RFR (S): 8204082: Add indication that this is the "Last Young GC before Mixed" to logs

[Stefan Johansson]

Hi Thomas,

On 2018-06-05 22:26, Thomas Schatzl wrote:
> Hi,
> 
> On Wed, 2018-05-30 at 14:50 +0200, Thomas Schatzl wrote:
>> Hi all,
>>
>>    can I have reviews for this change that adds an indication about
>> the "last young" gc before a mixed phase to the logs?
>>
>> I.e. instead of "GC Pause (Young)", that GC is called "GC Pause (Last
>> Young)".
>>
>> The reason for this potentially intrusive change to log parsers is
>> that in quite a few situations it is useful to be really sure what
>> kind of GC is being started without needing to either add gc+ergo
>> logging or restarting. This situation where I was trying to figure
>> out whether the given young GC I was looking at was the young gc
>> before the mixed gcs or just a young-gc because the Cleanup pause
>> figured out that we do not need a mixed phase.
>>
>> I am not too hung up about naming it "Last Young" in particular, but
>> I really would like to have this or a similar indication that is
>> generally available with minimal logging.
> 
> Alternatively we could just call it "Mixed" that does not collect any
> old gen regions at this time. Later we could start gc as soon as the
> pause time goal permits and add a few old gen regions.
> 
I think I like this better than "Last Young" or "Final Young".

> This would probably be a little confusing to users, but at least help
> diagnosing logs.
> 
> There also has been the suggestion to call it "Final Young" instead of
> "Last Young".
> 
> Any comments?
Another possible solution, not sure it's better would be to an extra tag 
to all Young GCs, something like:
Pause Young (Initial Mark) ...
Pause Young (Normal) ...
Pause Young (Finished Mark) ...
Pause Young (Mixed) ...

But I guess it's a bit harsh to call the Mixed GCs Young =)

A third solution would be to somehow use the GC cause to mark this state.

As usual naming is hard, I think I'm leaning towards just calling it 
Mixed and then we know that the first mixed GC is always young only =)

Thanks,
Stefan


> 
> Thomas
> 
>>
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8204082
>> Webrev:
>> http://cr.openjdk.java.net/~tschatzl/8204084/webrev/
>> Testing:
>> hs-tier 1-3