Tiered memory systems introduce an additional memory level with higher-than-local-DRAM access latency and require sophisticated memory management mechanisms to achieve cost-efficiency and high performance. In particular, recent works focus on byte-addressable tiered memory architectures which offer better performance than pure swap-based systems. We observe that adding disaggregation to a byte-addressable tiered memory architecture requires important design changes that deviate from the common techniques that target lower-latency non-volatile memory systems. Our comprehensive analysis of real workloads on a hardware-emulated tiered memory system shows that the high access latency to disaggregated memory undermines the utility of well-established memory management optimizations. In particular, we find that the use of huge pages and page migration in batches, advocated by recent works, are detrimental to performance in high-latency memory regime due to their negative side effects on the local memory hit rate. Based on these insights, we develop HotBox - a disaggregated memory management subsystem for Linux that strives to maximize the local memory hit rate with low memory management overhead. HotBox introduces only minor changes to the Linux kernel while outperforming state-of-the-art systems on memory-intensive benchmarks by up to 2.25$\times$.