Re: [PATCH v3 03/14] arm64: reword ARCH_FORCE_MAX_ORDER prompt and help text

From: Kefeng Wang <wangkefeng.wang@huawei.com>
To: Mike Rapoport <rppt@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Rich Felker <dalias@libc.org>,
	linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Max Filippov <jcmvbkbc@gmail.com>, Guo Ren <guoren@kernel.org>,
	linux-csky@vger.kernel.org, sparclinux@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Russell King <linux@armlinux.org.uk>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Zi Yan <ziy@nvidia.com>,
	linux-xtensa@linux-xtensa.org, Arnd Bergmann <arnd@arndb.de>,
	linux-m68k@lists.linux-m68k.org,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Dinh Nguyen <dinguyen@kernel.org>,
	linuxppc-dev@lists.ozlabs.org,
	"David S. Miller" <davem@davemloft.net>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v3 03/14] arm64: reword ARCH_FORCE_MAX_ORDER prompt and help text
Date: Sat, 25 Mar 2023 14:35:38 +0800	[thread overview]
Message-ID: <e2333d87-6442-0ddc-ee3d-5fb917600577@huawei.com> (raw)
In-Reply-To: <20230325060828.2662773-4-rppt@kernel.org>


On 2023/3/25 14:08, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@kernel.org>
> 
> The prompt and help text of ARCH_FORCE_MAX_ORDER are not even close to
> describe this configuration option.
> 
> Update both to actually describe what this option does.
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>

Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

> ---
>   arch/arm64/Kconfig | 24 ++++++++++++------------
>   1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7324032af859..cc11cdcf5a00 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1487,24 +1487,24 @@ config XEN
>   # 16K |       27          |      14      |       13        |         11         |
>   # 64K |       29          |      16      |       13        |         13         |
>   config ARCH_FORCE_MAX_ORDER
> -	int "Maximum zone order" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES)
> +	int "Order of maximal physically contiguous allocations" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES)
>   	default "13" if ARM64_64K_PAGES
>   	default "11" if ARM64_16K_PAGES
>   	default "10"
>   	help
> -	  The kernel memory allocator divides physically contiguous memory
> -	  blocks into "zones", where each zone is a power of two number of
> -	  pages.  This option selects the largest power of two that the kernel
> -	  keeps in the memory allocator.  If you need to allocate very large
> -	  blocks of physically contiguous memory, then you may need to
> -	  increase this value.
> +	  The kernel page allocator limits the size of maximal physically
> +	  contiguous allocations. The limit is called MAX_ORDER and it
> +	  defines the maximal power of two of number of pages that can be
> +	  allocated as a single contiguous block. This option allows
> +	  overriding the default setting when ability to allocate very
> +	  large blocks of physically contiguous memory is required.
>   
> -	  We make sure that we can allocate up to a HugePage size for each configuration.
> -	  Hence we have :
> -		MAX_ORDER = PMD_SHIFT - PAGE_SHIFT  => PAGE_SHIFT - 3
> +	  The maximal size of allocation cannot exceed the size of the
> +	  section, so the value of MAX_ORDER should satisfy
>   
> -	  However for 4K, we choose a higher default value, 10 as opposed to 9, giving us
> -	  4M allocations matching the default size used by generic code.
> +	    MAX_ORDER + PAGE_SHIFT <= SECTION_SIZE_BITS
> +
> +	  Don't change if unsure.
>   
>   config UNMAP_KERNEL_AT_EL0
>   	bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT