Uploaded image for project: 'JDK'
  1. JDK
  2. JDK-6722116

CMS: Incorrect overflow handling when using parallel concurrent marking

    Details

    • Subcomponent:
      gc
    • Introduced In Build:
      1.6
    • Introduced In Version:
      6
    • Resolved In Build:
      b06
    • CPU:
      generic, unknown
    • OS:
      generic, linux_redhat_5.2

      Backports

        Description

        Here's a description from the Evaluation field of 6578335 during the investigation
        of which this problem was first discovered:-

        There was a third bug found which relates to the handling of
        "second ring overflow" when using parallel concurrent marking
        -- the overflow of the global overflow stack (which itself handles
        the overflow from the local work queues). The intention was
        that this second ring overflow should use the "restart mechanism"
        to restart marking from the least overflown address.
        That mechanism was not completely extended to the parallel
        concurrent marking case. The restart_addr was not pushed
        all the way through to the parallel concurrent marking task that controls
        the parallel concurrent marking. Because of the partial
        change to the state of the parallel concurrent marking task,
        we can and often will end up missing the scan of some of the
        addresses at the higher extremes of the CMS-collected
        generations. Because second-ring overflow is a very rare
        event in practice, this appears to have not been detected
        before (or at least not until the first two bugs mentioned
        above were moved out of our way).

        The obvious workaround is to switch off parallel concurrent
        marking via -XX:-CMSConcurrentMTEnabled.

          Attachments

            Issue Links

              Activity

                People

                • Assignee:
                  ysr Y. Ramakrishna
                  Reporter:
                  ysr Y. Ramakrishna
                • Votes:
                  0 Vote for this issue
                  Watchers:
                  3 Start watching this issue

                  Dates

                  • Created:
                    Updated:
                    Resolved:
                    Imported:
                    Indexed: