[Bugfix][Qwen4Exp] Release the profiling KV cache held by QSA key views (#58961)

Signed-off-by: Zihua Wu <13583761+lucifer1004@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

tests/models/qwen4_exp/test_qsa_reference.py

@@ -17,6 +17,7 @@ from vllm.models.qwen4_exp.nvidia.ops import qsa as qsa_ops
 from vllm.models.qwen4_exp.nvidia.ops import qsa_indexer as qsa_indexer_ops
 from vllm.platforms import current_platform
 from vllm.triton_utils import HAS_TRITON
+from vllm.v1.worker.utils import clear_layer_kv_caches
 
 requires_qsa_kernels = pytest.mark.skipif(
     not current_platform.is_cuda() or not HAS_TRITON,
@@ -365,7 +366,9 @@ def test_qsa_circular_buffer_survives_one_speculative_step(chunk_start: int) ->
     assert set(slots.tolist()).isdisjoint((committed % capacity).tolist())
 
 
-def _qsa_key_cache(block_size: int, compress_ratio: int) -> qsa_cache.QSAKeyStateCache:
+def _qsa_key_cache(
+    block_size: int, compress_ratio: int, **kwargs
+) -> qsa_cache.QSAKeyStateCache:
     return qsa_cache.QSAKeyStateCache(
         head_size=64,
         dtype=torch.bfloat16,
@@ -375,6 +378,7 @@ def _qsa_key_cache(block_size: int, compress_ratio: int) -> qsa_cache.QSAKeyStat
             compilation_config=SimpleNamespace(static_forward_context={})
         ),
         compress_ratio=compress_ratio,
+        **kwargs,
     )
 
 
@@ -402,6 +406,23 @@ def test_qsa_state_caches_adapt_the_unified_logical_layout() -> None:
     assert compressed_cache.kv_cache.data_ptr() == compressed_view.data_ptr()
 
 
+def test_clearing_qsa_key_cache_releases_its_storage() -> None:
+    """Profiling teardown clears `kv_cache`; no derived view may keep it alive."""
+    raw_cache = _qsa_key_cache(
+        block_size=32, compress_ratio=4, cache_rope_positions=True
+    )
+    kv = torch.zeros(2, 1, 8, raw_cache.head_size, dtype=torch.bfloat16)
+    references_before_bind = torch._C._storage_Use_Count(kv.untyped_storage()._cdata)
+    raw_cache.bind_kv_cache(kv)
+    assert raw_cache.key_cache.shape[-1] == 64
+    assert raw_cache.rope_position_cache.dtype == torch.int64
+
+    clear_layer_kv_caches([raw_cache])
+
+    references = torch._C._storage_Use_Count(kv.untyped_storage()._cdata)
+    assert references == references_before_bind
+
+
 @pytest.mark.parametrize(
     ("compress_ratio", "num_spec", "expected"),
     [(4, 0, 4), (4, 1, 8), (4, 3, 8), (4, 4, 8), (4, 5, 12), (2, 3, 6)],

vllm/models/qwen4_exp/common/qsa_cache.py

@@ -825,15 +825,18 @@ class QSAKeyStateCache(_QSAStateCache):
             )
         super().__init__(head_size=storage_head_size, **kwargs)
 
-    def bind_kv_cache(self, kv_cache: torch.Tensor) -> None:
-        super().bind_kv_cache(kv_cache)
-        qsa_cache = self.kv_cache
-        self.key_cache = qsa_cache[..., : self.key_head_size]
-        if self.cache_rope_positions:
-            position_tail = qsa_cache[..., self.rope_position_offset :]
-            self.rope_position_cache = position_tail.view(torch.int64)
-        else:
-            self.rope_position_cache = None
+    # Derived on access so `kv_cache` stays the only reference to the bound
+    # storage: clearing it (e.g. after CUDA graph memory profiling) must free
+    # the cache, or the freed block stays pinned in the allocator.
+    @property
+    def key_cache(self) -> torch.Tensor:
+        return self.kv_cache[..., : self.key_head_size]
+
+    @property
+    def rope_position_cache(self) -> torch.Tensor | None:
+        if not self.cache_rope_positions:
+            return None
+        return self.kv_cache[..., self.rope_position_offset :].view(torch.int64)
 
     def get_kv_cache_spec(self, vllm_config: VllmConfig) -> KVCacheSpec:
         # Hold the open group's committed keys plus every row a speculative