mm/memcg_memfs_info: show files that having pages charged in mem_cgroup

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8PWEP


CVE: NA

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Support to print rootfs files and tmpfs files that having pages charged
in given memory cgroup. The files infomations can be printed through
interface "memory.memfs_files_info" or printed when OOM is triggered.

In order not to flush memory logs, we limit the maximum number of files
to be printed when oom through interface "max_print_files_in_oom". And
in order to filter out small files, we limit the minimum size of files
that can be printed through interface "size_threshold".

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>