The present disclosure is directed to efficient memory activation at runtime. A memory module (e.g., a memory riser) being added to a device would typically cause the device to enter system management mode (SMM) to activate the memory module. However, activation (e.g., memory module initialization, hardware training and system reconfiguration) in SMM may substantially delay the resumption of normal operations. Consistent with the present disclosure, at least the memory module initialization and hardware training portions of the activation may be performed by an operating system (OS) in the device, allowing normal device operation to continue during the activation. The OS portion of the activation may generate configuration data. In at least one embodiment, the configuration data may be applied for use in SMM. For example, a system management interrupt (SMI) handler may apply the configuration data during a quiescent period (e.g., a period of inactivity) that occurs during SMM.