Many codegen units plus full debug info produce large object files, and the final link loads them together - spiking memory at the link step. On a small runner that spike triggers an OOM kill.
What this error means
The build compiles all crates, then the linker (ld/lld) is killed or the job dies with exit 137 specifically during linking - not in any one rustc invocation. Lowering debug info or codegen units makes it pass.
cargo output
= note: collect2: fatal error: ld terminated with signal 9 [Killed]
compilation terminated.
error: linking with `cc` failed: signal: 9 (SIGKILL)
Common causes
Large object files at link time
High codegen-units plus full debug = 2 info produce many large objects; the linker maps them all into memory at once, peaking well above per-crate compile memory.
Debug symbols inflating the link
Full debuginfo in a workspace with many crates balloons the linker’s working set, which is what gets OOM-killed.
How to fix it
Lower codegen-units and debug info
Fewer, larger codegen units and reduced debuginfo cut the linker’s peak memory.
Cargo.toml
[profile.dev]
codegen-units = 16
debug = 1 # line tables only, much smaller
[profile.release]
codegen-units = 1
lto = "thin"
Split or strip debug info
Splitting debuginfo into separate files keeps it out of the link’s peak working set.
Tune codegen-units, debug, and lto for CI’s memory budget.
Use split-debuginfo so debug data doesn’t inflate the link.
Right-size the runner for the linker’s peak, not the average.
Frequently asked questions
What causes "codegen-units memory blowup"?
High codegen-units plus full debug = 2 info produce many large objects; the linker maps them all into memory at once, peaking well above per-crate compile memory.
How do I fix codegen-units memory blowup?
Fewer, larger codegen units and reduced debuginfo cut the linker’s peak memory.
Can Latchkey fix this automatically?
Yes. Latchkey runs your GitHub Actions on managed runners that detect this failure, apply the fix, and retry the job automatically - self-healing is on by default.
