It is based on the Slab allocator concept.
Functions in this library provide fast, scalable object-caching memory allocation with multithreaded application support.
In addition to the standard malloc(3C) family of functions and the more flexible umem_alloc(3MALLOC) family, libumem provides powerful object-caching services as described in umem_cache_create(3MALLOC).
[3] Getting started with libumem is easy; just set LD_PRELOAD to "libumem.so" and any program executed will use libumem's malloc(3C) and free(3C) (or new and delete).
[4] This slab allocator is designed for systems with many threads and many CPUs.