rdisp/rm_max_tbl_size is a SAP Parameter attribute which is used to control max. number of entries for resource table 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 .
This parameter configures the maximum size of the task handler resource
table. This is used to manage the kernel-internal resources.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.