Add env variable to bypass CUDACachingAllocator for debugging (#45294)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45294
While tracking down a recent memory corruption bug we found that
cuda-memcheck wasn't finding the bad accesses, and ngimel pointed out that
it's because we use a caching allocator so a lot of "out of bounds" accesses
land in a valid slab.
This PR adds a runtime knob (`PYTORCH_NO_CUDA_MEMORY_CACHING`) that, when set,
bypasses the caching allocator's caching logic so that allocations go straight
to cudaMalloc. This way, cuda-memcheck will actually work.
Test Plan:
Insert some memory errors and run a test under cuda-memcheck;
observe that cuda-memcheck flags an error where expected.
Specifically I removed the output-masking logic here:
https://github.com/pytorch/pytorch/blob/master/torch/csrc/jit/tensorexpr/cuda_codegen.cpp#L819-L826
And ran:
```
PYTORCH_NO_CUDA_MEMORY_CACHING=1 cuda-memcheck pytest -k test_superslomo test_jit_fuser_te.py
```
Reviewed By: ngimel
Differential Revision: D23964734
Pulled By: bertmaher
fbshipit-source-id: 04efd11e8aff037b9edde80c70585cb820ee6e39