linux-kernel - Re: [PATCH 10/11] x86, mem-hotplug: Support initialize page tables from low to high.

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Date:	Fri, 06 Sep 2013 11:09:12 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
CC:	rjw@...k.pl, lenb@...nel.org, tglx@...utronix.de, mingo@...e.hu,
	hpa@...or.com, akpm@...ux-foundation.org, tj@...nel.org,
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Subject: Re: [PATCH 10/11] x86, mem-hotplug: Support initialize page tables
 from low to high.

Hi Wanpeng,

On 09/06/2013 10:16 AM, Wanpeng Li wrote:
......
>>>> +#ifdef CONFIG_MOVABLE_NODE
>>>> +	unsigned long kernel_end;
>>>> +
>>>> +	if (movablenode_enable_srat&&
>>>> +	    memblock.current_order == MEMBLOCK_ORDER_LOW_TO_HIGH) {
>>>
>>> I think memblock.current_order == MEMBLOCK_ORDER_LOW_TO_HIGH is always
>>> true if config MOVABLE_NODE and movablenode_enable_srat == true if PATCH
>>> 11/11 is applied.
>>
>> memblock.current_order == MEMBLOCK_ORDER_LOW_TO_HIGH is true here if
>> MOVABLE_NODE
>> is configured, and it will be reset after SRAT is parsed. But
>> movablenode_enable_srat
>> could only be true when users specify movablenode boot option in the
>> kernel commandline.
>
> You are right.
>
> I mean the change should be:
>
> +#ifdef CONFIG_MOVABLE_NODE
> +       unsigned long kernel_end;
> +
> +       if (movablenode_enable_srat) {
>
> The is unnecessary to check memblock.current_order since it is always true
> if movable_node is configured and movablenode_enable_srat is true.
>

But I think, memblock.current_order is set outside init_mem_mapping(). And
the path in the if statement could only be run when current order is from
low to high. So I think it is safe to check it here.

I prefer to keep it at least in the next version patch-set. If others also
think it is unnecessary, I'm OK with removing the checking. :)

Thanks. :)
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