msgpack-rust | MessagePack implementation for Rust / msgpack.org | Serialization library

I have a large, somewhat complicated data structure that I can serialize and deserialize with serde and rmp-serde, but I find that deserialization is quite slow. I think this is because my data structure includes two rather large HashMaps. I don't know how efficiently rmp_serde::from_slice can create the HashMap -- will it initialize using .with_capacity or does it just create a HashMap and insert one-by-one? And besides, I've found that AHashMap gives me considerable performance improvements elsewhere, so I'm trying to avoid using the default HashMap.

I want to try deserializing with rmpv::decode::value::read_value, but I'd like to leave most of the deserialization to rmp_serde and only implement some deserialization myself given some Value. Is there a way to choose which pieces I manually deserialize?

Conceptually, what I'd like to do is something like: