[https://nvbugs/5816267][fix] Remove weight tensor holder to release memory earlier

[dongxuy04]

Summary by CodeRabbit

• Bug Fixes
  • Optimized memory management during model initialization. When the system recovers from model setup errors, it now more efficiently releases cached memory resources, reducing memory overhead and improving overall system performance during error recovery scenarios.

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Description

Fix issue #10759

Test Coverage

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[coderabbitai]

📝 Walkthrough

Walkthrough

A single line is added to the exception path in model initialization to explicitly delete the memo dictionary, freeing the memoized tensor cache used during meta-tensor initialization and improving memory cleanup.

Changes

Cohort / File(s)	Summary
Memory Management Cleanup tensorrt_llm/_torch/pyexecutor/model_loader.py	Added del memo statement in exception path to release memoized tensor cache after model initialization fallback

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The PR description is largely incomplete. While it references issue #10759 and the PR template is present, critical sections like 'Description' (to explain issue and solution) and 'Test Coverage' (to list relevant tests) are empty or unfilled.	Fill in the Description section explaining what issue #10759 is and how this change fixes it. Also add the Test Coverage section listing relevant tests that safeguard these memory management changes.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly follows the required template format with [https://nvbugs/5816267][fix] and a specific summary about removing weight tensor holder to release memory earlier, directly matching the changeset.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

tensorrt_llm/_torch/pyexecutor/model_loader.py (1)

254-259: del memo will raise NameError in the fallback path.

memo is defined at line 242, inside the try block. If an exception occurs before that point (e.g., during copy.deepcopy(config) or AutoModelForCausalLM.from_config(config_copy)), the except block executes but memo was never defined. The subsequent del memo will then raise NameError.

🐛 Proposed fix: Initialize memo before the try block

         with timing("Model init total"), maybe_create_moe_load_balancer(
                 config, self.mapping) as moe_load_balancer:
+            memo = {}
             try:
                 # config will be modified in-place for some models, like Qwen2
                 config_copy = copy.deepcopy(config)
                 with MetaInitMode():
                     model = AutoModelForCausalLM.from_config(config_copy)

-                memo = dict()
-
                 def init_meta_tensor(t: torch.Tensor):
                     if t.device != torch.device('meta'):
                         return t
                     if t not in memo:
                         memo[t] = torch.empty_like(t, device='cuda')
                     return memo[t]

                 model._apply(init_meta_tensor)
                 config = config_copy

             except Exception:
                 logger.info(
                     f"Fallback to regular model init: {traceback.format_exc(limit=10)}\n"
                 )
                 model = AutoModelForCausalLM.from_config(config)
             del memo

[dongxuy04]

/bot run --disable-fail-fast

[dongxuy04]

/bot kill

[tensorrt-cicd]

PR_Github #32881 [ run ] triggered by Bot. Commit: d8c433a

[tensorrt-cicd]

PR_Github #32883 [ kill ] triggered by Bot. Commit: d8c433a

[tensorrt-cicd]

PR_Github #32883 [ kill ] completed with state SUCCESS. Commit: d8c433a
Successfully killed previous jobs for commit d8c433a

[dongxuy04]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #32884 [ run ] triggered by Bot. Commit: c778f49

[tensorrt-cicd]

PR_Github #32884 [ run ] completed with state SUCCESS. Commit: c778f49
/LLM/main/L0_MergeRequest_PR pipeline #25436 completed with status: 'SUCCESS'