JDK-6920090 : G1: Disable ReduceInitialCardMarks at least until 6920109 is fixed
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs16,hs17
  • Priority: P2
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2010-01-26
  • Updated: 2013-09-18
  • Resolved: 2011-03-07
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JDK 6 JDK 7 Other
6u21Fixed 7Fixed hs17Fixed
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Description
This is a temporary measure to deal with observed lingering instability
with G1 when ReduceInitialCardMarks is enabled (the default today).
See comments section for email trail describing this and the test
case which exposes the issue.

Comments
EVALUATION ChangeSet=http://hg.openjdk.java.net/jdk7/hotspot/hotspot/rev/34fb2662f6c2,ChangeRequest=6920090
28-01-2010

EVALUATION ChangeSet=http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/34fb2662f6c2,ChangeRequest=6920090
27-01-2010

SUGGESTED FIX diff -r c81fa70144aa src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp --- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp Mon Jan 25 18:03:29 2010 -0500 +++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp Tue Jan 26 01:28:23 2010 -0800 @@ -1004,7 +1004,11 @@ public: // storage in the heap comes from a young region or not. // See ReduceInitialCardMarks. virtual bool can_elide_tlab_store_barriers() const { - return true; + // Temporarily turned off, because of lingering + // instabilities related to RICM with G1. In the + // interim, the option ReduceInitialCardMarksForG1 + // below is left solely as a debugging device. + return ReduceInitialCardMarksForG1; } virtual bool card_mark_must_follow_store() const { @@ -1026,6 +1030,7 @@ public: // However, non-generational G1 (-XX:-G1Gen) appears to have // bit-rotted so was not tested below. virtual bool can_elide_initializing_store_barrier(oop new_obj) { + assert(ReduceInitialCardMarksForG1, "Else cannot be here"); assert(G1Gen || !is_in_young(new_obj), "Non-generational G1 should never return true below"); return is_in_young(new_obj); diff -r c81fa70144aa src/share/vm/gc_implementation/g1/g1_globals.hpp --- a/src/share/vm/gc_implementation/g1/g1_globals.hpp Mon Jan 25 18:03:29 2010 -0500 +++ b/src/share/vm/gc_implementation/g1/g1_globals.hpp Tue Jan 26 01:28:23 2010 -0800 @@ -291,6 +291,10 @@ "a particular entry exceeds this value.") \ \ develop(bool, G1VerifyCTCleanup, false, \ - "Verify card table cleanup.") + "Verify card table cleanup.") \ + \ + develop(bool, ReduceInitialCardMarksForG1, false, \ + "When ReduceInitialCardMarks is true, this flag setting " \ + " controls whether G1 allows the RICM optimization") G1_FLAGS(DECLARE_DEVELOPER_FLAG, DECLARE_PD_DEVELOPER_FLAG, DECLARE_PRODUCT_FLAG, DECLARE_PD_PRODUCT_FLAG, DECLARE_DIAGNOSTIC_FLAG, DECLARE_EXPERIMENTAL_FLAG, DECLARE_NOTPRODUCT_FLAG, DECLARE_MANAGEABLE_FLAG, DECLARE_PRODUCT_RW_FLAG)
26-01-2010

WORK AROUND -XX:-ReduceInitialCardMarks when using G1.
26-01-2010

EVALUATION Yes.
26-01-2010