[Model] Add tower and connector LoRA support for LFM2-VL by zupengwang · Pull Request #51498 · vllm-project/vllm

zupengwang · 2026-08-08T11:13:11Z

Purpose

Part of #31479.

Enable tower and connector LoRA support for LFM2-VL.

LFM2-VL already implements SupportsLoRA and exposes its multimodal module mapping, but it is missing the token-budget helpers required by the tower/connector LoRA path. Its projector also uses plain nn.Linear layers, which cannot be replaced by vLLM's LoRA wrappers.

This change:

converts the two projector linear layers to ReplicatedLinear
preserves their weight names and tensor-only forward behavior
adds get_num_mm_encoder_tokens
adds get_num_mm_connector_tokens

The projector packs each downsample_factor × downsample_factor group of vision tokens into one connector token. Therefore:

encoder tokens = image tokens × downsample_factor²
connector tokens = encoder tokens ÷ downsample_factor²

Duplicate check:

searched open and closed PRs for LFM2 get_num_mm_encoder_tokens
searched open and closed PRs for lfm2_vl tower connector LoRA
found no LFM2-VL implementation covering this feature
[Bugfix] Shared MM text-LoRA mapper fallback for language_model wrappers #49525 changes text-LoRA key mapping for multimodal wrappers and is orthogonal to this change

AI assistance disclosure: OpenAI Codex assisted with issue triage, implementation, and test drafting. I reviewed, understand, and verified every changed line and the reported test results.

Test Plan

ruff check \
  vllm/model_executor/models/lfm2_vl.py \
  tests/models/multimodal/processing/test_lfm2_vl.py

ruff format --check \
  vllm/model_executor/models/lfm2_vl.py \
  tests/models/multimodal/processing/test_lfm2_vl.py

timeout 300 .venv/bin/python -m pytest -q \
  tests/models/multimodal/processing/test_lfm2_vl.py \
  tests/v1/worker/test_gpu_model_runner.py::test_set_active_mm_loras_builds_tower_and_connector_mappings

A focused RTX 3090 probe additionally checks:

ReplicatedLinear output against equivalent torch.nn.functional.linear operations
projector output length against the token helpers
actual conversion of both projector layers to ReplicatedLinearWithLoRA
loading projector weights and biases through AutoWeightsLoader

Test Result

Lint and formatting:

All checks passed!
2 files already formatted

Pytest:

7 passed, 14 warnings in 4.78s

The warnings are existing torch.jit.script_method deprecation warnings.

RTX 3090 projector probe:

downsample_factor: 2
encoder_tokens: 32
projector_output_tokens: 8
helper_connector_tokens: 8
helper_roundtrip_encoder_tokens: 32
output_shape: (8, 1024)
numeric_parity: true
lora_wrappers:
  ReplicatedLinearWithLoRA
  ReplicatedLinearWithLoRA

Weight-loading probe:

loaded_parameters:
  linear_1.bias
  linear_1.weight
  linear_2.bias
  linear_2.weight
weight_loading: true

A full generation test with a trained LFM2-VL tower/connector LoRA adapter was not run because no suitable public adapter was used for this change.

Convert the LFM2-VL projector linears to LoRA-wrappable replicated layers and add token budget helpers based on the projector downsample factor. Add focused coverage for the real 450M config, LoRA layer replacement, round trips, and zero-token inputs. Assisted-by: OpenAI Codex Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com>

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github-actions · 2026-08-08T11:13:20Z

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linitra24 · 2026-08-19T10:08:43Z

@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project


Can we remove this test?

Removed the entire newly added test file in 195e139. This drops the LFM2-specific token-count round-trip, zero-token, and projector LoRA-wrapping assertions. The existing GPU model runner test still covers generic tower/connector mapping construction, but it mocks the helper results and does not cover those LFM2-specific details.

linitra24 · 2026-08-19T10:21:47Z

        if self.projector_use_layernorm:
            self.layer_norm = nn.LayerNorm(in_channels)
-        self.linear_1 = nn.Linear(
+        self.linear_1 = ReplicatedLinear(


Should this be changed to ReplicatedLinear as well?

Yes. I changed it in 195e139. The layer is vision_tower.vision_model.embeddings.patch_embedding; as an nn.Linear, it was not discovered by get_supported_lora_modules() and could not be wrapped by ReplicatedLinearWithLoRA. I changed only this layer to ReplicatedLinear(..., return_bias=False), matching the existing Siglip2 NAFlex/Isaac pattern. The bias and state-dict names, tensor-only forward contract, weight loading, and fully replicated TP semantics are preserved.

Remove the standalone LFM2-VL processing test file per review. Convert the Siglip2 patch projection to ReplicatedLinear so tower LoRA targets are discoverable and wrappable while preserving its tensor-only forward contract. Assisted-by: OpenAI Codex Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com>

linitra24

LGTM after the latest changes.

jeejeelee · 2026-08-20T06:45:46Z

/ci run

github-actions · 2026-08-20T06:46:54Z

✅ Triggered Buildkite CI #84760 for commit 195e139807c3.

zupengwang · 2026-08-20T11:13:27Z

/ci run

github-actions · 2026-08-20T11:13:46Z

✅ Triggered Buildkite CI #84816 for commit 3cb8921c4b2f.

zupengwang · 2026-08-20T12:32:41Z

PR #51498 is approved and all required checks are green on 3cb8921c4b2f. Could a maintainer please merge it when convenient? Thank you!

…t#51498) Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com> Signed-off-by: Wyett <wyettzeng@gmail.com>

…t#51498) Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com> Signed-off-by: Zhu, Zufang <zufang.zhu@intel.com>

…t#51498) Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com> Signed-off-by: khushali9 <khushali.desai9@gmail.com>

…t#51498) Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com>

zupengwang requested review from AndreasKaratzas, DarkLight1337 and ywang96 as code owners August 8, 2026 11:13

claude Bot reviewed Aug 8, 2026

View reviewed changes

mergify Bot added the multi-modality Related to multi-modality (#4194) label Aug 8, 2026

DarkLight1337 requested a review from jeejeelee August 8, 2026 11:38

linitra24 reviewed Aug 19, 2026

View reviewed changes

linitra24 approved these changes Aug 20, 2026

View reviewed changes

jeejeelee approved these changes Aug 20, 2026

View reviewed changes

jeejeelee added the verified Run pre-commit for new contributors without triggering other tests label Aug 20, 2026

Merge branch 'main' into feat/lfm2-vl-mm-lora-token-mapping

3cb8921

DarkLight1337 merged commit df13769 into vllm-project:main Aug 20, 2026
88 checks passed

This was referenced Aug 20, 2026

[Feature]: Enable LoRA support for tower and connector in more MM models #31479

Closed

[Model] Enable LoRA support for tower and connector in GLM-ASR #53149

Open

zupengwang mentioned this pull request Aug 24, 2026

[Bugfix][LoRA] Restore tower and connector LoRA support for LFM2-VL #53519

Merged

am-cohere pushed a commit to am-cohere/vllm that referenced this pull request Sep 1, 2026

[Model] Add tower and connector LoRA support for LFM2-VL (vllm-projec…

3845418

…t#51498) Signed-off-by: zupengwang <71580390+zupengwang@users.noreply.github.com>

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[Model] Add tower and connector LoRA support for LFM2-VL - #51498

[Model] Add tower and connector LoRA support for LFM2-VL#51498
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		@@ -0,0 +1,88 @@
		# SPDX-License-Identifier: Apache-2.0
		# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

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zupengwang commented Aug 8, 2026

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