4.19新增memory reliable功能

Introduction
============

Memory reliable feature is a memory tiering mechanism. It is based on
kernel mirror feature, which splits memory into two sperate regions,
mirrored(reliable) region and non-mirrored (non-reliable) region.

for kernel mirror feature:

- allocate kernel memory from mirrored region by default
- allocate user memory from non-mirrored region by default

non-mirrored region will be arranged into ZONE_MOVABLE.

for kernel reliable feature, it has additional features below:

- normal user tasks never alloc memory from mirrored region with userspace
  apis(malloc, mmap, etc.)
- special user tasks will allocate memory from mirrored region by default
- tmpfs/pagecache allocate memory from mirrored region by default
- upper limit of mirrored region allcated for user tasks, tmpfs and
  pagecache

Support Reliable fallback mechanism which allows special user tasks, tmpfs
and pagecache can fallback to alloc non-mirrored region, it's the default
setting.

In order to fulfil the goal

- ___GFP_RELIABILITY flag added for alloc memory from mirrored region.

- the high_zoneidx for special user tasks/tmpfs/pagecache is set to
  ZONE_NORMAL.

- normal user tasks could only alloc from ZONE_MOVABLE.

This patch is just the main framework, memory reliable support for special
user tasks, pagecache and tmpfs has own patches.

To enable this function, mirrored(reliable) memory is needed and
"kernelcore=reliable" should be added to kernel parameters.

GVP openEuler/kernel

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GVPopenEuler/kernel

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