Add --offload-to-disk support to minifier (#100546)
When minifying extremely large repros, the minifier can run out of memory. This is because, for delta debugging, the minifier keeps a copy of every intermediate output in the network. This can easily put you over the memory limit for your GPU. To make matters worse, we cannot easily delta debug in such a situation, as delta debugging involves replacing intermediates with inputs, but doing so can cause an intermediate to become live longer than its actual extent in the original model (since inputs all have to be allocated up front).
The strategy in this PR is to use `load_tensor` from the previous PR to offer a low memory mode for delta debugging. Instead of putting intermediates as inputs, we instead load them in the middle of the graph in question. If, through DCE, the load_tensor ends up floating to the top of the graph, we can input-ify it. We now no longer save all intermediates in memory, but instead save them to disk. I used this to successfully minify the repro that helped us solve https://github.com/pytorch/pytorch/pull/100332
The testing is not very good. I can try to add more robust testing but it will involve a more involved refactor to FX minifier. Let me know if that's what you want.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100546
Approved by: https://github.com/anijain2305, https://github.com/voznesenskym
