RFR(S): 8008301: G1: guarantee(satb_mq_set.completed_buffers_num() == 0) failure

Bengt Rutisson bengt.rutisson at oracle.com
Mon Mar 18 02:10:07 PDT 2013

Hi John,

Looks good.


On 3/15/13 1:31 AM, John Cuthbertson wrote:
> Hi Everyone,
> Here's another one associated with overflowing the marking stack. The 
> webrev can be found at:
> http://cr.openjdk.java.net/~johnc/8008301/webrev.0/
> Summary:
> In this case the marking stack overflows during the actual remark task 
> - when the individual marking tasks are draining the completed SATB 
> buffers. As a result we exit the remark task (because of the overflow) 
> with some legitimately unprocessed completed SATB buffers and trip the 
> guarantee.
> The main part of the fix is between line 2575 and 2579 where I relax 
> the guarantee to allow for the overflow. Additionally I've also added 
> a heap verification for when we restart marking due to overflow. I 
> added it as part of the debugging and I think it makes sense to leave 
> it in.
> The change between lines 2408 and 2416 is to just skip reference 
> processing. While testing I was running into the hang reported in 
> 8009536 and added this to work around it. An equivalent change will be 
> pushed as part of the changes for 8009940.
> Testing:
> The failing test case in a loop (with and without instrumentation and 
> VerifyDuringGC)
> The GC test suite with a small mark stack size (2K, 4K)
> The Lucene tests for 8009536 to specifically test the verification 
> after overflow.
> Thanks,
> JohnC

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