[llvm-dev] [llvm-toolchain v3.8.1] LTO: Linking clang hangs with ld.gold and LLVMgold.so plugin

[Piotr Padlewski via llvm-dev]

How big is your project?
LTO eats RAM even faster than chrome. For example linking clang with LTO
could take 16GB of ram.

Have you tried using LTO on your project on that machine, or is it your
first time?

Piotr


On Sat, Jul 23, 2016 at 2:42 AM, Sedat Dilek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Thu, Jul 21, 2016 at 12:01 PM, Sedat Dilek <sedat.dilek at gmail.com>
> wrote:
> > Hi,
> >
> > unfortunately, my build somehow hangs when linking clang binary and my
> > system is in an unusable state.
> >
> > My toolchain is clang-3.8, gold-1.11 and LLVMgold.so from binutils
> > v2.26.1 (both selfmade) and LTO-flag is enabled.
> > My buildsystem uses cmake-3.6.0 and ninja-1.7.1 (both prebuilt).
> > I have 52 last steps left in my 3rd build.
> >
> > My Linux-kernel is v3.13.0-92 from official Ubuntu repositories.
> >
> > On my Ubuntu/precise AMD64 I have ***4GiB RAM and 256MiB SWAP***.
> > Is this not enough RAM/SWAP for building/linking?
> >
> > Need some additional informations?
> >
> > Any help appreciated.
> >
> > Regards,
> > - Sedat -
> >
> > [1] http://llvm.org/docs/GoldPlugin.html
> >
> > P.S.: More informations...
> >
> > [ First toolchain build ]
> >
> > I built a 1st llvm-toolchain v3.8.1 with GCC v4.9.2 and binutils v2.22.
> > No speedup settings, no extra-patches applied etc.
> >
> > [ Selfmade binutils ]
> >
> > As binutils v2.22 was somehow not able to generate a LLVMgold.so on
> > Ubuntu/precise AMD64, I have built binutils v2.26.1 manually and use
> > all its binaries for building/linking (GOLD for linking).
> >
> > [ 2nd llvm-toolchain LLVMgold.so ]
> >
> > In a 2nd llvm-toolchain v3.8.1 build a LLVMgold.so was generated.
> > I placed LLVMgold.so into my selfmade
> > /opt/binutils-2.26.1/lib/bfd-plugins/ directory.
> > ( I had to create a bfd-plugins subdir manually. )
> >
> > [ 3rd llvm-toolchain LTO ]
> >
> > Now, I am able with backported LTO-flag from upstream to build with
> '-flto'.
> >
> > - EOT -
>
> Hi,
>
> in the meantime I tried with Linux v4.4.y LTS and 2GiB swap-space.
> So I have 4 GiB RAM and 2GiB SWAP in total 6GiB.
>
> Paul Rouschal recommended to reduce parallel-compile-jobs from 2 to 1...
>
> LLVM_PARALLEL_COMPILE_JOBS=1
> LLVM_PARALLEL_LINK_JOBS=1
>
> ...but that did not help.
>
> My Ubuntu/precise hangs and looking at top shows MEM/SWAP to be eaten.
>
> Anyone has experiences how much RAM or SWAP I need when building a
> LTO-optimized llvm-toolchain with Clang, GNU/gold and LLVMgold-Plugin?
>
> My build-script is attached.
>
> Thanks.
>
> Regards,
> - Sedat -
>
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