> Hey all, as some keen-eyed commenters have pointed out, it looks like the rust program is not actually equivalent to the go program. The go program parses the string once, while the rust program parses it repeatedly inside every loop. […] The perf gains from jemalloc are real, but it's probably not the allocators fault. I've updated the post with this message as well.

I don't know that it would be a gain: Rust is pretty good at decoding UTF8 quickly given how absolutely fundamental that operation is, and "caching" the decoded data would increase pressure on the allocator.

Unless you also changed the interface of the levenshtein to hand it preallocated cache, source and destination buffers (or the caller did that).

edit: to the downvoter, burntsushi did the legwork of actually looking at this[0] and found caching the decoding to have no effect at best, unless the buffers get lifted out of the function entirely, which matches my comment's expectations.

[0] https://news.ycombinator.com/item?id=23059753

> But yes, I did benchmark this, even after reusing allocations, and I can't tell a difference. The benchmark is fairly noisy.