1. A system for determining a direct memory access (DMA) transfer mode, comprising: a DMA unit to receive a request for a DMA data transfer and to perform the requested DMA data transfer using a determined DMA transfer mode; and an I/O adapter to determine the DMA transfer mode for the requested DMA data transfer based on the size of the requested DMA data transfer and profile data of the I/O adapter, the DMA transfer mode being one of a first mode or a second mode, wherein, in the first mode, a first region of system memory is pre-allocated for use in DMA transfers, and wherein, in the second mode, a second region of system memory for use in a particular DMA transfer is allocated for the particular DMA transfer and deallocated when the particular DMA transfer is complete.