In many embedded systems, memory fragmentation is a concern. Particularly, for software that runs for long periods of time (months, years, etc...). For many projects, the solution is to simply not use dynamic memory allocation such as malloc/free and new/delete. Global memory is used whenever possible and memory pools for types that are frequently allocated and deallocated are good strategies to avoid dynamic memory management use.
In Embedded Linux how is this addressed? I see many libraries use dynamic memory. Is there mechanism that the OS uses to prevent memory fragmentation? Does it clean up the heap periodically? Or should one avoid using these libraries in an embedded environment?
There is no non-moving memory allocator that can avoid fragmentation of at least a log(M/m) factor, where M = the size of the largest object request, and m = the size of the smallest (this is a classic result due to Robson, 1971).
I work with folks who do real-time systems programming (including at Airbus), and they studiously avoid the use of dynamic memory allocation, instead using pools, as you mention.
There is, however, a big difference between an OS and memory allocation. Dynamic memory allocation, as exposed to the programmer, is part of the library and has little to do with the OS (except as a source of memory). Linux itself uses a slab-based memory allocator for its own internal purposes; I assume Embedded Linux does the same, but am not sure.