RFR (XXS) JDK-8153578,Default NewRatio is ignored when UseConcMarkSweepGC is used as GC algorithm

[Jesper Wilhelmsson]

And, by the way, I object to the subject. Changes in argument parsing are never 
XXS.  ;)
/Jesper

Den 20/4/16 kl. 21:35, skrev Jesper Wilhelmsson:
> Hi Joe,
>
> If I understand the bug description correctly the problem is that NewSize
> becomes too small. According to the bug the VM ignores the NewRatio setting.
>
> Your change removes the setting of MaxNewSize in the case where NewSize has the
> default value. It's not obvious to me how that is related to the bug.
>
> There is an if statement enclosing the code you are changing. It has a comment
> that I find interesting:
>
> 1755   // If either MaxNewSize or NewRatio is set on the command line,
> 1756   // assume the user is trying to set the size of the young gen.
> 1757   if (FLAG_IS_DEFAULT(MaxNewSize) && FLAG_IS_DEFAULT(NewRatio)) {
>
> The interesting part is that the comment says "MaxNewSize OR NewRatio" but the
> code says "MaxNewSize AND NewRatio". This could be a typo in the comment, or it
> could be related to your bug.
>
> I don't think the fix here is to ignore the calculated preferred_max_new_size,
> but rather to figure out why it has the wrong value. preferred_max_new_size is
> calculated a few lines up, and it is based on NewRatio. The number of threads
> seems to be involved as well. Should it be? Usually things based on the number
> of threads tend to be wrong...
>
> 1748     MIN2(max_heap/(NewRatio+1), ScaleForWordSize(young_gen_per_worker *
> ParallelGCThreads));
>
> young_gen_per_worker is CMSYoungGenPerWorker which defaults to things like 16M
> or 64M. ParallelGCThreads is usually just a handful, 8 on my machine. Since we
> take the smallest number of this thread based thing and the NewRatio
> calculation, I would guess the threads will limit the MaxNewSize quite a lot. I
> wonder if this isn't the bug you are looking for. It would make more sense to me
> if it was MAX of the two instead of MIN. You should probably consult whoever
> wrote this code.
>
> /Jesper
>
>
> Den 20/4/16 kl. 20:08, skrev Joseph Provino:
>> Please review this tiny change.  It only affects ParNew.  Are there any
>> unintended consequences?
>>
>> Passes JPRT.
>>
>> CR: JDK-8153578 Default NewRatio is ignored when UseConcMarkSweepGC is used as
>> GC algorithm <https://bugs.openjdk.java.net/browse/JDK-8153578>
>>
>> Webrev:  http://cr.openjdk.java.net/~jprovino/8153578/webrev.00
>>
>>