JDK-7007446 : G1: expand the heap with a single step, not one region at a time
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs20
  • Priority: P4
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2010-12-16
  • Updated: 2013-09-18
  • Resolved: 2011-03-08
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JDK 7 Other
7Fixed hs21Fixed
Related Reports
Relates :  
JDK-6941122 - G1: UseLargePages does not work with G1 garbage collector
Description
Currently, when we expand the heap in G1 we expand it one region at a time, even if we are going to expand it by a multiple of regions. We might want to optimize that and expand it in a more coarse-grain manner (at least by a multiple of the page size at a time?). I don't think this is a big performance bottleneck. But maybe expanding one region at a time, when large pages are used, might reduce G1's ability to use large pages.
Comments
SUGGESTED FIX Call VirtualSpace::expand_by once for the entire expansion ammount - rather than for each heap region. If the expansion succeeds then create the heap regions, add them to the free list and update the G1 memory regions.
02-02-2011
EVALUATION This RFE was addressed fixed as part of the changes for 6923430: Changeset: c33825b68624 Author: johnc Date: 2011-02-02 10:41 -0800 URL: http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/c33825b68624 6923430: G1: assert(res != 0,"This should have worked.") 7007446: G1: expand the heap with a single step, not one region at a time Summary: Changed G1CollectedHeap::expand() to expand the committed space by calling VirtualSpace::expand_by() once rather than for every region in the expansion amount. This allows the success or failure of the expansion to be determined before creating any heap regions. Introduced a develop flag G1ExitOnExpansionFailure (false by default) that, when true, will exit the VM if the expansion of the committed space fails. Finally G1CollectedHeap::expand() returns a status back to it's caller so that the caller knows whether to attempt the allocation. Reviewed-by: brutisso, tonyp ! src/share/vm/gc_implementation/g1/concurrentG1Refine.cpp ! src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp ! src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp ! src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp ! src/share/vm/gc_implementation/g1/g1RemSet.cpp ! src/share/vm/gc_implementation/g1/g1_globals.hpp
02-02-2011