FlashLib

A GPU library for classical machine-learning operators — kmeans, knn, ivf-flat, pca, svd, dbscan, hdbscan, umap, t-sne, regression, GEMM, and more — built on Triton and CuteDSL.

See the blog post for motivation, design, and benchmarks.

Installation

Install with pip:

pip install flashlib

From source:

git clone https://github.com/FlashML-org/flashlib.git
cd flashlib
pip install -e .

Usage

import torch
from flashlib import flash_kmeans

x = torch.randn(1_000_000, 128, device="cuda", dtype=torch.float32)
labels, centroids, n_iter = flash_kmeans(x, n_clusters=1024, max_iters=20)

Every primitive is exposed as a top-level flash_* function and as a sklearn-style class (KMeans, PCA, HDBSCAN, …).

Index-based primitives like IVF-Flat and IVF-PQ (GPU approximate nearest neighbours) build an index once and query it many times:

import torch
from flashlib import IVFFlat

db = torch.randn(1_000_000, 128, device="cuda")
queries = torch.randn(10_000, 128, device="cuda")

index = IVFFlat(nlist=1024, nprobe=16).fit(db)
distances, indices = index.kneighbors(queries, n_neighbors=10)  # squared L2

nprobe is the recall knob: at a fixed (nlist, nprobe) the probed candidate set — and thus recall — matches a reference IVF-Flat (FAISS / cuVS), so raising it trades speed for recall without changing the kernel.

For billion-scale corpora, IVFPQ adds product-quantization compression: each vector is stored as m 1-byte codes (8–32× smaller than fp32):

from flashlib import IVFPQ

# 128-dim fp32 (512 B/vec) -> m=16 PQ codes (16 B/vec) = 32x compression
index = IVFPQ(nlist=1024, m=16, nprobe=16).fit(db)
distances, indices = index.kneighbors(queries, n_neighbors=10)  # ADC squared L2
print(index.compression_ratio)  # 32.0

For maximum search throughput, CAGRA builds a proximity graph (exact kNN graph + detour pruning + reverse edges) and answers queries with a fused greedy traversal — one Triton program per query, the whole priority buffer in registers, bf16 candidate reads with an exact fp32 re-rank of the final top-k:

from flashlib import CAGRA

index = CAGRA(graph_degree=32, itopk_size=64).fit(db)
distances, indices = index.kneighbors(queries, n_neighbors=10)  # squared L2

itopk_size is the recall knob (raise it — and graph_degree — for higher recall). At equal recall the fused traversal outruns cuVS CAGRA on H100 across the 0.9–0.99 recall band (see benchmarks/vs_cuml/cagra.py for the recall/QPS frontier methodology).

Picking between the ANN indexes (measured H100, 1M rows): CAGRA wins online/small-batch serving at every recall and batched search up to ~0.99 recall; IVFFlat wins batched search above ~0.99 (its GEMM fine-scan shares list reads across the batch on tensor cores — ~1.5x at recall 0.999 on SIFT-1M, and the gap widens with dimensionality); IVFPQ trades recall ceiling for 8–32x memory compression.

Informative API

The flashlib.info submodule predicts runtime, FLOPs, and HBM bytes for any primitive in ~5 µs on pure CPU — useful for budgeting a pipeline before launching it, and small enough for an LLM agent to call in a GPU-less environment. It does not import torch, triton, or cutlass.

import flashlib.info as info

est = info.estimate("kmeans",
                    shape=(100_000, 64),
                    params={"K": 256, "max_iters": 20},
                    device="H200")
print(est.summary_line())

See the blog post for the full API, the tolerance-driven dispatch, and per-primitive benchmarks.

Coverage

The current release ships 18 high-level primitives across the following families:

family	primitives
Clustering	flash_kmeans, flash_dbscan, flash_hdbscan, flash_spectral_clustering
Nearest nbrs	flash_knn, flash_ivf_flat (IVF-Flat ANN), flash_ivf_pq (IVF-PQ ANN), flash_cagra (graph ANN)
Decomposition	flash_pca, flash_truncated_svd
Manifold	flash_umap, flash_tsne
Regression	flash_linear_regression, flash_ridge, flash_logistic_regression
Classification	flash_multinomial_nb, flash_random_forest
Preprocessing	flash_standard_scaler

Plus low-level linear-algebra primitives (cov_gemm, gram_gemm, ab_gemm, eigh, polar, msign, cholqr2, split_basis) and a Pareto-frontier set of multi-precision GEMM variants (gemm, gemm_tf32, gemm_3xtf32, gemm_bf16, gemm_fp16, gemm_fp16_x9, gemm_fp16_x3_kahan, gemm_ozaki2_int8, …).

Citation

@misc{yang2026flashlib,
  title  = {FlashLib: Bringing Flash Magic to Classical Machine Learning Operators},
  author = {Yang, Shuo and Xi, Haocheng and Zhao, Yilong and Mang, Qiuyang and
            Wang, Zhe and Sun, Shanlin and Keutzer, Kurt and Gonzalez, Joseph E. and
            Han, Song and Xu, Chenfeng and Stoica, Ion},
  year   = {2026},
  url    = {https://flashml-org.github.io/},
}

License

Apache License 2.0.