RFR (M): 8212657: Implementation of JDK-8204089 Promptly Return Unused Committed Memory from G1 [Was: RFR (M): 8212657: Implementation of JDK-8204089 Timely Reduce Unused Committed Memory]

[Thomas Schatzl]

Hi all,

On Tue, 2018-12-04 at 10:32 +0100, Stefan Johansson wrote:
> 
> On 2018-12-03 15:30, Thomas Schatzl wrote:
> > Hi Sangheon,
> > 
[...]
> > All fixed.
> > 
> > http://cr.openjdk.java.net/~tschatzl/8212657/webrev.1_to_2/ (diff)
> > http://cr.openjdk.java.net/~tschatzl/8212657/webrev.2/ (full)
> 
> Still good,
> StefanJ

  while doing testing of other changes (where I included this change) I
found that very rarely the test fails.

This happens if the test machine is loaded, and additional heap
resizing happens due to gctimeratio being too high while we are waiting
for a periodic gc.

E.g.

- <create garbage>
- some gcs happen
- concurrent mark starts
- g1 finds out that gc time ratio is too high -> expands the heap by
itself
- concurrent mark finds that we recently expanded too much, shrinks the
heap
- periodic gc finds no more opportunity to shrink -> test fails

I trimmed the test to never do any GC (not allocating anything) by
setting appropriate startup options but still find opportunity to
shrink with periodic gcs.

This makes the test much shorter in code and execution time, and much
more robust. :)

http://cr.openjdk.java.net/~tschatzl/8212657/webrev.2_to_3/ (diff)
http://cr.openjdk.java.net/~tschatzl/8212657/webrev.3/ (full)

Thanks,
  Thomas