mm: Introduce shmem mirrored memory limit for memory reliable

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


CVE: NA

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This limit is used to restrict the amount of mirrored memory by shmem.
This memory allocation will return no memory if reliable fallback is off
or fallback to non-mirrored region if reliable fallback on.

This limit can be set or access via
/proc/sys/vm/shmem_reliable_bytes_limit.
The default value of this limit is LONG_MAX. This limit can be set from 0
to the total size of mirrored memory.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>