G1 Logging and Phases

Highley, Ryan Ryan.Highley at sabre-holdings.com
Tue Mar 30 19:54:13 UTC 2010


Hello,

 

I have a few validation questions based on the following G1 GC log
excerpt.

 

19.298: [GC pause (young) (initial-mark) 2141M->1957M(4000M)20.433: [GC
concurrent-mark-start]

, 1.1346080 secs]

20.721: [GC pause (young)20.761: [GC concurrent-mark-end, 0.2501590 sec]

 2300M->2119M(4000M), 1.3597880 secs]

22.081: [GC remark, 0.0012060 secs]

22.083: [GC concurrent-count-start]

22.452: [GC pause (young) 2469M->2119M(4000M), 0.3101740 secs]

22.976: [GC concurrent-count-end, 0.8934030]

23.063: [GC cleanup 2435M->639M(4000M), 0.0142190 secs]

23.078: [GC concurrent-cleanup-start]

23.086: [GC concurrent-cleanup-end, 0.0083300]

23.108: [GC pause (young) 660M->338M(4000M), 0.2031580 secs]

23.632: [GC pause (partial) 668M->346M(4000M), 0.3303010 secs]

 

 

>From what I read in concurrentMarkThread.cpp and g1CollectorPolicy.cpp
in the current OpenJDK 7 G1 source code, could I please get the
following confirmed or denied to ensure my understanding is correct?

 

The "GC pause" lines are indeed stop-the-world pauses as blatantly
marked. J

 

The "GC pause (young)" lines are only evacuating young gen regions.

 

The "GC pause (young) (initial-mark)" line is both evacuating young gen
regions and prepping for a full collection with initial marking of
roots.

 

The "remark" line is also a stop-the-world pause, i.e. the G1 "Final
Marking Pause" noted in the G1 whitepaper.

 

The "cleanup" line is also a stop-the-world pause and finalizes the live
object counts and sizes.  The heap allocated size should be the ending
size reported on the "cleanup" line plus any allocations and/or GC
activity that occur during the concurrent cleanup phase.

 

All "concurrent" lines run concurrently with application threads,
similar to the CMS behavior, and in a set of one or more
ConcurrentMarkThread instances.

 

 

Thank you for your help,

 

Ryan

 

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