While the hmap struct can be stack allocated if it does not escape, I’m pretty sure the buckets still need to be heap-allocated. I do not believe hmap has a “flat structure” variant which could live entirely on the stack, though I could be wrong.
It's most definitely not. Logging is crucial for monitoring services, and making logging statements many times slower will either sink your service or push developers to avoid logging and making the service impossible to debug.
Most log metadata will be attached by libraries and middleware, so service/application devs won't even see most of it.