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Fri, 21 Oct 2022 03:38:24 +0000 Date: Fri, 21 Oct 2022 04:38:24 +0100 From: Matthew Wilcox To: Linus Torvalds Cc: Peter Zijlstra , the arch/x86 maintainers , Yu Zhao , Andrew Morton , Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Johannes Weiner , Jonathan Corbet , Mel Gorman , Michael Larabel , Michal Hocko , Mike Rapoport , Tejun Heo , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , Holger =?iso-8859-1?Q?Hoffst=E4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Subject: Re: [PATCH v14 08/14] mm: multi-gen LRU: support page table walks Message-ID: References: <20220815071332.627393-1-yuzhao@google.com> <20220815071332.627393-9-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; 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b=zLiCYOEdHA8qdNF/6oxuvnmxitp0O4KoJjLreGusFKRpragZ5oyWuLs2olWv7AvI0i+SGg vGFcyz/+RNNTLMmCEyBVmu3iHmranaN92NiZoR8yFZHKw4fzLz/BRmz0qAD3W/qRWwl6i2 g2tX89wXkmjhd6qtZelX288zyuk+SGs= X-Rspamd-Server: rspam12 X-Rspam-User: Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=jPWpIVKY; spf=none (imf28.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Stat-Signature: 9bfprmnrqtfq5qty4jsxy4nthc5oq5mw X-Rspamd-Queue-Id: 7AB36C0038 X-HE-Tag: 1666323539-699164 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: On Thu, Oct 20, 2022 at 07:10:46PM -0700, Linus Torvalds wrote: > Maybe we should just bite the bullet, and say that we only support > x86-32 with 'cmpxchg8b' (ie Pentium and later). > > Get rid of all the "emulate 64-bit atomics with cli/sti, knowing that > nobody has SMP on those CPU's anyway", and implement a generic x86-32 > xchg() setup using that try_cmpxchg64 loop. > > I think most (all?) distros already enable X86_PAE anyway, which makes > that X86_CMPXCHG64 be part of the base requirement. > > Not that I'm convinced most distros even do 32-bit development anyway > these days. > > (Of course, if we require X86_CMPXCHG64, we'll also hit some of the > odd clone CPU's that actually *do* support the instruction, but do not > report it in cpuid due to an odd old Windows NT bug. IOW, things like > the Cyrix and Transmeta CPU's did support the instruction, but had the > CX8 bit clear because otherwise NT wouldn't boot. We may or may not > get those cases right, but I doubt anybody really has any of those old > CPUs). > > We got rid of i386 support back in 2012. Maybe it's time to get rid of > i486 support in 2022? Arnd suggested removing i486 last year and got a bit of pushback. The most convincing to my mind was Maciej: https://lore.kernel.org/lkml/alpine.DEB.2.21.2110231853170.38243@angie.orcam.me.uk/ but you can see a few other responses indicating that people have shipped new 486-class hardware within the last few years (!)