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Rozycki" Cc: "Matthew Wilcox" , "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" , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , "Konstantin Kharlamov" , "Shuang Zhai" , "Sofia Trinh" , "Vaibhav Jain" Subject: Re: [PATCH v14 08/14] mm: multi-gen LRU: support page table walks Content-Type: text/plain ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666596792; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=MLgwl6qVQ1d5bswGgDHxIEJUCPcVEho8D9vRKEmhmk8=; b=sivCFzvhyw/HHVWkZ/2pkQ1WRphGagIKYPtKIXt59pAw8cCw6k7q5AeBlm/5T4FkY6uR8b O5XznolkyBja2QXEzQJalnYN32XU/FNQ7nRoGTf1gGkpD74W2Jfy1fRloi7A8qrCvsASlv 5RxjqG/DXsYDa8dMu/Z8YPZLn0xGGgA= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=arndb.de header.s=fm2 header.b=GHgwqBJ1; dkim=pass header.d=messagingengine.com header.s=fm3 header.b=aESBKGu4; spf=pass (imf26.hostedemail.com: domain of arnd@arndb.de designates 66.111.4.26 as permitted sender) smtp.mailfrom=arnd@arndb.de; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666596792; a=rsa-sha256; cv=none; b=bTUB4iArRb5MD6k1PKs1UpWHlY1/SujcW4gslIr8QgG2xTAEeNKciPhM/u0pa0/08U5wdQ HDt2DhM5lwE6G4nhPQAljYicyBr1Xr5Y/GPaERXeUJOiTsiz/NjR4+nNRv9AbES5l0DOdI 3a40YduFyWAs/NkczV0Sxx+9QnosGIU= X-Stat-Signature: ytcmspfhwumi3pk19js6q883m1yogega X-Rspam-User: Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=arndb.de header.s=fm2 header.b=GHgwqBJ1; dkim=pass header.d=messagingengine.com header.s=fm3 header.b=aESBKGu4; spf=pass (imf26.hostedemail.com: domain of arnd@arndb.de designates 66.111.4.26 as permitted sender) smtp.mailfrom=arnd@arndb.de; dmarc=none X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9658614000A X-HE-Tag: 1666596792-690912 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 Sun, Oct 23, 2022, at 20:35, Linus Torvalds wrote: > > Honestly, I wouldn't mind upgrading the minimum requirements to at > least M586TSC - leaving some of those early "fake Pentium" clones > behind too. Because 'rdtsc' is probably an even worse issue than > CMPXCHG8B. Kconfig treats X86_CMPXCHG64 as a strict subset of X86_TSC (except when enabling X86_PAE, which relies on cx8), so requiring both sounds like a good idea. >From the Kconfig history, I see you initially only enabled cx8 unconditionally for a couple of CPUs in 982d007a6eec ("x86: Optimize cmpxchg64() at build-time some more"), and Matthew Whitehead extended that list in f960cfd12650 ("x86/Kconfig: Add missing i586-class CPUs to the X86_CMPXCHG64 Kconfig group"). There are still a handful of CPUs that according to [1] claim cx8 support that we leave disabled, specifically the Kconfig symbols for MWINCHIP3D, MCRUSOE, MEFFICEON, MCYRIXIII, MVIAC3_2 and MVIAC7 should have both tsc and cx8, while the older MWINCHIPC6 and a small subset of M586 (Cyrix 6x86mx, C-II and AMD K5) apparently have cx8 but not tsc. Would you drop support for the 686-class chips that currently don't use cmpxchg8b, or just remove CONFIG_X86_CMPXCHG64 and assume they work after all? Arnd [1] https://reactos.org/wiki/Supported_Hardware/CPU