Tlsf

Two Level Segregated Fit memory allocator implementation. Written by Matthew Conte (matt@baisoku.org). Public Domain, no restrictions.

http://tlsf.baisoku.org

Notes

This code was written to the TLSF 1.4 spec and documentation found at:

http://rtportal.upv.es/rtmalloc/allocators/tlsf/index.shtml

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

Features

• O(1) cost for malloc, free, realloc, memalign
• Extremely low overhead per allocation (4 bytes)
• Low overhead per pool (~3kB)
• Low fragmentation
• Compiles to only a few kB of code and data

Caveats

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

Known Issues

• Due to the internal block structure size and the implementation details of tlsf_memalign, there is worst-case behavior when requesting small (<16 byte) blocks aligned to 8-byte boundaries. Overuse of memalign will generally increase fragmentation, but this particular case will leave lots of unusable "holes" in the heap. The solution would be to internally align all blocks to 8 bytes, but this will require significantl changes to the implementation. Contact me if you are interested.

History

2011/10/20 - v2.0

• 64-bit support
• More compiler intrinsics for ffs/fls
• ffs/fls verification during pool 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