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

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Date:	Wed, 06 Feb 2013 10:20:57 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 02/05/2013 07:26 AM, Andrew Morton wrote:
> 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?

Hi Andrew,

I think I made another mistake here. I meant to use min(4, strlen(p)) in 
case p is
something like 'aaa' whose length is less then 4. But I mistook it with 
max().

But after I dig into strcmp() in the kernel, I think it is OK to use 
strcmp().
min() or max() is not needed.

Thanks. :)

>
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