linux-kernel - Re: [PATCH 2/3] arm64/hugetlb: Enable HUGETLB_PAGE_SIZE

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Message-ID: <20210211080148.GB14448@lst.de>
Date:   Thu, 11 Feb 2021 09:01:48 +0100
From:   Christoph Hellwig <hch@....de>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, akpm@...ux-foundation.org,
        will@...nel.org, Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>,
        David Hildenbrand <david@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64/hugetlb: Enable HUGETLB_PAGE_SIZE_VARIABLE

On Thu, Feb 11, 2021 at 11:52:10AM +0530, Anshuman Khandual wrote:
> MAX_ORDER which invariably depends on FORCE_MAX_ZONEORDER can be a variable
> for a given page size, depending on whether TRANSPARENT_HUGEPAGE is enabled
> or not. In certain page size and THP combinations HUGETLB_PAGE_ORDER can be
> greater than MAX_ORDER, making it unusable as pageblock_order.
> 
> This enables HUGETLB_PAGE_SIZE_VARIABLE making pageblock_order a variable
> rather than the compile time constant HUGETLB_PAGE_ORDER which could break
> MAX_ORDER rule for certain configurations.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/Kconfig | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index f39568b28ec1..8e3a5578f663 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1909,6 +1909,10 @@ config ARCH_ENABLE_THP_MIGRATION
>  	def_bool y
>  	depends on TRANSPARENT_HUGEPAGE
>  
> +config HUGETLB_PAGE_SIZE_VARIABLE

Please move the definition of HUGETLB_PAGE_SIZE_VARIABLE to
mm/Kconfig and select it from the arch Kconfigfs instead of duplicating
the definition.