JDK-7199092 : NMT: NMT needs to deal overlapped virtual memory ranges
  • Type: Bug
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: hs25
  • Priority: P2
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2012-09-18
  • Updated: 2013-07-02
  • Resolved: 2012-10-20
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 7 JDK 8 Other
7u40Fixed 8Fixed hs24Fixed
Related Reports
Duplicate :  
Duplicate :  
Relates :  
Relates :  
Relates :  
After NPG changes, NMT sees different memory usage patterns, which it cannot deal with correctly. For example, it reserves a bigger range, then it re-reserve a smaller range within the bigger range. NMT does not expect and cannot deal with overlapped reserved range.

There is an example:

[fffffd7ffb800000 - fffffd7ffbe00000] [9] seq = 337     <== reserve a bigger range
[fffffd7ffb800000 - fffffd7ffbe00000] [9] seq = 338     <== dup record
[fffffd7ffb800000 - fffffd7ffb800000] [10b] seq = 339   <== mtClass 
[fffffd7ffb800000 - fffffd7ffba00000] [9] seq = 340     <== re-reserve a smaller range
[fffffd7ffb800000 - fffffd7ffba00000] [a] seq = 341     <== commit
[fffffd7ffb800000 - fffffd7ffba00000] [a] seq = 342     <== dup record

Hard to create a regression test

EVALUATION PermGen removal project introduced different virtual memory usage patterns vs. earlier version. As result, NMT has to track individual committed memory region, vs. track a reserved region as whole and only keep committed size within the region. The improved implementation, now, can generate virtual memory map.