linux-kernel - RE: [PATCH] ARC: Use max_high

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Date:   Mon, 26 Apr 2021 11:55:00 +0000
From:   Vladimir Isaev <Vladimir.Isaev@...opsys.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
CC:     "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

Hi Mike,

On Mon, April 26, 2021 2:29 PM, Mike Rapoport wrote:
> On Mon, Apr 26, 2021 at 01:10:04PM +0300, Vladimir Isaev wrote:
> > -	max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> > +	max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
> 
> This is correct with PAE40, but it will break !PAE40 when "highmem" has lower
> addresses than lowmem.
> 
> It rather should be something like:
> 
>         if (IS_ENABLED(CONFIG_ARC_HAS_PAE40))
>                 max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>         else
>             	max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> 

Not sure if I understand why we should have min_low_pfn here. In !PAE40 case max_high_pfn just will be smaller than min_low_pfn.

Thank you,
Vladimir Isaev