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Bug ID: 6948539 CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
6948539 : CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link

Details
Type:
Bug
Submit Date:
2010-04-29
Status:
Closed
Updated Date:
2011-04-22
Project Name:
JDK
Resolved Date:
2010-12-08
Component:
hotspot
OS:
generic,solaris_10
Sub-Component:
gc
CPU:
generic
Priority:
P2
Resolution:
Won't Fix
Affected Versions:
hs17,6u21
Fixed Versions:
hs18

Related Reports
Backport:
JDK-2193990 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2195906 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2197581 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2197875 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2199775 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2199485 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2193019 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Backport:
JDK-2193989 - CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Relates:
JDK-6872049 - CMS: Failure in CompactibleFreeListSpace::block_size from ::block_start_unsafe()
Relates:
JDK-6951188 - CMS: move PromotionInfo into its own file

Sub Tasks

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
2011-04-22 
EVALUATION

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

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

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

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


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