RFR (M): 8004687: G1: Parallelize object self-forwarding and scanning during an evacuation failure

Thomas Schatzl thomas.schatzl at oracle.com
Tue Jul 21 18:28:17 UTC 2015


Hi Jon,

On Tue, 2015-07-21 at 11:08 -0700, Jon Masamitsu wrote:
> 
> On 07/20/2015 07:16 AM, Thomas Schatzl wrote:
> > Hi Jon,
> >
> >
> > On Fri, 2015-07-17 at 12:57 -0700, Jon Masamitsu wrote:
> >> Thomas,
> >>
> >> Changes look good.
> >    thanks for the review.
> >
> >> Would it work to change
> >>
> >> OopAndMarkOop
> >> to
> >> OopAndOldMarkOop
> >>
> >> and change the constructor to
> >>
> >> 866     OopAndMarkOop(oop obj) : _o(obj), _m(markOop(obj))
> >>
> >> so that OopAndOldMarkOop specifically saves the oop and it's
> >> markword rather than just an oop and (not necessarily related)
> >> markword?
> >    the only problem I see is that we earlier (8006025) changed the code
> > to explicitly not re-read the markoop from the obj multiple times. The
> > markoop is volatile, so it prevents some optimizations which we want
> > here.
> >
> > It may not be a huge problem or one at all in this particular case,
> > depending on where the OopAndOldMarkOop is instantiated, but requires
> > checking.
> 
> If I understand this comment correctly, yes it does require
> checking but just as it requires checking when the read of the
> markoop was done (the one read of the markoop).  It seemed

I meant checking as in "do performance checking by running benchmarks on
all systems and look through logs for changes". Sorry for being obtuse.

> to me to be modestly more clear with now that there was
> an OopAndMarkOop (renamed OopAndOldMarkOop or
> OopAndPreservedMarkOop which I like even better) but
> sometimes less code is better (i.e., simpler not to use
> OopAndMarkOop data structure) so your call.

I agree that less code is typically better. 

> > I put a webrev with pure renaming of the struct at
> > http://cr.openjdk.java.net/~tschatzl/8004687/webrev.1/ (diff webrev:
> > http://cr.openjdk.java.net/~tschatzl/8004687/webrev.0_to_1/).
> 
> The diff (0_to_1) seem to be only the deletion of some code,
> not a renaming but maybe a moot point now if you still
> like explicitly reading the value of the markoop that you
> want to capture.

  better link:
http://cr.openjdk.java.net/~tschatzl/8004687/webrev.refactor/

Sorry, I already overwrote the original with implementation of Mikael's
suggestion.

Thanks,
  Thomas




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