f2fs: add a sysfs entry to reclaim POSIX_FADV_NOREUSE pages

f2fs: add a sysfs entry to reclaim POSIX_FADV_NOREUSE pages

[ Upstream commit a907f3a68ee26ba493a08a958809208d17f3347e ]

1. fadvise(fd1, POSIX_FADV_NOREUSE, {0,3});
2. fadvise(fd2, POSIX_FADV_NOREUSE, {1,2});
3. fadvise(fd3, POSIX_FADV_NOREUSE, {3,1});
4. echo 1024 > /sys/fs/f2fs/tuning/reclaim_caches_kb

This gives a way to reclaim file-backed pages by iterating all f2fs mounts until
reclaiming 1MB page cache ranges, registered by #1, #2, and #3.

5. cat /sys/fs/f2fs/tuning/reclaim_caches_kb
-> gives total number of registered file ranges.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Stable-dep-of: e462fc48ceb8 ("f2fs: maintain one time GC mode is enabled during whole zoned GC cycle")
Signed-off-by: Sasha Levin <sashal@kernel.org>