etmem: add swapcache reclaim to etmem

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4QVXW


CVE: NA

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etmem, the memory vertical expansion technology,

In the current etmem process, memory page swapping is implemented by
invoking shrink_page_list. When this interface is invoked for the first
time, pages are added to the swap cache and written to disks.The swap
cache page is reclaimed only when this interface is invoked for the
second time and no process accesses the page.However, in the etmem
process, the user mode scans pages that have been accessed, and the
migration is not delivered to pages that are not accessed by processes.
Therefore, the swap cache may always be occupied.
To solve the preceding problem, add the logic for actively reclaiming
the swap cache.When the swap cache occupies a large amount of memory,
the system proactively scans the LRU linked list and reclaims the
swap cache to save memory within the specified range.

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: Yang Yingliang <yangyingliang@huawei.com>