memory-hotplug: try to offline the memory twice to avoid dependence

memory-hotplug: try to offline the memory twice to avoid dependence

memory can't be offlined when CONFIG_MEMCG is selected.  For example:
there is a memory device on node 1.  The address range is [1G, 1.5G).  You
will find 4 new directories memory8, memory9, memory10, and memory11 under
the directory /sys/devices/system/memory/.

If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup
when we online pages.  When we online memory8, the memory stored page
cgroup is not provided by this memory device.  But when we online memory9,
the memory stored page cgroup may be provided by memory8.  So we can't
offline memory8 now.  We should offline the memory in the reversed order.

When the memory device is hotremoved, we will auto offline memory provided
by this memory device.  But we don't know which memory is onlined first,
so offlining memory may fail.  In such case, iterate twice to offline the
memory.  1st iterate: offline every non primary memory block.  2nd
iterate: offline primary (i.e.  first added) memory block.

This idea is suggested by KOSAKI Motohiro.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Wu Jianguo <wujianguo@huawei.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>