hypomnesis

ὑπόμνησις — External RAM and VRAM, measured.

🚀 0.2.0 widens the API without breaking callers. Adds Snapshot::all for multi-adapter enumeration on Windows, gpu_processes for compute-process listing, the hmn CLI binary behind a default-off cli feature, and report-feature free-VRAM print helpers (format_free / print_free on GpuDeviceInfo). The public API remains #[non_exhaustive] so further additions (AMD ROCm, Apple Metal) can land in 0.2.x patches without breaking callers. See CHANGELOG.md for the v0.2.0 entry and docs/roadmap-v0.2.0.md for the wave-by-wave rationale.

Table of Contents

• Install
• Usage
• Binary (hmn)
• Capabilities
• Feature Flags
• Used by
• License
• Development

Install

[dependencies]
hypomnesis = "0.2"

The default feature set (nvml, dxgi, nvidia-smi-fallback) covers process RSS and per-process / device-wide GPU memory on both Windows (IDXGIAdapter3 + NVML) and Linux (NVML), with a nvidia-smi subprocess fallback. The dxgi dependency on the windows crate is target-conditional — Linux users pay nothing for it.

For candle-mi-compatible delta and printing helpers (MemoryReport, print_delta, print_before_after, ram_mb, vram_mb):

hypomnesis = { version = "0.1", features = ["report"] }

For a stripped-down build (process RSS only, no GPU backends):

hypomnesis = { version = "0.1", default-features = false }

Usage

use hypomnesis::Snapshot;

fn main() -> Result<(), hypomnesis::HypomnesisError> {
    let snap = Snapshot::now(0)?;
    println!("RAM: {} bytes", snap.ram_bytes);

    if let Some(dev) = snap.gpu_device {
        let total_gib = dev.total_bytes as f64 / (1u64 << 30) as f64;
        let used_gib  = dev.used_bytes  as f64 / (1u64 << 30) as f64;
        println!(
            "GPU 0 [{}]: {:.1} / {:.1} GiB used",
            dev.name.as_deref().unwrap_or("unknown"),
            used_gib, total_gib,
        );
    }

    if let Some(proc_gpu) = snap.gpu {
        let kind = if proc_gpu.is_per_process { "per-process" } else { "device-wide" };
        let mib  = proc_gpu.used_bytes as f64 / (1u64 << 20) as f64;
        println!("This process: {:.0} MiB ({})", mib, kind);
    }

    Ok(())
}

Expected output (RTX 5060 Ti, Windows, idle process):

RAM: 142475264 bytes
GPU 0 [NVIDIA GeForce RTX 5060 Ti]: 1.8 / 16.0 GiB used
This process: 119 MiB (per-process)

Binary (hmn)

hypomnesis ships a small CLI binary, hmn, behind the default-off cli feature. Install it with:

cargo install hypomnesis --features cli

Two subcommands:

hmn                    # device summary (free / total per GPU)
hmn ps                 # all GPU processes — discovery command
hmn ps --pid 12345     # filter to one PID
hmn ps --device 0      # filter to one GPU on multi-GPU rigs
hmn ps --json          # scriptable output

Example default output (single NVIDIA dGPU, the maintainer's reference machine — Ryzen 9 5950X has no iGPU, so only one adapter surfaces):

GPU 0 [NVIDIA GeForce RTX 5060 Ti]: free 13284 MiB / 16384 MiB

Illustrative output on a heterogeneous machine (NVIDIA dGPU + Intel/AMD iGPU on Windows). Not yet verified end-to-end on real hardware — see docs/roadmap-v0.2.0.md "Verification plan":

GPU 0 [NVIDIA GeForce RTX 5060 Ti]: free 13284 MiB / 16384 MiB
GPU 1 [Intel Iris Xe Graphics]: free 32768 MiB / 32768 MiB

hmn ps (illustrative — empty on machines with no active CUDA workload):

PID    NAME              VRAM      DEVICE
12345  lm-studio.exe     8.2 GiB   NVIDIA GeForce RTX 5060 Ti
67890  python.exe        1.4 GiB   NVIDIA GeForce RTX 5060 Ti

A one-line summary is written to stderr after each hmn ps run:

hmn: 2 compute processes found.
hmn: 0 compute processes found matching pid=99 device=0.   # with filters

The stderr summary is always printed, even when the table is empty, so interactive users get an unambiguous "command worked, here's the count" line without breaking stdout's scriptability. Pipelines like hmn ps | awk 'NR>1 {print $1}' or hmn ps --json | jq work as expected. Redirect 2>/dev/null to suppress the summary.

Limitations (intrinsic to the underlying data sources, not bugs):

1. Compute-only. hmn ps enumerates only processes with an active CUDA context. Browsers using GPU compositing, games, and pure-graphics apps do not appear. This is a property of the NVML and nvidia-smi --query-compute-apps data sources.
2. Windows process names may be ?. nvidia-smi writes a literal ? for protected processes whose image name it cannot read. The library preserves this as Some("?") rather than failing the row.
3. WDDM bug parity. The R570 u64::MAX sentinel and used > total corruption checks the library handles for the calling process are applied per-row in hmn ps; affected rows are dropped rather than reported as garbage.
4. Windows compute-process attribution is nvidia-smi-backed. IDXGIAdapter3::QueryVideoMemoryInfo only answers for the calling process, and NVML's per-process query returns NVML_VALUE_NOT_AVAILABLE under WDDM. So hmn ps on Windows is honest-but-second-class compared to Linux's clean NVML enumeration.

Capabilities

hypomnesis uses IDXGIAdapter3 on Windows because WDDM means the kernel memory manager — not the NVIDIA driver — owns GPU allocations, so NVML's per-process query returns NOT_AVAILABLE under Windows. DXGI 1.4 is the only reliable per-process source. On Linux, NVML's nvmlDeviceGetComputeRunningProcesses_v3 returns true per-process figures.

The crate handles two known driver bugs out of the box:

1. NVML u64::MAX sentinel — some R570-series drivers report 0xFFFFFFFFFFFFFFFF for every running process's memory (observed on RTX 5060 Ti). hypomnesis detects this and falls back to nvidia-smi.
2. used > total corruption — sanity-checks each per-process reading against the device-wide total; falls back to nvidia-smi on detected corruption.

Feature Flags

Used by

No consumers yet — 0.2.0 adds the hmn CLI binary and multi-adapter enumeration on top of 0.1.0's core. Phase 2 will integrate with hf-fetch-model's inspect --check-gpu flag (path-dep first, then hypomnesis = "0.2" from crates.io once the API has settled under real use). Phase 3 may migrate candle-mi's in-tree memory module to depend on hypomnesis = "0.2" with features = ["report"].

License

Licensed under either of Apache License, Version 2.0 or MIT License at your option.

Development

• Exclusively developed with Claude Code (dev) and Augment Code (review)
• Git workflow managed with Fork
• All code follows CONVENTIONS.md, derived from Amphigraphic-Strict's Grit — a strict Rust subset designed to improve AI coding accuracy.