Memory price will continue dropping in the next few years according to Gartner. Such trend renders it affordable for in-memory key-value stores (IMKVs) to maintain redundant memory-resident copies of each key-value pair to provision enhanced reliability and high availability services. Though contemporary IMKVs have reached unprecedented performance, delivering single-digit microsecond-scale latency with up to tens of millions queries per second throughput, existing replication protocols are unable to keep pace with such an advancement of IMKVs, either incurring unbearable latency overhead or demanding intensive resource usage. Consequently, the adoption of those replication techniques always results in substantial performance degradation.In this paper, we propose MacR, a RDMA-based high-performance and lightweight replication protocol for IMKVs. The design of MacR centers around sharing the remote backup memory to enable RDMA-based replication protocol, and synthesizes a collection of optimizations, including memory allocator cooperative replication and adaptive bulk data synchronization to control the number of network operations and to enhance the recovery performance. Performance evaluations with a variety of YCSB workloads demonstrate that MacR can efficiently outperform alternative replication methods in terms of the throughput while preserving sufficiently low latency overhead. It can also efficiently speed up the recovery process.