Synthesized In-BramGarbage Collection for Accelerators with Immutable Memory

Abstract

Speed and ease of accelerator design is a growing need. High level programming languages have provided significant gains in the software world, but lag for hardware. We present a hardware implementation of a garbage collector that automates memory management, one of the major conveniences of modern software languages. Our garbage collector runs concurrently with the application it serves, using already-idle memory slots to do its work with little to no impact on performance. To achieve this, our collector exploits rapid synchronization that is straightforward in hardware but difficult in software. This synchronization enables the collector to interleave with fine pockets of idleness on a per-cycle, per-heap basis. Our collector typically incurred negligible overhead, only slowing the application to wait for collection to free memory when the heaps were so small that the collector could not keep pace with allocation. We also found that our concurrent collector performs best under an eager collection policy that collects garbage well before the application exhausts the available memory. Although this eager strategy performs more collection operations than strictly necessary, the application never pauses because our collector operates entirely in the background.