linux-kernel - Re: [PATCH 10/10] mm, treewide: Redefine MAX

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Date:   Thu, 16 Mar 2023 11:15:47 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] mm, treewide: Redefine MAX_ORDER sanely

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