Arrange hotpluggable memory as ZONE_MOVABLE

[Problem]

The current Linux cannot migrate pages used by the kerenl because of the kernel direct mapping. In Linux kernel space, va = pa + PAGE_OFFSET. When the pa is changed, we cannot simply update the pagetable and keep the va unmodified. So the kernel pages are not migratable.

There are also some other issues will cause the kernel pages not migratable. For example, the physical address may be cached somewhere and will be used. It is not to update all the caches.

When doing memory hotplug in Linux, we first migrate all the pages in one memory device somewhere else, and then remove the device. But if pages are used by the kernel, they are not migratable. As a result, memory used by the kernel cannot be hot-removed.

Modifying the kernel direct mapping mechanism is too difficult to do. And it may cause the kernel performance down and unstable. So we use the following way to do memory hotplug.

[What we are doing]

In Linux, memory in one numa node is divided into several zones. One of the zones is ZONE_MOVABLE, which the kernel won't use.

In order to implement memory hotplug in Linux, we are going to arrange all hotpluggable memory in ZONE_MOVABLE so that the kernel won't use these memory.

To do this, we need ACPI's help.

[How we do this]

In ACPI, SRAT(System Resource Affinity Table) contains NUMA info. The memory affinities in SRAT record every memory range in the system, and also, flags specifying if the memory range is hotpluggable.
(Please refer to ACPI spec 5.0 5.2.16)

With the help of SRAT, we have to do the following two things to achieve our goal:

1. When doing memory hot-add, allow the users arranging hotpluggable as ZONE_MOVABLE.
(This has been done by the MOVABLE_NODE functionality in Linux.)

2. when the system is booting, prevent bootmem allocator from allocating hotpluggable memory for the kernel before the memory initialization finishes.
(This is what we are going to do. See below.)

[About this patch-set]

In previous part's patches, we have made the kernel allocate memory near kernel image before SRAT parsed to avoid allocating hotpluggable memory for kernel. So this patch-set does the following things:

1. Improve memblock to support flags, which are used to indicate different memory type.

2. Mark all hotpluggable memory in memblock.memory[].

3. Make the default memblock allocator skip hotpluggable memory.

4. Improve "movable_node" boot option to have higher priority of movablecore and kernelcore boot option.

Change log v1 -> v2:
1. Rebase this part on the v7 version of part1
2. Fix bug: If movable_node boot option not specified, memblock still checks hotpluggable memory when allocating memory.

Tang Chen (7):
memblock, numa: Introduce flag into memblock
memblock, mem_hotplug: Introduce MEMBLOCK_HOTPLUG flag to mark
hotpluggable regions
memblock: Make memblock_set_node() support different memblock_type acpi, numa, mem_hotplug: Mark hotpluggable memory in memblock acpi, numa, mem_hotplug: Mark all nodes the kernel resides
un-hotpluggable
memblock, mem_hotplug: Make memblock skip hotpluggable regions if
needed
x86, numa, acpi, memory-hotplug: Make movable_node have higher
priority

Yasuaki Ishimatsu (1):
x86: get pg_data_t's memory from other node

 arch/metag/mm/init.c      |    3 +-
 arch/metag/mm/numa.c      |    3 +-
 arch/microblaze/mm/init.c |    3 +-
 arch/powerpc/mm/mem.c     |    2 +-
 arch/powerpc/mm/numa.c    |    8 ++-
 arch/sh/kernel/setup.c    |    4 +-
 arch/sparc/mm/init_64.c   |    5 +-
 arch/x86/mm/init_32.c     |    2 +-
 arch/x86/mm/init_64.c     |    2 +-
 arch/x86/mm/numa.c        |   63 +++++++++++++++++++++--
 arch/x86/mm/srat.c        |    5 ++
 include/linux/memblock.h  |   39 ++++++++++++++-
 mm/memblock.c             |  123 ++++++++++++++++++++++++++++++++++++++-------
 mm/memory_hotplug.c       |    1 +
 mm/page_alloc.c           |   28 ++++++++++-
 15 files changed, 252 insertions(+), 39 deletions(-)

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