rdisp/PG_SHM is a SAP Parameter attribute which is used to control Size of paging buffer 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 value specifies the size of the paging buffer in 8 KB blocks. A
paging buffer is no longer required for SAP Memory Management, because
internal tables and lists are not stored in SAP paging.
Value = 0 to save swap space Default value is calculated from the profile parameter
See SAP Parameter Documentation for full SAP documentation for this profile parameter.