CRR (S/M): 7075646: G1: fix inconsistencies in the monitoring data

Tony Printezis tony.printezis at
Fri Aug 12 08:20:12 PDT 2011

Hi all,

Thanks to Jon Masa for several good suggestions, here's the updated webrev:


Tony Printezis wrote:
> Hi all,
> I would like a couple of code reviews for some fixes in the G1 
> monitoring code:
> The main motivation behind these changes is that G1's jstat output has 
> inconsistencies and has been causing a few test failures. Here's a 
> quick summary of the changes:
> - Reworked the way the capacities of the various spaces are calculated 
> so that only the eden space used counter needs to be updated when a 
> new eden region is allocated.
> - Now the values of the various sizes that need to be reported are 
> calculated synchronously in all the appropriate places in the code and 
> stored so that they do not need to be recalculated every time they are 
> required.
> - The jstat counters for the young / old gen capacity are now 
> correctly updated.
> - We ensure that when we are reporting a capacity to jstat we 
> artficially pad it so that it's never 0 (as jstat does not handle 0 
> capacities gracefully).
> I attached a file that has before / after output comparisons, along 
> with some commentary, for the various jstat GC parameters.
> Tony

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