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An Efficient Pruner for Large Language Model with Theoretical Guarantee
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Reformulates one-shot layer-wise LLM pruning as an ℓ0-penalized problem solved by a monotone accelerated iterative hard thresholding (mAIHT) method, with convergence and risk-bound theory and LLaMA-7B experiments.
Problem
One-shot pruning of LLMs typically relies on heuristic approaches lacking theoretical guarantees, and prior optimization-based methods (ADMM, FISTA) either lack guarantees or relax the ℓ0 problem to ℓ1.
Approach
Casts layer-wise pruning as ℓ0-penalized least squares solved by proximal gradient with hard thresholding, adds a monotone Nesterov-style acceleration with a loss-monitoring safeguard, and adaptively tunes the penalty λ to hit a target sparsity.
Key results
- On WikiText2 at 0.5 sparsity, mAIHT reaches perplexity 7.0720 versus 7.0826 for ADMM, 7.2397 for SparseGPT and 7.2588 for Wanda.
- At 0.1 sparsity mAIHT (5.6928) is slightly worse than ADMM (5.6925) but better than other baselines.
- Across sparsity levels 0.2 to 0.5 on seven zero-shot tasks, mAIHT is among the top two on most datasets and has the best mean accuracy.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use mAIHT instead of ADMM | LLaMA-7B pruning · WikiText2, sparsity 0.1 | perplexity: 5.6925 -> 5.6928 | Hurt |
| Use mAIHT instead of ADMM | LLaMA-7B pruning · WikiText2, sparsity 0.2 | perplexity: 5.8045 -> 5.8042 | Helped |
| Use mAIHT instead of ADMM | LLaMA-7B pruning · WikiText2, sparsity 0.3 | perplexity: 5.9586 -> 5.9565 | Helped |
| Use mAIHT instead of ADMM | LLaMA-7B pruning · WikiText2, sparsity 0.4 | perplexity: 6.3268 -> 6.3240 | Helped |
| Use mAIHT instead of ADMM | LLaMA-7B pruning · WikiText2, sparsity 0.5 | perplexity: 7.0826 -> 7.0720 | Helped |
| Add monotone acceleration to IHT (ablation) | IHT pruning of LLaMA-7B layers · Layer reconstruction | reconstruction error | Helped |
Surprising findings
- At 0.1 sparsity, mAIHT is slightly inferior to ADMM on perplexity.
Limitations
- Advantage is mainly at low-to-moderate sparsity; at 0.1 sparsity ADMM is slightly better.
- Theoretical risk bounds rely on RIP-type assumptions and bounded data distribution assumptions.
- Evaluated only on LLaMA-7B.
Experimental setup
Datasets: C4 WikiText2
Benchmarks: WikiText2 BoolQ RTE HellaSWAG WinoGrande ARC easy ARC challenge OpenbookQA
Metrics: perplexity accuracy reconstruction error
Baselines: Magnitude Pruning Wanda SparseGPT ADMM-based pruning
Builds on: Wanda SparseGPT ADMM-based pruning Iterative hard thresholding Monotone accelerated proximal gradient (Li & Lin 2015)
Closest papers by meaning
- SlimLLM: Accurate Structured Pruning for Large Language Models (ICML 2025 · similarity 0.93)
- SlimGPT: Layer-wise Structured Pruning for Large Language Models (NeurIPS 2024 · similarity 0.93)
- Pruner-Zero: Evolving Symbolic Pruning Metric From Scratch for Large Language Models (ICML 2024 · similarity 0.93)
- AlphaPruning: Using Heavy-Tailed Self Regularization Theory for Improved Layer-wise Pruning of Large Language Models (NeurIPS 2024 · similarity 0.93)
- Toward Adaptive Large Language Models Structured Pruning via Hybrid-grained Weight Importance Assessment (AAAI 2025 · similarity 0.92)
- Fluctuation-Based Adaptive Structured Pruning for Large Language Models (AAAI 2024 · similarity 0.92)
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