cherry pick pingcap#27625 to release-5.3

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

util/logutil/slow_query_logger.go

@@ -29,14 +29,12 @@ var _pool = buffer.NewPool()
 
 func newSlowQueryLogger(cfg *LogConfig) (*zap.Logger, *log.ZapProperties, error) {
 
-	// copy global config and override slow query log file
-	// if slow query log filename is empty, slow query log will behave the same as global log
+	// copy the global log config to slow log config
+	// if the filename of slow log config is empty, slow log will behave the same as global log.
 	sqConfig := cfg.Config
 	if len(cfg.SlowQueryFile) != 0 {
-		sqConfig.File = log.FileLogConfig{
-			MaxSize:  cfg.File.MaxSize,
-			Filename: cfg.SlowQueryFile,
-		}
+		sqConfig.File = cfg.File
+		sqConfig.File.Filename = cfg.SlowQueryFile
 	}
 
 	// create the slow query logger