JDK-6631166 : CMS: better heuristics when combatting fragmentation
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs10,hs14,6u14,6u16,6u17,7
  • Priority: P2
  • Status: Closed
  • Resolution: Fixed
  • OS:
    generic,linux,linux_redhat_5.0,solaris_10 generic,linux,linux_redhat_5.0,solaris_10
  • CPU: generic,x86,sparc
  • Submitted: 2007-11-16
  • Updated: 2021-10-05
  • Resolved: 2010-07-02
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
6u19-revFixed 7Fixed hs16.2Fixed
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See comments section for pointers to logs from customer and
an email that hints at (some of) the issues involved.

EVALUATION http://hg.openjdk.java.net/jdk7/hotspot/hotspot/rev/e018e6884bd8

EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/e018e6884bd8

EVALUATION Under testing and review.

EVALUATION In the case of this customer, one problem had been the extremely large size of OldPLABSize chosen. Reducing it improved fragmentation behaviour. However, their workloads are sufficiently high and sufficiently bursty that any dynamic scheme will be unable to work well at all times within a 32-bit heap. They have been advised to either move to 64-bit heaps and/or to run multiple 32-bit jvms to make full use of their multicore boxes. In the meantime, our investigations have identified a number of incremental improvements to reduce fragmentation and these are being tested. A list of improvements made as part of this CR will be listed in the suggested fix section when we are done.

SUGGESTED FIX http://analemma.sfbay.sun.com/net/spot/workspaces/ysr/frag

EVALUATION Some improvements have been made, and we are studying the effect of this on performance of some applications/benchmarks.

EVALUATION We are investigating the defficiencies of the current scheme in order to improve the frgamentation-control heuristics.