Re: [PATCH 10/10] mm, treewide: Redefine MAX_ORDER sanely

[Mike Kravetz]

On 03/15/23 14:31, Kirill A. Shutemov wrote:
> MAX_ORDER currently defined as number of orders page allocator supports:
> user can ask buddy allocator for page order between 0 and MAX_ORDER-1.
> 
> This definition is counter-intuitive and lead to number of bugs all over
> the kernel.
> 
> Change the definition of MAX_ORDER to be inclusive: the range of orders
> user can ask from buddy allocator is 0..MAX_ORDER now.
> 
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -556,7 +556,7 @@ endmenu	 # "ARC Architecture Configuration"
>  
>  config ARCH_FORCE_MAX_ORDER
>  	int "Maximum zone order"
> -	default "12" if ARC_HUGEPAGE_16M
> -	default "11"
> +	default "11" if ARC_HUGEPAGE_16M
> +	default "10"

Is this Kconfig file wrong (off by 1) today?  It seems like it wants MAX_ORDER
to be sufficiently large to allocate 16M if ARC_HUGEPAGE_16M.  So, seems like
it should be 13 today?

-- 
Mike Kravetz