JDK-6687581 : Make CMS work with compressed oops
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 7
  • Priority: P3
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2008-04-11
  • Updated: 2011-03-08
  • Resolved: 2011-03-08
The Version table provides details related to the release that this issue/RFE will be addressed.

Unresolved : Release in which this issue/RFE will be addressed.
Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

To download the current JDK release, click here.
JDK 6 JDK 7 Other
6u14Fixed 7Fixed hs13Fixed
Related Reports
Relates :  
JDK-6689653 - JMapPerm fails with UseConcMarkSweepIncGC and compressed oops off
Relates :  
JDK-6459804 - Want client (c1) compiler for x86_64 (amd64) for faster start-up
Relates :  
JDK-6712278 - Better fix for CMS+Compressed Oops
Description
CMS doesn't work with compressed oops so it's turned off because it has these chunk headers that use the lsb of the _klass field which is not zero in the compressed oops case.

In 64 bit mode, use a bit in the markOop instead of the lsb in the _klass field to indicate free.  There's apparently 25 spare bits in the markOop in 64 bit.

btw, I volunteered to do this too.
Comments
EVALUATION Fixed 6687581: Make CMS work with compressed oops Make FreeChunk read markword instead of LSB in _klass pointer to indicate that it's a FreeChunk for compressed oops. Moved the size field first so that it is used consistently for 64 bits w/out compressed oops, and 32 bits to reduce ifdefs. Changed FreeChunk and associated code in SA. Fix verified: y Testing: nsk stress, sajdi and my sanity testlists with CMS+compressedoops. runthese refworkload/GCOld Reviewed-by:
05-06-2008