The only problem is that he is wrong on almost every detail. He has apparently never heard of mmap, which is awkward because mmap is how memory is obtained, nowadays.

And if you want, you know, performance, it needs to know something about threads, pre-allocating chunks to assign to threads, and batching free ops per thread.

Most of what you can find about writing allocators is written by people who don't actually know how; and actually useful allocators are made by people who don't write tutorials about it.