Pr Review

TorchRec PR/Diff Review Skill

Review TorchRec code changes focusing on what CI and linters cannot check: distributed correctness, sharding safety, backward compatibility, OSS boundary violations, and test adequacy. Linting, formatting, type checking, and import ordering are handled by CI.

Usage Modes

No Argument

If the user invokes /pr-review with no arguments, use sl status and sl diff (or sl show .) to review uncommitted changes or the current commit.

Diff ID Mode

The user provides a Phabricator diff ID:

/pr-review D12345678
/pr-review D12345678 detailed

Use mcp__plugin_meta_mux__get_phabricator_diff_details with include_raw_diff: true and include_diff_summary: true to fetch the diff.

Local Changes Mode

Review uncommitted changes or the current commit:

/pr-review local
/pr-review local detailed

1. Run sl status to check for uncommitted changes
2. Run sl diff for uncommitted changes, or sl show . for the current commit
3. For large diffs, use sl diff --stat first, then Read to examine specific files

Review Workflow

Step 1: Fetch and Understand Changes

1. Get the diff content (via Phabricator MCP or sl commands)
2. Read the diff summary/commit message to understand intent
3. Identify the scope: which TorchRec subsystems are affected (modules, distributed, sparse, metrics, fb/, etc.)

Step 2: Classify Changes

Group changes by type:

• Core logic - New features, bug fixes, algorithm changes
• Distributed/sharding - Anything touching distributed/, sharding strategies, collectives
• Public API - Changes to interfaces, configs, module signatures
• Tests - New or modified tests
• Internal - Changes within fb/ (Meta-only)
• Config/Build - BUCK files, configs, dependencies

Step 3: Deep Review

Perform thorough analysis using the review checklist. See review-checklist.md for detailed criteria covering:

• Distributed correctness and sharding safety
• FBGEMM integration
• Code quality and TorchRec patterns
• Testing adequacy
• Performance implications
• OSS boundary enforcement

Step 4: Check Backward Compatibility

Evaluate BC implications for any change touching public APIs. See bc-guidelines.md for:

• What constitutes a BC-breaking change in TorchRec
• Public API boundaries (everything outside fb/)
• Required deprecation patterns
• Common BC pitfalls with KJT, EBC, DMP, and sharding types

Step 5: Read Surrounding Code

For non-trivial changes, use Read to examine:

• The full file(s) being modified (not just the diff hunks)
• Related tests to verify coverage
• Similar implementations elsewhere in TorchRec for consistency

Step 6: Formulate Review

Structure your review with actionable feedback organized by category.

Review Areas

Output Format

Structure your review as follows:

## Review: D<number> / Local Changes

### Summary
Brief overall assessment of the changes (1-2 sentences).

### Distributed Safety
[Issues with collectives, sharding, rank consistency. Or "No concerns" if none]

### Code Quality
[Issues and suggestions, or "No concerns" if none]

### Testing
- [ ] Tests exist for new functionality
- [ ] Distributed tests use MultiProcessTestBase
- [ ] Edge cases covered (empty KJT, single rank, etc.)
[Additional testing feedback]

### Backward Compatibility
[BC concerns if any, or "No BC-breaking changes"]

### Performance
[Performance concerns if any, or "No performance concerns"]

### OSS Boundary
[Boundary violations if any, or "No boundary issues"]

### Recommendation
**Approve** / **Request Changes** / **Needs Discussion**

[Brief justification for recommendation]

Specific Comments (Detailed Review Only)

Only include this section if the user requests a "detailed" review.

Do not repeat observations already made in other sections. This section is for additional file-specific feedback.

When requested, add file-specific feedback with line references:

### Specific Comments
- `torchrec/distributed/sharding/rw_sharding.py:142` - This allreduce should use async_op=True to overlap with compute
- `torchrec/sparse/jagged_tensor.py:305-310` - Missing validation for empty lengths tensor
- `torchrec/distributed/tests/test_model_parallel.py:88` - Test only covers world_size=2, add world_size=4 case

Key Principles

1. No repetition - Each observation appears in exactly one section
2. Focus on what CI cannot check - Don't comment on formatting, linting, or type errors
3. Be specific - Reference file paths and line numbers
4. Be actionable - Provide concrete suggestions, not vague concerns
5. Be proportionate - Minor issues shouldn't block, but note them
6. Assume competence - The author knows TorchRec and distributed systems; explain only non-obvious context
7. Distributed correctness is paramount - Subtle bugs in collectives cause hard-to-debug hangs and data corruption

Files to Reference

When reviewing TorchRec code, consult:

• torchrec/CLAUDE.md - Coding style and testing patterns
• torchrec/distributed/test_utils/ - Test utilities and patterns
• torchrec/modules/ - Core module implementations
• torchrec/distributed/planner/ - Sharding planner reference

Instructions from User

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