SQL Server will allocate memory up to the max memory setting and keep that memory. It does not release the memory. What you are seeing is normal behavior.
On x64 hardware - you want to make sure you set max memory and, if you are running Enterprise Edition of SQL Server you need to set lock pages in memory policy for the service account running SQL Server (Group Policy Editor).
Jeffrey Williams
“We are all faced with a series of great opportunities brilliantly disguised as impossible situations.”
― Charles R. Swindoll
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