Man pages matching name mpi_free_mem in section 3:

MPI_Free_mem.3.en	debian 10 / lam4-dev
MPI_Free_mem.3.en	debian 10 / mpich-doc
MPI_Free_mem.3.en	debian 11 / lam4-dev
MPI_Free_mem.3.en	debian 12 / lam4-dev
MPI_Free_mem.3.en	debian 12 / mpich-doc