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This article is about writing a simple memory allocator in C. We will implement malloc() This is a beginner level article, so I will not spell out every detail. This memory allocator will not be fast and efficient, we will not adjust allocated memory to align to a page boundary, but we will build Before we get into building the memory allocator, you need to be familiar with the memory layout of a program. A process runs within its own virtual address space that’s distinct from the virtual address spaces of other processes. This virtual address space typically comprises of 5 sections: TEXT SECTION: The part that contains the binary instructions to be executed by the processor. DATA SECTION: Contains non-zero initialized static data. BSS (Block Started by Symbol) : Contains zero-initialized static data. Static data uninitialized in program is initialized 0 and goes here. HEAP: Contains the dynamically allocated data. STACK: Contains your automatic variables, function arguments, copy of the end of which is demarcated by a pointer named program break or BRK. Now if we want to allocate more memory in the heap, we need to request the system to increment brk. Similarly, to release memory we need to As*uming we run Linux (or a Unix-like system), we can make use of sbrk() system call that lets us manipulate the program break. Calling sbrk(0) gives the current address of program break. Calling sbrk(x) with a positive value increments brk by x bytes, as a result allocating memory. Calling sbrk(-x) with a negative value decrements brk by x bytes, as a thread safe. It can can only grow or shrink in LIFO order. If you do a man 2 sbrk on your macbook, it will tell you: So, we will go ahead with sbrk() for our simple memory allocator. which must have been returned by a previous call to malloc(), calloc() or realloc(). But to free a block of memory, the first order of business is to know the size of the memory block to be freed. In the current scheme of things, this is not possible as the size information is not stored anywhere. So, we will have to find a way to store the size of an