mdflush(8)

✨ mdflush(8) ✨

Okay bestie, this is the manual page for mdflush, and it's giving "trace md flush events" 🔍💖

🎀 NAME

mdflush - Trace md flush events. Uses Linux eBPF/bcc. 🦋

📜 SYNOPSIS

mdflush

💅 DESCRIPTION

okay so mdflush traces flush events issued by md, the Linux multiple device driver (aka software RAID) 🧚 Every time one happens, it prints the timestamp and the md device the flush hit. ⏰

This is lowkey super useful because knowing when these flushes happen lets you line them up with those unexplained spikes in disk latency. Main character debugging energy 😭✨

Under the hood, it works by dynamically tracing the kernel md_flush_request() function. That means it will need updating if that function ever changes, so keep that in mind 🙈

Heads up: the flushes themselves are likely coming from higher up in the I/O stack, such as from the file systems. The tool shows you the flush, not necessarily who started the whole chain. 💀

Also, since this uses BPF, only the root user can run this tool. No cap, no root, no tool 🔒👑

🎀 REQUIREMENTS

You need CONFIG_BPF and bcc 🌸

✨ EXAMPLES

Trace md flush events:

# mdflush

🌈 FIELDS

• TIME — when the flush event happened, in HH:MM:SS format ⏰
• PID — the process ID that was on-CPU when the event was issued. This can point to the cause of the flush (like the "sync" command), but honestly it's often a kernel worker thread that was managing I/O 🧵
• COMM — the command name for that PID 💜
• DEVICE — the md device name 🍓

🦋 OVERHEAD

Expected to be negligible. Basically zero drama for your system 💖

🫶 SOURCE

This one comes from bcc 🐝 Find it at:

https://github.com/iovisor/bcc

Also, go check the bcc distribution for a companion _examples.txt file. It has example usage, output, and commentary for this tool, so it's a total vibe 📚🌸

🌍 OS

Linux 🐧

🚧 STABILITY

Unstable - in development. Still cooking, bestie 🍳⭐

👩‍💻 AUTHOR

Brendan Gregg 👑

🔗 SEE ALSO

• biosnoop(8) 🫧

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Okay that's the whole tea, bestie! 💅✨ Mdflush(8) from the USER COMMANDS section, dated 2016-02-13, sending you big love 🩷🎀