jmalloc

jmalloc is a high-performance memory allocator on a different location of the high performance - low fragmentation scale than most allocators out there. It purposefully has an interface different from malloc. The difference is that jmalloc does not store the allocated block size anywhere, so the calling program needs to pass the block size to jmalloc when freeing a block.

Paging is needed to satisfy allocations larger than 2048 bytes, and most importantly, to allocate the arenas. So, don't use jmalloc on a system that lacks mmap!

Warning

Note that the allocators as-is use MAP_SHARED instead of MAP_PRIVATE. This means that forking and modifying the data from the forked process might not do what you want. On the other hand, forking overheads are lower with MAP_SHARED.

Usage

How to compile:

make

How to run:

time ./jmalloc2

The variant jmalloc2 is the current variant. The older jmalloc uses doubly linked lists instead of singly linked lists.

You can compare jmalloc performance to Linux allocator or various other allocators:

time ./lmalloc
LD_PRELOAD=../sfmalloc/libsfmalloc.so time ./lmalloc
LD_PRELOAD=../Hoard/src/libhoard.so time ./lmalloc
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.1 time ./lmalloc
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libtcmalloc.so.4 time ./lmalloc

Note the sfmalloc is buggy: it requires changing -lpthread to -pthread in the Makefile to actually work.

Link size

$ cd realapp
$ objdump -t allocreal|egrep '(text.*jm|lookup)'
0000000000000ac0 g     O .rodata  0000000000000100              lookup2
0000000000000810 g     F .text    0000000000000147              jmalloc
0000000000000bc0 g     O .rodata  0000000000000081              lookup
0000000000000960 g     F .text    00000000000000a7              jmfree

So, this version of jmalloc uses 879 bytes of memory, quite small for embedded systems. Note optimizations could compress both lookup tables to one 256-byte lookup table so it might be possible to fit jmalloc to even as small space as 768 bytes.

The simpler version of jmalloc not in the realapp directory is even smaller:

$ objdump -t jmalloc|egrep '(text.*jm|lookup)'
00000000000009e0 g     F .text   000000000000013c              jmalloc
0000000000000c60 g     O .rodata 0000000000000081              lookup
0000000000000b20 g     F .text   0000000000000087              jmfree

So, this simpler version uses only 580 bytes of memory. Note the simple version will be slower for large allocations, but has the benefit of being simpler and smaller.