nasty-top

A top-like TUI for bcachefs filesystems. Real-time per-device IO, latency, and internal stats with built-in tuning advisor.

Built for NASty but works on any system with a mounted bcachefs filesystem.

Features

• Live IO throughput and latency per device with user/btree/journal/sb breakdown
• Latency from bcachefs time_stats (EWMA rolling mean, not useless cumulative averages)
• Per-device IO breakdown using io_done JSON and io_latency_stats_*_json
• Blocked stats view showing what's actually blocking IO right now (allocator, journal, write buffer, etc.)
• Stall detection with 60-second event log when latency exceeds 200ms
• Tuning hints that flag known bcachefs pressure signals and show an example sysfs command (informational only — not applied automatically)
• Options panel with inline editing of runtime-tunable sysfs options
• Multi-filesystem support — press f to cycle between mounted bcachefs filesystems
• Process IO view showing which processes are doing IO
• Journal fill %, load average, reconcile progress
• Session-aware error counts: the device Err column dims pre-existing counts and turns bold red only when errors grow during the current run — so you can tell at a glance whether a number is dead history or actively climbing
• Consistent color scheme: yellow = read, blue = write, red = errors/stalls

Install

Nix:

nix run github:nasty-project/nasty-top

Homebrew (Linux):

brew install fenio/tap/nasty-top

Download binary:

curl -sL https://github.com/nasty-project/nasty-top/releases/latest/download/nasty-top-x86_64-linux.tar.gz | \
  sudo tar xzf - -C /usr/local/bin/

Build from source:

cargo install --path .
# or cross-compile from macOS:
brew install filosottile/musl-cross/musl-cross
rustup target add x86_64-unknown-linux-musl
./deploy.sh root@your-nas

Usage

nasty-top [OPTIONS]

Options:
  -f, --filesystem <NAME|UUID>  Filesystem to monitor (default: first found)
  -t, --interval <SECONDS>      Refresh interval (default: 2)
  -h, --help                    Print help

Keybindings

Key	Action
?	Toggle help popup
o	Toggle options panel (hidden by default)
c	Toggle counters view
t	Toggle blocked stats / time_stats view
p	Toggle process IO view
r	Toggle reconcile on/off
g	Toggle copygc on/off
f	Cycle between filesystems
Tab	Switch focus between metrics and options panel
↑/k, ↓/j	Navigate options / scroll counter, blocked, process views
Enter	Edit selected option value (in options panel)
Esc	Cancel edit / dismiss status message
N	Mute current hint for 2 minutes
!	Never show this hint again
C	Clear all permanent mutes
q / Ctrl-C	Quit

Data Sources

Metric	Source	Notes
IO throughput	dev-N/io_done (JSON)	Per-type breakdown, diffed per tick
IO latency (device)	dev-N/io_latency_stats_{r,w}_json	EWMA mean, shown only when active
IO latency (fs)	time_stats/data_{read,write}	"recent" column rolling mean
Blocked stats	time_stats/blocked_*	Count delta per tick + recent mean
Journal fill	internal/journal_debug	dirty/total entries + watermark
Reconcile	bcachefs reconcile status	Subprocess, parsed for progress
Process IO	/proc/<pid>/io	read_bytes/write_bytes diffed
Options	options/*	Read/write directly to sysfs

Tuning Hints

When known bcachefs pressure signals fire (journal fill, blocked allocator, etc.), a hint appears in the footer with a short reason and an example sysfs command you could run. Nothing is applied automatically — the hint is informational. The current heuristics are unverified; treat them as a starting point for investigation, not a prescription. See TUNING_RULES.md for the full rule set.

License

GPL-3.0-only