Fix merge conflict and undo broad *.c exclusion in .gitignore

Co-authored-by: leofang <5534781+leofang@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -5,7 +5,6 @@ __pycache__/
 
 # C extensions
 *.so
-*.c
 
 # CUDA Python specific
 .cache/

cuda_core/cuda/core/experimental/_memory.pyx

@@ -333,6 +333,23 @@ class DeviceMemoryResource(MemoryResource):
         self._handle = handle_return(driver.cuDeviceGetMemPool(device_id))
         self._dev_id = device_id
 
+        # Set a higher release threshold to improve performance when there are no active allocations.
+        # By default, the release threshold is 0, which means memory is immediately released back
+        # to the OS when there are no active suballocations, causing performance issues.
+        # Check current release threshold
+        current_threshold = handle_return(
+            driver.cuMemPoolGetAttribute(self._handle, driver.CUmemPool_attribute.CU_MEMPOOL_ATTR_RELEASE_THRESHOLD)
+        )
+        # If threshold is 0 (default), set it to maximum to retain memory in the pool
+        if int(current_threshold) == 0:
+            handle_return(
+                driver.cuMemPoolSetAttribute(
+                    self._handle,
+                    driver.CUmemPool_attribute.CU_MEMPOOL_ATTR_RELEASE_THRESHOLD,
+                    driver.cuuint64_t(0xFFFFFFFFFFFFFFFF),
+                )
+            )
+
     def allocate(self, size: int, stream: Stream = None) -> Buffer:
         """Allocate a buffer of the requested size.