mm/vmscan: fix frequent call of shrink_page_cache_work

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


CVE: NA

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If vmcache_reclaim_s > 120, it will call shrink_page_cache_work
after 120 seconds even shrinking is hard, that is shorter than
vmcache_reclaim_s, deviating from the original intention of extending
the interval.

In order to solve this, shrink_page_cache_work should be call
after vmcache_reclaim_s + 120.

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>