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Two-Level Segregated Fit memory allocator implementation. Written by Matthew Conte ( Released under the BSD license.


  • O(1) cost for malloc, free, realloc, memalign
  • Extremely low overhead per allocation (4 bytes)
  • Low overhead per TLSF management of pools (~3kB)
  • Low fragmentation
  • Compiles to only a few kB of code and data
  • Support for adding and removing memory pool regions on the fly


  • Currently, assumes architecture can make 4-byte aligned accesses
  • Not designed to be thread safe; the user must provide this


This code was based on the TLSF 1.4 spec and documentation found at:

It also leverages the TLSF 2.0 improvement to shrink the per-block overhead from 8 to 4 bytes.


2016/04/10 - v3.1

  • Code moved to github
  • tlsfbits.h rolled into tlsf.c
  • License changed to BSD

2014/02/08 - v3.0

  • This version is based on improvements from 3DInteractive GmbH
  • Interface changed to allow more than one memory pool
  • Separated pool handling from control structure (adding, removing, debugging)
  • Control structure and pools can still be constructed in the same memory block
  • Memory blocks for control structure and pools are checked for alignment
  • Added functions to retrieve control structure size, alignment size, min and max block size, overhead of pool structure, and overhead of a single allocation
  • Minimal Pool size is tlsf_block_size_min() + tlsf_pool_overhead()
  • Pool must be empty when it is removed, in order to allow O(1) removal

2011/10/20 - v2.0

  • 64-bit support
  • More compiler intrinsics for ffs/fls
  • ffs/fls verification during TLSF creation in debug builds

2008/04/04 - v1.9

  • Add tlsf_heap_check, a heap integrity check
  • Support a predefined tlsf_assert macro
  • Fix realloc case where block should shrink; if adjacent block is in use, execution would go down the slow path

2007/02/08 - v1.8

  • Fix for unnecessary reallocation in tlsf_realloc

2007/02/03 - v1.7

  • tlsf_heap_walk takes a callback
  • tlsf_realloc now returns NULL on failure
  • tlsf_memalign optimization for 4-byte alignment
  • Usage of size_t where appropriate

2006/11/21 - v1.6

  • ffs/fls broken out into tlsfbits.h
  • tlsf_overhead queries per-pool overhead

2006/11/07 - v1.5

  • Smart realloc implementation
  • Smart memalign implementation

2006/10/11 - v1.4

  • Add some ffs/fls implementations
  • Minor code footprint reduction

2006/09/14 - v1.3

  • Profiling indicates heavy use of blocks of size 1-128, so implement small block handling
  • Reduce pool overhead by about 1kb
  • Reduce minimum block size from 32 to 12 bytes
  • Realloc bug fix

2006/09/09 - v1.2

  • Add tlsf_block_size
  • Static assertion mechanism for invariants
  • Minor bugfixes

2006/09/01 - v1.1

  • Add tlsf_realloc
  • Add tlsf_walk_heap

2006/08/25 - v1.0

  • First release