Hint mechanism to require more "slots" to build a crate

[joshtriplett]

When building rust-lang/rust in parallel, I found that rustc_middle would take the vast majority of the compilation time and memory. I repeatedly ran into the OOM-killer because cargo would start up three more things building in parallel, and rustc_middle was already using 5-6GB of my 8GB of RAM. I'd like to be able to somehow hint to Cargo that it should treat rustc_middle as particularly heavy to build, and that it should count as multiple "slots" in the 4 parallel jobs Cargo would allow to run. That would have allowed me to successfully build within 8GB of RAM.

[luser]

Possibly a duplicate of #7437?

[epage]

#7437 is about package prioritization while this is about resource utilization.

[epage]

#12912 discusses the OOM problem and is exploring smaller and bigger solutions. To keep the conversation in one place, I'm closing this.