Cross Contamination in SFT Trainer

[elichen3051]

Dear HuggingFace

I've noted that in run_cpt.py and run_sft.py, we introduce packing=True. However, we didn't provide DataCollatorForCompletionOnlyLM into SFTtrainer; would it introduce cross contamination in training?

referenece article: Improving Hugging Face Training Efficiency Through Packing with Flash Attention
trl issue on github: huggingface/trl#805

[lewtun]

Hello @elichen3051 the task is the same whether one uses packing or not (i.e. next token prediction). The DataCollatorForCompletionOnlyLM is for the special case where you want to mask the inputs / prompts and in some cases gives a small performance boost