Difference Between Mmap and Malloc

Edited by Diffzy | Updated on: April 30, 2023


Difference Between Mmap and Malloc

Why read @ Diffzy

Our articles are well-researched

We make unbiased comparisons

Our content is free to access

We are a one-stop platform for finding differences and comparisons

We compare similar terms in both tabular forms as well as in points


Dynamic memory in C refers to memory allocation in the C programming language made possible by several functions in the C standard library. Malloc, which deals with memory allocation, is one of them. A memory-mapped system with its distinct I/O is known as mmap in the UNIX operating system. At first glance, mmap and malloc appear to execute the identical task, but closer examination exposes several distinctions. In C programming, a dynamic memory points to the memory allocation in the C standard library through a collection of functions. One of these is malloc, which is used to allocate memory. Mmap follows next. It is employed as a memory-mapped system with particular input and output. These two carry out identical tasks, but further research reveals specific distinctions.

Mmap vs. Malloc

The primary distinction between mmap and malloc is that mmap executes much faster than malloc. While mmap is a system, malloc is the primary memory allocation interface. This is what causes the kernel to look for addresses that are big enough to support mapping multiple pages. Mmap is a POSIX multi-tasking system used in computing that stores all data, files, and devices in its memory. Since data cannot be read directly from the disc, this technique, sometimes referred to as a memory-mapped file, copies data into the system's physical memory. The phrase "memory allocation," abbreviated "Malloc," is used to dynamically allocate a sizable block of data according to the requested size. If it is successful, malloc produces a pointer that links to the first byte of the memory allocated; if unsuccessful, it returns NULL. Malloc uses a variety of achievements that are present in the actual memory allocation method.

First, it is crucial to determine whether any data suggests that the available memory is significantly stifled. This is accomplished by evaluating the program's efficiency in memory management. Malloc is the primary memory allocation interface. The C library's largest is this. It includes mmap as a component of the management code. Malloc compiles all of the system resources when it is operating. One of the memory management techniques systems use to guarantee enough memory allocation is the kernel, which allows for the mobilization of additional system resources. The procedure is not easy, however, and has been made challenging to deter users from developing basic programs that may disrupt memory allocation and thus lead to subpar performance.

Difference Between Mmap and Malloc in Tabular Form

Parameters Of Comparison Mmap Malloc
Description Mmap is a system call that instructs the kernel to locate a prominent address for page mapping. Malloc is the primary memory allocation interface that collects the system's resources.
Functionality Mmap converts it to a kernel land by using the context switch. The memory block is allocated by malloc in apile.
Outcomes Mmap does not impact another system's performance. Malloc causes the system to become disorganized and operate poorly.
Commonly known As A system call is sometimes referred to as Mmap.

The primary memory

Allocation interface is another name for malloc.
Most appropriate for Mmap is the most effective tool for accelerating how quickly apps respond. Any system program that needs to allocate memory should use malloc.
Procedures Mmap employs a context switch that transforms into kernel land. Most of the memory management procedures typically use malloc.
Response Mmap can be used to accelerate how quickly programs respond. As opposed to using mmap, malloc is the better option for allocating memory in any program running on the system.

What Is A Mmap?

Mmap is a POSIX-compliant Unix system call that maps data, files, or devices into memory. It is a memory mapping technique using input and output. During the calling procedure, a new mapping is formed in the virtual address space. A new mapping's starting point is located in addr., and the length of the mapping is determined by the length parameter (which should be more than 0). If the addr is discovered to be NULL, the kernel chooses the address and creates the mapping, which is the simplest way to create a mapping.

A process address space can be mapped to files or devices using the mmap() method. A file can be accessed in a program like an array when mapped to a process address space. This is one of the fastest methods for accessing file data and offers a coding interface that is smooth and appropriate for a data structure that can be evaluated without the need for an abstraction of reading and writing from files. This post will discuss how to utilize Linux's mmap() function.

Features Of Mmap

  • Address - This parameter specifies a desired mapping beginning address. The kernel chooses a page boundary close by and creates the mapping if there are no existing mappings; otherwise, the kernel chooses a new address. If this parameter is NULL, the kernel is free to put the mapping anywhere it wants.
  • Length refers to the total amount of bytes that will be mapped.
  • Protect - By using this parameter, you may limit the types of access that are allowed. The following flags may constitute logical "OR" statements in this argument: PROT READ; PROT WRITE; PROT EXEC; PROT NONE. The permissions on the content are read, write, and execute access kinds.
  • Flags - This parameter modifies the map's appearance. The flags often have the following values:
  • MAP SHARED - This flag allows any processes mapped to this object to share the mapping. The file will be updated when the mapping region is modified.
  • When MAP PRIVATE is set, no other processes will be able to see the mapping, and no modifications will be saved to the file. C
  • Create an anonymous mapping by using the option MAP ANONYMOUS or MAP ANON. An unknown mapping is not associated with any files. The heap is extended using this mapping as the fundamental primitive.
  • MAP FIXED - The system must be compelled to utilize the precise mapping address supplied in the address when this flag is used. The mapping will be unsuccessful if this is not feasible.
  • Five. filedes - The file descriptor that has to be mapped is this one.
  • Offset - This is the distance from the beginning of the file mapping. For the file open on filedes descriptor, the mapping links to (offset) to (offset+length-1) bytes.

Some Examples Of Mmap

We will now examine an example program employing the mmap() system function for each of the following:

Memory Placement (Example1.c)

In Example1.c, we use mmap to allocate memory. Here, reading and writing to the mapped region were protected using PROT READ | PROT WRITE. The flags MAP PRIVATE | MAP ANONYMOUS were used. MAP ANONYMOUS is used since no files have been mapped here, and MAP PRIVATE is used because the mapping region is not shared with other processes. The offset value and file descriptor are set to 0 for the same reason.

File Reading (Example2.c)

The file "file1.txt" has been mapped in Example2.c. We generated the file first, then mapped it to the process. Because we want to read the file in this instance, we open it in O RDONLY mode.

Interprocess communication when writing a file (Example3.c) (Example4.c) - In Example4.c, the array is initially initialized with specific values before being updated by the child process. Because both methods share the mapped memory, the parent process reads the values that the child process modified.

What Is A Malloc?

A reference to the newly allocated memory is returned by the malloc () memory allocation function after allocating the specified number of bytes. There is no initialization of the RAM. If the size byte name is 0, malloc () will send either NULL or a unique value reference, which may subsequently be correctly supplied to free (). The free () function releases the memory area referred to by ptr, and that malloc was meant to send back (). If the free (ptr) has already been called, undefined behavior is stated to occur. No action is taken or executed if the ptr is found to be NULL. For any value of size, if the ptr is found to be NULL, the call value is equal to malloc (size); if it is equivalent to 0, and the ptr is not found to be NULL, the call value is equal to free (ptr).

The built-in function in C for allocating memory is called malloc. This function allocates a certain amount of memory to a newly constructed array. Additionally, a reference to the memory area this method used to allocate is returned. There are many instances where we only want an array to have a specified amount of space at run time in the world of programming, where every space matters. In other words, we want to dynamically generate an array that takes up a certain amount of space. Malloc is used in this process.

Only when the ptr is NULL should a prior call to malloc have sent it back (). A free (ptr) is completed once the area that was pointed at is modified. Linux uses an optimistic memory allocation approach by default. Therefore there is a potential that memory might be lost if malloc () returns a non-NULL. Additionally, the OOM killer will only kill a small number of processes if it turns out that the system is memory-constrained.

Need For Malloc In C Programming

The allocation of dynamic memory in the C programming language will be covered in this section. Memory allocation is the purpose of the built-in library function known as malloc. When a program runs, malloc is used to allocate memory blocks of a certain size. When the user or programmer does not know how much memory space is required in the application, it causes a dynamic memory allocation during runtime. To reserve a contiguous memory block that returns a pointer of type void, which is converted into a pointer of any form, the memory size (in bytes) is input at runtime. Because malloc does not populate the memory at execution time when creating dynamic memory, the memory block has some default trash values. The stdlib.h header file contains the definition of the malloc function. Therefore, while utilizing the malloc function in our application, we must utilize the header file.

Functions Of Malloc

How to Apply A pointer to the start of the allocated block is returned by the malloc () function, which allocates memory of the desired size. We need to make a variable to store this returned pointer. The pointer needs to be the same type as the malloc command.

Unlike other languages, C needs to be informed of the data type it is allocating memory for.

  1. int* arrayPtr: Fortunately, we can utilize the sizeof() function from the C language.

(int *)malloc(10 * sizeof(int));

  • ArrayPtr: This statement allocated memory for an array of 10 integers using the malloc function. Use the sizeof() method to determine the size of the machine because sizes might vary between computers. Before the program exits, any memory that was allocated during operation must be released. We may use the free() method to release memory.
  • Freely (arrayPtr): This command will deallocate the previously allocated RAM. C lacks a trash collector, unlike some other languages like Java. Because of this, a memory that wasn't correctly released will keep getting allocated even after the application is terminated.

Differences Between Mmap and Malloc in Points

  • Mmap is a system call, whereas malloc is the primary memory allocation interface.
  • Mmap aids page mapping, whereas malloc distributes devices and data in a system.
  • Malloc allocates memory in a device, but Mmap translates the context switch into kernel territory.
  • Mmap is chosen for responding quickly, but malloc is preferred for allocating memory in a system.
  • Mmap does not affect the performance of any other system program once it has completed its task, but malloc disrupts the performance to prevent it from being used by those who can disorganize the system.
  • Malloc is responsible for the majority of the memory management process. If the software demands more memory, it borrows it from the operating system. Mmap, on the other hand, employs a context switch to translate into kernel land.
  • Malloc, as opposed to mmap, is ideally suited for allocating memory in any program running on the system. Except in exceptional circumstances, this is expected to happen by default.
  • Mmap is preferable to malloc because memory utilized by mmap is promptly returned to the operating system. Unless there is a data segment break, the memory used by malloc is never recovered. This memory is saved specifically to be reused.


Malloc is an abbreviation for the main memory allocation point. A mmap system call asks the kernel to discover unoccupied areas in application addresses that can handle the mapping of multiple memory pages. Mmap is not recommended for memory allocation since it splits available memory and does not support system calls.  Finally, mmap is a system call that instructs the kernel to find an empty region in an application address that would fit in mapping various memory pages.

In contrast, malloc is a memory allocation point that creates a given size block of memory. The memory is configured at run time. Therefore no more space may be reserved before the program's execution. While mmap occasionally outperforms malloc, it is not advised to choose it when allocating memory since it divides the memory and is unable to make a system call afterward.

Cite this article

Use the citation below to add this article to your bibliography:



MLA Style Citation

"Difference Between Mmap and Malloc." Diffzy.com, 2023. Tue. 26 Sep. 2023. <https://www.diffzy.com/article/difference-between-mmap-and-malloc-760>.

Edited by

Share this article