SkewAdam: Rethinking MoE Optimizer Memory

SkewAdam drastically cuts MoE training memory by tailoring optimizer state to parameter populations, achieving superior perplexity and enabling training on accessible hardware.

Diagram illustrating the memory breakdown of AdamW vs SkewAdam for MoE training.
SkewAdam significantly reduces optimizer state memory in MoE models.
Visual TL;DR
MoE Optimizer MemoryDriver
AdamW requires 50.6 GB for moments, dwarfing 12.6 GB bfloat16 weights
From the article 3 mentionsThe memory overhead of optimizers, particularly for large Mixture-of-Experts (MoE) models, presents a significant bottleneck.
Memory BottleneckDriver
From the article 3 mentionsThe memory overhead of optimizers, particularly for large Mixture-of-Experts (MoE) models, presents a significant bottleneck.
SkewAdam OptimizerCore
recognizes distinct parameter populations within MoE models for tailored state management
From the article 6 mentionsThe SkewAdam optimizer tackles this challenge by recognizing that the distinct parameter populations within MoE models, dense backbone, experts, and router, exhibit differing size and gradient statistics.
Differentiated State ManagementContext
tailored state management for backbone, experts, and router based on gradient statistics
From the articleInstead of a uniform approach, SkewAdam applies tailored state management: float32 momentum with a factored second moment for the backbone (5% of parameters), a factored second moment alone for the experts (95%), and an exact second moment for the router (The benefits of SkewAdam extend beyond memory efficiency.
Memory Footprint ReductionEffect
drastically cuts MoE training memory by tailoring optimizer state to parameter populations
Superior PerplexityOutcome
From the articleIn a controlled comparison over 82 million tokens, SkewAdam achieved a validation perplexity of 108.4, outperforming AdamW (126.8), Muon (120.2), and Lion (393.7).
Accessible Hardware TrainingEffect
enables training on accessible hardware, expanding research and development

The memory overhead of optimizers, particularly for large Mixture-of-Experts (MoE) models, presents a significant bottleneck. For a 6.78B-parameter MoE, AdamW requires 50.6 GB for first and second moments, dwarfing the 12.6 GB of bfloat16 weights. This disparity highlights a critical area for optimization.

Memory Footprint Reduction via Differentiated State Management

The SkewAdam optimizer tackles this challenge by recognizing that the distinct parameter populations within MoE models, dense backbone, experts, and router, exhibit differing size and gradient statistics. Instead of a uniform approach, SkewAdam applies tailored state management: float32 momentum with a factored second moment for the backbone (5% of parameters), a factored second moment alone for the experts (95%), and an exact second moment for the router (<0.01%). This strategy slashes the total optimizer state to a mere 1.29 GB, a mere 2.6% of AdamW's requirement. Consequently, peak training memory plummets from 81.4 GB to 31.3 GB, fitting comfortably within a 40 GB accelerator budget.

Performance Gains Beyond Memory Savings

The benefits of SkewAdam extend beyond memory efficiency. In a controlled comparison over 82 million tokens, SkewAdam achieved a validation perplexity of 108.4, outperforming AdamW (126.8), Muon (120.2), and Lion (393.7). Crucially, this performance was attained without sacrificing router load balance, which settled within 1% of its uniform floor. Further analysis indicates that the accuracy gains stem from retaining momentum, a benefit shared across uniform optimizers, while the tiered allocation primarily yields memory savings at no accuracy cost. Even tuned baselines like AdamW (118.5) and Adafactor (139.7) could not close the performance gap, underscoring the efficacy of SkewAdam's approach.

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Daniel Singer

Written by

Daniel Singer

Editor, StartupHub.ai

Daniel Singer is the editor of StartupHub.ai, a technology expert and thought leader on AI and its applications across sectors, from fintech and healthcare to developer tooling and consumer software. He writes and tests the tools covered here thoroughly and regularly, and built StartupHub.ai to give founders, operators and buyers a clearer read on what they are actually being sold.

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