High memory usage for BigBirdForPreTraining
### System Info

DGX-A100 
transformers 4.29.2

### Who can help?

@ArthurZucker
@ydshieh 

### Information

- [ ] The official example scripts
- [X] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [X] My own task or dataset (give details below)

### Reproduction

Run BigBirdForPreTraining with the BigBirdConfig left at default (except vocab size set to 32k). Essentially I recreated pretraining from section F.1 of the original publication https://arxiv.org/pdf/2007.14062.pdf

### Expected behavior

Should be able to fit a batch size of 4 in ~16 GB according to the paper but in reality a batch size of 4 exceeds 40GB on the forward call.
Sorry, but this is lacking a lot of information, especially a reproducing script. Lots of things can impact the RAM taken by the model, this should be asked on the [forum](https://discuss.huggingface.co/top?period=weekly), not here. <|||||>I added a reproducing script here:
https://github.com/kuben-joz/bigbird-example/tree/master

I thought it would be better to make  a submission here rather than the forums as it concerns the implementation details of the model. If nevertheless you prefer for this to be moved to the forum I can do so.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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