Re: [PATCH] Revert arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER

From: Catalin Marinas <catalin.marinas@arm.com>
To: "Justin M. Forbes" <jforbes@fedoraproject.org>
Cc: Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, jmforbes@linuxtx.org,
	Mike Rapoport <rppt@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] Revert arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER
Date: Fri, 28 Apr 2023 18:01:30 +0100	[thread overview]
Message-ID: <ZEv76qfIiJcUvdql@arm.com> (raw)
In-Reply-To: <20230428153646.823736-1-jforbes@fedoraproject.org>

+ Mike and Andrew

On Fri, Apr 28, 2023 at 10:36:45AM -0500, Justin M. Forbes wrote:
> While the ARCH_FORCE_MAX_ORDER changes clarified the descriptions quite
> a bit, the aarch64 specific change moved this config to sit behind
> CONFIG_EXPERT. This becomes problematic when distros are setting this to
> a non default value already. Pushing it behind EXPERT where it was not
> before will silently change the configuration for users building with
> oldconfig.  If distros patch out if EXPERT downstream, it still creates
> problems for users testing out upstream patches, or trying to bisect to
> find the root of problem, as the configuration will change unexpectedly,
> possibly leading to different behavior and false results.
> 
> Whem I asked about reverting the EXPERT, dependency, I was asked to add
> the ranges back.
> 
> This essentially reverts commit 34affcd7577a232803f729d1870ba475f294e4ea
> 
> Signed-off-by: Justin M. Forbes <jforbes@fedoraproject.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> ---
>  arch/arm64/Kconfig | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b1201d25a8a4..dae18ac01e94 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1516,9 +1516,11 @@ config XEN
>  # 16K |       27          |      14      |       13        |         11         |
>  # 64K |       29          |      16      |       13        |         13         |
>  config ARCH_FORCE_MAX_ORDER
> -	int "Order of maximal physically contiguous allocations" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES)
> +	int "Order of maximal physically contiguous allocations" if ARM64_4K_PAGES || ARM64_16K_PAGES
>  	default "13" if ARM64_64K_PAGES
> +	range 11 13 if ARM64_16K_PAGES
>  	default "11" if ARM64_16K_PAGES
> +	range 10 15 if ARM64_4K_PAGES
>  	default "10"
>  	help
>  	  The kernel page allocator limits the size of maximal physically

The revert looks fine to me:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

For the record, the original discussion:

Link: https://lore.kernel.org/r/CAFxkdAr5C7ggZ+WdvDbsfmwuXujT_z_x3qcUnhnCn-WrAurvgA@mail.gmail.com

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