ft_malloc

This is a dynamic memory allocation library for C17, designed to mimic the behavior of malloc in libc.

Why build one ?

The operating system provides mechanisms to allocate memory from the heap using system calls. While C offers straightforward functions that wrap these system calls, they come with both advantages and disadvantages.

sbrk:

• Allocates memory in a contiguous manner, making arbitrary deallocation difficult and leading to inefficient long-term memory usage and fragmentation.
• Has a complex usage pattern.
• System calls introduce overhead, making them "slow".

mmap:

• Uses a page-based allocation strategy, making it inefficient for small memory allocations.
• System calls introduce overhead, making them "slow".

Intent of ft_malloc

Our goal is to enhance performance by reducing the amount of system calls, albeit at the cost of memory pre-allocation, memory fragmentation. In other words: additional overhead.

Ideally fragmentation is kept minial.

Gains:

• Fewer system calls through pre-allocation, enabling more efficient memory distribution via pointer arithmetic.
• Reduced fragmentation through optimized memory management techniques.
• Simplified memory management, making allocation easier to handle.

Losses:

• Increased memory usage due to additional metadata for tracking and managing allocations.
• Extra memory overhead from pre-allocation.

With our malloc implementation, we aim to optimize memory allocation while balancing performance and efficiency.

Internal structure

In this schema:

• The term header can be used interchangeably with metadata.
• Marena is the only element defined on the stack. Each thread has it's own instance as it is set as ThreadLocal.
• From left to right, the bigger element includes the smaller ones.

Is stored on the stack:

• The marena header (thus the pointers to the mregion heads).

Is stored on the heap (via mmap):

• Each mregion catalogued through their headers.

libft_mini

I was not satisfied by my original libft. I decided to recreate one that answers my needs while using a more modern approach, now that I know C better.

Usage

If you want to use this malloc implementation instead of the libc's one inside existing programs you have to:

• Prepend the path where libft_malloc.so is located in LD_LIBRARY_PATH environment variable. Ensure our *.so file is read first and has precedence.
  Please see how it's been done in my tester's Makefile.
• Ensure the existing program only uses functions that are present in both the header file of libc's malloc and ours.