mm: fix unable to use reliable memory in page cache

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


CVE: NA

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It is inaccurate when accumulate percpu variable without lock,
it will result in pagecache_reliable_pages to be negative in
sometime, and will prevent pagecache using reliable memory.

For more accurate statistic, replace percpu variable by percpu_counter.

The additional percpu_counter will be access in alloc_pages, the init
of these two percpu_conter is too late in late_initcall, allocations
that use alloc_pages should have to check if the two counter has been
inited, that will introduce latency, in order to sovle this, init the
two percpu_counter in advance.

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>