mm: Introduce watermark check for memory reliable

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S


CVE: NA

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Introuce min watermark to ensure kernel can use this reserved memory.
This watermark will prevent special user tasks, pagecache, tmpfs user from
using too many mirrored memory which will lead to kernel oom.

Memory allocation with ___GFP_RELIABILITY or special user tasks will be
blocked after this watermark is reached. This memory allocation will
fallback to non-mirrored region or trigger oom depends on memory reliable
fallback's status.

This limit can be set or access via /proc/sys/vm/reliable_reserve_size.
The default value of this limit is 256M. This limit can be set from 256M to
the total size of mirrored memory.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: Kefeng <Wang&lt;wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>