I'm trying to do a simple build from the git 8.0.0 sources. The sources seem to build OK but a link step fails from running out of memory. I need some clues how to figure out where the bottleneck might be.
I'm trying to do a simple build from the git 8.0.0 sources. The sources
seem to build OK but a link step fails from running out of memory. I
need some clues how to figure out where the bottleneck might be.
My hardware is a rather ancient HP a6745f (AMD) with 4GB memory, 200 GB
HDD. OS is Kubuntu 18.10.
By default the build system will do a static link including debug, and
will use up all available cores for parallelsim. If you happen to have
a small amount of memory but multiple cores there can be several
multi-gigabyte links going on in parallel. Some cmake flag
suggestions:
Prevent concurrent links:
-DLLVM_PARALLEL_LINK_JOBS=1
If you don't need debug information:
-DCMAKE_BUILD_TYPE=Release
If you do:
-DBUILD_SHARED_LIBS=True
It has been mentioned that ld.bfd can use significantly more memory
than gold or LLD on debug builds, may be worth trying a different
linker. The -DLLVM_USE_LINKER=linker can be used
(Building LLVM with CMake — LLVM 18.0.0git documentation).
It has also been suggested to try compiling with clang and linking with lld. The gold linker should be already installed and is also recommended to reduce memory use.
apt install clang
apt install lld
4G is very tight. You will want to run just the terminal emulator for the compile and another running top to see when you go into swap and what process is doing that. You will need to avoid running anything else that is not absolutely necessary to make the most memory available.
You can control-c out of the compile sequence and restart at any time. The sequence will resume.
If you have more than one core and it goes into swap, you might stop the compile and use
ninja -j 1
to try to squeak through. You can stop the compile, go back to more cores, and restart in more easy stretches.
this morning and it appeared in general to stay below 4G and perhaps with enough swap you will make it. But when it goes into heavy swap, you are doing a number on your disk with not much forward gain.
If you change compilers such as from GNU cpp to clang after running the above cmake you will need to delete the build directory for the new compiler to be used.
Change the compiler (after apt above) by adding the following lines to /etc/environment and reboot.
export CC=clang
export CXX=clang++