[OP][RL]update attn_mask_q 2

[ckl117]

Motivation

attn_mask_q最后一个维度仅需2个vec即可表示双向mask

💡 If this PR is a Cherry Pick, the PR title needs to follow the format by adding the [Cherry-Pick] label at the very beginning and appending the original PR ID at the end. For example, [Cherry-Pick][CI] Add check trigger and logic(#5191)

💡 如若此PR是Cherry Pick，PR标题需遵循格式，在最开始加上[Cherry-Pick]标签，以及最后面加上原PR ID，例如[Cherry-Pick][CI] Add check trigger and logic(#5191)

Modifications

Usage or Command

Accuracy Tests

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
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• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
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[paddle-bot]

Thanks for your contribution!

[PaddlePaddle-bot]

🤖 AI Code Review | 2026-04-13 21:33 CST

📋 Review 摘要

PR 概述：将 get_attn_mask_q 算子输出张量的最后一个维度从 4 优化为 2，减少内存占用。

变更范围：custom_ops/gpu_ops/get_attn_mask_q.cu

影响面 Tag：[OP]

📝 PR 规范检查

检查项	状态
标题 Tag	✅ 包含 [OP] 和 [RL]
Motivation	✅ 已填写
Modifications	❌ 未填写（建议补充说明变更逻辑）
Unit Tests	❌ 未添加（ Checklist 未勾选）

标题建议（当前已符合，但建议补充）：

• 当前：[OP][RL]update attn_mask_q 2
• 建议：[OP][Optimization] reduce attn_mask_q output dimension from 4 to 2

问题

级别	文件	概述
🟡 建议	custom_ops/gpu_ops/get_attn_mask_q.cu:52	需验证 Paddle flashmask_attention 是否支持 2 维输入
🟡 建议	custom_ops/gpu_ops/get_attn_mask_q.cu:70	缺少验证输出形状变更的单元测试

总体评价

这是一个内存优化 PR，减少了 attn_mask_q 输出张量的维度。但存在下游兼容性风险和缺少单元测试的问题，建议验证后再合入。

[PaddlePaddle-bot]

🟡 建议 startend_row_vec 从 4 维改为 2 维后，需要验证下游 Paddle 的 flashmask_attention 函数是否支持 2 维输入。

当前 flash_attn_backend.py:153,168 将 attn_mask_q 通过 startend_row_indices 参数传给 Paddle 的 flashmask_attention/flashmask_attention_v4。如果这些函数严格要求 4 维输入，会导致运行时错误。

建议：

1. 在 tests/layers/test_flash_attn_func.py 中使用 2 维输入运行 test_fa3_with_mask、test_fa4 等测试验证兼容性
2. 或确认 Paddle 的 flashmask_attention 函数支持 2 维 startend_row_indices

[PaddlePaddle-bot]

🟡 建议 变更了输出张量形状（从 [..., 4] 改为 [..., 2]），但未添加相应的单元测试验证。

建议：

1. 在 tests/operators/test_flash_mask_attn.py 中添加测试，验证输出形状确实为 2
2. 验证输出值的正确性（[q_end, min_q_idx]）
3. 更新 PR Checklist 勾选 "Add unit tests"

[zoooo0820]

LGTM

[codecov-commenter]

Codecov Report

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