RFR(S): 8223575: add subspace transitions to gc+metaspace=info log lines

[Thomas Schatzl]

Hi,

On Wed, 2019-06-05 at 13:25 -0400, Tony Printezis wrote:
> Thanks Thomas, still need to get clarification re: adding Twitter
> copyright notice to the new files. I’ll report back when I have an
> answer.
> 

Some minor nits:

- historically method that print log messages are prefixed with
"print_" and not with "log_" like "log_metaspace_change" (which
originally has also been called "print_metaspace_change"). There does
not seem to be lots of reason to change this given that this method
appears a few times in the vicinity of "print_" methods.

For the sake of uniformity I would prefer if that would be kept; I am
open to changing all of these at once (later). Just pointing out.

- just a thought: the units of the output for metaspace logging are
hardcoded with "K" (and previously were). It might be useful to adjust
the unit as needed like other similar output.
That's probably one for another CR though.

- it would be nice to have a test case for this, just checking the
general format of the output for with/without coops.

[... snipped long text...]
> > > > --
> > > > 
> > > > I am not sure if this needs a CSR and/or a Release Note since
> > > > we change the format of the Metaspace entgc log entries and
> > > > that may confuse people. If it does, I can review the CSR for
> > > > you and hopefully it goes fast. I wait for the second reviewers
> > > > opinion on this (preferably someone from Oracles GC group).
> > > 
> > > I have no idea if a CSR is needed. Was there a CSR for the
> > > -Xlog:safepoint* changes? I’ll assume one is not needed unless
> > > I’m told otherwise. ;-) 

Log messages are not part of the end user interface and can be changed
as needed (but should not randomly).
Potentially this change is worth mentioning in a release note though if
you want to get word out.

Hopefully I did not overlook some important question in the very long
email thread so far.

Thanks,
  Thomas