[Bugfix] Cap FULL decode cudagraph sizes for Mamba/hybrid models (#34094)

tests/compile/test_config.py

@@ -570,3 +570,45 @@ def test_compile_sizes_padding_validation():
     assert sorted(config.compile_sizes) == [3, 5, 7]
     dispatcher = CudagraphDispatcher(_create_vllm_config_for_validation(config))
     dispatcher.initialize_cudagraph_keys(CUDAGraphMode.NONE)  # Should not raise
+
+
+@pytest.mark.parametrize(
+    "capture_sizes, max_size, num_blocks, expected_sizes, expected_max",
+    [
+        # Normal capping: sizes filtered to <= num_blocks
+        (
+            [1, 2, 4, 8, 16, 32, 64, 128, 256, 512],
+            512,
+            200,
+            [1, 2, 4, 8, 16, 32, 64, 128],
+            128,
+        ),
+        # No capping needed: num_blocks >= max
+        ([1, 2, 4, 8, 16], 16, 1000, [1, 2, 4, 8, 16], 16),
+        # Exact boundary: num_blocks == max (no capping)
+        ([1, 2, 4, 8, 16, 32], 32, 32, [1, 2, 4, 8, 16, 32], 32),
+        # All sizes capped: num_blocks < smallest size
+        ([8, 16, 32], 32, 4, [], 0),
+        # num_blocks <= 0: early return, no change
+        ([1, 2, 4], 4, 0, [1, 2, 4], 4),
+    ],
+)
+def test_adjust_cudagraph_sizes_for_mamba_cache(
+    capture_sizes, max_size, num_blocks, expected_sizes, expected_max
+):
+    """Test that cudagraph capture sizes are correctly capped to fit
+    available Mamba cache blocks.
+
+    See: https://github.com/vllm-project/vllm/issues/34094
+    """
+    config = CompilationConfig(
+        cudagraph_capture_sizes=capture_sizes,
+        max_cudagraph_capture_size=max_size,
+        cudagraph_mode=CUDAGraphMode.NONE,
+    )
+    config.adjust_cudagraph_sizes_for_mamba_cache(num_blocks)
+    assert config.cudagraph_capture_sizes == expected_sizes
+    assert config.max_cudagraph_capture_size == expected_max
+    # Invariant: last element == max_cudagraph_capture_size
+    if expected_sizes:
+        assert config.cudagraph_capture_sizes[-1] == config.max_cudagraph_capture_size

tests/v1/worker/test_gpu_model_runner.py

@@ -1199,3 +1199,123 @@ def test_is_uniform_decode() -> None:
         num_reqs=15,
         force_uniform_decode=False,
     )
+
+
+@pytest.mark.skipif(
+    current_platform.is_rocm(),
+    reason="Attention backend FLASHINFER is not supported on ROCm.",
+)
+def test_cudagraph_sizes_capped_for_mamba_cache():
+    """Test that cudagraph capture sizes are capped to num_blocks for
+    hybrid models with Mamba layers.
+
+    See: https://github.com/vllm-project/vllm/issues/34094
+    """
+    set_random_seed(42)
+
+    update_environment_variables(
+        {
+            "RANK": "0",
+            "LOCAL_RANK": "0",
+            "WORLD_SIZE": "1",
+            "MASTER_ADDR": "localhost",
+            "MASTER_PORT": "12345",
+        }
+    )
+    from tests.utils import ensure_current_vllm_config
+
+    with ensure_current_vllm_config():
+        init_distributed_environment()
+        initialize_model_parallel(tensor_model_parallel_size=1)
+    torch.set_default_dtype(torch.float16)
+
+    model_config = ModelConfig(
+        model="ibm-granite/granite-4.0-tiny-preview",
+        dtype="float16",
+    )
+    scheduler_config = SchedulerConfig(
+        max_num_seqs=10,
+        max_num_batched_tokens=512,
+        max_model_len=512,
+        is_encoder_decoder=model_config.is_encoder_decoder,
+    )
+    cache_config = CacheConfig(
+        block_size=BLOCK_SIZE,
+        gpu_memory_utilization=0.9,
+        swap_space=0,
+        cache_dtype="auto",
+    )
+    parallel_config = ParallelConfig()
+    attention_config = AttentionConfig(backend=AttentionBackendEnum.FLASHINFER)
+    vllm_config = VllmConfig(
+        model_config=model_config,
+        cache_config=cache_config,
+        scheduler_config=scheduler_config,
+        parallel_config=parallel_config,
+        attention_config=attention_config,
+    )
+
+    with set_current_vllm_config(vllm_config):
+        hf_config = vllm_config.model_config.hf_config
+        fwd_context = {}
+        for key in ["model.layers.0.self_attn.attn", "model.layers.1.self_attn.attn"]:
+            fwd_context[key] = Attention(
+                num_heads=model_config.get_num_attention_heads(parallel_config),
+                num_kv_heads=model_config.get_num_kv_heads(parallel_config),
+                head_size=model_config.get_head_size(),
+                scale=1.0,
+                prefix=key,
+            )
+        for key in [
+            "model.layers.2.mixer",
+            "model.layers.3.mixer",
+            "model.layers.4.mixer",
+            "model.layers.5.mixer",
+        ]:
+            fwd_context[key] = MambaMixer2(
+                hidden_size=hf_config.hidden_size,
+                ssm_state_size=hf_config.mamba_d_state,
+                conv_kernel_size=hf_config.mamba_d_conv,
+                intermediate_size=hf_config.mamba_expand * hf_config.hidden_size,
+                use_conv_bias=hf_config.mamba_conv_bias,
+                use_bias=hf_config.mamba_proj_bias,
+                n_groups=hf_config.mamba_n_groups,
+                num_heads=hf_config.mamba_n_heads,
+                head_dim=hf_config.mamba_d_head,
+                rms_norm_eps=hf_config.rms_norm_eps,
+                activation=hf_config.hidden_act,
+                cache_config=cache_config,
+                model_config=model_config,
+                prefix=key,
+            )
+        assert fwd_context is not None
+
+        runner = GPUModelRunner(vllm_config, DEVICE)
+        kv_cache_spec = runner.get_kv_cache_spec()
+
+        available_memory = 5 * GiB_bytes
+        kv_cache_config = get_kv_cache_configs(
+            vllm_config, [kv_cache_spec], [available_memory]
+        )[0]
+        num_blocks = kv_cache_config.num_blocks
+
+        # Set max_cudagraph_capture_size to a value larger than num_blocks
+        # to trigger the Mamba capping logic.
+        large_max = num_blocks + 100
+        compilation_config = vllm_config.compilation_config
+        compilation_config.max_cudagraph_capture_size = large_max
+        compilation_config.cudagraph_capture_sizes = [
+            s for s in [1, 2, 4, 8, 16, 32, 64, 128, 256, 512] if s <= large_max
+        ]
+
+        runner.initialize_kv_cache(kv_cache_config)
+
+    # After initialization, cudagraph sizes should be capped
+    assert compilation_config.max_cudagraph_capture_size <= num_blocks
+    assert all(s <= num_blocks for s in compilation_config.cudagraph_capture_sizes)
+    # Invariant: last element == max
+    if compilation_config.cudagraph_capture_sizes:
+        assert (
+            compilation_config.cudagraph_capture_sizes[-1]
+            == compilation_config.max_cudagraph_capture_size
+        )

vllm/config/compilation.py

@@ -1190,6 +1190,58 @@ def adjust_cudagraph_sizes_for_spec_decode(
         self.max_cudagraph_capture_size = rounded_sizes[-1]
         self.cudagraph_capture_sizes = rounded_sizes
 
+    def adjust_cudagraph_sizes_for_mamba_cache(
+        self, num_mamba_cache_blocks: int
+    ) -> None:
+        """Cap cudagraph capture sizes to available Mamba cache blocks.
+
+        For hybrid Mamba/attention models, the Mamba conv_state and
+        ssm_state tensors have their first dimension equal to num_blocks
+        (from KVCacheConfig). During CUDA graph capture the decode batch
+        size equals num_tokens, so capture sizes exceeding num_blocks
+        would cause out-of-bounds access in Mamba kernels.
+
+        See: https://github.com/vllm-project/vllm/issues/34094
+        """
+        if not self.cudagraph_capture_sizes or num_mamba_cache_blocks <= 0:
+            return
+
+        assert self.max_cudagraph_capture_size is not None
+
+        if num_mamba_cache_blocks >= self.max_cudagraph_capture_size:
+            return
+
+        capped_sizes = [
+            s for s in self.cudagraph_capture_sizes if s <= num_mamba_cache_blocks
+        ]
+
+        if len(capped_sizes) == 0:
+            logger.warning(
+                "No valid cudagraph capture sizes remain after capping "
+                "to Mamba cache blocks (%d). The smallest capture size "
+                "was %d. Disabling cudagraph capture. Consider reducing "
+                "max_num_seqs or increasing available GPU memory.",
+                num_mamba_cache_blocks,
+                self.cudagraph_capture_sizes[0],
+            )
+            self.cudagraph_capture_sizes = []
+            self.max_cudagraph_capture_size = 0
+            return
+
+        logger.warning(
+            "Capping cudagraph capture sizes from max %d to %d to fit "
+            "Mamba cache blocks (%d blocks available). This limits the "
+            "maximum batch size that can use CUDA graphs. To increase "
+            "this limit, reduce max_num_seqs or increase available GPU "
+            "memory.",
+            self.max_cudagraph_capture_size,
+            capped_sizes[-1],
+            num_mamba_cache_blocks,
+        )
+
+        self.max_cudagraph_capture_size = capped_sizes[-1]
+        self.cudagraph_capture_sizes = capped_sizes
+
     def get_compile_ranges(self) -> list[Range]:
         """Get the compile ranges for the compilation config."""
         if self.compile_ranges_split_points is None:

vllm/v1/worker/gpu_model_runner.py

@@ -5700,6 +5700,22 @@ def _check_and_update_cudagraph_mode(
                 self.uniform_decode_query_len, self.parallel_config.tensor_parallel_size
             )
 
+        # If the model has Mamba layers and cudagraph mode includes FULL
+        # decode, cap cudagraph capture sizes to the number of available
+        # Mamba cache blocks. Each decode request needs one conv_state
+        # cache line, so capture batch sizes cannot exceed num_blocks.
+        # Only FULL decode graphs are affected because PIECEWISE captures
+        # run GDN/Mamba ops eagerly (prefill path, no causal_conv1d_update).
+        # See: https://github.com/vllm-project/vllm/issues/34094
+        if cudagraph_mode.has_full_cudagraphs():
+            has_mamba = any(
+                isinstance(g.kv_cache_spec, MambaSpec) for g in kv_cache_groups
+            )
+            if has_mamba and self.kv_cache_config is not None:
+                self.compilation_config.adjust_cudagraph_sizes_for_mamba_cache(
+                    self.kv_cache_config.num_blocks
+                )
+
         # Trigger cudagraph dispatching keys initialization after
         # resolved cudagraph mode.
         self.compilation_config.cudagraph_mode = cudagraph_mode