RFR(S): 8227225: ParallelGC: add subspace transitions for young gen for gc+heap=info log lines

[Thomas Schatzl]

Hi again,

On Fri, 2019-07-19 at 10:40 -0700, Tony Printezis wrote:
> Hey Thomas,
> 
> Thanks for taking a look and again apologies for the late reply, I
> was on vacation until earlier this week. Please see inline.
> 
> 
> —————
> Tony Printezis | @TonyPrintezis | tprintezis at twitter.com
> 
> 
> On July 10, 2019 at 11:19:37 AM, Thomas Schatzl (
> thomas.schatzl at oracle.com) wrote:
> > On Fri, 2019-07-05 at 11:06 -0700, Tony Printezis wrote: 
> > > Hi all, 
> > > 
> > > This is a follow-up to 8223575 and adds subspace info for eden 
> > > and from space to the gc+heap=info output for ParallelGC. I also
> > > added the before capacity, similar to 8223575, as it can change 
> > > during the GC (see, in fact, example below). 
> > > 
> > > Before: 
> > > 
> > > [11.123s][info][gc,heap ] GC(17) PSYoungGen: 4759616K- 
> > > >1664K(4545536K) 
> > > [11.123s][info][gc,heap ] GC(17) ParOldGen: 1280K- 
> > > >1280K(1376256K) 
> > > 
> > > After: 
> > > 
> > > [12.133s][info][gc,heap ] GC(25) PSYoungGen: 
> > > 2065952K(2066432K)->1536K(1983488K) Eden: 2064384K(2064384K)- 
> > > >0K(1981952K) 
> > > From: 1568K(2048K)->1536K(1536K) 
> > 
> > Note that I think this is confusing, or the "From" label should be 
> > renamed. The second part of this heap transition actually prints
> > the "To" space from what I understand. 
> 
> That’s not entirely true, though. The spaces do switch roles at the
> end of the GC, so the To space does become the From space of the
> following GC. So using From here is not entirely incorrect (but I do
> get your point).

Wait - on evac failure the generational collectors just do not switch
from and to-space, don't they? I can't think of any other situation
where To-space contains something for these collectors.

Then indeed printing To-space is useless as it is always empty. I can't
think of a situation where this would be the case.

Thanks,
  Thomas