linux-kernel - Re: [PATCH 3/3] acpi, memory-hotplug: Support getting hotplug info from SRAT.

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Date:	Mon, 4 Feb 2013 15:26:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	jiang.liu@...wei.com, wujianguo@...wei.com, hpa@...or.com,
	wency@...fujitsu.com, laijs@...fujitsu.com, linfeng@...fujitsu.com,
	yinghai@...nel.org, isimatu.yasuaki@...fujitsu.com,
	rob@...dley.net, kosaki.motohiro@...fujitsu.com,
	minchan.kim@...il.com, mgorman@...e.de, rientjes@...gle.com,
	guz.fnst@...fujitsu.com, rusty@...tcorp.com.au, lliubbo@...il.com,
	jaegeuk.hanse@...il.com, tony.luck@...el.com,
	glommer@...allels.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 3/3] acpi, memory-hotplug: Support getting hotplug info
 from SRAT.

On Fri, 25 Jan 2013 17:42:09 +0800
Tang Chen <tangchen@...fujitsu.com> wrote:

> We now provide an option for users who don't want to specify physical
> memory address in kernel commandline.
> 
>         /*
>          * For movablemem_map=acpi:
>          *
>          * SRAT:                |_____| |_____| |_________| |_________| ......
>          * node id:                0       1         1           2
>          * hotpluggable:           n       y         y           n
>          * movablemem_map:              |_____| |_________|
>          *
>          * Using movablemem_map, we can prevent memblock from allocating memory
>          * on ZONE_MOVABLE at boot time.
>          */
> 
> So user just specify movablemem_map=acpi, and the kernel will use hotpluggable
> info in SRAT to determine which memory ranges should be set as ZONE_MOVABLE.
> 
> ...
>  
> +	if (!strncmp(p, "acpi", max(4, strlen(p))))
> +		movablemem_map.acpi = true;

Generates a warning:

mm/page_alloc.c: In function 'cmdline_parse_movablemem_map':
mm/page_alloc.c:5312: warning: comparison of distinct pointer types lacks a cast

due to max(int, size_t).

This is easily fixed, but the code looks rather pointless.  If the
incoming string is supposed to be exactly "acpi" then use strcmp().  If
the incoming string must start with "acpi" then use strncmp(p, "acpi", 4).

IOW, the max is unneeded?

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