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Comment by vetinari | Hacker News Reader

Be sure to have enough RAM, so you will not run out of it.

(For some reason, when building projects like LLVM with -j 16, 32 GB w/o swap may be not enough. With -j 2, it is enough, but takes an eternity).

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If you build LLVM often, use the shared library build (BUILD_SHARED_LIBS=true). Most of the memory usage (and a large part of the time in incremental builds) comes from linking final artifacts if you do not use shared libraries.

Thanks for the tip, unfortunately, when I'm building it (occasionally), the LLVM itself is part of another project (AMDVLK) and changes too.

Indeed, if you're bottlenecked on RAM, memory bandwidth itself will also be an issue (it seems to be the foremost bottleneck in modern compute, outside of single-threaded workloads. Part of why C-like languages are again becoming popular these days - they economize on memory-bandwidth per core). Might want to skip Ryzen 9 altogether and wait until the Threadripper parts are announced.

Yes, building Ceph with less than 24 GB ram on a 16 core machine will make it run into Out Of Memory situations here, so that the OOM-Killer is summoned and kills the build..

Make sure to install and use ccache and give it a big cache size on a fast ssd (I use 96GiB). It speeds up rebuilds (after the cache is populated) quite significantly.

The initial plan is for a 32GB (2x 16GB sticks) with plans to move to 64GB when possible.

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