Please take my reply in the spirit of someone being replied to very unreasonably but who doesn't count you in that group: Many languages, probably most notably

Please take my reply in the spirit of someone being replied to very unreasonably but who doesn't count you in that group: Many languages, probably most notably among them C++, have implemented varying degrees of what we might call "custom allocator policy". This is a rather extreme case of a generally over-applied maxim: "defaults matter". While it is completely possible to do a custom bump-allocator (which is the only kind of allocation on the table if you need to be fast without the help of `tcmalloc` or `jemalloc`), it's sufficiently high-friction that most write their own vector rather than doing the language lawyer thing of doing a "custom allocator". What John Blow proposes, quite reasonably if not obviously to me, is making a call-frame level arena in which all "heap" allocations are just past the last one, basically burning "reclaim opportunity" in light of the abundance of evidence that no one ever cares about memory that `jemalloc` has already done fragmentation around.