We empirically study a simple layer-pruning strategy for popular families of
open-weight pretrained LLMs, finding minimal degradation of performance on
different question-answering benchmarks until after a large fraction (up to
half) of the layers are removed. To prune these models, we identify the optimal
block of layers to prune by considering similarity across layers; then, to
"heal" the damage, we perform a small amount of finetuning. In particular, we
use parameter-efficient finetuning (PEFT) methods, specifically quantization
and Low Rank Adapters (QLoRA), such that each of our experiments can be
performed on a single A100 GPU. From a practical perspective, these results
suggest that layer pruning methods can complement other PEFT strategies to
further reduce computational resources of finetuning on the one hand, and can
improve the memory and latency of inference on the other hand. From a
scientific perspective, the robustness of these LLMs to the deletion of layers
implies either that current pretraining methods are not properly leveraging the
parameters in the deeper layers of the network or that the shallow layers play
a critical role in storing knowledge.

通过对热门的开放式权重预训练 LLMs 进行实证研究，我们发现在移除大部分（最多一半）层之前，其在不同的问答基准测试中仅出现轻微性能下降；因此，层剪枝方法可以在减少计算资源的同时提高推理的内存和延迟，并暗示当前的预训练方法未充分利用网络较深层的参数，或者浅层起到了关键的存储知识的作用。