using too much RAM

[B. Todd Burruss]

 0.7.0-beta2

top is reporting my cassandra process as using 11g.  i have set 
"disk_access_mode: standard" and Xmx8G (verified via JMX)

i have only noticed using more RAM than Xmx when using mmap i/o.  this 
leads me to believe that disk_access_mode was not set properly, even 
though it is in the config.  is there a way to verify this via JMX?  (or 
some other way)

or any other ideas?