PTQ memory optimization
State: closed | Pull request: yes
Labels: name: Run CICD

name: skip-docs

# What does this PR do ?

Reduces the memory overhead of PTQ by leaving the DDP module uninitialised and changing parameters' `dtype` during model loading.

**Collection**: llm

# Changelog 
- Add specific line by line info of high level changes in this PR.

# Usage
* You can potentially add a usage example below

```python
# Add a code snippet demonstrating how to use this 
```

# GitHub Actions CI

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The GitHub Actions CI will run automatically when the "Run CICD" label is added to the PR.
To re-run CI remove and add the label again.
To run CI on an untrusted fork, a NeMo user with write access must first click "Approve and run".

# Before your PR is "Ready for review"
**Pre checks**:
- [ ] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [ ] New Feature
- [ ] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to # (issue)


<!-- pylint-output-strict-mode-false -->

beep boop 🤖: 🙏 The following files have warnings. In case you are familiar with these, please try helping us to improve the code base.

---

Your code was analyzed with PyLint. The following annotations have been identified:

```
************* Module nemo.collections.llm.gpt.model.base
nemo/collections/llm/gpt/model/base.py:226:0: C0301: Line too long (122/119) (line-too-long)
nemo/collections/llm/gpt/model/base.py:51:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:94:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:115:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:123:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:131:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:139:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:149:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:159:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:182:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:252:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:264:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:276:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:288:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:300:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:312:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:326:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/base.py:345:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:349:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:372:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:375:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:378:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:382:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:387:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:410:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:417:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:424:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:452:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/base.py:32:0: W0611: Unused OptimizerModule imported from nemo.lightning.pytorch.optim (unused-import)
nemo/collections/llm/gpt/model/base.py:43:4: W0611: Unused import fused_weight_gradient_mlp_cuda (unused-import)
************* Module nemo.collections.llm.quantization.quantizer
nemo/collections/llm/quantization/quantizer.py:232:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/quantization/quantizer.py:265:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/quantization/quantizer.py:317:0: C0116: Missing function or method docstring (missing-function-docstring)
************* Module nemo.collections.llm.quantization.utils
nemo/collections/llm/quantization/utils.py:46:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/quantization/utils.py:71:0: C0116: Missing function or method docstring (missing-function-docstring)

-----------------------------------
Your code has been rated at 9.58/10
```

---

Thank you for improving NeMo's documentation!

[🤖]: Hi @Laplasjan107 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/11840526698) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g

[🤖]: Hi @Laplasjan107 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/11846344687) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g

[🤖]: Hi @Laplasjan107 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/11895847591) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g