Can we Implement Malloc function without use of brk() system call

Question

Is it possible to implement the malloc library function without using brk ? Can I use sbrk(0) to find out the current position of the program break, and then use sbrk(size) to increment it?

If yes, then why was brk added in the first place?

Answer 1

The use of brk and sbrk is discouraged in most current Unixes. Instead, malloc typically calls mmap anonymously (without file backing), and the address of a page is returned.

brk and sbrk assume a contiguous address space, which is no longer the case. Nowadays, a process may have many mappings in different ranges, with unmapped gaps in between.

The POSIX standard also warns us that:

The behaviour of brk() and sbrk() is unspecified if an application also uses any other memory functions (such as malloc(), mmap(), free()). Other functions may use these other memory functions silently.