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Tue, 24 Feb 2026 11:03:16 -0800 (PST) Date: Tue, 24 Feb 2026 14:03:12 -0500 From: Johannes Weiner To: Usama Arif Cc: David Hildenbrand , "willy@infradead.org" , Lorenzo Stoakes , Zi Yan , Andrew Morton , lsf-pc@lists.linux-foundation.org, "linux-mm@kvack.org" , "riel@surriel.com" , Shakeel Butt , Kiryl Shutsemau , Barry Song , Dev Jain , Baolin Wang , Nico Pache , "Liam R . Howlett" , Ryan Roberts , Vlastimil Babka , Lance Yang , Frank van der Linden Subject: Re: [LSF/MM/BPF TOPIC] Beyond 2MB: Why Terabyte-Scale Machines Need 1GB Transparent Huge Pages Message-ID: References: <540c5c13-9cfb-44ea-b18f-8e4abff30a01@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <540c5c13-9cfb-44ea-b18f-8e4abff30a01@linux.dev> X-Rspamd-Server: rspam09 X-Stat-Signature: 89bp4ym14gmyqy4wjte7ryd5xip9acxj X-Rspamd-Queue-Id: 2489B40003 X-Rspam-User: X-HE-Tag: 1771959797-755729 X-HE-Meta: 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 Il4zJ+Jh XUvXINKgzB+54Rbl7SfiIvQ/ngAgZxZGS5eMoOskqDgUOLJp31FVQJOZS51/G6H5xcPFf3TVZxSXI21WQtcJ7Rj0zZnEhnyIVO+uHVbiVve5drpqjzhM+va3Ri7Dzx1nnfvTLeg0AXu1z/Grc5TJNS6U9zn3Lk/roY6M2KRGvMHWRjmAKgt9ZOyAhecd1vVviEKQZrolwvr4ALDpkdpayMF2ztk4zu+KCyqBG5W6j4NMBiqa+aBDDQUwO90dNZ0fUc3juTNd5y+Ehf6vwEWA3nHuCkSNoE02qdGVCXGAl+NFhgTi5jHL+EQdZAGYzZ9VLeHG4VPoSZGS454Tze9FTKtBSevJA1O9d3rgLtLnpSJL065zmOSF4wi4+9/BABJU6K4w8Y1R4VLP7ABI7l2ZaytQISZCUOkLuUQaj0IkUdhixp6SF5EVWcCjs3Me6syqi1YS2 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 19, 2026 at 03:53:35PM +0000, Usama Arif wrote: > Why 1G THP over hugetlbfs? > ========================== I know this isn't your intention, but one interesting aspect of supporting PUD mapped folios natively is that it could open the door to simplifying hugetlb as well. We currently have all kinds of huge_vma checks scattered over the page table code, and entirely parallel paths for unmapping etc. With native PUD mappings, this could allow pushing the special casing out of the virtual memory layer and into where we deal with the page objects. You might be able to take it as far as the only thing left of hugetlb is the reservation pool. Such that a naive application does mmap() as per usual, and it comes down to a separate allocation policy how the backing pages are served (buddy, CMA, boot-time reservations, ...) Approaching it this way could help separate out the discussion on code impact and tech debt of PUD mappings, from the allocation technique question, which in itself is a fairly large topic.