Fix off-by-2 error in RL sequence packing#3551
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yobibyte
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Feb 24, 2026
| f"cu_seqlens_q has size {params.cu_seqlens_q.shape[0]} but expected {expected_size} " | ||
| f"for {num_sequences} sequences" | ||
| ) | ||
| assert params.cu_seqlens_kv.shape[0] == expected_size |
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Let's also test the semantics. Please, check that the 0th and last elements are as we expect them to be. The other two checks are merely to check what we do by construction.
yobibyte
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Feb 24, 2026
| if len(cu_seqlens) < max_sequences_per_bin: | ||
| out = cu_seqlens.new_full((max_sequences_per_bin,), bin_size) | ||
| # We add 2 to account for the initial 0 and the final bin_size. | ||
| if len(cu_seqlens) < max_sequences_per_bin + 2: |
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I understand why we need space for initial zero. Why do we need the other?
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To ensure TE kernels work correctly; I'll link you to the private thread.
janEbert
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Feb 24, 2026
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🔄 Merge queue validation started! You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/22362684902 |
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🔄 Merge queue validation started! You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/22365095896 |
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