9.18.2 Prerequisites

This function is available if the total set size of each heap area (Java heap area and explicit heap area^#) is less than 32 GB. If the total set size is 32 GB or more, this function is disabled even if you specify -XX:+UseCompressedOops.

Value specified for the heap area size, which enables the object-pointer compression function
 
(1) When the Explicit Memory Management functionality is used
  (value-specified-for--Xmx-option) + (value-specified-for--XX:HitachiExplicitHeapMaxSize-option) < 32 GB
 
(2) When the Explicit Memory Management functionality is not used
  (value-specified-for--Xmx option) < 32 GB

#

The explicit heap area applies only when the Explicit Memory Management functionality is enabled.

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