If I understand correctly you have set Max Server Memory to 29GB and you're seeing memory used at 75% of that figure which is 21.75GB. That is not an awful lot for SQL Server. How many instances are you running and what sort of applications are your databases supporting, e.g. busy OLTP system, Operational Data Store, Data Warehouse...?
Have a look at the blog post below from Jonathan Kehayias.
EDIT: Removed incorrect link