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16GB M4, Qwen 35B SSD bottleneck

·2026.04.28 18:36

Key point

Running Qwen 35B-A3B always-on on a 16GB Mac M4 hit an SSD bottleneck before a RAM one.

Details

Running Qwen 3.5 35B-A3B UD-IQ3_XXS (disk 12GB) on an M4 Mac mini with 16GB unified memory via llama.cpp's --mmap, --flash-attn actually worked for batch jobs.

  • RAM usage via MoE expert paging: 4~6GB
  • Decode speed: about 17 tok/s
  • Run conditions: --threads 8, --ctx-size 4096

Extending the same model into an always-on agentic loop, running Ollama, llama-server, LiteLLM, Claude Code, and Codex CLI together, moved the bottleneck from RAM to SSD.

Continuous mmap paging overlapped with Claude Code's file watcher and indexer plus Codex's context retention, increasing SSD contention, and the Mac started rebooting without leaving a cause log. Cron jobs were also delayed or failed for over 5 minutes. Open issues in the claude-code repo about memory growth, idle CPU pegging, and process accumulation were also mentioned.

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