mm: mem_reliable: Introduce fallback mechanism for memory reliable

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8USBA


CVE: NA

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Introduce fallback mechanism for memory reliable. memory allocation will
fallback to non-mirrored region if zone's low watermark is reached and
kswapd will be awakened at this time.

This mechanism is enabled by default and can be disabled by adding
"reliable_debug=F" to the kernel parameters. This mechanism rely on
CONFIG_MEMORY_RELIABLE and need "kernelcore=reliable" in the kernel
parameters.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>