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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 4 Jan 2022 13:24:17 -0800
Message-ID: <CAHk-=wgvOqj6LUhNp8V5ddT8eZyYdFDzMZE73KgPggOnc28VWg@mail.gmail.com>
Subject: Re: [PATCH v6 2/9] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG
To:     Yu Zhao <yuzhao@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andi Kleen <ak@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
        Jesse Barnes <jsbarnes@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Michael Larabel <Michael@michaellarabel.com>,
        Michal Hocko <mhocko@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will@kernel.org>,
        Ying Huang <ying.huang@intel.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, page-reclaim@google.com,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Konstantin Kharlamov <Hi-Angel@yandex.ru>
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On Tue, Jan 4, 2022 at 12:23 PM Yu Zhao <yuzhao@google.com> wrote:
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5c2ccb85f2ef..5a4843242f09 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -85,6 +85,7 @@ config X86
> +       select ARCH_HAS_NONLEAF_PMD_YOUNG       if X86_64

Why is this limited to 64-bit?

I'm ok with that - maybe it's a simple case of "this is not worth
doing on 32-bit", but I'd like the explanation to be written out.

Right now the commit message literally points the architecture manual
that sio relevant for both 32-bit and 64-bit - and then the patch
itself makes it 64-bit only.

              Linus