Fastai: Memory Error: Loads the entire dataset into Memory

[srmsoumya]

The RAM is getting filled up after a few iterations, this causes a problem in handling large datasets. I am not sure but I think it is loading the entire data into Memory.

[farhanhubble]

I faced the same OOM issue. It's caused by ThreadPoolExecutor in DataLoader class defined in fastai/dataloader.py. I am able to run the code after replacing the thread pool by a single execution thread. Here's the diff:
``` def __iter__(self):

• with ThreadPoolExecutor(max_workers=self.num_workers) as e:
• for batch in e.map(self.get_batch, iter(self.batch_sampler)):
• yield get_tensor(batch, self.pin_memory)
• for batch in map(self.get_batch, iter(self.batch_sampler)):
• yield get_tensor(batch, self.pin_memory)
  ```
  I tried to set max_workers to 1 too but that didn't work. Understanding where memory is being lost will require more ananlysis.

[farhanhubble]

After a little bit of analysis, the OOM error is caused because ThreadPoolExecutor creates all batches and stores them in memory and then returns a generator to fetch the batches from. This behavior has changed from Python 3.5 to 3.6

[WilliamNurmi]

Linking a related forum thread. The pool executor change doesn't seem to solve issue for me. 30GB RAM is used up in no time by Kaggle's google landmark dataset.

EDIT: Maybe a slightly different issue since this one was reported to only occur after a few iterations..

[jph00]

Best off using the forum for this.

[jaideep11061982]

with ThreadPoolExecutor

making num workers =0 will execute the code that you are putting there is a if condition in a dataloader...
so that we dont have to modify the loader at all