mimalloc

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# mimalloc

&nbsp;

mimalloc (pronounced "me-malloc")
is a general purpose allocator with excellent [performance](#performance) characteristics.
Initially developed by Daan Leijen for the runtime systems of the
[Koka](https://koka-lang.github.io) and [Lean](https://github.com/leanprover/lean) languages.

Latest release   : `v3.6.1`  (2026-10-30) recommended.\
Latest v2 release: `v2.5.2`  (2026-09-12) stable, legacy.\
Latest v1 release: `v1.15.2` (2026-09-12) legacy.

mimalloc is a drop-in replacement for `malloc` and can be used in other programs
without code changes, for example, on dynamically linked ELF-based systems (Linux, BSD, etc.) you can use it as:
```
> LD_PRELOAD=/usr/lib/libmimalloc.so  myprogram
```
It also includes a way to dynamically override the default allocator in [Windows](#override_on_windows).
Notable aspects of the design include:

- __small and consistent__: the library is about 12k LOC using simple and
  consistent data structures. This makes it very suitable
  to integrate and adapt in other projects. For runtime systems it
  provides hooks for a monotonic _heartbeat_ and deferred freeing (for
  bounded worst-case times with reference counting).
  Partly due to its simplicity, mimalloc has been ported to many systems (Windows, macOS,
  Linux, WASM, various BSD's, Haiku, MUSL, etc) and has excellent support for dynamic overriding.
  At the same time, it is an industrial strength allocator that runs (very) large scale
  distributed services on thousands of machines with excellent worst case latencies.
- __free list sharding__: instead of one big free list (per size class) we have
  many smaller lists per "mimalloc page" which reduces fragmentation and
  increases locality --
  things that are allocated close in time get allocated close in memory.
  (A mimalloc page contains blocks of one size class and is usually 64KiB on a 64-bit system).
- __free list multi-sharding__: the big idea! Not only do we shard the free list
  per mimalloc page, but for each page we have multiple free lists. In particular, there
  is one list for th