I have been trying to find information on whether GNU libc malloc uses size classes like jemalloc. I haven't found any information. I'd like to be able make a better estimate of the savings obtained by using std::vector::reserve() against letting a vector grow incrementally with push_back. I know that GNU stlibc++ will double the vector size whenever it needs to grow, but I can't calculate the real savings without knowing how much malloc is really allocating.
The allocations that I'm looking at are all fairly small (from about 140 to 1500 bytes, but there are several million of them). That means that they are well below the MMAP_THRESHOLD limit.
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