RFR (S): 8022872: G1: Use correct GC cause for young GC triggered by humongous allocations

Tony Printezis tprintezis at twitter.com
Wed Aug 21 09:30:37 PDT 2013


Hi Bengt,

(surprise!)

This is a useful change. Both webrevs look good. I have a slight 
preference to the first one. I didn't like the use of 
_allocation_failure on the second one here:

  984       result = do_collection_pause(word_size, gc_count_before, &succeeded,
  985           GCCause::_allocation_failure);

given that the allocation didn't really fail - the eden is just full. 
The other use of _allocation_failure (in the VM_G1CollectorForAllocation 
closure) really implies that an allocation did fail and G1 is trying to 
take evasive action.

Tony




On 8/21/13 7:47 AM, Bengt Rutisson wrote:
> Hi All,
>
> Could I have a couple for reviews for this small change?
>
> http://cr.openjdk.java.net/~brutisso/8022872/webrev.00/
>
> This change makes sure that we report "humongous allocation" as the GC 
> cause when we trigger a young collection because we are attempting a 
> humongous allocation.
>
> Before the change a log entry for such a young GC looked like this:
>
> [GC pause (G1 Evacuation Pause) (young) 1364M->1364M(2048M), 0.0004200 
> secs]
>
> After the change it looks like this:
>
> [GC pause (G1 Humongous Allocation) (young) 1364M->1364M(2047M), 
> 0.0541270 secs]
>
> While doing this change I realized that the GC cause 
> _g1_inc_collection_pause was only used in one more place. The slow 
> path for allocations. There is already a cause called 
> _allocation_failure, so I suggest that we use that one instead. This 
> will eliminate the need for _g1_inc_collection_pause.
>
> In that case the webrev will look like this:
>
> http://cr.openjdk.java.net/~brutisso/8022872/webrev_incCause/
>
> I prefer this cleanup, but I'm fine with just doing the first one if 
> we think _g1_inc_collection_pause cause to keep for some reason.
>
> Thanks,
> Bengt

-- 
Tony Printezis | Staff Software Engineer | Twitter

@TonyPrintezis
tprintezis at twitter.com

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