1. A data storage method, comprising: in a memory controller that accepts memory access commands from a host via a first interface for execution in one or more memory units, holding a definition of a policy to be applied by the memory controller in the execution of the memory access commands in the one or more memory units, wherein the policy includes one or more rules; reporting the policy from the memory controller to the host using sideband signaling on a second interface so as to cause the host to format memory access commands based on the reported policy; and sending, to the host, information indicative of which rules in the policy in the memory controller are configurable, wherein the information includes an extent to which a given rule can be modified.