1. A method of executing an application on a parallel computer, the parallel computer comprising a plurality of compute nodes connected together through a data communications network, each compute node having a plurality of processors capable of operating independently for serial processing among the processors and capable of operating symmetrically for parallel processing among the processors, the application having parallel segments designated for parallel processing and serial segments designated for serial processing, the method comprising: booting up a first subset of the plurality of compute nodes in a serial processing mode; booting up a second subset of the plurality of compute nodes in a parallel processing mode; profiling, prior to application execution, the application to identify the serial segments of the application, the parallel segments of the application, and application data utilized by each of the serial segments and the parallel segments; and executing the application on the plurality of compute nodes, including: upon encountering the parallel segments during execution, migrating in dependence upon the profile for the application, only specific portions of the application and the application data from the nodes booted up in the parallel processing mode to the nodes booted up in the serial processing mode.