mysql双写double write的疑问

请问根据官方文档

https://dev.mysql.com/doc/refman/8.4/en/innodb-doublewrite-buffer.html

The doublewrite buffer is a storage area where InnoDB writes pages flushed from the buffer pool before writing the pages to their proper positions in the InnoDB data files.

说的是刷脏页之前写double write buffer。请问写完double write buffer以后，是从内存刷脏页到数据页还是从double write buffer刷脏页到数据页？

谢谢！