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

Bengt Rutisson bengt.rutisson at oracle.com
Tue Jul 8 06:49:44 UTC 2014


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?

Thanks,
Bengt

>
> Testing:
> JPRT
>
> Thanks,
>    Thomas
>
>



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