Re: [PATCH v5 6/6] mem-hotplug: Introduce movablenode boot option

[Zhang Yanfei <zhangyanfei.yes@gmail.com>]

On 09/26/2013 10:53 PM, Tejun Heo wrote:
> On Wed, Sep 25, 2013 at 02:35:14AM +0800, Zhang Yanfei wrote:
>> From: Tang Chen <tangchen@cn.fujitsu.com>
>>
>> The hot-Pluggable field in SRAT specifies which memory is hotpluggable.
>> As we mentioned before, if hotpluggable memory is used by the kernel,
>> it cannot be hot-removed. So memory hotplug users may want to set all
>> hotpluggable memory in ZONE_MOVABLE so that the kernel won't use it.
>>
>> Memory hotplug users may also set a node as movable node, which has
>> ZONE_MOVABLE only, so that the whole node can be hot-removed.
>>
>> But the kernel cannot use memory in ZONE_MOVABLE. By doing this, the
>> kernel cannot use memory in movable nodes. This will cause NUMA
>> performance down. And other users may be unhappy.
>>
>> So we need a way to allow users to enable and disable this functionality.
>> In this patch, we introduce movablenode boot option to allow users to
>> choose to not to consume hotpluggable memory at early boot time and
>> later we can set it as ZONE_MOVABLE.
>>
>> To achieve this, the movablenode boot option will control the memblock
>> allocation direction. That said, after memblock is ready, before SRAT is
>> parsed, we should allocate memory near the kernel image as we explained
>> in the previous patches. So if movablenode boot option is set, the kernel
>> does the following:
>>
>> 1. After memblock is ready, make memblock allocate memory bottom up.
>> 2. After SRAT is parsed, make memblock behave as default, allocate memory
>>    top down.
>>
>> Users can specify "movablenode" in kernel commandline to enable this
>> functionality. For those who don't use memory hotplug or who don't want
>> to lose their NUMA performance, just don't specify anything. The kernel
>> will work as before.
>>
>> Suggested-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
>> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> 
> I hope the param description and comment were better.  Not necessarily
> longer, but clearer, so it'd be great if you can polish them a bit

OK. Trying below:

movablenode	[KNL,X86] This option enables the kernel to arrange
		hotpluggable memory into ZONE_MOVABLE zone. If memory
		in a node is all hotpluggable, the option may make
		the whole node has only one ZONE_MOVABLE zone, so that
		the whole node can be hot-removed after system is up.
		Note that this option may cause NUMA performance down.

As for the comment in cmdline_parse_movablenode():

	/*
	 * ACPI SRAT records all hotpluggable memory ranges. But before
	 * SRAT is parsed, we don't know about it. So by specifying this
	 * option, we will use the bottom-up mode to try allocating memory
	 * near the kernel image before SRAT is parsed.
	 * 
	 * Bottom-up mode prevents memblock allocating hotpluggable memory
	 * for the kernel so that the kernel will arrange hotpluggable
	 * memory into ZONE_MOVABLE zone when possible.
	 */

Thanks.

> more.  Other than that,
> 
>  Acked-by: Tejun Heo <tj@kernel.org>
> 
> Thanks.
> 


-- 
Thanks.
Zhang Yanfei

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