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Fri, 21 Oct 2022 10:12:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A5EDF300155; Fri, 21 Oct 2022 12:12:27 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8DB9E209A1C9E; Fri, 21 Oct 2022 12:12:27 +0200 (CEST) Date: Fri, 21 Oct 2022 12:12:27 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: the arch/x86 maintainers , Yu Zhao , Andrew Morton , Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , 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; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666347175; a=rsa-sha256; cv=none; b=e7Bwf91fncqMo13VpBS648Q9WP/mXAu4MedOHS/L14h3MRFE/3Can3j6V2TqMR57RRwqZB 7ulGUDVtG/B4aXPjb996iOpj+Ab3tDRTOo5rLRchNBahgq3wRRRDLMuQR45JN6HF0xmsYZ nFPV7D5ir0nwyS0/hT5YukLNHoRjEno= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=u2LjmYm+; dmarc=none; spf=none (imf22.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666347175; 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=ooz5VtSjs4RZMmj3qfhcsaEMXb528lP3FjIYWM1xcMc=; b=3QlNRkREzgr5Kyv3jRdJd1svyG9eO9kqI8uGjLsNi7WmvLMTpk8wSbvCTdbTBtg7ZrSKfH o+pB78Gaiv9deYO2rVe1accMeJcURmGQqpJBgoWCCxuWor5wjzCAPXGmY4CFeEhxHg0gK6 FXV0m1B8AX/ZtHbdNkSRVoQvEDT8H6s= X-Rspamd-Queue-Id: B45E1C0032 Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=u2LjmYm+; dmarc=none; spf=none (imf22.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org X-Rspam-User: X-Rspamd-Server: rspam08 X-Stat-Signature: mamo8hwfzdha7qakgi1r4mxbmkrfbk1b X-HE-Tag: 1666347174-215604 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? > > That way we could finally get rid of CONFIG_MATH_EMULATION too. Would love that; but as pointed out, there's still a few stragglers out there. OTOH, they *could* use one of the LTS kernels.