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

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Message-ID: <aV4zZ8D5eaLC6K-w@kernel.org>
Date: Wed, 7 Jan 2026 12:20:23 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Ritesh Harjani <ritesh.list@...il.com>
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Subject: Re: [PATCH v2 14/28] powerpc: introduce arch_zone_limits_init()

Hi,

On Wed, Jan 07, 2026 at 09:57:34AM +0530, Ritesh Harjani wrote:
> 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);

You are right, I'll update it for v3. 
 
> -ritesh

-- 
Sincerely yours,
Mike.