Two issues:

1. With all the submodules, the git pack files alone are 3.7GiB and with everything checked out it's in the neighborhood of 6 GiB... It would be nice to try and slim that down if possible. (Can git submodules be set to do a shallow fetch?)

2. Building in parallel (make -j) on a VM with 32 cores exposed (the physical hardware is 2x Xeon 8-core with hyperthreading, so 16 threads/CPU) results in ~64 parallel jobs running - at least in the llvm/bolt phase. The trouble with this is:

• Massive memory usage (something like 20GB)
• Probably slower build times (depending on what I'm building, I find that 24-30 jobs is actually fastest ... because the hyperthreading isn't actually another core.)
• The normal make options like -j16 aren't respected - when I try this, bolt and llvm appear to build in parallel but using one thread each.
• I haven't tested the I/O impact specifically, but using all the cores can definitely run into interesting situations where the build is I/O limited and not processor limited. (I'm not using NVMe drives in this case...)