At a glance
Today’s critical services and applications are often highly concurrent, using hundreds of threads. They also operate at large memory scales, frequently hundreds of gigabytes, especially when using large language models.
mimalloc is an open-source, modern, scalable memory allocator that is a drop-in replacement for malloc and free. It is relatively small (~12K lines), with clear internal data structures, and is easy to build and integrate into other projects. It provides bounded worst-case allocation times (up to OS primitives), bounded space overhead, low internal fragmentation, and minimal contention by relying almost exclusively on atomic operations.
mimalloc is available on GitHub (opens in new tab) and has over 12K stars.
At the RiSE group at Microsoft Research (MSR), we conduct fundamental research into formal methods, programming languages, and software engineering (including emerging agentic systems), with a particular focus on systems that can be provably correct, secure, and performant. The mimalloc memory allocator was initially designed in 2020 as a fast allocator for the state-of-the-art Lean (opens in new tab) and Koka (opens in new tab) programming languages developed at RiSE, both of which use novel compiler-guided reference counting (see Perceus).
