RFR (S): 7057939 : jmap shows MaxNewSize=4GB when Java is using parallel collector

[Krystal Mok]

For SurvivorRatio, the handling in ParallelScavenge is a little bit
different than other collectors in HotSpot. The collectors in the
Generational GC framework and G1 use SurvivorRatio directly, so the value
shown by jmap is the one that's taking effect. But ParallelScavenge doesn't
use SurvivorRatio directly, instead it uses IntialSurvivorRatio and
MinSurvivorRatio, with the latter two set ergonomically when the former is
set explicitly. So with ParallelScavenge the SurvivorRatio value shown in
jmap might not reflect what's really taking effect.

Thank you very much for fixing this. It's been annoying for a long time,
and I've been bugged a lot by people confused by the values shown in jmap
-heap.

Regards,
Kris


On Thu, Apr 18, 2013 at 9:13 PM, Thomas Schatzl
<thomas.schatzl at oracle.com>wrote:

> Hi,
>
> On Thu, 2013-04-18 at 02:33 +0800, Krystal Mok wrote:
> > Hi Thomas,
> >
> > Could the same kind of update be done for OldSize and SurvivorRatio?
> > For OldSize, if it's not explicitly set then it'll always show a
> > default value which is like 5MB or something, regardless of the
> > collector used.
>
> Going with the naming convention, OldSize would show the initial old
> generation size.
>
> > For SurvivorRatio, when using UseParallelGC or UseParallelOldGC, if
> > it's not explicitly set then InitialSurvivorRatio is the flag that
> > actually takes effect. It's better if SurvivorRatio could be updated
> > accordingly too.
>
> I think all collectors show these problems, just like in the MaxNewSize
> case.
>
> I created a CR which will become available later at
> http://bugs.sun.com/view_bug.do?bug_id=8012591 . It is a bit more
> generic as it requests to look at the other flags directly printed by
> jmap as well.
>
> Hth,
> Thomas
>
>
>
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