[BugFix][Multimodal] Pick worst-case DeepSeek-V4 VL dummy image size (#59271)

[YidaWeng]

Purpose

Fixes #59271.

DeepseekV4VLProcessingInfo.get_image_size_with_most_features assumed a square maximizes ViT patches within the token budget. Because each aligner row costs an extra IMAGE_NEW_LINE, a wide grid (1932x336) produces more placeholder tokens and patches than the previous 756x756 dummy, so memory profiling under-estimated peak multimodal usage.

Search budget-feasible LLM grids (respecting vision_max_wh_ratio) and pick the one with the most ViT patches, breaking ties by sentinel-block length. For the default config this returns 1932x336.

Test Plan

.venv/bin/python -m pytest tests/models/multimodal/processing/test_deepseek_v4_vl.py -q

Also re-ran the issue reproducer against the local CPU editable install.

Test Result

2 passed

Issue reproducer after fix:

dummy ImageSize(width=1932, height=336) (378, 3312)
1932x336 (378, 3312)

Duplicate-work check

• gh issue view 59271 --repo vllm-project/vllm --comments — no claims
• gh pr list --repo vllm-project/vllm --state open --search "59271 in:body" — none
• Keyword searches (DeepseekV4VLProcessingInfo, DeepSeek-V4 VL dummy, vision_max_wh_ratio, mm_preprocess most features) — no open PR for this fix
• Note: deepseek_v41 already searches non-square grids; only deepseek_v4 had the square assumption

AI assistance

AI assistance was used to reproduce the bug, apply the grid search described in the issue, and add regression tests. The human submitter reviewed every changed line and ran the tests above.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[DarkLight1337]

Maybe redundant since #57898 was merged

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[YidaWeng]

@DarkLight1337 Thanks for the pointer — I looked at #57898 closely. I don't think this is redundant: the two PRs touch different model trees, and V4 is still broken on current main.

• [Bugfix] Profile maximum DeepSeek V4.1 vision features #57898 only changed vllm/models/deepseek_v41/common/mm_preprocess.py (DeepSeek-V4.1).
• This PR fixes vllm/models/deepseek_v4/common/mm_preprocess.py (DeepSeek-V4). On current main, get_image_size_with_most_features still assumes a square and returns 756×756, which under-counts multimodal tokens (346 vs 378) and ViT patches (2916 vs 3312) relative to the true worst case 1932×336 (repro from [Bug]: DeepSeek-V4 VL dummy image is not the worst case for multimodal profiling #59271; I re-confirmed these numbers on this branch).

DeepSeek-V4 VL is still a supported path (DeepseekV4ForConditionalGeneration / deepseek-ai/DeepSeek-V4-Flash-Vision-Exp in the supported-models table), so the V4.1 fix does not cover it. The selectors also differ slightly (V4 reserves COMPRESS_PAD_TO - 1 and searches via grid_tokens), so #57898 is not a drop-in for V4.

Related: #57898 removed its mock-based regression tests during review. This PR adds processor-level tests (no mocks) that assert the dummy maximizes tokens/patches within budget and respects vision_max_wh_ratio. Happy to extend similar coverage to deepseek_v41 if useful; otherwise I'd prefer to keep this PR scoped to the V4 fix.

[DarkLight1337]

Oh, I missed that this PR is for V4, not V4.1. Should be ok then. cc @Isotr0py

[DarkLight1337]

/ci run

[github-actions]

✅ Triggered Buildkite CI #92134 for commit c2d3523d9a83.

[mergify]

Hi @YidaWeng, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

[DarkLight1337]

Pre-commit is failing on main, trying to fix it now...

[DarkLight1337]

/ci run

[github-actions]

✅ Triggered Buildkite CI #92156 for commit 2f6f8fa860d1.