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Howlett" , Mike Rapoport , Johannes Weiner , Usama Arif Subject: Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Feedback-ID: :c73c7b77566af2c:ham:b89b32586f6d122 X-Infomaniak-Routing: alpha X-Rspamd-Queue-Id: C12F8C000D X-Stat-Signature: 5zgpy7isz98wd36e7dtqwrstnkmwnyu4 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1784502008-947738 X-HE-Meta: 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 3UQ78afp IexStI3VD7kgJBDAzU2JM0SWYDd6iPWQtB0BGf1Y1qBfSoAe1dZzN9qOD5zthKeUZfjgJSLcXNMzBL5bfoWdGbXuIMrb1++Bavf6NfkCmzp5CwzNOI0MM0YdFpDCT2WAK0JN7cVUJlMPDvthvp8DTpsnbRJpNZKARfCytKrR0WyBfFK1HeGZEfNmYLJbzkXxzlNrYCeKoZUxakws+EyCvOakU9SDSkCIUldF4510ufCQj+yHf9AAwv70eOGWW4gGAhTBPECSXDslI/xnOda0e7oFPiMlLQlEaA51D 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 03:08:51PM +0000, Kiryl Shutsemau wrote: >> On x86, page tables are allocated from the buddy allocator and if PG_SIZE >> is greater than 4 KB, we need a way to pack multiple page tables into a >> single page. We could use the slab allocator for this, but it would >> require relocating the page-table metadata out of struct page. Am Do, Feb 19, 2026 um 17:47:22 +0000, Matthew Wilcox schrieb: > Have you looked at the s390/ppc implementations (yes, they're different, > no, that sucks)? slab seems like the wrong approach to me. Yes, they both required fair amounts of debugging. I don't remember what went wrong in s390 early boot. ppc64 mm/slub.c item-within-page indices ended up notably overflowing 16-bit counters. PA-RISC had some issues surrounding a race with setup or teardown of I think accounting data structures for some IO bus among other things. SPARC had an interesting issue because its page order growth increment / Sprungweite was 3 where the PAGE_MMUSHIFT increment used in testing was 2. Something odd happened with SHMLBA on a bunch of architectures and I can't remember whether there were hardware factors involved or if it was just include and config messes leaking PAGE_SIZE. Am Do, Feb 19, 2026 um 17:47:22 +0000, Matthew Wilcox schrieb: > There's a third approach that I've never looked at which is to allocate > the larger size, then just use it for N consecutive entries. Strangely, I think the mechanical assistant did that for MIPS and few or no others. It was simpler in various ways, but I didn't like the space or locking overheads. Given the chance, I'll likely redo it bes. if I ever get to demo MIPS' 1 KiB PageGrain extension running high performance with a near-VAX minimum MMU/TLB mapping granularity. My energies are more likely to be directed elsewhere if anywhere at all from what you're telling me, though. -- nyc