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  1. JDK
  2. JDK-8017629

G1: UseSHM in combination with a G1HeapRegionSize > os::large_page_size() falls back to use small pages

    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: hs24, hs25
    • Fix Version/s: 9
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
      gc
    • Resolved In Build:
      b120

      Backports

        Description

        JDK-8007074 fixes crashes due to incorrect alignment with G1HeapRegionSize > os::large_page_size() and UseSHM (originally tracked by JDK-8016666) has been enabled, and if allocation of SHM/huge pages has actually been successful.

        With JDK-8007074, instead of crashing, if the memory area allocated returned by SHM functions is not aligned with G1HeapRegionSize (or actually the requested alignment), the VM falls back to use small pages.

        This kind of fallback is different to the fallback to use small pages when there are no (or not enough) large pages available at all.

        See os::reserve_memory_special_shm() for details.

        This may represent a performance issue.

        Improve that by e.g. manual alignment or additional allocation of small pages at the start and end to align the heap.

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                • Assignee:
                  stefank Stefan Karlsson
                  Reporter:
                  tschatzl Thomas Schatzl
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                  • Created:
                    Updated:
                    Resolved: