Thank you all for helping me on this!

Thank you! We are actually planning move to a more power server. 
I had stopped the archive script for 2 days but buffer cache did not go up. It stays...

The archiving is something new. It moves one days of data from production to archive db to keep production only contain 180 days data.
After archiving job completed every night,...

Thanks Kevin,
A) DBCC MEMORYSTATUS: 
Process/System Counts       Value
---------------------------------------- --------------------
Available Physical Memory      373526528
Available Virtual Memory      8209852002304
Available Paging File       130824531968
Working Set          131080753152
Percent of Committed...

Hi Kevin,

Thanks for the quick reply. To answer your question:

1) You posted this on SQL 2012 forum, but I thought Free Pages went away in that...