f2fs: detect idle time depending on user behavior

This patch adds last time that user requested filesystem operations.
This information is used to detect whether system is idle or not later.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -293,7 +293,7 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 	if (!available_free_memory(sbi, NAT_ENTRIES) ||
 			excess_prefree_segs(sbi) ||
 			!available_free_memory(sbi, INO_ENTRIES) ||
-			f2fs_time_over(sbi, CP_TIME)) {
+			(is_idle(sbi) && f2fs_time_over(sbi, CP_TIME))) {
 		if (test_opt(sbi, DATA_FLUSH))
 			sync_dirty_inodes(sbi, FILE_INODE);
 		f2fs_sync_fs(sbi->sb, true);