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These module docs are in beta and may be incomplete.

modm:tlsf: TLSF Allocator

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



Number of subdivisions per memory pool: 16{ 16, 32 }


Minimum pool size in byte: 524288{ 4096 .. 524288 .. 536870912 }


modm:tlsf modm_tlsf modm: tlsf modm_platform_core modm: platform: core modm_platform_core->modm_tlsf