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[142.114.225.85]) by smtp.gmail.com with ESMTPSA id gb12-20020a05622a598c00b0039a55f78792sm284511qtb.89.2022.10.24.11.20.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Oct 2022 11:20:58 -0700 (PDT) Message-ID: <11616e14-f8a6-e0fe-3e11-9b884fe4ce33@gmail.com> Date: Mon, 24 Oct 2022 15:20:55 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH v14 08/14] mm: multi-gen LRU: support page table walks Content-Language: en-US To: Linus Torvalds , Peter Zijlstra , the arch/x86 maintainers Cc: 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 , =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain References: <20220815071332.627393-1-yuzhao@google.com> <20220815071332.627393-9-yuzhao@google.com> From: Gareth Poole In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As someone who still regularly uses hardware from this era, and often runs Linux on it, this would definitely be a blow to which machines I can actively use. Linux support is a big part of how I use these machines, since DOS and Windows 95 really can’t keep up with modern networking standards. I would be very disappointed, and impacted, if Linux dropped 486 support. On 10/20/22 23:10, Linus Torvalds wrote: > On Thu, Oct 20, 2022 at 11:55 AM Peter Zijlstra wrote: >> On Thu, Oct 20, 2022 at 10:35:28AM -0700, Linus Torvalds wrote: >>> That said, I reacted to that cmpxchg loop: >>> >>> } while (cmpxchg64(&pmdp->pmd, old.pmd, 0ULL) != old.pmd); >>> >>> is this series just so old (but rebased) that it doesn't use "try_cmpxchg64()"? >> Yep -- it's *that* old :-/ You're not in fact the first to point that >> out. >> >> I'll make time tomorrow to fix it up and respin and send out. This is as >> good a time as any to get rid of carrying these patches myself. > Hmm. Thinking some more about it, even if you do it as a > try_cmpxchg64() loop, it ends up being duplicated twice. > > 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. > > Linus >