swapin(8)

📦 version 0.36.1, in alpine 3.24, nixpkgs unstable, opensuse-leap 16.0

🫧 NAME 🫧

okay so the manual name is swapin, and it's a BCC/eBPF tool that counts swapins by process ✨ swapin is the whole vibe.

Quick heads up, this page lives in the System Manager's Manual section 8 (swapin(8)) 💅

✨ SYNOPSIS ✨

swapin
  • -h, --help — show the help message and bounce 🙈
  • -T, --notime — skip the timestamp column (HH:MM:SS) 🕒

💖 DESCRIPTION 💖

okay so bestie, this tool counts swapins by process, so you can see exactly which process is getting hit by swapping (if you've got swap devices in use) 🥺 this can explain a seriously big chunk of app latency, especially if something started swapping because the system is under memory pressure. main character energy for debugging 💀

how it works: it traces the swap_readpage() kernel function using dynamic instrumentation 🦋

⚠️ hot take, but this tool might need maintenance to keep working if that function changes in later kernels. so don't be shocked if it breaks someday 😭

and since it uses BPF, only the root user can run it. sorry not sorry 🔐

🎀 REQUIREMENTS 🎀

you'll need CONFIG_BPF and BCC ✨

🌸 EXAMPLES 🌸

Count swapins by process, with per-second summaries:

# swapin

🧚 FIELDS 🧚

  • 1st — the process name 🏷️
  • 2nd — the process ID 🔢
  • 3rd — the count of swapins during that interval 📈

🔥 OVERHEAD 🔥

the rate of swapins should be low (it's bounded by swap device IOPS), so the overhead of this tool is expected to be negligible. basically zero drama 💅

🍓 SOURCE 🍓

okay this one's a good story 🥹 it originated as a bpftrace tool from the book "BPF Performance Tools", published by Addison Wesley (2019):

http://www.brendangregg.com/bpf-performance-tools-book.html

go read the book for more docs on this tool, it's iconic 📚

the version you're looking at is in the BCC repository:

https://github.com/iovisor/bcc

also, peek in the bcc distribution for a companion _examples.txt file. it has example usage, output, and commentary for this tool, so iykyk 🫶

🌈 OS 🌈

Linux only 🐧

🫠 STABILITY 🫠

Unstable - in development. so it's still cooking 🍳

👑 AUTHOR 👑

Brendan Gregg is the queen behind this one 👸

🦋 SEE ALSO 🦋

swapon(8) 💜

and that's a wrap, bestie 🎀 this was the USER COMMANDS manual page, last updated 2019-07-05, for swapin(8) 💖✨

📦 where this page comes from