What command does dm-writecache flush data to disk ?

[aug7744]

Hello.
Using rapiddisk being a wrapper to dm-writecache creating a writeback cache in RAM;
The writeback cache is working.
The problem is when OS shutdown files not are written in disk.
Module dm-writecache is in kernel thus what command need to dm-writeback flush data from writeback cache in RAM to disk ?

Thanks for reply.