Reservoir of Importance: Learning Semi-Structured Sparsity with Differentiable Subset Sampling

Ha Dinh, Xuan Duy Ta, Khoat Than, Khac-Hoai Nam Bui


Abstract
Semi-structured N:M sparsity has emerged as a practical direction for accelerating large language models (LLMs). However, existing learnable-mask approaches incur substantial parameter and memory overhead, limiting their scalability to large models and aggressive sparsity regimes. In this work, we revisit semi-structured pruning from a perspective that reconciles efficiency with scalability. We propose Reservoir of Importance (RoI), a lightweight semi-structured pruning framework that learns sparsity masks through differentiable subset sampling. Unlike prior methods that model full categorical distributions over all feasible N:M patterns, RoI introduces a compact-logit parameterization for sparsity mask learning and performs sampling without replacement to select masks, thereby reducing trainable parameters from combinatorial complexity to 𝒪(M). As a result, RoI requires 1.5–8.75× fewer learnable parameters and significantly lower memory cost, while remaining fully aligned with hardware-friendly sparsity patterns. Extensive evaluations across multiple scales of the Qwen2.5 LLM family (0.5-7B parameters) demonstrate that RoI achieves competitive performance with strong memory efficiency, stability, and scalability to more aggressive N:M sparsity patterns, offering a practical path toward efficient LLM deployment.
Anthology ID:
2026.emnlp-main.1212
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
27702–27718
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1212/
DOI:
Bibkey:
Cite (ACL):
Ha Dinh, Xuan Duy Ta, Khoat Than, and Khac-Hoai Nam Bui. 2026. Reservoir of Importance: Learning Semi-Structured Sparsity with Differentiable Subset Sampling. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 27702–27718, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Reservoir of Importance: Learning Semi-Structured Sparsity with Differentiable Subset Sampling (Dinh et al., EMNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.emnlp-main.1212.pdf