What exactly is FS cache or file system cache in AIX. Most of the time our performance charts show that main memory is mainly allocated for FS cache. Is this frequently read file data? or is this something else at FS level ?
The file system cache stores portions of the file system in RAM for faster access than a disk read. How the cache is sized, populated, and invalidated is often dependent on the file system used, running applications, and the underlying operating system.
Some links that might help you understand what AIX and its applications are doing with this are:
I'm sure there are plenty of other links out there that will be more specific to your circumstances, but this should definitely get you started.