filemap: dont shrink_page_cache in add_to_page_cache

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


CVE: NA

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The reason of disable shrink_page_cache in add_to_page_cache are:

1. Synchronous memory reclamation will affect performance.
2. add_to_page_cache will not increase the number of LRU size in
   HugeTLB situation, so shrink_page_cache will not be triggered.

Now, add_to_page_cache in mm/filemap.c and include/linux/pagemap.h
are same, don't delete add_to_page_cache in mm/filemap.c, just keep
interface for KABI.

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