About [1] Sorry about that: the document you linked to is amazingly stale. tcmalloc has been releasing memory to the system for many years. See for example the IncrementalScavenge routine in a version of page_heap.cc from Dec 2008:

https://code.google.com/p/gperftools/source/browse/trunk/src...

One caveat: physical memory and swap space is released, but the process's virtual size will not decrease since tcmalloc uses madvise(MNONE) to release memory.

About [2], code using tcmalloc-specific features/symbols is definitely a problem. I would strongly advise against doing that and sticking to the libc interfaces instead for the reason you pointed out.