[NobleExpress]

Using microbenchmarks to measure allocation performance is a bit misleading. The optimizations that occurred in the microbenchmarks may not actually occur for real-world code. Three branches vs two branches also makes no real difference as you are better served optimizing inefficiencies/performance somewhere else.

Also realloc'ing the most recently allocated object is not a common operation, at least in my experience building memory management systems.

[o11c]

Every time you stream the creation of an object, you're doing a recent-object-realloc. This shows up all the time for serialization, strings, vectors, etc. If you don't think you're doing it, you're probably using a library that hides it from you - or else doing something completely inefficient (in some languages, repeated string concatenation is O(n²)).

If your allocator exposes a "give me an arbitrarily large buffer up front to use, and I will give back what I don't need" that can beat realloc but otherwise you really do need it. I suppose on platforms without `mremap` you might want ?

The other alternative of course is "keep a list of small fragments, and join them at the end", but that just moves the `realloc` up a level, and is likely to give you fragmentation (which in some cases might even prevent the final allocation from succeeding).