flang-20 port is building VERY SLOWLY, "memory pressure" (Activity monitor) is very high

[Chris Jones]

Just to be clear, the issue might not be a traditional C/C++ byild step. All LLVM projects at times run something called llvm-tblgen that takes X.td files (target description) and produces c++ and other formats from them. These can take as much or sometimes more memory than just the regular clang build steps. That said, i have not seen them take anything that would make an allocation of 1GB per process not enough, but I just mention it as you need to watch out for these as much as anything else.

> On 7 Mar 2025, at 6:19 pm, Ryan Carsten Schmidt <ryandesign at macports.org> wrote:
> 
> On Mar 7, 2025, at 04:32, Chris Jones via wrote:.
>> 
>> Kenneth please open a trac ticket with more details, how many thread are start for you, where in the build specifically do you have issues etc.
> 
> And please check Activity Monitor's Memory tab while a flang-20 build that is exhibiting this problem is underway. I checked a few build machines that are currently building flang-20 and did not see high memory use at that moment, but it might only happen at certain times during the build. If you see high memory use, attach to the ticket a screenshot from Activity Monitor or let us know about how much memory the clang processes were taking. Also make sure you're not low on disk space since that can also lead to slowness.
> 
> And just to answer the question you asked, yes, you can tell MacPorts not to start multiple simultaneous build commands with:
> 
> sudo port install flang-20 build.jobs=1
> 
> However, to reproduce the problem to get the information from Activity Monitor, just do the build normally, letting MacPorts start many jobs.