Hybrid memory systems are able to achieve both high performance and large capacity when combining fast commodity DDR memories with larger but slower non-volatile memories in a heterogeneous way. However, it is critical to best utilize the limited fast memory capacity and slow memory bandwidth in such systems to gain the maximum efficiency. In this paper, we propose a novel hybrid memory design, Baryon, that leverages both memory compression and data sub-blocking techniques to improve the utilization of fast memory capacity and slow memory bandwidth, with only moderate metadata overheads and management complexity. Baryon reserves a small fast memory area to efficiently manage and stabilize the irregular and frequently varying data layouts resulted from compression and sub-blocking, and selectively commits only stable blocks to the rest fast memory space. It also adopts a novel dual-format metadata scheme to support flexible address remapping under such complex data layouts with low storage cost. Baryon is completely transparent to software, and works with both cache and flat schemes of hybrid memories. Our evaluation shows Baryon achieves up to 1.68× and on average 1.27× performance improvements over state-of-the-art designs.