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

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Message-ID: <5113483C.8070509@cn.fujitsu.com>
Date:	Thu, 07 Feb 2013 14:22:52 +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 02/07/2013 05:54 AM, Andrew Morton wrote:
> On Wed, 06 Feb 2013 10:20:57 +0800
> Tang Chen<tangchen@...fujitsu.com>  wrote:
>
>>>>
>>>> +	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.
>
> OK, I did that.
>
> But the code still looks a bit more complex than we need.  Could we do
>
> static int __init cmdline_parse_movablemem_map(char *p)
> {
> 	char *oldp;
> 	u64 start_at, mem_size;
>
> 	if (!p)
> 		goto err;
>
> 	/*
> 	 * If user decide to use info from BIOS, all the other user specified
> 	 * ranges will be ingored.
> 	 */
> 	if (!strcmp(p, "acpi")) {
> 		movablemem_map.acpi = true;
> 		if (movablemem_map.nr_map) {
> 			memset(movablemem_map.map, 0,
> 				sizeof(struct movablemem_entry)
> 				* movablemem_map.nr_map);
> 			movablemem_map.nr_map = 0;
> 		}
> 		return 0;
> 	}
>
>
No, I don't think so.

If user specified like this:

1) movablemem_map=aaa@bbb ---------- will be added into array
2) movablemem_map=acpi    ---------- will empty the array
3) movablemem_map=ccc@ddd ---------- will be added into array again (wrong!)

So, we need to code like this:

+	if (!strncmp(p, "acpi", max(4, strlen(p))))
+		movablemem_map.acpi = true;

In this way, 3) movablemem_map=ccc@ddd will not go into this if segment.

+
+	/*
+	 * If user decide to use info from BIOS, all the other user specified
+	 * ranges will be ingored.
+	 */
+	if (movablemem_map.acpi) {
+		if (movablemem_map.nr_map) {
+			memset(movablemem_map.map, 0,
+				sizeof(struct movablemem_entry)
+				* movablemem_map.nr_map);
+			movablemem_map.nr_map = 0;
+		}
+		return 0;
+	}

But it will go into this if segment, and will not add the range into array.

Thanks. :)




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