JDK-8221896 : Uncommit space on memory mapped heaps
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 13
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2019-04-03
  • Updated: 2019-04-03
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Other
tbdUnresolved
Related Reports
Relates :  
JDK-8220347 - JEP 351: ZGC: Uncommit Unused Memory (Experimental)
Description
Since kernel 2.6.38 Linux has the capability to "uncommit" space in memory mapped files (FALLOC_FL_PUNCH_HOLE, http://man7.org/linux/man-pages/man2/fallocate.2.html).

This would allow collectors mapping the Java heap from a file (via e.g. AllocateHeapAt) for e.g. providing Java heap on NVDIMM uncommit unused space.

ZGC will also use this facility planned with JEP 351: ZGC: Uncommit Unused Memory, however it is useful for all collectors.