f2fs: run fstrim asynchronously if runtime discard is on

We don't need to wait for whole bunch of discard candidates in fstrim, since
runtime discard will issue them in idle time.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -2439,9 +2439,18 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
 
 	__init_discard_policy(sbi, &dpolicy, DPOLICY_FSTRIM, cpc.trim_minlen);
 	__issue_discard_cmd_range(sbi, &dpolicy, start_block, end_block);
-	trimmed = __wait_discard_cmd_range(sbi, &dpolicy,
+
+	/*
+	 * We filed discard candidates, but actually we don't need to wait for
+	 * all of them, since they'll be issued in idle time along with runtime
+	 * discard option. User configuration looks like using runtime discard
+	 * or periodic fstrim instead of it.
+	 */
+	if (!test_opt(sbi, DISCARD)) {
+		trimmed = __wait_discard_cmd_range(sbi, &dpolicy,
 					start_block, end_block);
-	range->len = F2FS_BLK_TO_BYTES(trimmed);
+		range->len = F2FS_BLK_TO_BYTES(trimmed);
+	}
 out:
 	return err;
 }