mtop

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A Linux memory analysis TUI. htop answers "how much RSS does each process have"; mtop answers "who is actually using the memory, and on what" — with PSS/USS, per-mapping drill-down, cgroup accounting and an app-level treemap.

Why PSS

RSS counts every shared page once per process, so any multi-process app looks inflated. Measured on one desktop at the same instant:

RSS sums to roughly 2.2× the real number system-wide (2.4× for Chrome). mtop uses PSS for ranking and area, USS for "what would I free if I killed it", and shows the composition (anonymous / file / shmem / swap) so you can tell a heap leak from page cache.

Features

• Process view — RSS / PSS / USS / PSS÷RSS / Δ·s⁻¹, share bars and a theme-coloured PSS-composition bar (legend in the process view).
• VMA detail — aggregate by mapping, then expand one mapping into its individual VMAs (address range, perms, PSS/USS/anon/swap/size).
• cgroup v2 view — memory.current / memory.stat / memory.max / memory.events, PSI (some/full), OOM deltas, and drill-down into a subtree's processes.
• App treemap — processes grouped into applications (systemd app-*.scope → exe → comm), area ∝ PSS, long tail folded into others.
• Scriptable — --json (with --fields projection), --diff (with --min-delta / --top), stable pid ordering for diffing.
• Mouse — click a table row or treemap tile to select, click it again to open/expand/drill, wheel to scroll, and click the footer buttons (help, theme, language, view, sort, filter, enter, back, quit).
• Bilingual help — ? opens page-specific help for processes, cgroups, apps, VMA detail and drill-down; --lang auto|en|zh, MTOP_LANG, or l switches Chinese/English.
• Themes — seven palettes, including btop-derived btop, dracula, gruvbox-dark and kanagawa-wave; pick one with --theme, MTOP_THEME, or t while running (no config file). Themes are authored in truecolor and auto-rendered to 256 or 16 colours when the terminal cannot display RGB; --color overrides detection.

Install

Prebuilt packages are produced by GitHub Actions for amd64 and arm64; every asset ships with a SHA256 checksum.

# Debian / Ubuntu
gh release download v0.3.0 --repo baka-world/mtop --pattern '*.deb'
sudo dpkg -i mtop_0.3.0-1_amd64.deb

# Fedora / RHEL
gh release download v0.3.0 --repo baka-world/mtop --pattern '*.rpm'
sudo rpm -i mtop-0.3.0-1.x86_64.rpm

# From crates.io (installs the `mtop` binary)
cargo install metop

# From source
cargo build --release && sudo install -m755 target/release/mtop /usr/local/bin/

Binaries are statically linked (musl), and the .deb has an empty Depends:.

Usage

mtop                       # whole system
mtop --pid 1234            # start with a process selected
mtop --theme dracula       # default | btop | dracula | gruvbox-dark |
                           # kanagawa-wave | light | ansi16 (or MTOP_THEME)
mtop --color 256           # auto | truecolor | 256 | 16
mtop --lang zh             # auto | en | zh (or MTOP_LANG / l)
mtop --json --fields procs.pid,procs.rss_kb
mtop --diff a.json b.json --min-delta 50M

Help and i18n

Press ? for a page-specific explanation of the header, columns, colour codes, markers and keys. --lang auto|en|zh, MTOP_LANG or l switch between English and Chinese; the footer buttons are clickable. Screenshots use the dracula theme.

Process view

The header reports the sampler's own cost (sweep/pss ms, PSS coverage, sample age) so partial data is never presented as complete. Rows with n/a need privileges; a dimmed ~ marks a cached value older than the freshness window. The footer is a clickable command bar and the PSS mix legend only appears here.

VMA detail

Enter on a process aggregates its mappings by name; Enter again expands one group into individual VMAs. f filters mapping names, z/Z collapse or expand everything.

cgroup v2

Values are hierarchical: a parent already includes its children, so the list sorts by current instead of summing levels. Enter lists the processes in that subtree:

Apps treemap

Area is PSS by default; s switches to USS (private only) or RSS (which overcounts shared pages, and says so in the title). Tiles use the active theme's bright palette, with dark labels; Enter drills into that app's processes.

Scripting

mtop --json > a.json                      # one snapshot, stable pid order
mtop --json --fields procs.pid,procs.rss_kb > small.json   # 194 KB -> 23 KB
sleep 30; mtop --json > b.json
mtop --diff a.json b.json --min-delta 50M

--diff prints ΔRSS / ΔPSS, current values and new/gone markers; the snapshot writer itself is excluded via self_pid.

Requirements and permissions

• Linux with /proc; cgroup v2 optional (the view explains its absence).
• /proc/PID/smaps_rollup requires ptrace-read permission: a normal user only sees their own processes (and kernel threads have no address space at all). Run sudo mtop for full coverage — verified at 264/264 covered, denied=0.
• The usage model is documented in docs/REQUIREMENTS.md; the root checklist is docs/VERIFY-ROOT.md.

Known issues

• Counts are partial without privileges. Non-root runs only cover your own user's processes; kernel threads never have a PSS and are excluded from coverage denominators.
• Two history windows. Process/apps keep 120 samples at 1 Hz (2 min); cgroup/PSI keep 120 samples at the 5 s cadence (10 min). Comparing the two trends side by side is misleading.
• App grouping falls back to the executable. Without a systemd app-*.scope, two Chromium installs merge into one tile; others (N) is synthetic and cannot be drilled into.
• cgroup v1 is unsupported — the view states why instead of showing zeros.
• Sampling perturbs the target. Reading smaps walks page tables under the mmap lock, so walks are budgeted (150 ms/tick) and the detail view is on-demand.

TODO

• Configurable history window (--history 600), so all views share one time axis.
• Include app groups in --json.
• Optional: KSM / hugepage / pagemap metadata per VMA (via wora-observability-linux-mm).
• Optional: per-view metric defaults and a config file.

Development

cargo build --release
cargo test --release     # 69 tests
cargo clippy --all-targets -- -D warnings
cargo fmt --check

License

MIT — see LICENSE.