RFR (S/M): 8178105: Switch mark bitmaps during Remark

[Thomas Schatzl]

Hi all,

  while looking at some parallelizing work in this area I noticed that
one assert in the rebuild remsets code that has been changed in this
change already needs an update too.
It uses a wrong value for the informational text, which makes it really
confusing.

Since this change touches this code already, I would like to amend this
change with this small fix:

Webrev:
http://cr.openjdk.java.net/~tschatzl/8178105/webrev.2_to_3/ (diff)
http://cr.openjdk.java.net/~tschatzl/8178105/webrev.3/ (full)

Sorry for the trouble.

Thanks,
  Thomas

On Tue, 2018-04-03 at 17:00 +0200, Stefan Johansson wrote:
> 
> On 2018-04-03 16:55, Thomas Schatzl wrote:
> > Hi,
> > 
> >    thanks for your patience...
> > 
> > On Tue, 2018-04-03 at 14:49 +0200, Stefan Johansson wrote:
> > > 
> > > On 2018-04-03 14:25, Thomas Schatzl wrote:
> > > > Hi Stefan,
> > > > 
> > > > On Tue, 2018-04-03 at 12:58 +0200, Stefan Johansson wrote:
> > > > > Hi Thomas,
> > > > > 
> > > > > On 2018-03-29 16:35, Thomas Schatzl wrote:
> > > > > > Hi all,
> > > > > > [...]
> > > > > > 
> > > > > > CR:
> > > > > > https://bugs.openjdk.java.net/browse/JDK-8178105
> > > > > > Webrev:
> > > > > > http://cr.openjdk.java.net/~tschatzl/8178105/
> > > > > 
> > > > >    Looks good, but a few comments:
> > > > > 
> > 
> > [...]
> > > > I added a different kind of check that verifies what you
> > > > probably
> > > > thought of, and that is that the number of words to add to the
> > > > current region must always be larger than zero. If it is zero,
> > > > there is something really wrong.
> > > 
> > > Exactly, that's what I wanted. But I don't see that check now,
> > > just
> > > having a assert(marked_words != 0, "") on row 1032 would be
> > > enough.
> > 
> > My fault. I did not upload the latest version of the change :( It
> > is up
> > now, the only difference to previous is line
> > 
> > 1036       assert(words_to_add > 0, "Out of space to distribute
> > before
> > end of humongous object in region %u (starts %u)", i, region_idx);
> > 
> > But there is a new webrev anyway... in the 1_to_2 webrev it is line
> > 1033
> > 
> > > > > 
> > > > > 1047       log_trace(gc)("Added " SIZE_FORMAT " words to
> > > > > region
> > > > > %u
> > > > > (%s)", marked_words, region_idx, hr->get_type_str());
> > > > > I think the logging should use at least one more tag, maybe
> > > > > "region" or "marking", but you probably know what makes most
> > > > > sense in this area. I also think it would be nice if we got
> > > > > this
> > > > > same log-line for all regions. Now we get this for "normal"
> > > > > regions, but we get "Distributing..." for humongous start
> > > > > regions
> > > > > and "Not Added..." for humongous continuous. So I would
> > > > > suggest
> > > > > adding the same log-line  to the distribute-function after
> > > > > line
> > > > > 1034.
> > > > 
> > > > Done.
> > > 
> > > Sorry for being picky but the current solution won't print
> > > anything
> > > for continuous humongous. Adding the log to
> > > distribute_marked_bytes()
> > > would solve this and we would still get info on region type so I
> > > see
> > > no need for:
> > 
> > Okay. I think I got your intention right this time :)
> > 
> > > 1052         log_trace(gc, marking)("Adding " SIZE_FORMAT " words
> > > to
> > > humongous start region %u (%s), word size %d (%f)",
> > > 1053                                marked_words, region_idx,
> > > hr->get_type_str(),
> > > 1054                                oop(hr->bottom())->size(),
> > > (double)oop(hr->bottom())->size() / HeapRegion::GrainWords);
> > 
> > [...]
> > > > All fixed.
> > > > 
> > > > Webrevs:
> > > > http://cr.openjdk.java.net/~tschatzl/8178105/webrev.0_to_1/
> > > > (diff)
> > > > http://cr.openjdk.java.net/~tschatzl/8178105/webrev.1/ (full)
> > > 
> > > Apart from the small things above this looks great.
> > 
> > http://cr.openjdk.java.net/~tschatzl/8178105/webrev.1_to_2/ (diff)
> > http://cr.openjdk.java.net/~tschatzl/8178105/webrev.2/ (full)
> 
> Looks good!
> 
> Thanks,
> StefanJ
> 
> > 
> > Ran gc/g1 tests successfully with that change.
> > 
> > Thanks,
> >    Thomas
> >