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  1. JDK
  2. JDK-8257040

[posix] os::split_reserved_memory will not work as expected on SysV shm

    Details

    • Type: Bug
    • Status: Closed
    • Priority: P4
    • Resolution: Won't Fix
    • Affects Version/s: 8, 11, 16
    • Fix Version/s: None
    • Component/s: hotspot
    • Labels:
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      Description

      On Posix, os::spit_reserved_memory() does assume that the underlying range had been allocated with mmap and follows mmap semantics (mainly, that it can be munmapped page-wise).

      Therefore it does not a split at all, but does a "shallow split", where it just adjusts the info in NMT and thats it.

      If the underlying memory had been reserved with System V shm, this will fail, since it follows the same semantics as Windows VirtualAlloc. The mapping will still be a combined one, and releasing the first part of the split will release the whole mapping.

      We use System V shm in two places:
      - on Linux, when we work with large pages and UseSHM
      - on AIX, where we use System V shared memory for almost everything to get 64K pages

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              • Assignee:
                stuefe Thomas Stuefe
                Reporter:
                stuefe Thomas Stuefe
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                • Created:
                  Updated:
                  Resolved: