how to reduce system's ram usage
I noticed that Lion is eating up about 90% of my MBA's 2GB RAM. With Snow Leopard, the laptop has almost never ran out of memory (it occasionally did when I ran very memory-intensive app such as Windows XP in VirtualBox). With Lion, my memory is almost always at 10-20 MB free (the same level of free memory when I ran WindowsXP VirtualBox). System usage up to 33% most of the time. And the exhaust fan is running like crazy. Most notably is that all of that happens when I run a normal load: browsing Safari while listenning to iTunes.
I don't know which system threads are running in the background that eat up that whole lot of memory. So what are the most memory-hogging system features and how can I turn them off to reduce the system's usage of memory? Thanks.
MacBook Air, Mac OS X (10.7), Macbook Air with 2GB RAM