linux-kernel - Re: [PATCH v2 14/28] powerpc: introduce arch_zone_limits

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Message-ID: <87ldia9he1.ritesh.list@gmail.com>
Date: Wed, 07 Jan 2026 09:57:34 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Mike Rapoport <rppt@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>
Cc: Alex Shi <alexs@...nel.org>, Alexander Gordeev <agordeev@...ux.ibm.com>, 
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Subject: Re: [PATCH v2 14/28] powerpc: introduce arch_zone_limits_init()

Mike Rapoport <rppt@...nel.org> writes:

> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
>
> Move calculations of zone limits to a dedicated arch_zone_limits_init()
> function.
>
> Later MM core will use this function as an architecture specific callback
> during nodes and zones initialization and thus there won't be a need to
> call free_area_init() from every architecture.
>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  arch/powerpc/mm/mem.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 3ddbfdbfa941..32c496bfab4f 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -221,13 +221,23 @@ static int __init mark_nonram_nosave(void)
>   * anyway) will take a first dip into ZONE_NORMAL and get otherwise served by
>   * ZONE_DMA.
>   */
> -static unsigned long max_zone_pfns[MAX_NR_ZONES];
> +void __init arch_zone_limits_init(unsigned long *max_zone_pfns)
> +{
> +#ifdef CONFIG_ZONE_DMA
> +	max_zone_pfns[ZONE_DMA]	= min(zone_dma_limit, max_low_pfn - 1) + 1;

Hi Mike, 

This doesn't look correct. Isn't the zone_dma_limit value in bytes actually?
Shouldn't it be -

     max_zone_pfns[ZONE_DMA] = min((zone_dma_limit >> PAGE_SHIFT) + 1, max_low_pfn);


-ritesh


> +#endif
> +	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
> +#ifdef CONFIG_HIGHMEM
> +	max_zone_pfns[ZONE_HIGHMEM] = max_pfn;
> +#endif
> +}
>  
>  /*
>   * paging_init() sets up the page tables - in fact we've already done this.
>   */
>  void __init paging_init(void)
>  {
> +	unsigned long max_zone_pfns[MAX_NR_ZONES];
>  	unsigned long long total_ram = memblock_phys_mem_size();
>  	phys_addr_t top_of_ram = memblock_end_of_DRAM();
>  	int zone_dma_bits;
> @@ -259,15 +269,7 @@ void __init paging_init(void)
>  
>  	zone_dma_limit = DMA_BIT_MASK(zone_dma_bits);
>  
> -#ifdef CONFIG_ZONE_DMA
> -	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
> -				      1UL << (zone_dma_bits - PAGE_SHIFT));
> -#endif
> -	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
> -#ifdef CONFIG_HIGHMEM
> -	max_zone_pfns[ZONE_HIGHMEM] = max_pfn;
> -#endif
> -
> +	arch_zone_limits_init(max_zone_pfns);
>  	free_area_init(max_zone_pfns);
>  
>  	mark_nonram_nosave();
> -- 
> 2.51.0