JDK-6948539 : CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs17,6u21
  • Priority: P2
  • Status: Closed
  • Resolution: Won't Fix
  • OS: generic,solaris_10
  • CPU: generic
  • Submitted: 2010-04-29
  • Updated: 2011-04-22
  • Resolved: 2010-12-08
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JDK 6 JDK 7 Other
6u21-revFixed 7Fixed hs17Fixed
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Description
If the CMS old gen happens to be placed at the right virtual addresses, the
cms_free bit can interfere with the promoted link used by objects
promoted into the old gen. This can cause BOT walks during card-scanning
to crash.

Comments
EVALUATION http://hg.openjdk.java.net/hsx/hsx17/baseline/rev/01e81d81d4cb
22-04-2011

EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/a00b51b2dda4
17-05-2010

SUGGESTED FIX The most expedient fix appears to be to compress the promoted object link when running with compressed oops.
10-05-2010

WORK AROUND Don't use -XX:+UseConcMarkSweepGC and -XX:+UseCompressedOops together.
29-04-2010

EVALUATION See 6872049 for some more background, the relevant portion of which will be copied into this CR (by and by).
29-04-2010