vmcj/option/gc/sharedWaterMark is a SAP Parameter attribute which is used to control VMC: watermark for shared garbage collector information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
With this parameter you can configure from which fill level a VM is to
trigger a shared garbage collection within the virtual machine container
(VMC). The value must be within interval [0, 100] and specifies the fill
level as a percentage. Value 100% means that shared GCs are triggered
only after failed memory requests.
Example
vmcj/option/gc/sharedWaterMark = 60 --> A shared GC is triggered after a
60% fill level.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.