# Heaps do lie: debugging a memory leak in vLLM.

DevFeed: [Heaps do lie: debugging a memory leak in vLLM.](<https://devfeed.tech/articles/heaps-do-lie-debugging-a-memory-leak-in-vllm-6997.md>)

Original publisher: [Read original article](<https://mistral.ai/news/debugging-memory-leak-in-vllm/>)

Published: 2026-01-21T16:00:00Z

Content type: article

Language: en

Sources: [Mistral AI Blog](<https://devfeed.tech/sources/mistral-ai-blog.md>)

Topics: [Memory Leaks](<https://devfeed.tech/topics/memory-leaks.md>), [vllm](<https://devfeed.tech/topics/vllm.md>), [debug](<https://devfeed.tech/topics/debug.md>), [Inference](<https://devfeed.tech/topics/inference.md>), [Grafana](<https://devfeed.tech/topics/grafana.md>)

Tags: [cache](<https://devfeed.tech/tags/cache.md>), [debugging](<https://devfeed.tech/tags/debugging.md>), [deep-dive](<https://devfeed.tech/tags/deep-dive.md>), [engineering](<https://devfeed.tech/tags/engineering.md>), [grafana](<https://devfeed.tech/tags/grafana.md>), [inference](<https://devfeed.tech/tags/inference.md>), [memory](<https://devfeed.tech/tags/memory.md>), [vllm](<https://devfeed.tech/tags/vllm.md>)

## AI overview

Mistral AI investigates a vLLM memory leak that appeared during pre-production testing of disaggregated serving with Mistral Medium 3.1 and graph compilation enabled. The investigation moved from Python-level tools to kernel-level tracing and identified KV Cache transfer through NIXL in the decode side of a Prefill/Decode setup as the likely root cause.

## Source excerpt

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