[Feature]: Remove Chunking From FusedMoE

[SouthWest7]

Purpose

Remove the kernel-level chunking mechanism from FusedMoE.

Resolves #30620

Test Plan

pytest tests/kernels/moe/test_moe.py

Test Result

============================================== test session starts ===============================================
platform linux -- Python 3.12.4, pytest-9.0.2, pluggy-1.6.0
rootdir: /home/mxn/llm/vllm
configfile: pyproject.toml
plugins: anyio-4.12.1, asyncio-1.3.0
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 3551 items                                                                                             

tests/kernels/moe/test_moe.py ............................................................................ [  2%]
.......................................................................................................... [  5%]
.......................................................................................................... [  8%]
.......................................................................................................... [ 11%]
.......................................................................................................... [ 14%]
.......................................................................................................... [ 17%]
.......................................................................................................... [ 20%]
.......................................................................................................... [ 23%]
.......................................................................................................... [ 26%]
.......................................................................................................... [ 29%]
.......................................................................................................... [ 31%]
.......................................................................................................... [ 34%]
.......................................................................................................... [ 37%]
.......................................................................................................... [ 40%]
.......................................................................................................... [ 43%]
.......................................................................................................... [ 46%]
.......................................................................................................... [ 49%]
.......................................................................................................... [ 52%]
.......................................................................................................... [ 55%]
.......................................................................................................... [ 58%]
.......................................................................................................... [ 61%]
.......................................................................................................... [ 64%]
.......................................................................................................... [ 67%]
.......................................................................................................... [ 70%]
.......................................................................................................... [ 73%]
.......................................................................................................... [ 76%]
.......................................................................................................... [ 79%]
.......................................................................................................... [ 82%]
.......................................................................................................... [ 85%]
.......................................................................................................... [ 88%]
.......................................................................................................... [ 91%]
.......................................................................................................... [ 94%]
.......................................................................................................... [ 97%]
...ssssssss..s..........ss..s..s.................s.................................                              [100%]

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[mergify]

Documentation preview: https://vllm--34086.org.readthedocs.build/en/34086/

[gemini-code-assist]

Code Review

This pull request removes the kernel-level chunking mechanism from FusedMoE, which simplifies the codebase significantly. The changes are mostly about removing code related to chunking and relying on the scheduler's chunked prefill to handle large inputs. A safety check has been added to the non-modular path to prevent illegal memory access with Triton kernels when the number of tokens is too large. However, my review identified that a similar safety check is missing in the modular kernel path for Triton-based experts, which could lead to memory corruption issues. I've added a critical comment to address this.

[ZJY0516]

Chunked prefill now guarantees that the scheduler never sends more tokens than ~65K in a single forward pass

Do we have any assertion for this?

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @SouthWest7.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[SouthWest7]

Chunked prefill now guarantees that the scheduler never sends more tokens than ~65K in a single forward pass

Do we have any assertion for this?

Sorry, there is actually no related assertion — I misunderstood the original issue. I’ll be more careful in future changes.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @SouthWest7.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[ProExpertProg]

Lgtm but let's wait for @robertgshaw2-redhat & bill's response for the 1 recent comment before merging

[SouthWest7]

@ProExpertProg I marked the previous comment as resolved because reviewer said it was only related to chunking.

[ProExpertProg]

Thank you for the contribution! Let's hope CI passes