JFS2 AIX P570 RAC: Filesystemio_options async vs. setall

 I'm in the process of testing parameter filesystemio_options.  async vs. setall - The scenareo is as follows:

(2) node rac P570/aix w/raw/asm/Oracle 10.2.0.4.  The question is whether changing filesystemio_options=setall which includes async and force_direct_io has any implications for asm which is manageing raw luns for the database.  Another by-product of this configuration is that aix will cache much data using most if not all of available memory.  Current sga is 1.5 GB of 8 GB available and are running into 99% memory usage.  Will this parameter change -  change the file caching behavior at the os level? Improve performance?  What can be used to pinpoint the memory utilization by other non Oracle processes.  Any info on this would be helpful.