RFR: 8143251: HeapRetentionTest.java Test is failing on jdk9/dev

Thomas Schatzl thomas.schatzl at oracle.com
Tue Nov 24 16:03:33 UTC 2015


Hi,

On Tue, 2015-11-24 at 10:15 +0100, Stefan Johansson wrote:
> Thanks for looking at this Thomas,
> 
> On 2015-11-23 13:27, Thomas Schatzl wrote:
> > Hi,
> >
> >    some added comments about the problem:
> >
> > On Fri, 2015-11-20 at 18:07 +0100, Stefan Johansson wrote:
> >> Hi,
> >>
> >> Please review this fix for:
> >> https://bugs.openjdk.java.net/browse/JDK-8143251
> >>
> >> Webrev:
> >> http://cr.openjdk.java.net/~sjohanss/8143251/hotspot.00/
> >>
> >> Summary:
> >> After some refactoring and fixing in the G1 state machine it was
> >> possible to enter a state where we will ignore user requested concurrent
> >> GCs.
> > ^^ that is not true. G1 does not ignore these requests. It's just that
> > they will be delayed, that is delayed until the "next" GC. There are
> > situations like test cases where this next GC does not occur because
> > after sending that request, the application would stop allocating, so
> > that request would "never" be executed.
> >
> >> This changes adds special treatment for the GC causes that are
> >> currently user requested to allow them to always trigger a new
> >> concurrent marking cycle.
> > ... and potentially stopping the current reclamation phase, i.e. mixed
> > gcs. This comes with a big risk with adaptive IHOP, as at that time G1
> > is already (by definition of that feature) at low extra memory.
> >
> >> Testing:
> >> * JPRT
> >> * RBT with the failing tests and additional GC tests.
> >   - I would prefer that the comment in g1CollectedHeap.hpp at
> >
> >   248   // These are defined in user_requested_concurrent_full_gc()
> > because
> >   249   // these sometimes need to be treated differently:
> >
> > would be moved below the list, and "these" qualified directly. E.g.
> > "Cases c)-f) are defined..."
> >
> > I am not sure if the comment helps a lot. It seems to confuse the reader
> > more by being so unspecific, but ymmv.
> I agree, removed lines 248, 249.
> >
> >   - in g1CollectorPolicy.cpp:1657, maybe the message should add the kind
> > of user requested concurrent mark too? Not really necessary because the
> > message in force_initial_mark_outside_cycle() already contains it. It's
> > your call.
> This was my first idea as well but the ergo_verbose-macros made me back 
> of =) Also, as you say, we have the information in nearby logging, but 
> if you want I can file an RFE to add this once UL is in.
> 
> >
> >   - I would prefer if the comment in 1651 would directly mention why 1653
> > and 1654 are required: that G1 an initial mark gc must be a young-only
> > gc.
> Updated comment.
> >
> >   - maybe the declaration of
> > G1CollectedHeap::user_requested_concurrent_full_gc() moved closer to
> > should_do_concurrent_full_gc(). Not sure, and I am not insisting on
> > that. It's just that the referenced should_do_... is rather far away.
> >
> > Also please add a "is_" prefix to that getter. The comment also does not
> > tell what this method does. Or remove the existing comment. It sounds
> > like a justification why this needed to be split out. Simple
> > cross-referencing makes that understandable I think.
> I added the is_ and removed the comment, but left it at its current 
> location since the reference is now gone.
> 
> New webrev:
> http://cr.openjdk.java.net/~sjohanss/8143251/hotspot.01/
> 
> Inc webrev:
> http://cr.openjdk.java.net/~sjohanss/8143251/hotspot.00-01/

  looks good.

Thomas



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