mm: Count reliable shmem used based on NR_SHMEM

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


CVE: NA

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With this patch, reliable memory counter will be updated when NR_SHMEM is
updated. Pervious shmem reliable memory counter is not accurate if swap is
enabled.

NR_SHMEM update in memcg secenario is ignored because this has nothing to
do with the global counter. If shmem pages is migrated or collapsed from
one region to another region, reliable memory counter need to be updated
because these pages's reliable status may not be the same.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>