1. A parallel computer system comprising a network of interconnected compute nodes that operates a global message-passing application for performing communications across the network, wherein each of the compute nodes comprises one or more individual processors with memories, wherein local instances of the global message-passing application operate at each compute node to carry out local processing operations independent of processing operations carried out at other compute nodes, and wherein each compute node further comprises: a DMA engine constructed to interact with the application via Injection FIFO Metadata, wherein the Injection FIFO Metadata comprises an address that points to an Injection FIFO buffer having one or more message descriptors, and the DMA engine is operable to retrieve a message descriptor from the Injection FIFO buffer, the DMA engine injecting a message that corresponds to the message descriptor into the network, the DMA engine having a fixed processing overhead for said injecting irrespective of the number of message descriptors stored in the Injection FIFO buffer, wherein if there is a greater number of communication patterns than available Injection FIFO Metadata, the local instance of the global message-passing application determines whether an Injection FIFO buffer described by the Injection FIFO Metadata at the DMA network interface has completed the messages of the current communication pattern and is available for a new communication pattern and deactivates that Injection FIFO Metadata to control that the DMA engine does not access the current content of the Injection FIFO buffer while it is rewritten for the Injection FIFO buffer of the new communication pattern.