f2fs: move dir data flush to write checkpoint process

BugLink: https://bugs.launchpad.net/bugs/1818813

[ Upstream commit b61ac5b7 ]

This patch move dir data flush to write checkpoint process, by
doing this, it may reduce some time for dir fsync.

pre:
	-f2fs_do_sync_file enter
		-file_write_and_wait_range  <- flush & wait
		-write_checkpoint
			-do_checkpoint	    <- wait all
	-f2fs_do_sync_file exit

now:
	-f2fs_do_sync_file enter
		-write_checkpoint
			-block_operations   <- flush dir & no wait
			-do_checkpoint	    <- wait all
	-f2fs_do_sync_file exit
Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/f2fs/file.c

@@ -200,6 +200,9 @@ int f2fs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 
 	trace_f2fs_sync_file_enter(inode);
 
+	if (S_ISDIR(inode->i_mode))
+		goto go_write;
+
 	/* if fdatasync is triggered, let's do in-place-update */
 	if (get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
 		set_inode_flag(fi, FI_NEED_IPU);