UNET Module in a forloop gives an error when .backward() (RuntimeError: Unable to find a valid cuDNN algorithm to run convolution)

I combined conventional unet module and a custom function in a forward model.
This custom function cannot take input as a batch, so I use forloop to feed the data one by one.
However, it gives me an error when batchsize >=2 (works when =1).
(It also works for >=2 when I only use custom_func, without UNET.)
Therefore I think I’m doing something wrong with evaluating the module multiple times in a single forward process.
Can anyone help please? Thanks!!

model_UNET = UNET()  # conventional unet
optvars = [{'params': custom_vars, 'lr':lr_custom}] # custom_vars used in custom_func
optimizer1 = optim.Adam(optvars)
optimizer2 = optim.Adam(UNET.parameters(), lr=lr_Unet)

# My forward model
for aa in range(batch_size):
     temp=custom_func(input, custom_vars)
     loss_total=loss_total + loss(output)

# backward & update
custom_vars.retain_grad() #<-- Maybe I need something like this for parameters in UNET?
loss_total.backward() #<-- This line gives the error

Actually, when I changed the network size smaller, it worked.
Maybe it was just a GPU memory problem?
I still have a question: Can I make my forward model using forloop like this, not batch tensor format?


Is this a double post from here or a new issue?

It’s a double post. I re-uploaded my question because the system blocked my original thread. Thanks