Linux 為什麼還沒 OOM 就開始卡頓？用 PSI 讀懂 CPU、記憶體與 I/O 壓力 / Before OOM: Reading Linux Pressure Stall Information
現象：為什麼還沒 OOM 就開始卡？ / Symptom: Why does Linux stall before OOM? 你是否遇過這種情況：記憶體還有剩、CPU 也沒有 100%，但 SSH 變慢、服務延遲突然拉高，甚至工作負載尚未被 OOM Killer 終止就已經「像死機」？這不是單看使用率就能回答的問題。Linux Pressure Stall Information（PSI）量的是工作真的因資源不足而等待了多久，讓「還能跑」與「已經在浪費時間」分開。 Have you seen a Linux host become sluggish while memory is still available and CPU is below 100%? PSI addresses the missing signal: not how full a resource looks, but how long runnable work is actually delayed by contention. A machine can be operational and already wasting latency before the OOM killer appears. PSI 的核心不是額外的效能計數器，而是把資源競爭轉成「停滯時間」。核心分別在 /proc/pressure/cpu、memory、io 匯出資料；some 表示至少一部分工作正在等待，full 則表示所有非閒置工作同時卡住。memory full 或 io full 長時間上升，比單獨看到 free 變少更接近「系統正在失去生產力」的現象。 PSI turns contention into stall time. The kernel exports cpu, memory, and io pressure files under /proc/pressure. “some” means at least some work is stalled; “full” means all non-idle work is stalled at once. A sustained memory-full or io-full signal is often more actionable tha...