtdnBN9kqfbEOA1t2Fw7892WsmzlseiC2e9U/NDToOC6pX9+JrG7YzEzJ2z+7e9/ GD/Agse4pYisw== Message-ID: <169a3438-40f9-40bc-86cf-a24535494115@kernel.org> Date: Tue, 17 Mar 2026 13:47:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv7 09/18] mm/hugetlb: Defer vmemmap population for bootmem hugepages To: Kiryl Shutsemau 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 References: <20260227194302.274384-1-kas@kernel.org> <20260227194302.274384-10-kas@kernel.org> <4e52f70d-e0c3-471f-8073-68c0e9bc94ca@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 42B8BA0009 X-Stat-Signature: 3m1hq6kzcen6simdw3hsacqnkq5cbxrq X-Rspam-User: X-HE-Tag: 1773751652-766951 X-HE-Meta: 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 82egqPzk CBQy64ZWpIzT1NbFODuCXaEFRm9I+wgrlCmSFJhylz3D8OEaNhatY9abhtl4eYitlaKCwy4UR/eOJkC3lmwl5Dxe03t+Fk2QeWkZxjSpnPiFNBQdEng0mfRiIPt4RU80pIrtjbbUOSqBAvI97N+hbgwK7iZ9RV19SWLRi8p6kF1pYyb2DRnO0O8l4tHIn1uo0cu2bFCQ5AERlZReW/k0P/uQYRUoiSm3aw3wsQgEd0J/ETa6D24Z56WXfAoTTfI+lIXJ+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/17/26 12:28, Kiryl Shutsemau wrote: > 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(). Makes sense. -- Cheers, David