From https://github.com/microsoft/mimalloc

> mimalloc (pronounced "me-malloc") is a general purpose allocator with excellent performance characteristics. Initially developed by Daan Leijen for the run-time systems of the Koka and Lean languages.

mimalloc has several interesting properties that make it useful for CPython. Amongst other it is fast, thread-safe, and NUMA-aware. It has built-in free lists with multi-sharding and allocation heaps. While Python's obmalloc requires the GIL to protect its data structures, mimalloc uses mostly thread-local and atomic instructions (compare-and-swap) for efficiency. Sam Gross' nogil relies on mimalloc's thread safety and uses first-class heaps for heap walking GC.

mimalloc works on majority of platforms and CPU architectures. However it requires a compiler with C11 atomics support. CentOS 7's default GCC is slightly too old, more recent GCC from Developer Toolset is required. 

For 3.11 I plan to integrate mimalloc as an optional drop-in replacement for obmalloc. Users will be able to compile CPython without mimalloc or disable mimalloc with PYTHONMALLOC env var. Since mimalloc will be optional in 3.11, Python won't depend or expose on any of the advanced features yet. The approach enables the community to test and give feedback with minimal risk of breakage.

mimalloc sources will vendored without any option to use system libraries. Python's mimalloc requires several non-standard compile-time flags. In the future Python may extend or modify mimalloc for heap walking and nogil, too.

(This is a tracking bug until I find time to finish a PEP.)