Ganglia is a piece of software used to monitor cluster load.
The amount of used memory reported by Linux includes unused memory the operating system uses for disk caching, which makes the system run faster. Memory that Linux "borrows" for disk caching is available for your application. For an accurate report of free memory available, run 'free -m' and the amounts reported on the second line (-/+ buffers/cache) show how much memory is used and free.
Currently, ganglia will sometimes show nodes as having one processor core at full load. The only solution to fix this is to reboot that node (but, ultimately, that node does not have any load)