I realized that my backup memory consumption has been growing since last March (See image). When searching for the cause I realized that
target folders from rust projects were taking up 30GiB of physical memory. Apparently cargo doesn't clean up old build artifacts and every new version of the compiler creates new build artifacts for all dependencies. Therefore, there is a lot of garbage floating around in these
target folders. I found a nice cargo tool called cargo-sweep. With it you can delete those unneeded build artifacts. It even allows for recursive search. So I did a
cargo sweep -r -i $HOME
This cleans all artifacts for toolchains that aren't installed anymore. It deleted almost 20GiB of physical memory from my system! I thought I'd give you a heads up so you can do the same if you need the space .
Btw, I am not saying that cargo's behavior is wrong. Just that the occasional clean up could make a lot of sense. I also excluded target folder from my backups now.