RFR (XXS): 8049051: Use of during_initial_mark_pause() in G1CollectorPolicy::record_collection_pause_end() prevents use of seperate object copy time prediction during marking

Thomas Schatzl thomas.schatzl at oracle.com
Thu Jul 10 09:08:47 UTC 2014


Hi Bengt,

  thanks for the review. See below for my comments.

On Tue, 2014-07-08 at 08:49 +0200, Bengt Rutisson wrote:
> Hi Thomas,
> 
> On 2014-07-02 14:33, Thomas Schatzl wrote:
> > Hi all,
> >
> >    some apparent bug in the G1 pause time prediction logic: when ending
> > an initial mark pause, G1 is supposed to switch to different predictors
> > for the object copy time.
> >
> > Since the code that sets the flag to indicate to the prediction that the
> > other predictor should be used for object copy time prediction wrongly
> > reuses during_initial_mark_pause() that has been unconditionally set to
> > false before, G1 never switches predictors.
> >
> > The fix is to use the backup ("last_pause_included_initial_mark") value
> > for during_initial_mark_pause() already used in several places in that
> > method.
> >
> > Bug:
> > https://bugs.openjdk.java.net/browse/JDK-8049051
> >
> > Webrev:
> > http://cr.openjdk.java.net/~tschatzl/8049051/webrev/
> 
> The fix looks good.
> 
> One question.
> 
> Why do we need these local variables?
> 
>    bool new_in_marking_window = _in_marking_window;
>    bool new_in_marking_window_im = false;
> 
> 
> They are only used in one place further down to set the corresponding 
> instance variables:
> 
>    _in_marking_window = new_in_marking_window;
>    _in_marking_window_im = new_in_marking_window_im;
> 
> 
> Can't we just move the if (last_pause_included_initial_mark)  check to 
> that place and skip the local variables?

Yes, we can :)

New webrev at
http://cr.openjdk.java.net/~tschatzl/8049051/webrev.1/

Testing:
JPRT

Thanks,
  Thomas




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