JDK-8067433 : Keep waste at end of regions for further allocation during GC
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 9
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2014-12-15
  • Updated: 2019-02-11
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Other
tbdUnresolved
Related Reports
Blocks :  
JDK-8067455 - [NEWTEST] Test flexible allocation at end of G1 region
Duplicate :  
JDK-8067455 - [NEWTEST] Test flexible allocation at end of G1 region
Relates :  
JDK-8140330 - Keep multiple retained old gen regions across GCs
Relates :  
JDK-8067336 - Allow that PLAB allocations at the end of regions are flexible
Relates :  
JDK-8030849 - Investigate high fragmentation/waste in some situations during allocation during GC in G1
Description
If an inline allocation does not fit into the current region G1 simply retires the current region and grabs the next region.

For PLAB allocation this is mostly solved by JDK-8067336, however it may happen G1 still throws away hundreds of kB per region during inline allocation.

Fix this.
Comments
Existing review thread at http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2015-September/014827.html and http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2015-October/014841.html
24-11-2015
Attached patch with recent changes. After some internal discussion we agreed to delay this change due to existing and increased code complexity in this area, unless we find some important current application that needs this change.
24-11-2015
Would be nice to test. RFE JDK-8067455 is filed for that case.
15-12-2014