Memory fragmentation

Question

When I use malloc()s and free()s randomly, nested and with different sizes, at some point the memory will be fragmented because these operations leave a large list of small memory areas behind that are non-contiguous and therefore can't be allocated as one bigger piece.

A few questions on this:

• When this is done quite often so that memory is forced to be fragmented and then all these memory areas are free()d, can I assume these free areas are concatenated back to its original, contiguous size?

• When I always do a malloc() followed by free() for the same memory and never nest these calls, is the memory fragmented in this scenario too when allocated/freed sizes are always different?

Answer 1

No, there is no guarantee. According to N1570, 7.22.3 Memory management functions:

The order and contiguity of storage allocated by successive calls to the aligned_alloc, calloc, malloc, and realloc functions is unspecified.

Anyway, you have two choices to choose from:

1. Totally trust the library memory management functions.
2. Write you own memory managers, if you're really confident.

If I were you, I would definitely trust the existing functions, because modern implementations are super smart.