Since yesterday, my MacBook Pro 13" 2011 with 4 GB of RAM started doing a strange thing: A lot of times my Inactive RAM will go from 200 MB to 1.3 GB, making my free RAM less than 100 MB and slowing down the machine. I have to fire up Terminal and type "purge" in order to restore my Free RAM to almost 2 GB again and the system to normal state. I have inspected my Activity Monitor and neither process appears to use lot of CPU nor RAM. I don't understand why the Inactive RAM is doing this. Anyone else experiencing this too since the Lion upgrade?