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Gmane
From: Zhang Yanfei <zhangyanfei <at> cn.fujitsu.com>
Subject: [PATCH -mm 0/8] Arrange hotpluggable memory as ZONE_MOVABLE
Newsgroups: gmane.linux.kernel
Date: Tuesday 1st October 2013 09:42:53 UTC (over 3 years ago)
Hello guys, this is the part2 of our memory hotplug work. This part
is based on the part1:
    "x86, memblock: Allocate memory near kernel image before SRAT parsed"

You could refer part1 from: https://lkml.org/lkml/2013/9/24/421

Any comments are welcome! Thanks!

[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 make 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.

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 by
    default.
  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/kernel/setup.c        |    7 --
 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             |   13 ++++
 include/linux/memblock.h       |   22 +++++++-
 include/linux/memory_hotplug.h |    5 ++
 mm/memblock.c                  |  124
++++++++++++++++++++++++++++++++++------
 mm/memory_hotplug.c            |    3 +
 mm/page_alloc.c                |   30 +++++++++-
 17 files changed, 253 insertions(+), 46 deletions(-)

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