Last night I just migrated one of my busiest databases from SQL 2008 to 2012. Max server memory allocated to SQL Server In 2008 was 50000 and now in 2012 is 51200. Also 2012 has better processing power. However what I am seeing from my monitoring tool that SQL is having issues looking for some query plans in cache. Could this be because so many processes are being run for the first time and possibly has to recompile? How do I make this go away?
First of all you are using the default settings and boundaries which aren't close to any "one size fits all", take it with a grain of salt. Secondly, are there any page buffer cache fluctuations or any other signs of pressure? I guess not and directly after a migration, you will see this kind of fluctuations, perfectly normal and to answer you question "How do I make this go away?" , be as the Doctor said, stay calm and wait.
Quick question, is the 2012 instance fully patched?