Fix Buffer.is_managed to merge driver and resource signals

Previous fix unconditionally delegated Buffer.is_managed to
_memory_resource.is_managed, which returns False for any
MemoryResource subclass that does not opt in.  That broke
DummyUnifiedMemoryResource (and any user-defined MR wrapping
cuMemAllocManaged) where the driver pointer attribute correctly
reports IS_MANAGED=1 but the resource does not override is_managed.

Query the driver first; only fall back to the memory resource when
the driver does not report IS_MANAGED (the pool-allocated managed
memory path).  This keeps both old-style cuMemAllocManaged buffers
and ManagedMemoryResource pool allocations correctly classified.

Also rework the regression test parametrization to skip the pinned
case when PinnedMemoryResource is unavailable (CUDA < 13.0), and pick
up the ruff-format reflow of the helper call site.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cpcloud

cuda_core/cuda/core/_memory/_buffer.pyx

@@ -390,10 +390,12 @@ cdef class Buffer:
     @property
     def is_managed(self) -> bool:
         """Return True if this buffer is CUDA managed (unified) memory, otherwise False."""
-        if self._memory_resource is not None:
-            return self._memory_resource.is_managed
         _init_mem_attrs(self)
-        return self._mem_attrs.is_managed
+        if self._mem_attrs.is_managed:
+            return True
+        # Pool-allocated managed memory does not set CU_POINTER_ATTRIBUTE_IS_MANAGED,
+        # so fall back to the memory resource when it advertises managed allocations.
+        return self._memory_resource is not None and self._memory_resource.is_managed
 
     @property
     def is_mapped(self) -> bool:

cuda_core/tests/test_memory.py

@@ -617,9 +617,7 @@ def test_managed_memory_resource_buffer_dlpack_device_type():
     device = Device()
     device.set_current()
     skip_if_managed_memory_unsupported(device)
-    mr = create_managed_memory_resource_or_skip(
-        ManagedMemoryResourceOptions(preferred_location=device.device_id)
-    )
+    mr = create_managed_memory_resource_or_skip(ManagedMemoryResourceOptions(preferred_location=device.device_id))
     buf = mr.allocate(1024)
 
     assert mr.is_managed
@@ -630,23 +628,21 @@ def test_managed_memory_resource_buffer_dlpack_device_type():
     assert view.__dlpack_device__() == (int(DLDeviceType.kDLCUDAManaged), 0)
 
 
-@pytest.mark.parametrize(
-    ("mr_factory", "expected_managed"),
-    [
-        (lambda dev: DeviceMemoryResource(dev), False),
-        (lambda dev: PinnedMemoryResource(), False),
-    ],
-)
-def test_non_managed_resources_report_not_managed(mr_factory, expected_managed):
+@pytest.mark.parametrize("mr_kind", ["device", "pinned"])
+def test_non_managed_resources_report_not_managed(mr_kind):
     """Non-managed memory resources must report is_managed=False."""
     device = Device()
     device.set_current()
     if not device.properties.memory_pools_supported:
         pytest.skip("Device does not support mempool operations")
-    mr = mr_factory(device)
-    assert mr.is_managed is expected_managed
+    if mr_kind == "device":
+        mr = DeviceMemoryResource(device)
+    else:
+        skip_if_pinned_memory_unsupported(device)
+        mr = PinnedMemoryResource()
+    assert mr.is_managed is False
     buf = mr.allocate(1024)
-    assert buf.is_managed is expected_managed
+    assert buf.is_managed is False
     buf.close()