etmem: Add a scan flag to support specified page swap-out

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7RO5Q
CVE: NA
Reference: https://gitee.com/openeuler/kernel/commit/4f0eedb8c688ea61bcb129ed78c1784fb939103a



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etmem, the memory vertical expansion technology,

The existing memory expansion tool etmem swaps out all pages that can be
swapped out for the process by default, unless the page is marked with
lock flag.

The function of swapping out specified pages is added. The process adds
VM_SWAPFLAG flags for pages to be swapped out. The etmem adds filters to
the scanning module and swaps out only these pages.

Signed-off-by: liubo <liubo254@huawei.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>