What is needed to integrate jemalloc into a Swift application?

taylorswift · December 7, 2024, 11:22pm

for a long time, i have been using export LD_PRELOAD=/usr/lib/aarch64-linux-gnu/libjemalloc.so.2 to add jemalloc to Swift applications, which i understand is sufficient for the default, dynamically-linked standard library build configuration.

according to the jemalloc wiki, this doesn’t necessarily work “if [the] application does not statically link a malloc implementation”. so i want to understand what this means in the context of --static-swift-stdlib.

if i build with --static-swift-stdlib, but still dynamically link Glibc, will export LD_PRELOAD still work?
if i build with --static-swift-stdlib, and also statically link Musl, will export LD_PRELOAD still work?

0xTim · December 8, 2024, 3:06am

We've solved question 1 in Vapor, you can pass a linker flag to the compiler

github.com

vapor/template/blob/main/Dockerfile#L27


      
          # as long as your Package.swift/Package.resolved
          # files do not change.
          COPY ./Package.* ./
          RUN swift package resolve \
                  $([ -f ./Package.resolved ] && echo "--force-resolved-versions" || true)
          
          # Copy entire repo into container
          COPY . .
          
          # Build everything, with optimizations, with static linking, and using jemalloc
          # N.B.: The static version of jemalloc is incompatible with the static Swift runtime.
          RUN swift build -c release \
                          --static-swift-stdlib \
                          -Xlinker -ljemalloc
          
          # Switch to the staging area
          WORKDIR /staging
          
          # Copy main executable to staging area
          RUN cp "$(swift build --package-path /build -c release --show-bin-path)/App" ./

taylorswift · December 8, 2024, 10:52pm

does that mean export LD_PRELOAD is not doing anything in that scenario?

0xTim · December 8, 2024, 11:12pm

Correct