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Mon, 23 Feb 2026 10:45:50 -0500 (EST) Date: Mon, 23 Feb 2026 15:45:49 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Dave Hansen , Kalesh Singh , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Wilcox , Johannes Weiner , Usama Arif Subject: Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86 Message-ID: References: <17c5708d-3859-49a5-814e-bc3564bc3ac6@kernel.org> <32ed82dd-62c3-4a5c-8bae-9465afd7e75f@kernel.org> <06684dc4-3902-4452-824a-ee2064314d24@kernel.org> <7b414e68-4d0b-4d2b-a664-bbbdf314c0d3@intel.com> <89cc554e-9c6a-4c8d-8c30-573b2eabccac@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <89cc554e-9c6a-4c8d-8c30-573b2eabccac@kernel.org> X-Rspamd-Queue-Id: 8084040008 X-Stat-Signature: 8xgynb6annseoaxfag7chhwb1xq6umt3 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1771861554-83623 X-HE-Meta: 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 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 Mon, Feb 23, 2026 at 04:31:56PM +0100, David Hildenbrand (Arm) wrote: > On 2/23/26 16:14, Dave Hansen wrote: > > On 2/23/26 03:27, David Hildenbrand (Arm) wrote: > > ... > > > > BTW, x86-64 SysV ABI allows for 64k page size: > > > > > > > >     Systems are permitted to use any power-of-two page size between > > > >     4KB and 64KB, inclusive. > > > > > > > > But it doesn't work in practice. > > > > > > Even in well controlled environments you would run in a hyperscaler? > > > > I think what Kirill is trying to say is that "it breaks userspace". ;) > > Yes. Probably similar to Intel proposing an actual 64k page size. Expected. > :) > > > > > A hyperscaler (or other "embedded" environment) might be willing or able > > to go fix up userspace breakage. I would suspect our high frequency > > trading friends would be all over this if it shaved a microsecond off > > their receive times. > > > > The more important question is what it breaks and how badly it breaks > > things. 5-level paging, for instance, broke some JITs that historically > > used the new (>48) upper virtual address bits for metadata. The gains > > from 5-level paging were big enough and the userspace breakage was > > confined and fixable enough that 5-level paging was viable. > > > > I'm not sure which side a larger base page side will fall on, though. Is > > it going to be an out-of-tree hack that a few folks use, or will it be > > more like 5-level paging and be good enough that it goes into mainline? > > Just thinking about VMAs spanning partial pages makes me shiver. Or A > single page spanning multiple VMAs. Hate to break it to you, but we have it now upstream :P THP can span multiple VMAs. And can be partially mapped. The only new thing is that we allow this for order-0 page now. And you cannot realistically recover wasted memory -- no deferred split. > I haven't seen the code yet, but I am certain that I will not like it. > > I'm happy to be proven wrong :) I will do my best, but no promises :) -- Kiryl Shutsemau / Kirill A. Shutemov