add warning for when UCX_MEM_MMAP_HOOK_MODE is set

tests/test_mmap_warn.py

@@ -0,0 +1,17 @@
+import os
+
+
+def test_mem_mmap_hook_warn(caplog):
+    """
+    Test warning for UCX_MEM_MMAP_HOOK_MODE
+    """
+    import logging
+
+    os.environ["UCX_MEM_MMAP_HOOK_MODE"] = "none"
+
+    # ucp.init will only print INFO LINES
+    with caplog.at_level(logging.INFO):
+        import ucp
+
+        ucp.init()
+    assert any(["UCX_MEM_MMAP_HOOK_MODE" in rec.message for rec in caplog.records])

ucp/__init__.py

@@ -39,6 +39,13 @@
 if not os.environ.get("UCX_TCP_RX_SEG_SIZE", False):
     os.environ["UCX_TCP_RX_SEG_SIZE"] = "8M"
 
+if os.environ.get("UCX_MEM_MMAP_HOOK_MODE", False):
+    msg = (
+        "Setting `UCX_MEM_MMAP_HOOK_MODE` disable IB registration cache "
+        "which disable GPURDMAincluding GPU direct. \nPlease unset "
+        "UCX_MEM_MMAP_HOOK_MODE"
+    )
+    logger.warning(msg)
 
 # After handling of environment variable logging, add formatting to the logger
 logger = get_ucxpy_logger()