PYTHON-6140 [v4.18] [Build Failure] TestBSON.test_encode_size_limit MemoryError on Windows

test/test_bson.py

@@ -75,6 +75,25 @@
 _NUMPY_AVAILABLE = importlib.util.find_spec("numpy") is not None
 
 
+def _total_memory():
+    """Return total physical memory in bytes, or None if it cannot be determined."""
+    try:
+        return os.sysconf("SC_PAGE_SIZE") * os.sysconf("SC_PHYS_PAGES")
+    except (ValueError, OSError, AttributeError):
+        return None
+
+
+# PYTHON-6140: on Linux, skip if the host cannot allocate the ~4GiB this test
+# needs.  On other platforms, run the test and skip on MemoryError.
+_TOTAL_MEMORY = _total_memory()
+_ENCODE_SIZE_LIMIT_MIN_MEMORY = 6 << 30
+_SKIP_ENCODE_SIZE_LIMIT = (
+    sys.platform == "linux"
+    and _TOTAL_MEMORY is not None
+    and _TOTAL_MEMORY < _ENCODE_SIZE_LIMIT_MIN_MEMORY
+)
+
+
 class NotADict(abc.MutableMapping):
     """Non-dict type that implements the mapping protocol."""
 
@@ -692,12 +711,22 @@ def test_overflow(self):
         self.assertRaises(OverflowError, encode, {"x": -9223372036854775809})
 
     @unittest.skipUnless(bson.has_c(), "This test requires the C extension")
+    @unittest.skipIf(
+        _SKIP_ENCODE_SIZE_LIMIT,
+        "Test requires at least 6GiB of memory (PYTHON-6140)",
+    )
     def test_encode_size_limit(self):
         # PYTHON-5996: encoding must raise when a document's encoded size
         # exceeds the BSON size limit.
-        big_value = "a" * (1 << 30)
-        with self.assertRaises(ValueError):
-            encode({"a": big_value, "b": big_value, "c": big_value})
+        try:
+            big_value = "a" * (1 << 30)
+            with self.assertRaises(ValueError):
+                encode({"a": big_value, "b": big_value, "c": big_value})
+        except MemoryError:
+            # PYTHON-6140: some hosts report enough installed memory but
+            # cannot actually commit it (pagefile limits, mongod running on
+            # the same host).  Skip rather than fail.
+            self.skipTest("Could not allocate enough memory (PYTHON-6140)")
 
     def test_small_long_encode_decode(self):
         encoded1 = encode({"x": 256})