RFR(s): 8145204: JVM can hang when ParGCArrayScanChunk=4294967296 and ParallelGC is used

sangheon sangheon.kim at oracle.com
Fri Mar 4 15:08:33 UTC 2016


Hi all,

Could I get a couple of reviews for this tiny change for 
ParGCArrayScanChunk flag?

This flag is 'intx' and has a maximum range of 'max_intx' which makes an 
overflow issue.
I'm proposing to change to 'int' and limit its maximum to 'max_jint/3'.

This flag is used when we want to process long object array into smaller 
pieces.
The max array length is almost max_jint[1] and the decision for split is 
made like below:

int remainder = array length - ParGCArrayScanChunk;
if (remainder > 2 * ParGCArrayScanChunk) {
   // split to smaller pieces
}

So larger than 'max_jint/3 (approximate)' would not be handled separately.

CR: https://bugs.openjdk.java.net/browse/JDK-8145204
Webrev: http://cr.openjdk.java.net/~sangheki/8145204/webrev.00
Testing: JPRT, manual test[2]

[1]: our implementation is 'align_size_down(max_jint - obj header size, 
MinObjAlignment)'
[2]: Call System.gc() with VM option of '-XX:+{GC modes} 
-XX:MarkSweepAlwaysCompactCount=715827883' (=max_jint/3 + 1).

Thanks,
Sangheon



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