How are malloc and free implemented?

Question

I want to implement my own dynamic memory management system in order to add new features that help to manage memory in C++.

I use Windows (XP) and Linux (Ubuntu). What is needed to implement functions like 'malloc' and 'free'? I think that I have to use lowest level system calls.

For Windows, I have found the functions: GetProcessHeap, HeapAlloc, HeapCreate, HeapDestroy and HeapFree.

For Linux, I have not found any system calls for heap management. On Linux, malloc and free are system calls, are not they?

Thanks

Edit:
C++ does not provide garbage collector and garbage collector is slow. Some allocations are easy to free, but there are allocations that needs a garbage collector.

I want to implement these functions and add new features:
* Whenever free() be called, check if the pointer belongs to heap.
* Help with garbage collection. I have to store some information about the allocated block.
* Use multiple heaps (HeapCreate/HeapDestroy on Windows). I can delete an entire heap with its allocated blocks quickly.

Answer 1

On linux, malloc and free are not system calls. malloc/free obtains memory from the kernel by extending and shrinking(if it can) the data segment using the brk system calls as well as obtaining anonymous memory with mmap - and malloc manages memory within those regions. Some basic information any many great references can be found here