How do you handle memory allocation in your system programs?

1 Memory management

Memory management is the process of allocating and freeing memory for different purposes, such as code execution, data storage, stack frames, heap objects, and memory-mapped files. Memory management can be done either statically, dynamically, or automatically. Static memory allocation is done at compile time or load time, and does not change during the program's execution. Dynamic memory allocation is done at run time, and allows the program to request and release memory as needed. Automatic memory allocation is done by a garbage collector, which periodically reclaims memory that is no longer used by the program.

2 Memory models

Memory models are abstract representations of how the program views and accesses the memory, and the choice of model depends on the hardware architecture, programming language, and system requirements. A flat memory model has a single, contiguous address space that covers the entire physical memory, making it simple and efficient. However, this limits the amount of memory that can be used and does not provide any protection or isolation between different processes or segments. Alternatively, a segmented memory model has multiple, non-contiguous address spaces divided into segments of different sizes and types. This allows more flexibility and security, but adds complexity and overhead to memory management and addressing. Finally, a paged memory model has a single, logical address space split into fixed-size units called pages. This enables virtual memory and allows for sharing of memory between different processes or segments.

3 Memory allocation strategies

Memory allocation strategies are methods of finding and assigning free memory blocks to satisfy the program's requests. Different strategies have different trade-offs between speed, space, and fragmentation. For example, the first fit strategy is fast and simple, but it can cause external fragmentation due to the gaps between allocated blocks. On the other hand, the best fit strategy minimizes external fragmentation, but it can be slow and cause internal fragmentation. The worst fit strategy maximizes the size of the remaining free blocks, but it can also cause internal fragmentation and degrade performance over time. Lastly, the buddy system reduces external fragmentation and simplifies allocation and deallocation, but it can also cause internal fragmentation and overhead.

4 Memory allocation functions

Memory allocation functions are the interfaces that the program uses to request and release memory from the system. These functions differ in semantics and behavior, depending on the programming language, the library, and the operating system. For instance, malloc and free are standard C library functions for dynamic memory allocation; malloc takes a size argument and returns a pointer to a block of memory, while free takes a pointer argument and releases the block of memory it points to. C++ operators new and delete also handle dynamic memory allocation; new takes a type argument and returns a pointer to a newly constructed object, while delete takes a pointer argument and destroys the object it points to. Additionally, POSIX system calls mmap and munmap are used for memory-mapped file allocation; mmap takes a file descriptor, size, protection mode, and flag, while munmap takes a pointer and size. Memory allocation functions can be used to access files or devices as memory or create shared memory between processes. It is important for programmers to manage pointers and sizes carefully in order to avoid memory leaks, double frees, or dangling pointers.

5 Memory allocation tips

Memory allocation is a complex and error-prone task, and it can significantly impact the performance, reliability, and security of your system programs. To handle memory allocation effectively, you should use the appropriate memory model and strategy for your system requirements and constraints. Additionally, you should use the appropriate memory allocation function for your programming language and library, checking the return values and handling any errors gracefully. Furthermore, it is important to free allocated memory when it is no longer needed and protect it from unauthorized or malicious accesses or modifications. Additionally, you should align the allocated memory to the natural boundaries of the data types and the hardware architecture, as well as use padding or alignment attributes to avoid misaligned accesses or undefined behaviors.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?