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

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Message-ID: <616578ec-8a61-ce0a-a467-50915b3a9967@redhat.com>
Date:   Fri, 5 Feb 2021 09:20:42 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        akpm@...ux-foundation.org
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] arm64/hugetlb: Enable HUGETLB_PAGE_SIZE_VARIABLE

On 04.02.21 08:01, 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.

Just so I understand correctly, this does not imply that we have THP 
that exceed the pageblock size / MAX_ORDER size, correct?


> 
> 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 175914f2f340..c4acf8230f20 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1918,6 +1918,10 @@ config ARCH_ENABLE_THP_MIGRATION
>   	def_bool y
>   	depends on TRANSPARENT_HUGEPAGE
>   
> +config HUGETLB_PAGE_SIZE_VARIABLE
> +	def_bool y
> +	depends on HUGETLB_PAGE
> +
>   menu "Power management options"
>   
>   source "kernel/power/Kconfig"
> 


-- 
Thanks,

David / dhildenb