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Date: Tue, 18 Sep 2012 09:11:27 +0900
From: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: qiuxishi <qiuxishi@gmail.com>, <mgorman@suse.de>, <tony.luck@intel.com>,
        Jiang Liu <jiang.liu@huawei.com>, <qiuxishi@huawei.com>,
        <bessel.wang@huawei.com>, <wujianguo@huawei.com>,
        <paul.gortmaker@windriver.com>, <kamezawa.hiroyu@jp.fujitsu.com>,
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        Minchan Kim <minchan@kernel.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Wen Congyang <wency@cn.fujitsu.com>
Subject: Re: [PATCH RESEND] memory hotplug: fix a double register section
 info bug
References: <5052A7DF.4050301@gmail.com> <50530E39.5020100@jp.fujitsu.com> <20120914131428.1f530681.akpm@linux-foundation.org>
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2012/09/15 5:14, Andrew Morton wrote:
> On Fri, 14 Sep 2012 20:00:09 +0900
> Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> wrote:
>
>>> @@ -187,9 +184,10 @@ void register_page_bootmem_info_node(struct pglist_data *pgdat)
>>>    	end_pfn = pfn + pgdat->node_spanned_pages;
>>>
>>>    	/* register_section info */
>>> -	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION)
>>> -		register_page_bootmem_info_section(pfn);
>>> -
>>> +	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>>> +		if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))
>>
>> I cannot judge whether your configuration is correct or not.
>> Thus if it is correct, I want a comment of why the node check is
>> needed. In usual configuration, a node does not span the other one.
>> So it is natural that "pfn_to_nid(pfn) is same as "pgdat->node_id".
>> Thus we may remove the node check in the future.
>
> yup.  How does this look?

Looks good to me.

Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

>
> --- a/mm/memory_hotplug.c~memory-hotplug-fix-a-double-register-section-info-bug-fix
> +++ a/mm/memory_hotplug.c
> @@ -185,6 +185,12 @@ void register_page_bootmem_info_node(str
>
>   	/* register_section info */
>   	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> +		/*
> +		 * Some platforms can assign the same pfn to multiple nodes - on
> +		 * node0 as well as nodeN.  To avoid registering a pfn against
> +		 * multiple nodes we check that this pfn does not already
> +		 * reside in some other node.
> +		 */
>   		if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))
>   			register_page_bootmem_info_section(pfn);
>   	}
> _
>
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