f2fs: don't bother wait_ms by foreground gc

f2fs_gc returns -EINVAL via f2fs_balance_fs when there is enough free
secs after write checkpoint, but with gc_merge enabled, it will cause
the sleep time of gc thread to be set to no_gc_sleep_time even if there
are many dirty segments can be selected.

Signed-off-by: qixiaoyu1 <qixiaoyu1@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -150,8 +150,11 @@ do_gc:
 		gc_control.nr_free_secs = foreground ? 1 : 0;
 
 		/* if return value is not zero, no victim was selected */
-		if (f2fs_gc(sbi, &gc_control))
-			wait_ms = gc_th->no_gc_sleep_time;
+		if (f2fs_gc(sbi, &gc_control)) {
+			/* don't bother wait_ms by foreground gc */
+			if (!foreground)
+				wait_ms = gc_th->no_gc_sleep_time;
+		}
 
 		if (foreground)
 			wake_up_all(&gc_th->fggc_wq);