icm/wp_mpi_available is a SAP Parameter attribute which is used to control Min. number of MPIs which have to be available for roll-in 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 .
The parameter determines the minimum number of MPI buffers (granularity
of the Memory Pipes) read by the network so that a rolled out context
can be rolled back into a work process (by the ICM).
To make sure that no work processes are occupied unnecessarily if the
network connection is slow, you can use this parameter to ensure that
the context only occupies one work process if data are also available.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.