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

[Stefan Johansson]

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/

Thanks,
Stefan
>
> Thanks,
>    Thomas
>
>