From the tcmalloc paper[0]:

> Speed is important for a malloc implementation because if malloc is not fast enough, application writers are inclined to write their own custom free lists on top of malloc. This can lead to extra complexity, and more memory usage unless the application writer is very careful to appropriately size the free lists and scavenge idle objects out of the free list.

An example of such an optimization is the arena allocator[1][2] employed by protobuf. Custom memory management schemes are not uncommon in performance critical code.

0: http://goog-perftools.sourceforge.net/doc/tcmalloc.html

1: https://en.m.wikipedia.org/wiki/Region-based_memory_manageme...

2: https://developers.google.com/protocol-buffers/docs/referenc...