gcc/clang "virtual memory exhausted: Cannot allocate memory" in CI

By Kaveh Alemi·Latchkey

The compiler could not allocate more memory mid-compile. Like an OOM kill, this is a resource limit, not a code defect - heavy templates, LTO, or parallel jobs drove memory past the cap.

What this error means

gcc/clang aborts with "virtual memory exhausted: Cannot allocate memory" on a large file or under high -j parallelism, often intermittently.

g++: error: virtual memory exhausted: Cannot allocate memory

Common causes

How to fix it

Lower memory pressure

1. Reduce parallelism and disable LTO for the heaviest targets.
2. Raise or remove an overly tight address-space ulimit if one is set.

make -j2
ulimit -v unlimited   # if a virtual-memory cap was set

Use a larger-RAM runner

1. Move the build to a runner with more memory headroom.
2. Split monolithic translation units to cut peak usage.

How to prevent it

• Size runner memory to your heaviest compile. On self-healing managed runners like Latchkey, memory-exhaustion failures are treated as transient and auto-retried, and larger-RAM runners are available when a build needs more headroom.

Frequently asked questions

Related guides

References

• CMake documentation
• GitHub Actions documentation