The chemical reactions and pathways resulting in the formation of S-methyl-methionine (SMM) from methionine and S-adenosyl-methionine (Ado-Met), catalyzed by methionine S-methyltransferase (MMT). SMM can be reconverted to methionine by donating a methyl group to homocysteine, and concurrent operation of this reaction and that mediated by MMT sets up the SMM cycle.