[Core][KVConnector] Support HMA+NixlConnector (#35758)

Signed-off-by: NickLucche <nlucches@redhat.com>

tests/v1/kv_connector/nixl_integration/config_sweep_accuracy_test.sh

@@ -12,6 +12,7 @@ tp_configs=(
   "GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=deepseek-ai/deepseek-vl2-tiny" # MLA case
   "GPU_MEMORY_UTILIZATION=0.8 PREFILLER_TP_SIZE=1 DECODER_TP_SIZE=2 MODEL_NAMES=deepseek-ai/deepseek-vl2-tiny"
   "GPU_MEMORY_UTILIZATION=0.8 PREFILLER_TP_SIZE=2 DECODER_TP_SIZE=1 MODEL_NAMES=deepseek-ai/deepseek-vl2-tiny"
+  "GPU_MEMORY_UTILIZATION=0.8 MODEL_NAMES=google/gemma-3-4b-it VLLM_SERVE_EXTRA_ARGS=--max-model-len,8192" # SW model
 )
 dp_ep_configs=(
 "DP_EP=1 GPU_MEMORY_UTILIZATION=0.8 PREFILLER_TP_SIZE=1 DECODER_TP_SIZE=2 MODEL_NAMES=deepseek-ai/deepseek-vl2-tiny" # MLA+P-TP1, D-DPEP=2 (TP=1)
@@ -26,6 +27,14 @@ else
   configs=("${tp_configs[@]}")
 fi
 
+if [[ -n "${ENABLE_HMA_FLAG:-}" ]]; then
+  # Append ENABLE_HMA_FLAG=1 to each config in the selected array
+  echo "ENABLE_HMA_FLAG is set, appending ENABLE_HMA_FLAG=1 to each config"
+  for i in "${!configs[@]}"; do
+    configs[$i]="ENABLE_HMA_FLAG=1 ${configs[$i]}"
+  done
+fi
+
 run_tests() {
   local label=$1
   local extra_args=$2

tests/v1/kv_connector/nixl_integration/run_accuracy_test.sh

@@ -5,6 +5,12 @@ set -xe
 KV_BUFFER_DEVICE="cuda"  # Default to cuda
 ATTENTION_BACKEND=""  # Default to empty (use vllm default)
 CROSS_LAYERS_BLOCKS="False"
+ENABLE_HMA_VAR=""  # Default to empty (HMA disabled by default for kv connector)
+# Check for ENABLE_HMA_FLAG environment variable
+if [[ -n "${ENABLE_HMA_FLAG:-}" ]]; then
+  ENABLE_HMA_VAR="--no-disable-hybrid-kv-cache-manager"
+fi
+
 while [[ $# -gt 0 ]]; do
   case $1 in
     --kv_buffer_device)
@@ -31,6 +37,12 @@ echo "Running accuracy tests with kv_buffer_device=$KV_BUFFER_DEVICE"
 if [[ -n "$ATTENTION_BACKEND" ]]; then
   echo "Using attention backend: $ATTENTION_BACKEND"
 fi
+if [[ -n "$ENABLE_HMA_VAR" ]]; then
+  echo "HMA (Hybrid KV Cache Manager) enabled"
+fi
+if [[ -n "$VLLM_SERVE_EXTRA_ARGS" ]]; then
+  echo "vLLM serve extra args: $VLLM_SERVE_EXTRA_ARGS"
+fi
 
 DECODER_KV_LAYOUT=${DECODER_KV_LAYOUT:-"HND"} # Default to HND, optional NHD
 if [[ "$DECODER_KV_LAYOUT" == "NHD" ]]; then
@@ -70,6 +82,8 @@ DECODER_TP_SIZE=${DECODER_TP_SIZE:-1}
 GPU_MEMORY_UTILIZATION=${GPU_MEMORY_UTILIZATION:-0.2}
 PREFILL_BLOCK_SIZE=${PREFILL_BLOCK_SIZE:-128}
 DECODE_BLOCK_SIZE=${DECODE_BLOCK_SIZE:-128}
+# Comma-separated extra args for vllm serve (e.g. --max-model-len,2048)
+VLLM_SERVE_EXTRA_ARGS=${VLLM_SERVE_EXTRA_ARGS:-}
 
 # Find the git repository root directory
 GIT_ROOT=$(git rev-parse --show-toplevel)
@@ -151,14 +165,24 @@ run_tests_for_model() {
     --gpu-memory-utilization $GPU_MEMORY_UTILIZATION \
     --tensor-parallel-size $PREFILLER_TP_SIZE \
     --kv-transfer-config '$KV_CONFIG'"
+    if [[ -n "$VLLM_SERVE_EXTRA_ARGS" ]]; then
+      IFS=',' read -r -a extra_args <<< "$VLLM_SERVE_EXTRA_ARGS"
+      for arg in "${extra_args[@]}"; do
+        BASE_CMD="${BASE_CMD} $arg"
+      done
+    fi
 
     # Add attention backend config if specified
     if [[ -n "$ATTENTION_BACKEND" ]]; then
       BASE_CMD="${BASE_CMD} --attention-backend=$ATTENTION_BACKEND"
     fi
 
+    # Add HMA flag if specified
+    if [[ -n "$ENABLE_HMA_VAR" ]]; then
+      BASE_CMD="${BASE_CMD} $ENABLE_HMA_VAR"
+    fi
+    
     FULL_CMD="$BASE_CMD"
-
     eval "$FULL_CMD &"
 
     # Store host and port for proxy configuration
@@ -193,12 +217,23 @@ run_tests_for_model() {
     --block-size ${DECODE_BLOCK_SIZE} \
     --gpu-memory-utilization $GPU_MEMORY_UTILIZATION \
     --kv-transfer-config '$KV_CONFIG'"
+    if [[ -n "$VLLM_SERVE_EXTRA_ARGS" ]]; then
+      IFS=',' read -r -a extra_args <<< "$VLLM_SERVE_EXTRA_ARGS"
+      for arg in "${extra_args[@]}"; do
+        BASE_CMD="${BASE_CMD} $arg"
+      done
+    fi
 
     # Add attention backend config if specified
     if [[ -n "$ATTENTION_BACKEND" ]]; then
       BASE_CMD="${BASE_CMD} --attention-backend=$ATTENTION_BACKEND"
     fi
 
+    # Add HMA flag if specified
+    if [[ -n "$ENABLE_HMA_VAR" ]]; then
+      BASE_CMD="${BASE_CMD} $ENABLE_HMA_VAR"
+    fi
+
   # DP-EP attention mode
   if [[ -z "$DP_EP" ]]; then
     BASE_CMD="${BASE_CMD} --tensor-parallel-size $DECODER_TP_SIZE"

tests/v1/kv_connector/nixl_integration/test_accuracy.py

@@ -17,6 +17,7 @@ EXPECTED_VALUES = {
     "deepseek-ai/deepseek-vl2-small": 0.59,
     "deepseek-ai/deepseek-vl2-tiny": 0.19,
     "deepseek-ai/DeepSeek-V2-Lite-Chat": 0.65,
+    "google/gemma-3-4b-it": 0.74,
 }
 
 SIMPLE_PROMPT = (

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -59,7 +59,12 @@ from vllm.v1.request import RequestStatus
 from vllm.v1.worker.kv_connector_model_runner_mixin import KVConnectorModelRunnerMixin
 from vllm.v1.worker.utils import AttentionGroup
 
-from .utils import create_request, create_scheduler, create_vllm_config
+from .utils import (
+    create_request,
+    create_scheduler,
+    create_vllm_config,
+    make_kv_cache_config,
+)
 
 
 @pytest.fixture(scope="module", autouse=True)
@@ -263,7 +268,7 @@ def test_basic_interface():
     req_meta = kv_connector_metadata.reqs_to_recv[request_id]
 
     for block_id, block in zip(
-        req_meta.local_block_ids,
+        req_meta.local_block_ids[0],
         scheduler.kv_cache_manager.coordinator.single_type_managers[0].req_to_blocks[
             request_id
         ],
@@ -327,7 +332,9 @@ def test_kv_transfer_handshake(dist_init):
 
         # Prefill connector will register KV cache to populate proper handshake
         # metadata.
-        prefill_connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        prefill_connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         kv_cache_shape = FlashAttentionBackend.get_kv_cache_shape(
             num_blocks=2, block_size=16, num_kv_heads=4, head_size=64
         )
@@ -367,13 +374,17 @@ def test_kv_transfer_handshake(dist_init):
             do_remote_decode=True,
         )
         request.status = RequestStatus.FINISHED_LENGTH_CAPPED
-        delay, kv_connector_metadata = scheduler.get_kv_connector().request_finished(
-            request, [0, 1, 2]
+        delay, kv_connector_metadata = (
+            scheduler.get_kv_connector().request_finished_all_groups(
+                request, ([0, 1, 2],)
+            )
         )
         assert delay
 
         # Decode connector will be able to create handshake with the prefill connector.
-        decode_connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        decode_connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         decode_connector.register_kv_caches(kv_caches)
 
         # Here we are testing the retrieval of NIXLAgentMetadata.
@@ -404,9 +415,16 @@ class FakeNixlConnectorWorker(NixlConnectorWorker):
     REMOTE_ENGINE_ID = "remote_engine"
 
     def __init__(
-        self, *args, hand_shake_latency: float = 1.8, kv_cache_layout="HND", **kwargs
+        self,
+        *args,
+        hand_shake_latency: float = 1.8,
+        kv_cache_layout="HND",
+        kv_cache_config=None,
+        **kwargs,
     ):
-        super().__init__(*args, **kwargs)
+        if kv_cache_config is None:
+            kv_cache_config = make_kv_cache_config(block_size=16)
+        super().__init__(*args, kv_cache_config=kv_cache_config, **kwargs)
         self._hand_shake_latency = hand_shake_latency
         self.kv_cache_layout = kv_cache_layout
         # Mock register_kv_caches attribute needed for tests that do not call it.
@@ -507,7 +525,9 @@ class TestNixlHandshake:
         request_id = "req_id"
 
         # Test worker role in decode server.
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         connector.connector_worker = FakeNixlConnectorWorker(
             vllm_config, connector.engine_id, hand_shake_latency=0
         )
@@ -528,13 +548,15 @@ class TestNixlHandshake:
                 num_xfers -= 1
                 metadata.add_new_req_to_recv(
                     request_id=request_id,
-                    local_block_ids=[num_xfers + 1, num_xfers + 2, num_xfers + 3],
+                    local_block_ids=([num_xfers + 1, num_xfers + 2, num_xfers + 3],),
                     kv_transfer_params={
-                        "remote_block_ids": [
-                            num_xfers + 4,
-                            num_xfers + 5,
-                            num_xfers + 6,
-                        ],
+                        "remote_block_ids": (
+                            [
+                                num_xfers + 4,
+                                num_xfers + 5,
+                                num_xfers + 6,
+                            ],
+                        ),
                         "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
                         "remote_request_id": f"prefill-{request_id}",
                         "remote_host": "localhost",
@@ -594,16 +616,18 @@ class TestNixlHandshake:
         vllm_config.parallel_config.tensor_parallel_size = decode_tp_size
 
         # Test worker role in decode server.
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         connector.connector_worker = FakeNixlConnectorWorker(
             vllm_config, connector.engine_id
         )
         metadata = NixlConnectorMetadata()
         metadata.add_new_req_to_recv(
             request_id="id",
-            local_block_ids=[1, 2, 3],
+            local_block_ids=([1, 2, 3],),
             kv_transfer_params={
-                "remote_block_ids": [4, 5, 6],
+                "remote_block_ids": ([4, 5, 6],),
                 "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
                 "remote_request_id": "prefill-id",
                 "remote_host": "localhost",
@@ -652,7 +676,9 @@ class TestNixlHandshake:
         local_tp_size = 1
         vllm_config.parallel_config.tensor_parallel_size = local_tp_size
 
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         connector.connector_worker = FakeNixlConnectorWorker(
             vllm_config, connector.engine_id, hand_shake_latency=0
         )
@@ -717,8 +743,12 @@ class TestNixlHandshake:
         p_tp_size = 2
 
         # Build two separate connectors/workers to emulate P TP=2 ranks.
-        conn_p0 = NixlConnector(vllm_config, KVConnectorRole.WORKER)
-        conn_p1 = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        conn_p0 = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
+        conn_p1 = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         conn_p0.connector_worker = FakeNixlConnectorWorker(
             vllm_config, conn_p0.engine_id, hand_shake_latency=0
         )
@@ -815,7 +845,9 @@ class TestNixlHandshake:
         vllm_config = create_vllm_config()
 
         # Test worker role in decode server.
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         connector.connector_worker = FakeNixlConnectorWorker(
             vllm_config, connector.engine_id
         )
@@ -827,9 +859,9 @@ class TestNixlHandshake:
         for i in range(total_reqs):
             metadata.add_new_req_to_recv(
                 request_id=f"id_{i}",
-                local_block_ids=[1, 2, 3],
+                local_block_ids=([1, 2, 3],),
                 kv_transfer_params={
-                    "remote_block_ids": [4, 5, 6],
+                    "remote_block_ids": ([4, 5, 6],),
                     "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
                     "remote_request_id": f"prefill-id-{i}",
                     "remote_host": "localhost",
@@ -884,7 +916,9 @@ class TestNixlHandshake:
             return_value=2,
         ):
             # Initialize connector and worker (with fake NIXL wrapper)
-            connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+            connector = NixlConnector(
+                vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+            )
             connector.connector_worker = FakeNixlConnectorWorker(
                 vllm_config, connector.engine_id, hand_shake_latency=0
             )
@@ -934,7 +968,9 @@ class TestNixlHandshake:
             return_value=2,
         ):
             # Initialize connector and worker (with fake NIXL wrapper)
-            connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+            connector = NixlConnector(
+                vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+            )
             connector.connector_worker = FakeNixlConnectorWorker(
                 vllm_config,
                 connector.engine_id,
@@ -979,7 +1015,9 @@ def test_kv_connector_stats(default_vllm_config, dist_init):
     vllm_config = create_vllm_config()
 
     # Test worker role in decode server.
-    connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+    connector = NixlConnector(
+        vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     connector.connector_worker = FakeNixlConnectorWorker(
         vllm_config, connector.engine_id, hand_shake_latency=0
     )
@@ -993,9 +1031,9 @@ def test_kv_connector_stats(default_vllm_config, dist_init):
     metadata = NixlConnectorMetadata()
     metadata.add_new_req_to_recv(
         request_id=request_id,
-        local_block_ids=[1, 2, 3],
+        local_block_ids=([1, 2, 3],),
         kv_transfer_params={
-            "remote_block_ids": [4, 5, 6],
+            "remote_block_ids": ([4, 5, 6],),
             "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
             "remote_request_id": f"prefill-{request_id}",
             "remote_host": "localhost",
@@ -1448,7 +1486,9 @@ def test_register_kv_caches(
         mock_get_attn_backend.return_value = backend_cls
 
         # Create connector
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
         connector.connector_worker = FakeNixlConnectorWorker(
             vllm_config, connector.engine_id, hand_shake_latency=0
         )
@@ -1676,7 +1716,9 @@ def test_kv_buffer_to_nixl_memory_types(
         ),
     ):  # noqa: E501
         # Create connector and replace its worker with a fake one for isolation
-        connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+        connector = NixlConnector(
+            vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+        )
 
         # Verify get_reg_descs was called with the correct memory_type
         assert connector.connector_worker.kv_buffer_device == kv_buffer_device
@@ -1692,9 +1734,15 @@ def test_shutdown_cleans_up_resources(default_vllm_config, dist_init):
     vllm_config = create_vllm_config()
 
     scheduler = NixlConnectorScheduler(
-        vllm_config, vllm_config.kv_transfer_config.engine_id
+        vllm_config,
+        vllm_config.kv_transfer_config.engine_id,
+        make_kv_cache_config(block_size=16),
+    )
+    worker = NixlConnectorWorker(
+        vllm_config,
+        vllm_config.kv_transfer_config.engine_id,
+        make_kv_cache_config(block_size=16),
     )
-    worker = NixlConnectorWorker(vllm_config, vllm_config.kv_transfer_config.engine_id)
     nixl_wrapper = worker.nixl_wrapper
 
     with (
@@ -1756,7 +1804,9 @@ def test_aborted_request_removed_from_worker_in_batch(default_vllm_config, dist_
 
     scheduler = create_scheduler(vllm_config)
     # KVConnector Worker in P
-    connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+    connector = NixlConnector(
+        vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     connector.connector_worker = FakeNixlConnectorWorker(
         vllm_config, connector.engine_id, hand_shake_latency=0
     )
@@ -1875,12 +1925,14 @@ class FailingNixlWrapper(FakeNixlWrapper):
         ("transfer_exception", {"fail_transfer_exception": True}, True),
     ],
 )
+@pytest.mark.parametrize("enable_hma", [False, True])
 def test_transfer_failure_logging(
     default_vllm_config,
     dist_init,
     failure_type,
     wrapper_config,
     needs_get_finished,
+    enable_hma,
 ):
     """Test that transfer failures are logged with structured context.
 
@@ -1897,9 +1949,16 @@ def test_transfer_failure_logging(
 
     vllm_config = create_vllm_config()
 
-    connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+    connector = NixlConnector(
+        vllm_config,
+        KVConnectorRole.WORKER,
+        make_kv_cache_config(block_size=16, hma_enabled=enable_hma),
+    )
     connector.connector_worker = FakeNixlConnectorWorker(
-        vllm_config, connector.engine_id, hand_shake_latency=0.0
+        vllm_config,
+        connector.engine_id,
+        hand_shake_latency=0.0,
+        kv_cache_config=connector._kv_cache_config,
     )
 
     # Configure FailingNixlWrapper to fail in the specified way
@@ -1910,8 +1969,17 @@ def test_transfer_failure_logging(
 
     # For notification_failed, we need empty local blocks
     # (full cache hit path to trigger send_notif)
-    local_blocks = [] if failure_type == "notification_failed" else [10, 11, 12]
-    remote_blocks = [20, 21, 22]
+    local_blocks: tuple[()] | tuple[list[int], ...]
+    if enable_hma:
+        # HMA enabled: multiple groups (FA + SW)
+        local_blocks = (
+            () if failure_type == "notification_failed" else ([10, 11, 12], [13, 14])
+        )
+        remote_blocks = [[20, 21, 22], [23, 24]]
+    else:
+        # HMA disabled: single group
+        local_blocks = () if failure_type == "notification_failed" else ([10, 11, 12],)
+        remote_blocks = [[20, 21, 22]]
 
     metadata = NixlConnectorMetadata()
     metadata.add_new_req_to_recv(
@@ -2007,7 +2075,9 @@ def test_handshake_failure_returns_finished(default_vllm_config, dist_init):
     """Test that handshake failures mark blocks invalid and return via get_finished."""
     vllm_config = create_vllm_config()
 
-    connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+    connector = NixlConnector(
+        vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     connector.connector_worker = FakeNixlConnectorWorker(
         vllm_config, connector.engine_id, hand_shake_latency=0.1
     )
@@ -2017,9 +2087,9 @@ def test_handshake_failure_returns_finished(default_vllm_config, dist_init):
     metadata = NixlConnectorMetadata()
     metadata.add_new_req_to_recv(
         request_id=request_id,
-        local_block_ids=[1, 2, 3],
+        local_block_ids=([1, 2, 3],),
         kv_transfer_params={
-            "remote_block_ids": [4, 5, 6],
+            "remote_block_ids": ([4, 5, 6],),
             "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
             "remote_request_id": f"prefill-{request_id}",
             "remote_host": "localhost",
@@ -2058,7 +2128,9 @@ def test_transfer_setup_failure_returns_finished(default_vllm_config, dist_init)
     and return via get_finished."""
     vllm_config = create_vllm_config()
 
-    connector = NixlConnector(vllm_config, KVConnectorRole.WORKER)
+    connector = NixlConnector(
+        vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     connector.connector_worker = FakeNixlConnectorWorker(
         vllm_config, connector.engine_id, hand_shake_latency=0
     )
@@ -2068,9 +2140,9 @@ def test_transfer_setup_failure_returns_finished(default_vllm_config, dist_init)
     metadata = NixlConnectorMetadata()
     metadata.add_new_req_to_recv(
         request_id=request_id,
-        local_block_ids=[7, 8, 9],
+        local_block_ids=([7, 8, 9],),
         kv_transfer_params={
-            "remote_block_ids": [10, 11, 12],
+            "remote_block_ids": ([10, 11, 12],),
             "remote_engine_id": FakeNixlConnectorWorker.REMOTE_ENGINE_ID,
             "remote_request_id": f"prefill-{request_id}",
             "remote_host": "localhost",
@@ -2154,7 +2226,9 @@ def test_compatibility_hash_validation(
             "enforce_handshake_compat": enforce_handshake_compat
         },
     )
-    decode_connector = NixlConnector(local_vllm_config, KVConnectorRole.WORKER)
+    decode_connector = NixlConnector(
+        local_vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     decode_worker = decode_connector.connector_worker
     kv_cache_shape = decode_worker.attn_backend.get_kv_cache_shape(
         num_blocks=2, block_size=16, num_kv_heads=4, head_size=64
@@ -2267,7 +2341,9 @@ def test_handshake_decode_errors(default_vllm_config, dist_init, error_scenario)
         model="facebook/opt-125m",
         block_size=16,
     )
-    decode_connector = NixlConnector(local_vllm_config, KVConnectorRole.WORKER)
+    decode_connector = NixlConnector(
+        local_vllm_config, KVConnectorRole.WORKER, make_kv_cache_config(block_size=16)
+    )
     decode_worker = decode_connector.connector_worker
 
     backend = get_current_attn_backend(local_vllm_config)

tests/v1/kv_connector/unit/test_nixl_connector_hma.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Unit tests for NixlConnectorScheduler sw_sizes calculation with HMA."""
+
+from unittest.mock import patch
+
+import pytest
+
+from vllm import LLM, SamplingParams
+from vllm.config import KVTransferConfig
+from vllm.v1.core.single_type_kv_cache_manager import (
+    FullAttentionManager,
+    SlidingWindowManager,
+)
+
+from .utils import (
+    create_vllm_config,
+    make_kv_cache_config,
+)
+
+
+@pytest.mark.cpu_test
+@pytest.mark.parametrize(
+    "hma_enabled,expected_sw_sizes",
+    [
+        # HMA enabled: FullAttentionSpec (0) + SlidingWindowSpec (2048/16=128)
+        (True, [0, 128 + 1]),
+        # HMA disabled: only FullAttentionSpec (0)
+        (False, [0]),
+    ],
+)
+@patch("vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector.current_platform")
+def test_sw_sizes(mock_platform, hma_enabled, expected_sw_sizes):
+    """Test sw_sizes is correctly computed based on HMA enabled/disabled."""
+    from vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector import (
+        NixlConnectorScheduler,
+    )
+
+    mock_platform.device_type = "cpu"
+
+    block_size = 16
+    vllm_config = create_vllm_config(block_size=block_size)
+    # SW 2048 tokens=>128 blocks
+    kv_cache_config = make_kv_cache_config(
+        block_size=block_size, hma_enabled=hma_enabled, sw_size=2048
+    )
+
+    scheduler = NixlConnectorScheduler(
+        vllm_config=vllm_config,
+        engine_id="test-engine",
+        kv_cache_config=kv_cache_config,
+    )
+    # in number of blocks
+    assert scheduler.blocks_per_sw == expected_sw_sizes, (
+        f"Expected sw_sizes={expected_sw_sizes}, got {scheduler.blocks_per_sw}"
+    )
+
+
+@pytest.mark.cpu_test
+def test_logical_to_kernel_block_ids_with_hma():
+    """Test _logical_to_kernel_block_ids expands blocks when HMA is enabled.
+
+    When HMA is enabled, the logical block size may differ from the kernel
+    block size. Each logical block maps to multiple kernel blocks.
+    """
+    from vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector import (
+        NixlConnectorWorker,
+    )
+
+    # Create a mock worker with just the required attributes
+    # (use __new__ to skip __init__)
+    worker = object.__new__(NixlConnectorWorker)
+
+    # Simulate HMA scenario: logical block size = 32, kernel block size = 16
+    # So each logical block maps to 2 kernel blocks eg [0]->[0,1]
+    worker._physical_blocks_per_logical_kv_block = 2
+
+    # Test conversion: FA + SW group
+    logical_block_ids = [[0, 1, 2], [3, 4]]
+    kernel_block_ids = worker._logical_to_kernel_block_ids(logical_block_ids)
+
+    expected_kernel_block_ids = [[0, 1, 2, 3, 4, 5], [6, 7, 8, 9]]
+    assert kernel_block_ids == expected_kernel_block_ids, (
+        f"Expected {expected_kernel_block_ids}, got {kernel_block_ids}"
+    )
+
+
+@pytest.mark.parametrize("model_name, sw_size", [("google/gemma-3-1b-it", 512)])
+def test_fewer_blocks_with_hma(monkeypatch, model_name, sw_size):
+    """Test that a prefill instance returns fewer "remote blocks" for the SWA groups
+    when sequence exceeds the sliding window.
+    """
+    kv_transfer_config = KVTransferConfig(
+        kv_connector="NixlConnector",
+        kv_role="kv_both",
+    )
+    block_size = 16
+    llm_kwargs = {
+        "model": model_name,
+        "enforce_eager": True,
+        "gpu_memory_utilization": 0.5,
+        "kv_transfer_config": kv_transfer_config,
+        "max_model_len": 2048,
+        # NOTE: Make sure HMA is enabled
+        "disable_hybrid_kv_cache_manager": False,
+        "max_num_batched_tokens": 1024,
+        "enable_prefix_caching": False,
+        "block_size": block_size,
+    }
+
+    monkeypatch.setenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0")
+
+    def run_hma_test(llm: LLM):
+        remote_prefill_opts = {
+            "do_remote_decode": True,
+            "do_remote_prefill": False,
+            "remote_engine_id": None,
+            "remote_block_ids": None,
+            "remote_host": None,
+            "remote_port": None,
+        }
+        # Simulate sidecar request
+        sampling_params = SamplingParams(
+            temperature=0.0,
+            max_tokens=1,
+            extra_args={"kv_transfer_params": remote_prefill_opts},
+        )
+        scheduler = llm.llm_engine.engine_core.engine_core.scheduler
+        kv_managers = scheduler.kv_cache_manager.coordinator.single_type_managers
+        # HMA enabled with FA + SWA groups
+        assert len(kv_managers) > 2
+        for kv_manager in kv_managers:
+            assert isinstance(kv_manager, (SlidingWindowManager, FullAttentionManager))
+        req_to_blocks = kv_managers[0].req_to_blocks
+        assert len(req_to_blocks) == 0
+
+        # Process some request with length exceeding the sliding window
+        outputs = llm.generate(["hi" * 1401], sampling_params)
+        kv_params = outputs[0].kv_transfer_params
+
+        # +1 to account for overlapping window across blocks.
+        expected_num_remote_blocks = sw_size // block_size + 1
+        remote_block_ids = kv_params["remote_block_ids"]
+        assert (
+            len(remote_block_ids[0])
+            == expected_num_remote_blocks
+            < len(remote_block_ids[-1])
+        )
+        for group_block_ids in remote_block_ids[:-1]:
+            assert len(group_block_ids) == expected_num_remote_blocks
+
+    def run_test_and_cleanup():
+        llm = LLM(**llm_kwargs)
+        try:
+            run_hma_test(llm)
+        finally:
+            llm.llm_engine.engine_core.shutdown()
+
+    run_test_and_cleanup()
+
+
+@pytest.mark.cpu_test
+def test_nixl_metadata_hma_block_ids_structure():
+    """
+    Test that NixlConnectorMetadata correctly stores block IDs for multiple
+    KV cache groups when HMA is enabled.
+    """
+    from vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector import (
+        NixlConnectorMetadata,
+    )
+
+    metadata = NixlConnectorMetadata()
+
+    # Add request with block IDs for 2 groups (FA + SW)
+    fa_blocks = [0, 1, 2, 3, 4, 5, 6, 7]  # 8 blocks for FA
+    sw_blocks = [8, 9, 10, 11]  # 4 blocks for SW (clipped)
+
+    metadata.add_new_req_to_recv(
+        request_id="test-req-hma",
+        local_block_ids=(fa_blocks, sw_blocks),
+        kv_transfer_params={
+            "remote_block_ids": ([10, 11, 12, 13, 14, 15, 16, 17], [18, 19, 20, 21]),
+            "remote_engine_id": "remote-engine",
+            "remote_request_id": "prefill-test-req-hma",
+            "remote_host": "localhost",
+            "remote_port": 1234,
+            "tp_size": 1,
+        },
+    )
+
+    assert "test-req-hma" in metadata.reqs_to_recv
+    req_meta = metadata.reqs_to_recv["test-req-hma"]
+
+    # Verify local block IDs structure
+    assert len(req_meta.local_block_ids) == 2
+    assert list(req_meta.local_block_ids[0]) == fa_blocks
+    assert list(req_meta.local_block_ids[1]) == sw_blocks
+
+    # Verify remote block IDs structure
+    assert req_meta.remote is not None
+    assert len(req_meta.remote.block_ids) == 2
+    assert list(req_meta.remote.block_ids[0]) == [10, 11, 12, 13, 14, 15, 16, 17]
+    assert list(req_meta.remote.block_ids[1]) == [18, 19, 20, 21]

tests/v1/kv_connector/unit/test_remote_decode_lifecycle.py

@@ -208,7 +208,9 @@ def test_prefix_cache_lifecycle():
 
     # Ensure we send all block ids, including the partial blocks,
     # even if there is a cache hit.
-    assert len(kv_transfer_params["remote_block_ids"]) == (NUM_EXTERNAL_FULL_BLOCKS + 1)
+    # remote_block_ids is BlockIds (tuple of lists); sum block counts across groups.
+    num_remote_blocks = sum(len(g) for g in kv_transfer_params["remote_block_ids"])
+    assert num_remote_blocks == (NUM_EXTERNAL_FULL_BLOCKS + 1)
 
     # STEP (2): Ensure it is freed.
     scheduler_output = scheduler.schedule()

tests/v1/kv_connector/unit/utils.py

@@ -36,6 +36,7 @@ from vllm.v1.kv_cache_interface import (
     FullAttentionSpec,
     KVCacheConfig,
     KVCacheGroupSpec,
+    SlidingWindowSpec,
 )
 from vllm.v1.outputs import KVConnectorOutput, ModelRunnerOutput
 from vllm.v1.request import Request
@@ -142,24 +143,26 @@ def create_vllm_config(
 def create_scheduler(
     vllm_config: VllmConfig,
     num_blocks: int = 10000,
+    kv_cache_config: KVCacheConfig | None = None,
 ) -> Scheduler:
     """Initialize Scheduler For Testing."""
     block_size = vllm_config.cache_config.block_size
-    kv_cache_config = KVCacheConfig(
-        num_blocks=num_blocks,  # A large number of blocks to hold all requests
-        kv_cache_tensors=[],
-        kv_cache_groups=[
-            KVCacheGroupSpec(
-                ["layer"],
-                FullAttentionSpec(
-                    block_size=block_size,
-                    num_kv_heads=1,
-                    head_size=1,
-                    dtype=torch.float32,
-                ),
-            )
-        ],
-    )
+    if kv_cache_config is None:
+        kv_cache_config = KVCacheConfig(
+            num_blocks=num_blocks,  # A large number of blocks to hold all requests
+            kv_cache_tensors=[],
+            kv_cache_groups=[
+                KVCacheGroupSpec(
+                    ["layer"],
+                    FullAttentionSpec(
+                        block_size=block_size,
+                        num_kv_heads=1,
+                        head_size=1,
+                        dtype=torch.float32,
+                    ),
+                )
+            ],
+        )
     vllm_config.cache_config.num_gpu_blocks = num_blocks
     return Scheduler(
         vllm_config=vllm_config,
@@ -412,3 +415,38 @@ KVConnectorFactory.register_connector(
 KVConnectorFactory.register_connector(
     "MockKVConnector", __name__, MockKVConnector.__name__
 )
+
+
+def make_kv_cache_config(
+    block_size: int,
+    hma_enabled: bool = False,
+    sw_size: int = 128,
+    num_blocks: int = 100,
+) -> KVCacheConfig:
+    kv_cache_groups = [
+        KVCacheGroupSpec(
+            ["layer0", "layer2"],
+            FullAttentionSpec(
+                block_size=block_size,
+                num_kv_heads=4,
+                head_size=16,
+                dtype=torch.float16,
+            ),
+        )
+    ]
+    if hma_enabled:
+        kv_cache_groups.append(
+            KVCacheGroupSpec(
+                ["layer1", "layer3"],
+                SlidingWindowSpec(
+                    block_size=block_size,
+                    num_kv_heads=4,
+                    head_size=16,
+                    dtype=torch.float16,
+                    sliding_window=sw_size,
+                ),
+            )
+        )
+    return KVCacheConfig(
+        num_blocks=num_blocks, kv_cache_tensors=[], kv_cache_groups=kv_cache_groups
+    )

vllm/distributed/kv_transfer/kv_connector/utils.py

@@ -24,6 +24,9 @@ if TYPE_CHECKING:
 logger = init_logger(__name__)
 
 EngineId = str
+# block ids as returned by the hybrid KV cache manager. list[list[int]] are allow
+# mutability and are for connector internal use only.
+BlockIds = tuple[list[int], ...] | list[list[int]]
 
 
 def get_kv_connector_cache_layout():

vllm/v1/core/kv_cache_manager.py

@@ -84,6 +84,18 @@ class KVCacheBlocks:
         assert len(self.blocks) == 1, "Only one group is supported"
         return [block.block_id for block in self.blocks[0] if block.block_hash is None]
 
+    def get_unhashed_block_ids_all_groups(self) -> list[list[int]]:
+        """Get block_ids of unhashed blocks from KVCacheBlocks instance."""
+        # Skip padding blocks.
+        return [
+            [
+                block.block_id
+                for block in group
+                if block.block_hash is None and not block.is_null
+            ]
+            for group in self.blocks
+        ]
+
     def new_empty(self) -> "KVCacheBlocks":
         """
         Creates a new KVCacheBlocks instance with no blocks.