Hi Jiang,

2012/07/11 1:50, Jiang Liu wrote:

On 07/10/2012 05:58 PM, Yasuaki Ishimatsu wrote:

quoted

Hi Christoph,

2012/07/10 0:18, Christoph Lameter wrote:

quoted

On Mon, 9 Jul 2012, Yasuaki Ishimatsu wrote:

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Even if you apply these patches, you cannot remove the physical memory
completely since these patches are still under development. I want you to
cooperate to improve the physical memory hot-remove. So please review these
patches and give your comment/idea.

Could you at least give a method on how you want to do physical memory
removal?

We plan to release a dynamic hardware partitionable system. It will be
able to hot remove/add a system board which included memory and cpu.
But as you know, Linux does not support memory hot-remove on x86 box.
So I try to develop it.

Current plan to hot remove system board is to use container driver.
Thus I define the system board in ACPI DSDT table as a container device.
It have supported hot-add a container device. And if container device
has _EJ0 ACPI method, "eject" file to remove the container device is
prepared as follow:

# ls -l /sys/bus/acpi/devices/ACPI0004\:01/eject
--w-------. 1 root root 4096 Jul 10 18:19 /sys/bus/acpi/devices/ACPI0004:01/eject

When I hot-remove the container device, I echo 1 to the file as follow:

#echo 1 > /sys/bus/acpi/devices/ACPI0004\:02/eject

Then acpi_bus_trim() is called. And it calls acpi_memory_device_remove()
for removing memory device. But the code does not do nothing.
So I developed the continuation of the function.

quoted

You would have to remove all objects from the range you want to
physically remove. That is only possible under special circumstances and
with a limited set of objects. Even if you exclusively use ZONE_MOVEABLE
you still may get cases where pages are pinned for a long time.

I know it. So my memory hot-remove plan is as follows:

1. hot-added a system board
    All memory which included the system board is offline.

2. online the memory as removable page
    The function has not supported yet. It is being developed by Lai as follow:
    http://lkml.indiana.edu/hypermail/linux/kernel/1207.0/01478.html
    If it is supported, I will be able to create movable memory.

3. hot-remove the memory by container device's eject file

We have implemented a prototype to do physical node (mem + CPU + IOH) hotplug
for Itanium and is now porting it to x86. But with currently solution, memory
hotplug functionality may cause 10-20% performance decrease because we concentrate
all DMA/Normal memory to the first NUMA node, and all other NUMA nodes only
hosts ZONE_MOVABLE. We are working on solution to minimize the performance
drop now.

Thank you for your interesting response.

I have a question. How do you move all other NUMA nodes to ZONE_MOVABLE?
To use ZONE_MOVABLE, we need to use boot options like kernelcore or movablecore.
But it is not enough, since the requested amount is spread evenly throughout
all nodes in the system. So I think we do not have way to move all other NUMA
node to ZONE_MOVABLE.

Thanks,
Yasuaki Ishimatsu

quoted

Thanks,
Yasuaki Ishimatsu

quoted

I am not sure that these patches are useful unless we know where you are
going with this. If we end up with a situation where we still cannot
remove physical memory then this patchset is not helpful.