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  1. JDK
  2. JDK-8214455

Relocate CDS archived regions to the top of the G1 heap

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    • Resolved In Build:
      b18

      Description

      When the runtime heap and dump time heap have different sizes, it's possible that the archived heap regions are mapped to the middle of the runtime heap. Because the archived heap regions are pinned, this could reduce the size of the largest "humongous" array allocation.

      In the worst case, the maximum allocatable array length may be half of the optimal value.

      The condition that needs to be changed is here:

      https://github.com/openjdk/jdk/blob/104e925dfdac0af3b1c6862f9a7d3442484f9241/src/hotspot/share/memory/filemap.cpp#L1835

          if (!CompressedOops::is_in(range)) {
            log_info(cds)("CDS heap data need to be relocated because");
            log_info(cds)("the desired range " PTR_FORMAT " - " PTR_FORMAT, p2i(range.start()), p2i(range.end()));
            log_info(cds)("is outside of the heap " PTR_FORMAT " - " PTR_FORMAT, p2i(CompressedOops::begin()), p2i(CompressedOops::end()));
            _heap_pointers_need_patching = true;
      >>>> Add
          } else if (header()->heap_end() != CompressedOops::end()) {
           log_info(cds)("CDS heap data need to be relocated to the end the runtime heap to reduce fragmentation");
        }
       <<<< end

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              Assignee:
              iklam Ioi Lam
              Reporter:
              iklam Ioi Lam
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