JDK-6952079 : With UseParallelScavenge use MinHeapFreeRation/MaxHeapFreeRatio if UseAdaptiveSivePolicy is off.
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 7
  • Priority: P3
  • Status: Closed
  • Resolution: Won't Fix
  • OS: generic
  • CPU: generic
  • Submitted: 2010-05-13
  • Updated: 2016-12-15
  • Resolved: 2016-03-07
Related Reports
Relates :  
JDK-8037924 - CMM Testing: Check Min/MaxHeapFreeRatio flags allows to shrink the heap when using ParallelGC
Description
Currently when UseAdaptiveSizePolicy is off for UseParallelGC the generations do not
change from their initial sizes.  This change makes UseParallelGC generations grow and
shrink using MinHeapFreeRation/MaxHeapFreeRatio in a way similar to the other
collectors.  Additionally, based on a new flag on a System.gc() the
MinHeapFreeRation/MaxHeapFreeRatio sizing is used when UseAdaptiveSizePolicy is
on.
Comments
If we want to replace SerialGC with ParallelGC using 1 thread, we'll need to do something here. Making ParallelGC use the heap-free-ratios makes sense except for the compatibility issue (i.e., -UseAdaptiveSizePolicy has a behavior for ParallelGC). One possibility would be yet another flag to say use the heap-free-ratios with ParallelGC if UseAdaptiveSizePolicy is turned off. In jdk9 we could issue a warning that -UseAdaptiveSizePolicy is going to change behavior for ParallelGC in a future release and then in jdk10 make -UseAdaptiveSizePolicy cause ParallelGC to use the heap-free-ratios.
02-10-2014
Talked to Jesper about this, and we do not think it is worthwhile doing: - parallel gc never grew/shrink if -XX:-UseAdaptiveSizePolicy has been set. It would be strange if it started now to be "a little" adaptive - people actively turning off adaptive sizing probably have a clear idea why they do it, so doing it anyway might not be useful to them Thoughts?
29-09-2014