JDK-6951686 : Using large pages on Linux prevents zero based compressed oops
  • Type: Bug
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: hs18
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • OS: linux_2.6
  • CPU: x86
  • Submitted: 2010-05-11
  • Updated: 2010-09-24
  • Resolved: 2010-06-01
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JDK 6 JDK 7 Other
6u21pFixed 7Fixed hs18Resolved
Related Reports
Relates :  
Description
> java -d64 -XX:+UseCompressedOops -XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode -Xmx26g

heap address: 0x000000017ac00000, zero based Compressed Oops


> java -d64 -XX:+UseLargePages -XX:+UseCompressedOops -XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode -Xmx26g

heap address: 0x00002aaaae400000, Compressed Oops with base: 0x00002aaaae3ff000

Comments
EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/79bf863697eb
17-05-2010

EVALUATION The java heap with COOP is not reserved at specified address because of next (in os_linux.cpp): // Linux does not support anonymous mmap with large page memory. The only way // to reserve large page memory without file backing is through SysV shared // memory API. The entire memory region is committed and pinned upfront. // Hopefully this will change in the future... bool os::can_commit_large_page_memory() { return false; } As result the method os::reserve_memory_special() is called but req_addr parameter is not used: addr = (char*)shmat(shmid, NULL, 0);
11-05-2010