For now, x86 does not support memory-less node. A node without memory
will not be onlined, and the cpus on it will be mapped to the other
online nodes with memory in init_cpu_to_node(). The reason of doing this
is to ensure each cpu has mapped to a node with memory, so that it will
be able to allocate local memory for that cpu.

But we don't have to do it in this way.

In this series of patches, we are going to construct cpu <-> node mapping
for all possible cpus at boot time, which is a persistent mapping. It means
that the cpu will be mapped to the node which it belongs to, and will never
be changed. If a node has only cpus but no memory, the cpus on it will be
mapped to a memory-less node. And the memory-less node should be onlined.

Allocate pgdats for all memory-less nodes and online them at boot
time. Then build zonelists for these nodes. As a result, when cpus on these
memory-less nodes try to allocate memory from local node, it will
automatically fall back to the proper zones in the zonelists.
Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: mika.j.penttila@gmail.com
Cc: len.brown@intel.com
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: rafael@kernel.org
Cc: rjw@rjwysocki.net
Cc: yasu.isimatu@gmail.com
Cc: linux-mm@kvack.org
Cc: linux-acpi@vger.kernel.org
Cc: isimatu.yasuaki@jp.fujitsu.com
Cc: gongzhaogang@inspur.com
Cc: tj@kernel.org
Cc: izumi.taku@jp.fujitsu.com
Cc: cl@linux.com
Cc: chen.tang@easystack.cn
Cc: akpm@linux-foundation.org
Cc: kamezawa.hiroyu@jp.fujitsu.com
Cc: lenb@kernel.org
Link: http://lkml.kernel.org/r/1472114120-3281-2-git-send-email-douly.fnst@cn.fujitsu.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>