[JDK 6u21]: does CMS report concurrent mode failure on perm gen expansion ?

Charlie Hunt chunt at salesforce.com
Thu Sep 13 21:09:18 UTC 2012


Hi Jon,

As often is the case, thanks for confirming my suspicions!

Increasing PermSize is definitely in order. :-)

thanks again,

charlie ...

On Sep 13, 2012, at 2:37 PM, Jon Masamitsu wrote:

Charlie,

It is probably a case of mislabeling.   I think in earlier
releases we were just dumbly labeling any full GC as
a concurrent mode failure.  But it is a concurrent mode
failure if the perm gen fills up.  Ramki had done some
work to start a concurrent collection for perm gen with
a different trigger.

Increase your PermSize so that we don't have to look
at it :-).

Jon


On 09/13/12 11:26, Charlie Hunt wrote:
I'm looking at a GC log and surprised by the "concurrent mode failure" messages.

I'm seeing the following GC log entries as the first 8 GCs:

3.398: [Full GC 3.398: [CMS (concurrent mode failure)[YG occupancy: 594957 K (1887488 K)]3.489: [weak refs processing, 0.0000140 secs]: 0K->0K(6291456K), 0.1308660 secs] 594957K->594957K(8178944K), [CMS Perm : 21247K->21247K(21248K)], 0.1310260 secs] [Times: user=0.13 sys=0.03, real=0.14 secs]

3.529: [Full GC 3.529: [CMS (concurrent mode failure)[YG occupancy: 594957 K (1887488 K)]3.617: [weak refs processing, 0.0000110 secs]: 0K->0K(6291456K), 0.1010290 secs] 594957K->594957K(8178944K), [CMS Perm : 21248K->21248K(42496K)], 0.1011530 secs] [Times: user=0.12 sys=0.00, real=0.10 secs]

3.638: [Full GC 3.638: [CMS (concurrent mode failure)[YG occupancy: 662071 K (1887488 K)]3.730: [weak refs processing, 0.0000140 secs]: 0K->0K(6291456K), 0.1068710 secs] 662071K->662071K(8178944K), [CMS Perm : 21319K->21319K(42688K)], 0.1069610 secs] [Times: user=0.15 sys=0.00, real=0.11 secs]

3.772: [Full GC 3.772: [CMS (concurrent mode failure)[YG occupancy: 729184 K (1887488 K)]3.915: [weak refs processing, 0.0000140 secs]: 0K->0K(6291456K), 0.1582170 secs] 729184K->729184K(8178944K), [CMS Perm : 21499K->21499K(42880K)], 0.1583500 secs] [Times: user=0.20 sys=0.00, real=0.16 secs]

3.962: [Full GC 3.962: [CMS (concurrent mode failure)[YG occupancy: 804686 K (1887488 K)]4.107: [weak refs processing, 0.0000130 secs]: 0K->0K(6291456K), 0.1598050 secs] 804686K->804686K(8178944K), [CMS Perm : 21702K->21702K(43072K)], 0.1599420 secs] [Times: user=0.21 sys=0.00, real=0.16 secs]

4.497: [Full GC 4.497: [CMS (concurrent mode failure)[YG occupancy: 939150 K (1887488 K)]4.672: [weak refs processing, 0.0000130 secs]: 0K->0K(6291456K), 0.1895350 secs] 939150K->939150K(8178944K), [CMS Perm : 22202K->22202K(43408K)], 0.1896680 secs] [Times: user=0.23 sys=0.00, real=0.19 secs]

5.054: [Full GC 5.054: [CMS (concurrent mode failure)[YG occupancy: 992483 K (1887488 K)]5.274: [weak refs processing, 0.0000130 secs]: 0K->0K(6291456K), 0.2347170 secs] 992483K->992483K(8178944K), [CMS Perm : 24058K->24058K(44408K)], 0.2348700 secs] [Times: user=0.28 sys=0.00, real=0.23 secs]

6.662: [Full GC 6.662: [CMS (concurrent mode failure)[YG occupancy: 1292895 K (1887488 K)]6.953: [weak refs processing, 0.0000140 secs]: 0K->0K(6291456K), 0.3063690 secs] 1292895K->1292895K(8178944K), [CMS Perm : 30692K->30692K(48120K)], 0.3065860 secs] [Times: user=0.66 sys=0.01, real=0.30 secs]

After these 8 GCs, the GC log is much inline with what I'd expect, i.e. ParNew GCs, initial-marks, remarks, etc.

In each of the above GCs:
- young gen is increasing in occupancy
- old gen remains empty
- perm gen space size is expanding

I can understand the Full GC being reported since perm gen is expanding, but I don't understand the reporting of "concurrent mode failure".  Am I missing something?  Is it possible HotSpot is reporting concurrent mode failure when perm gen is expanding?

Here's the set of command line options in use:
-Xmx8G -Xms8G -Xmn1500m -XX:+UseCompressedOops -XX:-UseGCOverheadLimit -XX:+UseConcMarkSweepGC -XX:MaxDirectMemorySize=5000m

thanks,

charlie ...

PS:  I didn't go look at / investigate OpenJDK HotSpot source code since this is JDK 6u21 and thought it might be possible something may have changed between 6u21 and what's in OpenJDK.


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