mm/vmscan: dont do shrink_slab in reclaim page cache

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


CVE: NA

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If page cache is over limit, it will trigger page cache reclaimation,
only page cache should be reclaimed, but slab will be reclaimed by
default in shrink_node, so disable shrink_slab by adding a control
parameter in scan_control.

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