Engineering: Heaps Do Lie — Debugging a Memory Leak in vLLM
Mistral AI News40 days agoTutorialMathis Felardos, a Mistral AI engineer, shares a technical deep-dive into tracking down a memory leak in vLLM, the widely adopted open-source LLM inference server. The investigation exposed a core frustration in systems debugging: heap profiling tools can actively mislead engineers rather than illuminate the true source of memory growth. The post offers practical engineering insight for teams operating LLM serving infrastructure in production.
Heaps do lie: debugging a memory leak in vLLM
Mistral AI News50 days agoTutorialMistral AI published an engineering deep dive on a memory leak found during vLLM disaggregated serving tests. The leak appeared only with a specific stack involving Mistral Medium 3.1, NIXL, UCX, graph compilation, and P/D disaggregation, with RSS growing steadily despite heap profilers looking normal. The team used pmap, BPFtrace, and targeted GDB automation to trace the issue to UCX mmap hooks and applied configuration fixes plus a vLLM patch.