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

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Date:   Mon, 26 Apr 2021 19:15:55 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Vladimir Isaev <Vladimir.Isaev@...opsys.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

On Mon, Apr 26, 2021 at 11:55:00AM +0000, Vladimir Isaev wrote:
> 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.

Hmm, actually, you are right. This should be fine.

-- 
Sincerely yours,
Mike.