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Message-ID: <Y1IUMDJFScAMrCS5@casper.infradead.org>
Date: Fri, 21 Oct 2022 04:38:24 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
the arch/x86 maintainers <x86@...nel.org>,
Yu Zhao <yuzhao@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <ak@...ux.intel.com>,
Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
Catalin Marinas <catalin.marinas@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
Johannes Weiner <hannes@...xchg.org>,
Jonathan Corbet <corbet@....net>, Mel Gorman <mgorman@...e.de>,
Michael Larabel <Michael@...haellarabel.com>,
Michal Hocko <mhocko@...nel.org>,
Mike Rapoport <rppt@...nel.org>, Tejun Heo <tj@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
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Oleksandr Natalenko <oleksandr@...alenko.name>,
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Suleiman Souhlal <suleiman@...gle.com>,
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Holger Hoffstätte
<holger@...lied-asynchrony.com>,
Konstantin Kharlamov <Hi-Angel@...dex.ru>,
Shuang Zhai <szhai2@...rochester.edu>,
Sofia Trinh <sofia.trinh@....works>,
Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v14 08/14] mm: multi-gen LRU: support page table walks
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 (!)
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