hulk inclusion
category: bugfix
bugzilla: 46904 https://gitee.com/openeuler/kernel/issues/I4Y0XO

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When all processes in the memory cgroup are finished, some memory may still be
occupied such as file cache. Use mem_cgroup_force_empty to reclaim these pages
that charged in the memory cgroup before merging all pages.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>