  We propose a new method for defragmenting the module layout of a
reconfigurable device, enabled by a novel approach for dealing with
communication needs between relocated modules and with inhomogeneities found in
commonly used FPGAs. Our method is based on dynamic relocation of module
positions during runtime, with only very little reconfiguration overhead; the
objective is to maximize the length of contiguous free space that is available
for new modules. We describe a number of algorithmic aspects of good
defragmentation, and present an optimization method based on tabu search.
Experimental results indicate that we can improve the quality of module layout
by roughly 50 % over static layout. Among other benefits, this improvement
avoids unnecessary rejections of modules
