Improved techniques are disclosed for performing an in-service upgrade of software associated with a network or packet processor. By way of example, a method of performing an in-service upgrade of code, storable in a memory associated with a packet processor and executable on the packet processor, from a first code version to a second code version, includes the following steps. A first step includes preparing for the upgrade by generating one or more write operations to effectuate the code upgrade from the first code version to the second code version. A second step includes updating the code from the first code version to the second code version by propagating the one or more write operations to the packet processor. A third step includes cleaning up after the updating step by reclaiming one or more memory locations available after the update step. As such, the storage of only a single version of the code in the memory associated with the packet processor is required.