Fix model argument issue (#1198)

[ngocbh]

A quick fix to issue #1198 that makes sure one model is used throughout inject_adapter function in BaseTuner.

[HuggingFaceDocBuilderDev]

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[younesbelkada]

Looks good! What do you think @BenjaminBossan ?

[BenjaminBossan]

Thanks, Ngoc, for working on this fix.

Right now, in _mark_only_adaption_prompts_as_trainable, you allow model to be None and then do model = model or self.model. I would prefer to make model a required argument and remove the mentioned line. This way, it's not possible to accidentally forget to pass model and get unexpected results.

If this change is made, _mark_only_adaption_prompts_as_trainable could even be a standalone function, but that's not really a big concern.

Furthermore, there is one place where this method still needs to be adjusted, which should also make the CI pass:

peft/src/peft/tuners/mixed/model.py

Line 132 in 5bad88b

def _mark_only_adapters_as_trainable(self) -> None:

Apart from that, this change looks good.

[ngocbh]

The reason I want to _mark_only_adapters_as_trainable can also work without passing the model argument is the BaseTuner is already a model. So if we want to use this function outside the class we might have to call model._mark_only_adapters_as_trainable(model.model). I think this is the main use case of this function outside the class. But calling like this seems a little bit weird to me. That's why I let this function work without passing the model argument. What do you think?

If you still prefer to make model a required argument, I will change it back.

[BenjaminBossan]

I think this is the main use case of this function outside the class.

I'm not quite sure I understand this. Do you mean that PEFT users may want to call model._mark_only_adapters_as_trainable? If that is so, I think we should add an explicit method/function for that, as _mark_only_adapters_as_trainable is supposed to be "private" and thus not called directly in user code.

[ngocbh]

Sorry for the delay, I fixed the issue according to your suggestions.

[BenjaminBossan]

Looks good, thanks.