I have allocated memory using malloc() in embedded Linux (around 10 MB). And checked the free memory it was 67080 kB but even after freeing it using free() it remains the same. It is only after the application is terminated the memory is available again. Does free() not make the freed memory available to the system, if so how to make it available.
Does free() not make the freed memory available to the system.
No, usually not.
malloc() normally requests memory from the OS by the low level sbrk() or mmap() call. Once assigned to the application, free() just returns the memory to a memory pool that belongs to the application. That is, it's not returned back to the OS for use in another process. (Though some heuristics are in-place to do so in certain circumstances).
If swap space is in place, this becomes less of a problem, the OS will swap out the unused memory of applications to make room for additional physical memory that's required.
if so how to make it available.
Exit the application.
Or you would need to write your own memory allocator that could do this.(which in the general case is not an easy task especially if you don't want to sacrifice overhead and speed).
For a relatively big single piece of 10MB, you could simply request anonymous memory with mmap() and the memory will be released back to the OS when you munmap() that piece of memory.