Invalid gradient and Dx?

[YicongHong]

Hi @Hprairie, I previously built mamba-2/hydra-based models, and I am now trying to replace the layers with your bi-mamba2 module. However, I found the new model can easily get invalid gradients (e.g., infinite gradient norm) that never appeared with mamba-2/hydra.

I tested with both torch==2.1.0, triton==3.0.0, cu122 and torch==2.4.0, triton==3.0.0, cu121, it seems that the more bi-mamba2 layers I stack or the more multi-processes I used, the easier the model gets this problem.

• I tested with single-GPU-processing 1~16 layers, and the issue became very profound after stacking more than 12 layers.
• Also, tested with multi-GPU-processing with DDP or FSDP. Even with just 2 layers and 2 processes, the problem always appeared.

Any ideas?

Besides, you mentioned that the kernel implements y=SS(x)+flip(SS(flip(x)))+Dx, but in BiMamba2() Line 108, the skip parameters self.D and self.fc_D are not used for Dx. Can I ask how to pass these parameters to bimamba_chunk_scan_combined(), or we should do something similar as in Hydra?

Thanks!!!

[Hprairie]

Whoops that's a great catch. I'll go ahead and push something in a couple minutes to fix it. All you need to do is set D=D when the module layer when calling the function.

As for NaN gradients, I'm looking for parts of the kernel which cause this. Haven't identified anything yet, but I'll lyk.

[Hprairie]

Should be the same for z. My classes resumed so I was rather quick to push the layer out. Thanks for the catch :)

[Hprairie]

Alright, I pushed a fix. Lmk if NaNs still occur, as this is something I haven't been able to test for personally.

[YicongHong]

Thanks @Hprairie; after passing D=self.D, I got the following error: bimamba2/src/ssd/bi/ssd_chunk_scan.py":138:11): error: operation scheduled before its operands

Also, it seems that self.fc_D is still not used? I thought self.fc_D is for Dx and self.D is a bias term?

[Hprairie]

1) The first error is with triton and I found occurs when you compile for the first time. It shouldn't keep occuring and shouldn't affect anything from what I have seen. 2) You are right, hydra does use self.D as a bias and self.fc_D. I am away from a computer, but will make a fix tmrw. I will give two options, as using D without fc_D is more canonical to Mamba. If you want access to it immediately just use F.linear as in Hydra and then don't pass D to the optimized kernel.

Thanks again for pointing this out, I learned something new.

[YicongHong]

Thanks @Hprairie,

1. NaNs still occur easily.
2. Yes, the error: operation scheduled before its operands only occurs at the start and doesn't stop anything.
3. "using D without fc_D is more canonical to Mamba", I see, thanks!

[Hprairie]

Hmmm okay I'll try to block out some time to look into the NaN problem.

[GLOMQuyet]

Yes, I have the same problem no matter how high you set the batch size or learning rate, they are the same. Colab link With ViT, remove the attetion and replace it with Bi-Mamba 2:https://colab.research.google.com/drive/1rgXkwnlevzZ0YPbefQS8qHRe7gFlb4J-?authuser=3. The loss result is always NaN, Bi-Mamba 2 gives too high gradient