On 11/30/2012 11:15 AM, Yasuaki Ishimatsu wrote:

Hi Jiang,

quoted

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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