ipc/shm_psize_20 is a SAP Parameter attribute which is used to control SHM Pool 20 Size 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 .
Size of shared memory pool 20. It should not be changed in 7.4* Kernel
because the use of shared memory pools is not necessary and not
recommended in most cases.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.