Re: [PATCH 14/21] x86, acpi, numa: Reserve hotpluggable memory at early time.

[Tang Chen <tangchen@cn.fujitsu.com>]

On 07/24/2013 05:32 AM, Tejun Heo wrote:
> On Tue, Jul 23, 2013 at 04:55:57PM -0400, Tejun Heo wrote:
>> On Fri, Jul 19, 2013 at 03:59:27PM +0800, Tang Chen wrote:
>>> +		/*
>>> +		 * In such an early time, we don't have nid. We specify pxm
>>> +		 * instead of MAX_NUMNODES to prevent memblock merging regions
>>> +		 * on different nodes. And later modify pxm to nid when nid is
>>> +		 * mapped so that we can arrange ZONE_MOVABLE on different
>>> +		 * nodes.
>>> +		 */
>>> +		memblock_reserve_hotpluggable(base_address, length, pxm);
>>
>> This is rather hacky.  Why not just introduce MEMBLOCK_NO_MERGE flag?

The original thinking is to merge regions with the same nid. So I used pxm.
And then refresh the nid field when nids are mapped.

I will try to introduce MEMBLOCK_NO_MERGE and make it less hacky.

>
> Also, if memblock is gonna know about hotplug memory, why not just let
> it control its allocation too instead of blocking it by reserving it
> from outside?  These are all pretty general memory hotplug logic which
> doesn't have much to do with acpi and I think too much is implemented
> on the acpi side.

At the very beginning, a long time ago, we just did this.
Please refer to: https://lkml.org/lkml/2012/12/10/656

In order to let memblock control the allocation, we have to store the
hotpluggable ranges somewhere, and keep the allocated range out of the
hotpluggable regions. I just think reserving the hotpluggable regions
and then memblock won't allocate them. No need to do any other limitation.

And also, the acpi side modification in this patch-set is to get SRAT
and parse it. I think most of the logic in 
acpi_reserve_hotpluggable_memory()
is necessary. I don't think letting memblock control the allocation will
make the acpi side easier.

Thanks.