rdisp/attach_disp_to_all_shm_seg is a SAP Parameter attribute which is used to control 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 .
Some operating systems delete a shared memory area as soon as no
processes are connected to the area. For areas that are only used by
work processes, this could lead to the loss of areas, if all work
processes are restarted at the same time. To prevent this, the d
ispatcher also connects with shared memory areas of this type. You can
configure this behavior with this parameter.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.