mem-hotplug: introduce movable_node boot option

mem-hotplug: introduce movable_node boot option

The hot-Pluggable field in SRAT specifies which memory is hotpluggable.
As we mentioned before, if hotpluggable memory is used by the kernel, it
cannot be hot-removed.  So memory hotplug users may want to set all
hotpluggable memory in ZONE_MOVABLE so that the kernel won't use it.

Memory hotplug users may also set a node as movable node, which has
ZONE_MOVABLE only, so that the whole node can be hot-removed.

But the kernel cannot use memory in ZONE_MOVABLE.  By doing this, the
kernel cannot use memory in movable nodes.  This will cause NUMA
performance down.  And other users may be unhappy.

So we need a way to allow users to enable and disable this functionality.
In this patch, we introduce movable_node boot option to allow users to
choose to not to consume hotpluggable memory at early boot time and later
we can set it as ZONE_MOVABLE.

To achieve this, the movable_node boot option will control the memblock
allocation direction.  That said, after memblock is ready, before SRAT is
parsed, we should allocate memory near the kernel image as we explained in
the previous patches.  So if movable_node boot option is set, the kernel
does the following:

1. After memblock is ready, make memblock allocate memory bottom up.
2. After SRAT is parsed, make memblock behave as default, allocate memory
   top down.

Users can specify "movable_node" in kernel commandline to enable this
functionality.  For those who don't use memory hotplug or who don't want
to lose their NUMA performance, just don't specify anything.  The kernel
will work as before.

Signed-off-by: Tang Chen <[email protected]>
Signed-off-by: Zhang Yanfei <[email protected]>
Suggested-by: Kamezawa Hiroyuki <[email protected]>
Suggested-by: Ingo Molnar <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Acked-by: Toshi Kani <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Thomas Renninger <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: Jiang Liu <[email protected]>
Cc: Wen Congyang <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Yasuaki Ishimatsu <[email protected]>
Cc: Taku Izumi <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Nazarewicz <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Johannes Weiner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>