Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/5725#discussion_r29284519
--- Diff:
unsafe/src/main/java/org/apache/spark/unsafe/memory/MemoryBlock.java ---
@@ -0,0 +1,74 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.unsafe.memory;
+
+import javax.annotation.Nullable;
+
+import org.apache.spark.unsafe.PlatformDependent;
+
+/**
+ * A consecutive block of memory, starting at a {@link MemoryLocation}
with a fixed size.
+ */
+public class MemoryBlock extends MemoryLocation {
+
+ private final long length;
+
+ /**
+ * Optional page number; used when this MemoryBlock represents a page
allocated by a
+ * MemoryManager. This is package-private and is modified by
MemoryManager.
+ */
+ int pageNumber = -1;
--- End diff --
My original motivation for making this an int was the fact that our page
table is indexed by an integer, but now that I look more closely it looks like
it's most-often read by `encodePageNumberAndOffset`, which does the long cast.
If we wanted to go a bit further in terms of saving instructions here, I guess
we could store the pre-shifted page number then do the reverse shift for the
accesses in `freePage`, since that's performed far fewer times.
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