🧠 ft_malloc

custom memory allocator written in C, inspired by the behavior of the libc malloc, free, and realloc.

it uses dynamic memory management using low-level system calls such as mmap and munmap, with a focus on performance && memory efficiency.

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🚀 Features

• custom implementations of:
  • malloc
  • free
  • realloc
• memory zones:
  • TINY allocations
  • SMALL allocations
  • LARGE allocations
• page-based memory management using mmap
• lazy allocation strategy (no full pre-initialization)
• thread safety w/ pthread_mutex

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architecture

memory is divided into zones:

Type	Size Range	Storage Strategy
TINY	small allocations <= 128	pre-mapped zones
SMALL	medium allocations <= 1024	pre-mapped zones
LARGE	large allocations > 1024	one mmap per allocation

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📦 zone layout

each zone contains:

[t_page][t_block][data][t_block][data]...

• t_page → metadata: whole zone
• t_block → metadata: for each allocation
• data → user raw memory

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⚙️ allocation Strategy

🔹 lazy initialization

instead of pre-creating all blocks:

• 1 large free block is created initially, blocks are split on demand during each allocation

significantly reduces:

• page reclaims
• memory overhead
• initialization cost
• & avoids touching unused memory pages (lazy paging)

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🔹 block Splitting

allocating:

[FREE BLOCK]
↓ split
[ALLOCATED][FREE REMAINDER]

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🔹 free Strategy

• block are returned to the free list of corresponding page -> minimizes page reclaims
• no immediate munmap for TINY/SMALL zones
• munmap is used only for LARGE allocations

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🧪 testing

example test:

while (i<1024)
{
addr=malloc(1024);
addr[0] =42;
free(addr);
i++;
}

char*addr1; char*addr3; addr1= (char*)malloc(16*M); strcpy(addr1, "Bonjours\n"); print(addr1); addr3= (char*)realloc(addr1, 128*M); addr3[127*M] =42; print(addr3); 

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🛠 Build

make

this produces (library):

libft_malloc.dylib (macOS)
libft_malloc.so (Linux)

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▶️ USAGE

macOS

export DYLD_INSERT_LIBRARIES=./libft_malloc.dylib
export DYLD_FORCE_FLAT_NAMESPACE=1
./your_program

linux

export LD_PRELOAD=./libft_malloc.so
./your_program

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debug

inspect allocations with:

show_alloc_mem();

test my malloc performance with:

/urs/bin/time -l ./your_test

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possible improvements

• block-coalescing (no advanced coalescing of adjacent free blocks)
• Better fit strategies (best-fit / segregated lists)

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