linux-kernel - Re: [PATCH] arch : arm : add a criteria for pfn

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Date:   Fri, 16 Aug 2019 20:34:42 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Doug Berger <opendmb@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch : arm : add a criteria for pfn_valid

On Sat, Aug 17, 2019 at 11:00:13AM +0800, Zhaoyang Huang wrote:
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>  int pfn_valid(unsigned long pfn)
>  {
> -	return memblock_is_map_memory(__pfn_to_phys(pfn));
> +	return (pfn > max_pfn) ?
> +		false : memblock_is_map_memory(__pfn_to_phys(pfn));
>  }

This is a really awkward way to use the ternary operator.  It's easier to
read if you just:

+	if (pfn > max_pfn)
+		return 0;
 	return memblock_is_map_memory(__pfn_to_phys(pfn));

(if you really wanted to be clever ... er, obscure, you'd've written:

	return (pfn <= max_pfn) && memblock_is_map_memory(__pfn_to_phys(pfn));

... but don't do that)

Also, why is this diverged between arm and arm64?