Table Summary in WCF RIA service, Silverlight

Question

I am now using WCF-RIA Service to create a domaindatasource in a xaml. It works great to bind the data to the datagrid and datapager.

I am looking for how to display in the page that how many row in the whole dataset. As I set the pagesize in 20 ...with say ...3 pages What is the proper way to get there is 53 rows in whole dataset?

*PS: I found that although I dont set loadsize should me load all records, but when I get the record set in code by dds.data.cast().count(), it returns 20, ie the pagesize ...