Re: [PATCH v2 0/5] Add movablecore_map boot option

[Jiang Liu]

On 11/30/2012 11:15 AM, Yasuaki Ishimatsu wrote:
> Hi Jiang,
> 
>>
>> For the first issue, I think we could automatically convert pages
>> from movable zones into normal zones. Congyan from Fujitsu has provided
>> a patchset to manually convert pages from movable zones into normal zones,
>> I think we could extend that mechanism to automatically convert when
>> normal zones are under pressure by hooking into the slow page allocation
>> path.
>>
>> We rely on hardware features to solve the second and third issues.
>> Some new platforms provide a new RAS feature called "hardware memory
>> migration", which transparent migrate memory from one memory device
>> to another. With hardware memory migration, we could configure one
>> memory device on a NUMA node to host normal zone, and the other memory
>> devices to host movable zone. By this configuration, it won't cause
>> performance drop because each NUMA node still has local normal zone.
>> When trying to remove a memory device hosting normal zone, we just
>> need to find another spare memory device and use hardware memory migration
>> to transparently migrate memory content to the spare one. The drawback
>> is we have strong dependency on hardware features so it's not a common
>> solution for all architectures.
> 
> I agree with you. If BIOS and hardware support memory hotplug, OS should
> use them. But if OS cannot use them, we need to solve in OS. I think
> that our proposal which used ZONE_MOVABLE is first step for supporting
> memory hotplug.
Hi Yasuaki,
	It's true, we should start with first step then improve it.
Regards!
Gerry

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