Fix MAXIMUM_PAGE_SIZE_BYTES comment + value

core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java

@@ -151,6 +151,7 @@ private long getMemoryUsage() {
     }
     return sorter.getMemoryUsage() + totalPageSize;
   }
+
   @VisibleForTesting
   public int getNumberOfAllocatedPages() {
     return allocatedPages.size();

unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java

@@ -111,7 +111,6 @@ public final class BytesToBytesMap {
 
   private final double loadFactor;
 
-
   /**
    * The size of the data pages that hold key and value data. Map entries cannot span multiple
    * pages, so this limits the maximum entry size.

unsafe/src/main/java/org/apache/spark/unsafe/memory/TaskMemoryManager.java

@@ -58,8 +58,13 @@ public class TaskMemoryManager {
   /** The number of entries in the page table. */
   private static final int PAGE_TABLE_SIZE = 1 << PAGE_NUMBER_BITS;
 
-  /** Maximum supported data page size (in bytes). */
-  public static final long MAXIMUM_PAGE_SIZE_BYTES = (1L << OFFSET_BITS);
+  /**
+   * Maximum supported data page size (in bytes). In principle, the maximum addressable page size is
+   * (1L << OFFSET_BITS) bytes, which is 2+ petabytes. However, the on-heap allocator's maximum page
+   * size is limited by the maximum amount of data that can be stored in a  long[] array, which is
+   * (2^32 - 1) * 8 bytes (or 16 gigabytes). Therefore, we cap this at 16 gigabytes.
+   */
+  public static final long MAXIMUM_PAGE_SIZE_BYTES = (2^32 - 1) * 8L;
 
   /** Bit mask for the lower 51 bits of a long. */
   private static final long MASK_LONG_LOWER_51_BITS = 0x7FFFFFFFFFFFFL;