Write data mask for power reduction

Devices, systems, and methods having increased efficiency selective writing to memory are disclosed and described. A memory controller, upon receiving a dirty data segment, performs a read-modify-write to retrieve a corresponding data line from memory, saves a copy of the data line, merges the dirty data segment into the appropriate location in the data line to create a modified data line, and generates a write mask from the modified data line and the copy of the data line.