Re: [RFC PATCH]: ACPI: Automatically online hot-added memory

[Prarit Bhargava <prarit@redhat.com>]

chen gong wrote:
> On 2010-3-11 16:07, ykzhao wrote:
>   
>> On Thu, 2010-03-11 at 10:18 +0800, Prarit Bhargava wrote:
>>     
>>>> Yes. The nehalem processor has the integrated memory controller. But it
>>>> is not required that the hot-added memory should be onlined before
>>>> bringing up CPU.
>>>>     I do the following memory-hotplug test on one Machine.
>>>>     a. Before hot plugging memory, four CPUs socket are installed and
>>>> all the logical CPU are brought up. (Only one node has the memory)
>>>>     b. The memory is hot-plugged and then the memory is onlined so that
>>>> it can be accessed by the system.
>>>>
>>>> In the above testing case the CPU is brought up before onlining the
>>>> hot-added memory. And the test shows that it can work well.
>>>>   
>>>>         
>>> That doesn't work when you have multiple nodes AFAICT.  The cpus do not 
>>> come into service because of a lack of memory on the node....  per node 
>>> allocations will fail.
>>>       
>> In the test the system has multiple nodes. The reason is that the cpu
>> without memory can turn to other node and allocate the memory.
>>     
>
> I agree with Yakui. The memory and CPU are irrelevant in some way. CPU can
> get memory from other nodes if it hasn't local memory, though for now it has some issues.
> Andi is working on it now (http://lkml.org/lkml/2010/2/3/343)
>   

Right -- I'm working with Andi on this to get RHEL working.  So I have 
his slab patches, etc..  That's one of the reasons it isn't working 
right now.

> BTW, how about using UDEV rules to do this operation. It looks more smooth. I know some
> Novell guy is working on it.
>
>   

I was thinking about that, but the CPU comes online automatically, so 
why not memory?  It seems to be a discrepancy between the two.   And ... 
the two of you still aren't considering the obvious performance hit 
which I would think makes this a must have.

P.


>